Possible fuel pump issue..

[Timebender]

Hi everyone,
I'm hoping that I can get some thoughts, what might be going on from any of you.
As you might or not know, my car was converted by the original owner, a long time ago, into a Chevy 350 small block. It's been running the stock fuel pump, and turns out there's what looks like even a secondary fuel pump. This was discovered by the guys at DMC California when I had it up there for some initial work after I bought it - fuel system cleaning, clean the tank, replace hoses, and put in a new combo pump. They went and did all that, only to find the car wouldn't run with the new pump. That's when the discovered pump #2, and decided to put the old pump back in, but cleaned it up.

So now, at first only once in a while but now more frequently, everything seems to be running fine, but at times I'll lose power - not electrical, but the engine just dies. I can crank it a few times and it fires back up and all is good, except for this morning, it did it a couple times. It originally would do it just idling in the garage, or if I increased the RPM's giving it gas, and it would be going then just die. Start it up and it was fine. Then it happened after I turned a corner at a stoplight.
And today, going downhill with foot slightly on the gas - twice.

I turned around and headed back home, uphill, and no issues. Tank is almost full - the gauge shows 3/4 and I don't know how accurate it is, but I have a new sender I put in as the old one was shot, and when I pull it out it was practically falling apart. I was kind of surprised as when they did the tank cleaning and stuff, they didn't even mention the sender might need to be replaced. The bottom had almost come off completely. I'm guessing when they clean the tank they leave the sender in? It had never been removed as it took a lot of work to get the collar loose to replace it (it had a ton of dirt and gunk around it). They also replaced the fuel filter - but now I'm wondering if they did. I know a bad filter can cause this to happen.

I've taken care of other issues - replaced the alternator (it was going bad), new HEI coil, distributor cap, rotor, new spark plugs.

So I'm getting spark just fine.

Thoughts and ideas?

It could be the secondary pump (why the original owner had that put on I don't know), but my gut tells me it's the old pump or the filter. And is the filter easy to replace?


Thanks for any help!

Greg

[Bitsyncmaster]

If your still using the RPM relay, it can cause intermittent loss of fuel pump power. Is your engine fuel injected?

[Timebender]

If your still using the RPM relay, it can cause intermittent loss of fuel pump power. Is your engine fuel injected?

Nope, it's carb'd. However I don't think I ever swapped out the relay when I changed out some others. And that would be a very easy, cheap fix.

How much for one of yours?

[Bitsyncmaster]

Nope, it's carb'd. However I don't think I ever swapped out the relay when I changed out some others. And that would be a very easy, cheap fix.

How much for one of yours?

My price list.

Fan Fail, $94
Electronic fused Fan Fail, $114
Dome unit, $88
RPM relay, $83 with your old unit
Fan relay, $77
Blower relay, $72
Head Light relay, $72
Hot Start relay, $66
Pair of window switch LED boards, $20, $25 installed, requires the new DMCH switches.
Idle ECU, $138 with your old unit. I have 11 pin units also for $150 with your 9 pin unit returned.
LED AC panel, $110. Your choice of blue or green backlighting.
Front Relay Bank Ground Buss, $15. $10 if combined with another product.

Prices include shipping to lower 48 states

[David T]

An easy way to tell if the motor is dying because of lack of fuel on a car with a carburetor. When it dies pull the air cleaner off and pump the throttle. If you don't see the accelerator pump spaying in any fuel the carb is dry. There is no need for 2 fuel pumps. DMCH sells a combo unit for cars without fuel injection, they operate at much lower pressure. Difficult to offer much advice without being able to see what was done to the car because it is no longer stock. I doubt there is an RPM relay, how would it get a signal that the motor is running? The inertia switch may still be hooked up but who knows? If there IS an RPM relay jump it out and see what happens.

[Timebender]

The few times where it's died on the road, I pulled over, tried a couple times to start it again and it fired up - I was more concerned about just getting it running and getting off the highway - we travel on one of the most dangerous highways in the US. This weekend I'll try and get it to do the same thing. But when trying to start it, it does take a couple tries before the engine gets any gas.

I'll also take a look to see if the RPM relay is there - couldn't hurt.

As far as the combo unit with the pump and sender, Danny's guys put one in, and it wasn't putting out enough pressure for the engine, so they put the old one back in after they cleaned it up, whatever that entails.
I'm running a Holley 4 barrel carb.

