Fuel pressure adjustment

[Helirich]

I've got my car to a point that it starts and idles good. It runs fairly good until it warms up. Then it loses power. I've done lots of checking of things and the most obvious issue is the primary fuel pressure is low. (58 psi) The thing is, I've put washers behind the adjustment spring and it doesn't change. I've checked the pressure from the pump and it's 90 psi.

So I'm thinking the pressure is bleeding off some where before it gets to the PPV. It can't be the warm up control because I've got that locked out. I've checked the frequency valve and it's not that. That pretty much leaves the cold start valve or its leaking inside the distributor. (There's no gas leaking out the car, so it must be going in the engine or back to the tank.)

The start valve is probably the next thing I will check. But I doubt that's the issue. I'm hoping for some expertise on the fuel distributor. Is there a place inside that fuel could leak from the primary pressure to the return line? (Other than the PPV)

Also, has anyone had the symptoms of running good for 10-15 minutes and then poorly? (It never quits completely, just has no power.)

[Ron]

I've got my car to a point that it starts and idles good. It runs fairly good until it warms up. Then it loses power. I've done lots of checking of things and the most obvious issue is the primary fuel pressure is low. (58 psi) The thing is, I've put washers behind the adjustment spring and it doesn't change. I've checked the pressure from the pump and it's 90 psi.

So I'm thinking the pressure is bleeding off some where before it gets to the PPV. It can't be the warm up control because I've got that locked out. I've checked the frequency valve and it's not that. That pretty much leaves the cold start valve or its leaking inside the distributor. (There's no gas leaking out the car, so it must be going in the engine or back to the tank.)

The start valve is probably the next thing I will check. But I doubt that's the issue. I'm hoping for some expertise on the fuel distributor. Is there a place inside that fuel could leak from the primary pressure to the return line? (Other than the PPV)

Also, has anyone had the symptoms of running good for 10-15 minutes and then poorly? (It never quits completely, just has no power.)Not sure how you locked out the warm up control... If you mean the WUR/CPR, it might help to know that the FD has a tiny port inside that feeds it.

Even if were leaking somewhere, adding shims should increase the primary pressure some. I.E., if it holds 58 psi with a leak and you increase the pressure, only a percentage of the increase would escape via the leak...

[Bitsyncmaster]

58 PSI seems pretty low. Most are running around 68 or higher on primary pressure. My guess would be your PPR o-ring is bad. It takes a lot of washer thickness to even make a 5 PSI change in the PPR.

[Helirich]

Not sure how you locked out the warm up control... If you mean the WUR/CPR, it might help to know that the FD has a tiny port inside that feeds it.

Even if were leaking somewhere, adding shims should increase the primary pressure some. I.E., if it holds 58 psi with a leak and you increase the pressure, only a percentage of the increase would escape via the leak...

Yes, I'm talking about the WUR/CPR. I just closed the valve on the pressure gauge. If the fuel can't get to it, it can't bleed off pressure. I've got a rebuild kit for the WUR, but that is obviously not going to fix the PP.

I agree, it should increase, but two thick washers did nothing. I tried to look in the PPV seat with a mirror when I had the valve out. It looked good from what I could see. I can check it out good if I rebuild the whole distributor.

Some one else remarked they had this problem. (No pressure change with washers) I asked them what their outcome was, no response. I guess I'm going to order a rebuild kit for the distributor. All the diagrams I googled are kind of like cartoons. You can understand how it works, but you can't really see if there's a path from the primary pressure to the return. (Except for the intentional ones)

I thought maybe someone on here rebuilt a distributor and could say "Yes there's a thin gasket between the PP and the return that blows out".

Of course, even if I get the PP fixed, that doesn't mean that's my problem. I don't really understand how it can run good for ten minutes when the PP is never higher than 58.

In any case, I will report back if I find anything. I've got four differnt projects going right now, so it might be a bit.

[Ethan Rode]

Are you extracting the piston from the bore of the PPR, or just the cap/spring pin/shim assembly? If not, there is an o-ring on the end of the piston that may cause low primary pressure if damaged. Pic is from a Porsche FD, but same idea. 65882

If you have serviced this O-ring, I'd suggest verifying that the fuel pump is getting battery voltage with less than .5v drop. Watch the voltage as the car warms up and see if it changes. low volt = low flow

Dumb question...Is your gauge on the correct side of the tester? Looking from the back of the car, gauge should be to the right of the valve. Fuel flows FROM the top port on FD to large port on CPR. Sorry if obvious.