And I don't know why they put in a secondary pump when the conversion was done back in 1981. I do now have the original owner's name, thanks to the DMC Museum - just need to Google it and see if I can track him down. But I've never seen a car with one before. Actually I'd almost love to go back to hooking up the mechanical pump, but don't know if there's a way to just run a siphon into the tank, and bypass the DeLorean filter for a nice glass one somewhere up top that I can see what's going on.

[Jonathan]

My first thought was about "flow and pressure."

Back when they did the engine swap, sounds like the original set-up wasn't sufficient in one or both of those things. For all we know, it might have been something else they failed to determine causing the restriction and it still isn't sorted out.

As the Guru mentioned, help us understand what your car has and we'll try to help back:

- How are both pumps plumbed in together? I assume you don't have two fuel tanks? So the second pump is also mounted on top of the tank then?
- Where do the discharge lines go from each pump? Do they tee together somehow? If they presumably meet up to supply fuel to the same place, then what is installed to prevent one pump from competing with the other? There would likely be check valves involved to stop one pump from forcing fuel down the throat of the other (weaker) pump, but regardless, they could be negating each other somehow.
- And what electrically powers them on or tells them to pump? Do they both pump all the time or does one only come on when extra fuel is needed?

Assuming the way they are plumbed in at least would work in theory, then maybe it is a plugged filter issue. Could be two filters installed depending on how you answer the "how is it plumbed" question. Or if the system still takes advantage of a return line in some way, perhaps too much fuel is coming back to the tank and not getting to the engine?

These are a lot of guesses on a car no one has a good idea of what is installed. See if you can trace that out or post pictures of what you do see and let the group try and help you figure it out. Or maybe DMCCA already traced it all out and they can explain it to you/everyone?

[Bitsyncmaster]

Carbs usually only require 3 to 5 PSI if the hoses are large enough to not restrict the fuel flow. The RPM relay does require the ignition coil signal to run but most likely your engine swap guys have that connected. You would not need a fuel accumulator but it would not hurt to leave it installed. How is the second pump plumbed? If it is just boosting from the first pump, I would think it not running would actually reduce fuel flow.

[Jonathan]

Good point Dave... about the fuel hoses. That could be another restriction conceivably if the inside diameter of them has gotten scaled up or gummed or somehow and become effectively smaller. Maybe not scale like from hard water, but maybe from the disintegration of certain hose material types or something.

Yea, another good reason to know how it is plumbed in with thinking the second pump might be in series. That could do a number of different things to the fluid dynamics whether it is running, or not running, or otherwise blocking the flow path.

[Timebender]

Good questions all around.
I know the main fuel pump (or could be the secondary) comes on when I turn the ignition on as you can hear it running. I don't know which one - I'll have to pop the front hood and listen to where it's coming from. Even with the fuse out, it's still running - so it if is the main tank pump then they rewired it.

Danny and Co. found the second pump when they were replacing all the fuel lines earlier this year, but didn't say where it was. I did have the car up on a rack recently, and it looked like there was another pump in front of the tank off to the driver side, not too far behind the radiator. But then it could be something else I'm not used to seeing, as that was really the first time under the car to get a good look. From what I could make out when I had the access cover off the top when replacing the sender, there was nothing else but it and the main pump. The lines ran normally off to the passenger side and then where after that - as they're connected to the hard lines in the body, I don't know off hand.

I'll have to ask to see if he remembers what the line up was. I do know the return from the engine compartment is going straight to the tank. Don't ask me how, but let's say I found out the hard way (with no damage fortunately).

As far as I know, for the 30 some years between the original and second owner, they didn't have this problem. But it was garaged with some occasional driving to keep it running over the last 20 years when the guy i bought it from had it.

When I first got it back from Danny, it didn't exhibit this behavior. But it's old, and things are going to give out one by one. I'd jack it up to take a look, but it's lowered so much I can't get a small jack under it along with a 2x4 to protect the frame.

I'll let you know once I get some pics as well as have a chance to listen to which pump is on with the ignition on.

[Jonathan]

I'd jack it up to take a look, but it's lowered so much I can't get a small jack under it along with a 2x4 to protect the frame.

As an aside, a quick trick to get around this is to drive the car up on a pair of 2x6s, and then once parked on those pieces of wood, you should be able to slide your jack underneath, with the additional piece of wood on the jacking surface to still protect the frame.

[DMCMW Dave]

I doubt there is an RPM relay, how would it get a signal that the motor is running? .