Also, as someone who's done a few, don't mess with the CPR. Send it out. Fuel distributor can be done if you're well organized, and are working in a surgically clean environment, but CPR takes more experience than us mere mortals have.

[Ron]

Yes, I'm talking about the WUR/CPR. I just closed the valve on the pressure gauge. If the fuel can't get to it, it can't bleed off pressure. I've got a rebuild kit for the WUR, but that is obviously not going to fix the PP.

I agree, it should increase, but two thick washers did nothing. I tried to look in the PPV seat with a mirror when I had the valve out. It looked good from what I could see. I can check it out good if I rebuild the whole distributor.

Some one else remarked they had this problem. (No pressure change with washers) I asked them what their outcome was, no response. I guess I'm going to order a rebuild kit for the distributor. All the diagrams I googled are kind of like cartoons. You can understand how it works, but you can't really see if there's a path from the primary pressure to the return. (Except for the intentional ones)

I thought maybe someone on here rebuilt a distributor and could say "Yes there's a thin gasket between the PP and the return that blows out".

Of course, even if I get the PP fixed, that doesn't mean that's my problem. I don't really understand how it can run good for ten minutes when the PP is never higher than 58.

In any case, I will report back if I find anything. I've got four differnt projects going right now, so it might be a bit.
I think I'm with you now.

System/Primary pressure is isolated to the lower half of the FD by a metal gasket/diaphragm in the FD. There are no other gaskets. There is a tiny hole in the metal gasket connecting a restrictor passage to the upper half. Beyond it is Control pressure, fed to and controlled by the WUR/CPR. I can't imagine how it could happen to a good FD, but if enough fuel was passing from one of the lower chambers, under the metal gasket, and into the passage, you would have Control Pressure everywhere with the gauge valve open and Primary Pressure everywhere with the gauge valve shut. (I'd have to see it to believe it ;-) Otherwise, I see no way PP could get to the return to tank line, unless there is a flaw in the casting.

65884

65885 65883

I think I may have said this before, but I'd try another FD before breaking yours down or purchasing another one...

[Helirich]

Are you extracting the piston from the bore of the PPR, or just the cap/spring pin/shim assembly? If not, there is an o-ring on the end of the piston that may cause low primary pressure if damaged. Pic is from a Porsche FD, but same idea. 65882

If you have serviced this O-ring, I'd suggest verifying that the fuel pump is getting battery voltage with less than .5v drop. Watch the voltage as the car warms up and see if it changes. low volt = low flow

Dumb question...Is your gauge on the correct side of the tester? Looking from the back of the car, gauge should be to the right of the valve. Fuel flows FROM the top port on FD to large port on CPR. Sorry if obvious.

Also, as someone who's done a few, don't mess with the CPR. Send it out. Fuel distributor can be done if you're well organized, and are working in a surgically clean environment, but CPR takes more experience than us mere mortals have.

Yes, I have changed the O-ring on the PPV. (Twice, even though it looks good) The seat where it goes looks good from what I can see in a mirror.

I'm doing the pressure test with the battery on a charger and the fuel pump "jumped".

Yes, the guage is correct side, but I don't mind obvious questions. (Their only obvious if I'm doing it right)

From watching Utube, it looks like the CPR is easier then the fuel dist. But either way, I'm probably going to do both. If I screw them up, I'll just buy new. I got my car at a very reasonable price, so cost is no object. I just like to do things myself.


I think I'm with you now.

System/Primary pressure is isolated to the lower half of the FD by a metal gasket/diaphragm in the FD. There are no other gaskets. There is a tiny hole in the metal gasket connecting a restrictor passage to the upper half. Beyond it is Control pressure, fed to and controlled by the WUR/CPR. I can't imagine how it could happen to a good FD, but if enough fuel was passing from one of the lower chambers, under the metal gasket, and into the passage, you would have Control Pressure everywhere with the gauge valve open and Primary Pressure everywhere with the gauge valve shut. (I'd have to see it to believe it ;-) Otherwise, I see no way PP could get to the return to tank line, unless there is a flaw in the casting.

65884

65885 65883

I think I may have said this before, but I'd try another FD before breaking yours down or purchasing another one...

The hypothetical you came up with does not explain why washers don't increase the pressure when the gauge valve is closed. But thanks for speculating. (And the pics) It sure is a puzzle.

I still haven't checked the cold start valve. If that was leaking into the manifold all the time I have been testing things with the engine not running, I would think it would start rough the next time I hit the key. But maybe not.

Again this may not be my power drop off issue. But it is something that isn't right. I don't have access to another FD.

[David T]

A bad accumulator will dump some pressure back to the tank.

[Helirich]

58 PSI seems pretty low. Most are running around 68 or higher on primary pressure. My guess would be your PPR o-ring is bad. It takes a lot of washer thickness to even make a 5 PSI change in the PPR.

Will 68 run normal? Maybe not optimum, but drive OK? I had heard that the washers was very sensitive. I'm glad you told me that.


A bad accumulator will dump some pressure back to the tank.

When I checked the pressure at the line going to the fuel distributor, it was 88 psi. Would that not rule out the accumulator?

Anyways, I just checked the cold start valve. With its line plugged, I get 64 psi. (From 58 psi) Could I get confirmation that it should not let any fuel through when unplugged? If so, there's some of my problem. I'll order a new one before the end of the day.

I just removed the WUR/CP unit. I found the electrical plug was slightly burnt. The resistance was OK. I'm going to rebuild it today. (Crossing my fingers)

[David T]

A bad CPR should not affect the primary pressure. A leaking CSV can. It should not leak at all and only open when the TT switch sends power to it.

[Bitsyncmaster]

Will 68 run normal? Maybe not optimum, but drive OK? I had heard that the washers was very sensitive. I'm glad you told me that.



When I checked the pressure at the line going to the fuel distributor, it was 88 psi. Would that not rule out the accumulator?

Anyways, I just checked the cold start valve. With its line plugged, I get 64 psi. (From 58 psi) Could I get confirmation that it should not let any fuel through when unplugged? If so, there's some of my problem. I'll order a new one before the end of the day.

I just removed the WUR/CP unit. I found the electrical plug was slightly burnt. The resistance was OK. I'm going to rebuild it today. (Crossing my fingers)

Mine was low and I shimmed it to 75 PSI and it made no noticeable change to engine operation. When I tested pressure from my pump it completely pegged my 100 PSI gauge. I have the Tahoe pump so not sure if all pumps run that high.

The CSV should not pass any fuel not powered.

[Rich]

Quoting two points from your post and asking separate questions about these points.

You report the engine runs fine (and has power?) until it warms up, at which point it loses power.

Question 1: Does the engine "have power" when it is warming up, while it "runs fairly good"?

Question 2: Is the primary pressure different when the engine is warming up and runs OK vs pressure after it warms up? 58psi in both conditions?

Questions 3-5: Can you share more details about the "no power" condition? It won't rev up in neutral? Or it doesn't accelerate well? Does it seem like there's any misfiring when it "has no power" or is it just sluggish/slow?


I've got my car to a point that it starts and idles good. It runs fairly good until it warms up. Then it loses power. I've done lots of checking of things and the most obvious issue is the primary fuel pressure is low. (58 psi)

Also, has anyone had the symptoms of running good for 10-15 minutes and then poorly? (It never quits completely, just has no power.)

[Helirich]

A bad CPR should not affect the primary pressure. A leaking CSV can. It should not leak at all and only open when the TT switch sends power to it.

That's what I figured. I'll order one right away. I'm rebuilding the CPR because it's bad, not to increase primary pressure.


Quoting two points from your post and asking separate questions about these points.

You report the engine runs fine (and has power?) until it warms up, at which point it loses power.

Question 1: Does the engine "have power" when it is warming up, while it "runs fairly good"?

Question 2: Is the primary pressure different when the engine is warming up and runs OK vs pressure after it warms up? 58psi in both conditions?

Questions 3-5: Can you share more details about the "no power" condition? It won't rev up in neutral? Or it doesn't accelerate well? Does it seem like there's any misfiring when it "has no power" or is it just sluggish/slow?