From the ignition ECU, just like a stock DeLorean.

[opethmike]

Would love to see pictures of the engine bay. I'm always curious about DeLorean engine swaps.

[DMC5180]

Does this car still have the OEM high pressure Bosch type fuel pump in the tank? If so, I wonder if you are hearing that pump run or actually hearing the other pump running. The OEM pump would likely supply too much fuel pressure. Who ever did the original conversion might have just left OEM stuff in the tank for lack of a better way to keep the tank sealed. The fuel can be drawn through the original pump and check valve with the second inline low pressure pump.

Pictures would be nice.

Dennis

[Ron]

DMCH sells a combo unit for cars without fuel injection, they operate at much lower pressure.Sounds like one of those and deleting the 2nd pump is the ticket to me...

[Timebender]

Would love to see pictures of the engine bay. I'm always curious about DeLorean engine swaps.

Here you go!

3858438585

[Timebender]

As an aside, a quick trick to get around this is to drive the car up on a pair of 2x6s, and then once parked on those pieces of wood, you should be able to slide your jack underneath, with the additional piece of wood on the jacking surface to still protect the frame.

Great idea

[Timebender]

From the ignition ECU, just like a stock DeLorean.

I took a pic of the relay/fuse compartment. There's one big black relay still connected to the harness (with a red wire tapped in going somewhere- couldn't tell as it was too dark to see), and another relay plug with nothing on it.
I'm going to guess this is the RPM relay?

38586

Also, I checked tonight what's running when I turn on the ignition- it is the second pump. So could be the first one is failing - as it was never replaced, or could be the relay. I'll swap that first, but still plan on replacing the pump. And yes, it's the original stock pump -
All they did at DMC Ca was clean it up and put it back in when they discovered the new combo unit didn't supply enough fuel pressure. Could be the secondary pump was keeping it from doing its job though. That cost me $1200 or so for them to figure out it wasn't going to work (that did include replacing the fuel lines though).

[Timebender]

Does this car still have the OEM high pressure Bosch type fuel pump in the tank? If so, I wonder if you are hearing that pump run or actually hearing the other pump running. The OEM pump would likely supply too much fuel pressure. Who ever did the original conversion might have just left OEM stuff in the tank for lack of a better way to keep the tank sealed. The fuel can be drawn through the original pump and check valve with the second inline low pressure pump.

Pictures would be nice.

Dennis

You might have something there. The sound is the second pump as I mentioned a couple posts ago.
I wonder why though when DMC Ca put in the combo unit that there wasn't enough pressure at all? Could it be it was restricting any flow?

The OEM pump is still wired up, the fuse is still in, and I think that's the RPM relay.

I'll remove the access panel this weekend to see if the main pump is running when the ignition is on, but I couldn't hear anything coming from there- unless it's very quiet.

[opethmike]

Yes, that is the RPM relay.

[Nicholas R]

Are you running the stock fuel lines on the frame?

I know that when I first started doing research on my swap, I had questions about the original fuel line sizes being able to supply enough pressure while maintaining enough flow at high RPMs (especially with all the Ts and junctions. I talked to a local tuning shop that specialized in LS engines and they gave me specs on fuel system requirements that they live by. Based on the info they have me, it was pretty clear that the original fuel lines would not be suitable, especially if I wanted to perform any upgrades in the future. Thats why I deleted the original lines and ran 2 braided steel lines down the frame, directly from the pump to the regulator, filter, to the rail, and back.

This would probably only start to affect you once you get into the middle of the powerband but it still might be something to think about. I'm wondering if this could have been some of the thought behind the extra fuel pump perhaps?

Are the pumps in parallel or in series? From the sounds of it, I'm guessing in series? I'd be surprised if you need both fuel pumps; seems like its more likely to give problems than to actually help. Depending on the design of the second pump, it may not be designed to be receiving high pressure, unregulated fuel. There is a reason why fuel systems have regulators; because the fuel directly from the pump isn't always consistent. The first pump directly feeding a second pump could just result in cavitating the second pump and in turn, loosing fuel pressure. All speculation of course but something to consider. Best of luck! :wrenchin:

[Bitsyncmaster]

Yes that photo is the RPM relay. Looks like they also run another circuit that spliced into one of the outputs of the RPM relay. So your first pump probably only runs when the engine is running since the RPM relay requires the ignition coil signal.