1. Yes, I'm just driving it around my ten acres, but I can hit second gear and get to 45 mph before I have to let off.

2. I haven't checked the pressures after it's warmed up.

3. Won't rev past 4000 with foot on the floor.

4. Won't go past 2000 in first or second gear.

5. Not much misfire, just won't go. Seems like if I accelerate slowly, it just gets to a point and falls off.

I haven't actually measured how much fuel the pump can deliver, but it can fill a cup pretty quick. I can't believe it uses more than that driving. (The pump is new)

[Helirich]

So I got the WUR/CP rebuilt. (That was fun) Put back on the car. Didn't effect primary pressure at rest, but if I run the car, I can't check primary pressure because the car shuts off when I close the gauge valve.

One thing I found when rebuilding the WUR is both spades have some connection to ground. (There is resistance) I would have thought they should be "open" to ground. I took it back apart to see if I had some lead touching. But it appears the central mount bolt for the bi-metalic strip is the source. Does that sound right?

[Bitsyncmaster]

So I got the WUR/CP rebuilt. (That was fun) Put back on the car. Didn't effect primary pressure at rest, but if I run the car, I can't check primary pressure because the car shuts off when I close the gauge valve.

One thing I found when rebuilding the WUR is both spades have some connection to ground. (There is resistance) I would have thought they should be "open" to ground. I took it back apart to see if I had some lead touching. But it appears the central mount bolt for the bi-metalic strip is the source. Does that sound right?

The heater in the WUR has two powers. When the thermal switch is closed it heats with more power (has less resistance) when that switch opens the heater has less power.

[Helirich]

So I hook up my guage check the pressures. PP=64 and CP=58

I start the car and the PP is maybe 60 and the CP is still 58. I notice it is not idling as good as before. It's like it is surging from 600 to 900. My guage has a quick disconnect and I can leave the hose hooked up for CP. I close the hood and take it for a drive.

Drives good in the yard. I hit 4500 in first and second is pulling good. (I didn't try in neutral) I pull out of my gate onto the road. First is good, second is good till about 3500 and then it starts falling off. The temp is just coming up on my water gauge. I go back to the house and hook the pressure gauge back up. At first it only reads about 15 psi. I close the gauge valve and it stumbles and then runs good. The guage climbs to 58. When I open the valve again, the gauge barely moves to 60. The idle is still rough. I shut it off.

I'm pondering what to do next when I happen to notice the gauge is up to 62. After about five minutes of cleaning up tools, I check it again. Now it's up to 72 psi. Can the accumulator do that? I thought maybe just heat rising off the engine is doing it. So I start it and the gauge stays at 72. The idle is smooth at 750 now. I unhook the gauge and drive down to the gate. Out on the road, I give it some gas and it won't go above 3500 in first.

I think the car is possessed.

Oh, I also pulled the whole start valve out and jumped the pump. No gas comes out.

[Ron]

The hypothetical you came up with does not explain why washers don't increase the pressure when the gauge valve is closed. But thanks for speculating. (And the pics) It sure is a puzzle.YW, but I was focusing on the original question, "Is there a place inside that fuel could leak from the primary pressure to the return line?".
(Not likely ;-)

At this point, I'm wondering if your FV is defective (dumping too much fuel). They rarely go bad and I don't know if a bad FV could dump fuel fast enough to make the system lack ~1/4 of the PP. But it is connected to the lower chambers of the FD (builds to primary pressure when shut). So, unless someone knows better, I think rigging a way to block it off and then check the PP might be a good test...

I don't think the WUR/CPR has anything to do with the PP problem, but you might try this:
With the engine dead cold (cooled over night), start the engine and watch the control pressure. Assuming ~70°F ambient, it should start at ~35psi and rises quickly to 50-55°psi and stay there. (If it rises, but to 58psi, as expected, don't worry. We can deal with that after the PP is corrected.)

It's not possessed -- It's a DeLorean!
Hang in there!

EDIT: If it holds rest pressure, I'd forget about the accumulator for now.

[Bitsyncmaster]

As Ron suggested, if it holds rest pressure then forget about the accumulator.

Your control pressure is to high which I think means the WUR is bad. A cold engine it starts around 20 PSI and quickly (a few minutes) ends up to 50 PSI on a good engine.

My guess is your fuel pump is bad and your WUR is also bad.

Have you measured the voltage on the fuel pump when engine is running? Also can measure that voltage without engine running by jumping the RPM relay and see if it changes with the pump running for a few minutes. You need to attach a meter right to both terminals of the fuel pump.

[Helirich]

At this point, I'm wondering if your FV is defective (dumping too much fuel). They rarely go bad and I don't know if a bad FV could dump fuel fast enough to make the system lack ~1/4 of the PP. But it is connected to the lower chambers of the FD (builds to primary pressure when shut). So, unless someone knows better, I think rigging a way to block it off and then check the PP might be a good test...
.

I did remove the frequency valve return line and jump the pump. It did not let any fuel through. I don't know about when it's running though.


As Ron suggested, if it holds rest pressure then forget about the accumulator.

Your control pressure is to high which I think means the WUR is bad. A cold engine it starts around 20 PSI and quickly (a few minutes) ends up to 50 PSI on a good engine.

My guess is your fuel pump is bad and your WUR is also bad.

Have you measured the voltage on the fuel pump when engine is running? Also can measure that voltage without engine running by jumping the RPM relay and see if it changes with the pump running for a few minutes. You need to attach a meter right to both terminals of the fuel pump.

My CP is adjustable now. I drilled a hole in the bottom so I can get a Allen key in and adjust it. I saw this on Utube. The kit came with no instructions, so I didn't even have a place to adjust it when assembling it. (I just set approximately the same as I found it.) I haven't touched it yet because I figured I need the PP up to spec before attempting it. I'm not sure how much adjustment there is or how sensitive it is. I guess since it's so high, I should try to get it close. I have to remove the WUR from the engine to get at the adjustment.

My fuel pump is brand new and I did get 88 psi right from the filter. The WUR should be good now that I rebuilt it. There was nothing obviously wrong with it. The rebuild kit did not include new springs which I wonder about.

I haven't measured voltage at the pump with the engine running. But I have 13.5 at the battery, so I know the alternator works. I will try it at the pump. Again, I got 88 psi at the filter, so I kind doubt the pump is the issue.

Also, I jumped the pump one time and it was not very loud. So I checked the voltage at the battery and the terminals under the hood. Both were at 11.8 V. I hooked the battery charger up and the voltage went to 13.5 at both locations. I could hear a differnt tone to the pump very quickly.


Time for conjecture.
What if I unplug the WUR? If it has the CP high at start and runs, maybe it is leaning it out after a few minutes. Obviously this is not a fix, but it would explain what is happening.

[FABombjoy]

I drilled a hole in the bottom so I can get a Allen key in and adjust it. I saw this on Utube.
Did you plug the hole once done? If not you'll have a big vacuum leak during warmup. A 1c piece fits perfectly :D

[Bitsyncmaster]

You should see a return flow into the tank with the pump running. But if your only getting 60 PSI I don't think anything will return. I measured my pump flow by measuring the return line flow. So that flow rate was at 75 PSI since it overcomes the PPR.

Did you replace the fuel filter? I helped one owner and his filter completely plugged the fuel flow from the pump.

[Helirich]

Did you plug the hole once done? If not you'll have a big vacuum leak during warmup. A 1c piece fits perfectly :D

Yea, I was thinking about that. It would be a big vacuum leak all the time.

[Helirich]

You should see a return flow into the tank with the pump running. But if your only getting 60 PSI I don't think anything will return. I measured my pump flow by measuring the return line flow. So that flow rate was at 75 PSI since it overcomes the PPR.

Did you replace the fuel filter? I helped one owner and his filter completely plugged the fuel flow from the pump.

I definitely had return flow when I installed the pump. If I can get 88 psi to the distributor and the PP is 60, it must be going somewhere. I guess I will take the cover off and check the voltage at the pump and the return flow at the same time.

Filter was new when I changed the pump. (month ago) If I get 88 psi after the filter, I would say that rules plugging out.

[Ron]

I did remove the frequency valve return line and jump the pump. It did not let any fuel through. I don't know about when it's running though.
The lambda relay passes power to the FV only when the engine is running.



Your control pressure is to high which I think means the WUR is bad. A cold engine it starts around 20 PSI and quickly (a few minutes) ends up to 50 PSI on a good engine.
...
My guess is your fuel pump is bad and your WUR is also bad.
Hmmmm...random comments/thoughts:
I was going by the chart at D:02:01, which matches my experiences. 20psi would be ~50°F.

The spec shows 3.4-3.8 Bar, warm, vac disconnected. 3.8 Bar = 55.11psi. The 58psi is only off ~5%...Too high but the wrong direction WRT the PP problem.

As yours, every working D pump (early/late) I've tested would peg a 100psi gauge.