You must have a pressure regulator somewhere in the fuel feed line to reduce the high pressure from a stock pump to a pressure a carb can use. Typically a carb setup does not need a return line to the tank. But with a stock fuel pump you would need a return from a pressure regulator.

Maybe the second pump was used to prime the system for quicker starting.

[Timebender]

The second pump is always running on ignition. I'l fire up the car after this week - other issues right now to deal with on R2 and his broken center leg and two events tomorrow...

I'm going to guess the pumps are in series, and both are running. Also, they are the stock lines in the car as well.
Interestingly enough, it only seems to exhibit this with less than a full tank (maybe a little more than half a tank according to the gauge), coming to a stop or going downhill - yesterday's events happened heading to work downhill, twice within 10 seconds of each other and foot kind of off the gas. Could be the in take pump needs to be running to get gas when it's low or toward the front of the tank and there's not enough vacuum from the second pump to do so unless there's gas being pushed back. If that pump cuts out because of the relay, or just needing a new one, then it could prevent any gas from being sucked out vs. there being a line with a filter/screen directly in the tank.

When heading back uphill to the house, there were no issues. Also, the car sat in my driveway the other day idling while I was cleaning out my garage for about a half hour, on a slight incline nose up, and no cut outs. But on a flat surface when there's less than half a tank (or maybe more than less), it'll idle then suddenly die, and after one or two tries start back up again.

[Timebender]

I saw on the DeLorean Wiki that a Volvo relay would work. I'm guessing it's what they call the EFI relay and is this part?


http://www.oreillyauto.com/site/c/search/EFI+Main+Relay/01704/C0116.oap?keyword=rpm+relay&year=1981&make=Volvo&model=265&vi=1288289

[Bitsyncmaster]

I saw on the DeLorean Wiki that a Volvo relay would work. I'm guessing it's what they call the EFI relay and is this part?


http://www.oreillyauto.com/site/c/search/EFI+Main+Relay/01704/C0116.oap?keyword=rpm+relay&year=1981&make=Volvo&model=265&vi=1288289

Some of the Volvo RPM relays will work in the DeLorean. Some do not even though they have the same case and connector, they are completely different inside. I don't know which part numbers work.

[Timebender]

Some of the Volvo RPM relays will work in the DeLorean. Some do not even though they have the same case and connector, they are completely different inside. I don't know which part numbers work.
Good to know. I'll wait for one of yours.

[Bitsyncmaster]

Good to know. I'll wait for one of yours.

Last thing, open your RPM relay just in case it's already one of mine. My will always prime for 1.5 seconds when you turn the key on. So I think you don't have mine or you would hear the main fuel pump run for that 1.5 seconds.

You just use a little screw driver to pry the lip on the case ends up.

[Timebender]

Last thing, open your RPM relay just in case it's already one of mine. My will always prime for 1.5 seconds when you turn the key on. So I think you don't have mine or you would hear the main fuel pump run for that 1.5 seconds.

You just use a little screw driver to pry the lip on the case ends up.

If you we're making these 20 years ago, then it might be. Aside from being driven by the previous owner and his son-in-law once in a while to keep it running, it sat in a garage for those 20 years. Before that, the original owner had been taking it to shows mostly.

I'll take a look anyhow. I'm guessing if it's solid state parts vs. mechanical relay parts, then it's one of yours. The last time it was at DMC California was maybe 15 years ago when Don had the shop.

Greg

[Bitsyncmaster]

If you we're making these 20 years ago, then it might be. Aside from being driven by the previous owner and his son-in-law once in a while to keep it running, it sat in a garage for those 20 years. Before that, the original owner had been taking it to shows mostly.

I'll take a look anyhow. I'm guessing if it's solid state parts vs. mechanical relay parts, then it's one of yours. The last time it was at DMC California was maybe 15 years ago when Don had the shop.

Greg

It's been about 7 or 8 years I've been selling the RPM relays. That was my first product because my OEM one was faulty. It never powered the second output for the lambda system. I would estimate 30% of the returned cores have broken solder joints. They fail due to thermal cycling of the unit. The OEM units get very hot.

[Ron]

I'm dying to see how it is actually plumed ;-) ...wonder if there is an easy way to ID the integrated pump WRT OEM/Low output
pressure??

[Timebender]

If I can get it up on a rack again soon I'll take some pics, and maybe while at it take out the secondary and replace the old OEM with the combo unit.