[Ron]

Yeah, seems like the return must be flowing.

FWIW, vertically mounted filters are very prone to pack and then release trash after resting a little while...and, iirc, your D sat long enough to accumulate plenty to be released as time goes on. (Maybe you flushed the system.)

I'm curious as to how you went about plugging the FV return hose since the end is at the double banjo. Fittings in the gauge kit??

For future reference, you can adjust the CPR using washers and not have to remove it.
Also want to stress how important it is to let the engine sit overnight when you get to where it needs tweaking in.

[Helirich]

More puzzling info, but getting somewhere.

First, I have never been happy with this guage set. It was cheap off eBay. I have checked the guage compared to another and it read the same. The part I'm not happy with was the fittings need to be over tight to seal. So while I was looking at the set up, I noticed I can hook the "quick disconnect" at either end of the hose. (Right at the valve or right where the hose connects to the the other hose. It should be the same pressure because both are on the same side of the valve. So for fun, I plugged it in to the other fitting. Bang! I got 72 psi. (60 at the other end) Not sure what's going on. Maybe the T at the valve is bad.

So I check the CP and it's slightly lower. Maybe 68 psi. I removed the WUR and adjusted the Allen screw. One way the CP goes higher, the other it runs out of adjustment at 68 psi.

I removed the electrical plug from the WUR and take the car for a drive. No change, won't rev up. Plug it in while it's idling and maybe it idles better after a few minutes. Still won't rev in neutral beyond 3200.

Now for the kicker. I took Bitsy's advice and pulled the tank cover. Pulled the pump plug and check voltage with the jumper wire. Same voltage as the battery and the posts under the hood. Then I snaked a couple thin wires in the plug and plugged it back in to the pump. Now I can check voltage while the pump is running. Viola! I'm getting 8 volts. I go back and check the battery and hood posts. They are 11.9 volts. I hook the battery charger to the battery and now I get 13.5 at both battery and hood posts. Back to the pump I'm now getting 10 volts.

So what gives? Is there something I should be checking? I guess I'm going to run a seperate wire from the battery to the pump somehow. Kind of like to keep the inertial switch in there.

Suggestions welcome.

[Bitsyncmaster]

You get a voltage drop on the ground side from the wiring to the inertia switch and the inertia switch grounds to common on the binnacle gauges and then back to the ground in the relay compartment. Also a drop in the wiring from the RPM relay to the pump. But connectors in the washer bottle and the two pin connector at the pump are common problems. I think normal drop is about one volt (a lot of wire length).

My two pin pump connector was dropping 1 volt so I removed it. You don't really need that connector since you can undo the wires at the pump.

[Ron]

So I check the CP and it's slightly lower. Maybe 68 psi. I removed the WUR and adjusted the Allen screw. One way the CP goes higher, the other it runs out of adjustment at 68 psi.There ya go! The CP should never be higher than 55.1 psi.
Fix that and, if the PP was actually 72psi all along due to a goofy gauge setup (or is now), you'll be grinning soon.
Either the WUR/CPR is still off, it's return hose has restrictions, there is something like a piece of o-ring where it connects to the FD port (took hours to find that one), or the main return hose has restrictions.

EDIT: I missed a WUR/CPR input hose restriction.

[Helirich]

You get a voltage drop on the ground side from the wiring to the inertia switch and the inertia switch grounds to common on the binnacle gauges and then back to the ground in the relay compartment. Also a drop in the wiring from the RPM relay to the pump. But connectors in the washer bottle and the two pin connector at the pump are common problems. I think normal drop is about one volt (a lot of wire length).

My two pin pump connector was dropping 1 volt so I removed it. You don't really need that connector since you can undo the wires at the pump.

I'm getting about 3 volt drop. I wonder if it doesn't drop that much at first. Then the wire heats up and drops more. So do you think I should run 12 ga wire from the inertia switch to the pump?


There ya go! The CP should never be higher than 55.1 psi.
Fix that and, if the PP was actually 72psi all along due to a goofy gauge setup (or is now), you'll be grinning soon.
Either the WUR/CPR is still off, it's return hose has restrictions, there is something like a piece of o-ring where it connects to the FD port (took hours to find that one), or the main return hose has restrictions.

Not sure what I believe about pressures. I may have to revarify everything. As far as a restriction in the return, how would I test this? I guess I could put the WUR return in a bucket. If the CP goes down, that would prove a clogg.

[Bitsyncmaster]

I'm getting about 3 volt drop. I wonder if it doesn't drop that much at first. Then the wire heats up and drops more. So do you think I should run 12 ga wire from the inertia switch to the pump?.

The pump normaly draws 6 to 7 amps. so 14 AWG or !2 AWG would be great to reduce voltage drop. But if your dropping 3 volts I bet you have some bad connectors.

What you can do to pin it down is get a long meter wire and connect the ground of the meter to the battery ground. Then your the plus side of the meter to measure drops at each connector pin on both sides. First check your ground drop at the neg. terminal of the fuel pump. Then check the pos. side of the fuel pump connecting the long meter wire to the battery pos. It may be your inertia switch may be bad.

[David T]

Make sure you have the updated inertia switch with a white splotch of paint on it and it is mounted on the side of the footwell. Very common to have a bad connection in the harness plug up inside where the washer fluid reservoir is.

[Helirich]

The pump normaly draws 6 to 7 amps. so 14 AWG or !2 AWG would be great to reduce voltage drop. But if your dropping 3 volts I bet you have some bad connectors.

What you can do to pin it down is get a long meter wire and connect the ground of the meter to the battery ground. Then your the plus side of the meter to measure drops at each connector pin on both sides. First check your ground drop at the neg. terminal of the fuel pump. Then check the pos. side of the fuel pump connecting the long meter wire to the battery pos. It may be your inertia switch may be bad.

I did this and the drop is mostly in the power side. I think I'm going to run just the power wire. Not sure where to hook it in back. There must be a main switched power back there. I find it tomarrow. I've got to work on some other (more boring) stuff today.

[Helirich]

Make sure you have the updated inertia switch with a white splotch of paint on it and it is mounted on the side of the footwell. Very common to have a bad connection in the harness plug up inside where the washer fluid reservoir is.

I do have that inertia switch. Haven't checked the washer fluid resivoir. What am I looking for there? As far as I can see the pump harness goes forward to tie in to the fan/lights.

[David T]

There is a large connector plug that hooks the body harness to the front harness and the fuel pump circuit goes through it. When you remove the W/W reservoir you will see the wiring harness coiled up and tucked up inside. A lot of fun getting that reservoir out. The screws rust up and then the rivnuts turn in the fiberglass. You wind up having to grind the heads off of the screws. While you have the reservoir out it's a good time to wash out the slime from 30 years of junk.

[Helirich]

There is a large connector plug that hooks the body harness to the front harness and the fuel pump circuit goes through it. When you remove the W/W reservoir you will see the wiring harness coiled up and tucked up inside. A lot of fun getting that reservoir out. The screws rust up and then the rivnuts turn in the fiberglass. You wind up having to grind the heads off of the screws. While you have the reservoir out it's a good time to wash out the slime from 30 years of junk.

Sounds like fun. I'm running one of the new style pumps that DMC sells. I wonder if it draws more power. Does that plug melt or just lose connection?

[Helirich]

Up date,

So I run the new 12 ga. Aircraft wire from the rpm relay thing to the pump connector. I spliced the wire in and soldered it at both ends. It brought my 3 volt drop to 2 volt drop. While I was doing testing I noticed a smell like burning. Started checking around and there is a fuse that has been removed from the fuse box and a stand alone, inline fuse holder installed. I've heard of people doing this, so not a major concern. But in this case, they used a cheap fuse holder with wires that were skinnier than the wires they hook to. I felt the wires and they got hot right where they neck down.

I cut that out and installed a maxifuse holder. I'm still using a 20 amp fuse, but now my voltage drop is only a 1.5 volts and there's no heat on the wires. If I ground the pump locally, it gains another volt. Haven't decided on that yet because it cuts out the inertial switch. The PP goes to 72-74 right away now, so not a big rush.

I removed the return line from the tank and placed it in a 5 gal bucket. It will fill it a 1/2" in less than 15 seconds. I don't believe there is any restriction there. One thing I noticed is I couldn't blow in the tank. Is there a vent somewhere?

I took it for a drive and it did drive better. There still is a reving issue.

[Ron]

Short answer, no.
It's a sealed system. Basically, vapors are stored in a canister and purged to the cold start tube, when engine warm, upon acceleration.