Proofing my work after fuel distribution re-assembly?

[rjd2]

Bitsyncmaster-thanks. My rest pressure with the FPG valve open is about 30. I can't get it anywhere near 50PSI running, but the engine won't idle, so i can't get it to run for too long. With the FPG valve closed, it jumps to about 44PSI.

It seems to me it's likely I have a vacuum issue, maybe? If so, where should I start investigating? Nothing changed at all upstream of the CPR, so I'd have to imagine the first place I should investigate is the mixture unit and fuel distribution unit?

[Bitsyncmaster]

Bitsyncmaster-thanks. My rest pressure with the FPG valve open is about 30. I can't get it anywhere near 50PSI running, but the engine won't idle, so i can't get it to run for too long. With the FPG valve closed, it jumps to about 44PSI.

It seems to me it's likely I have a vacuum issue, maybe? If so, where should I start investigating? Nothing changed at all upstream of the CPR, so I'd have to imagine the first place I should investigate is the mixture unit and fuel distribution unit?

If your only getting 44 PSI with the fuel pressure test valve closed (RPM relay jumpered), that is a problem. Primary pressure regulator, fuel filter or fuel pump must bad. You should get 70 to 75 PSI.

[rjd2]

is it possible this could be an electrical connection issue? when i retrace my steps, the only things that have been disconnected were the fuel distributor, mixture unit, and the related electrical harnesses. while i'm not ruling it out, if a part of the fuel delivery system has failed, it would have happened literally while i was replacing the thermister. the car idled perfectly right before i started the thermister job, and didn't hold an idle the very first time i attempted a start after the thermister job. it seems extremely likely that it would be related to the connections/disconnections related to that job.

[Ron]

Just in case, did you ever check the routing for the CPR/WUR fuel line with the small banjo bolt ?

[Bitsyncmaster]

is it possible this could be an electrical connection issue? when i retrace my steps, the only things that have been disconnected were the fuel distributor, mixture unit, and the related electrical harnesses. while i'm not ruling it out, if a part of the fuel delivery system has failed, it would have happened literally while i was replacing the thermister. the car idled perfectly right before i started the thermister job, and didn't hold an idle the very first time i attempted a start after the thermister job. it seems extremely likely that it would be related to the connections/disconnections related to that job.

What the thermistor in the valley does is set how wide the idle motor opens at when you turn the key on. If it was and open circuit, the stock idle ECU tries to hold the idle RPM at around 2500. You can test the resistance right on the idle ECU connector pretty easily. I don't think the thermistor would prevent the engine from starting.

Another electrical connection is the vacuum advance solenoid. It's common that connector falls off the solenoid when your moving the engine harness. You will get a poor idle if that connection is bad but it does not prevent the engine from starting.

Other connections are the ignition resistors which connect the ignition coil. Since your engine fires cold I would think these connections are OK.

An important ignition connection is the pickup coil in the ignition distributor. That coil connection goes to a two pin connector. On my car that connector was very corroded so bad, I just removed the connector and connected the wires. You should inspect that connector (pull it apart and look at the pins).

[NckT]

If your only getting 44 PSI with the fuel pressure test valve closed (RPM relay jumpered), that is a problem. Primary pressure regulator, fuel filter or fuel pump must bad. You should get 70 to 75 PSI.

I've seen that and it was due to a split O ring(s) in the fuel distributor pressure regulator ie the usual problem for hot start problems.

[rjd2]

hey NickT-I have a hunch you may be on to something....

So when I completed the job, I was left with one leftover O-ring. I could never figure out where it went. There's a ~1 1/2" o-ring that lies between the black fuel distributor body, and the top of the mixture unit(the downward shaft of the fuel distributor goes thru it). I got that one in place, but there was an identical size o-ring in the gasket kit, and i never figured out where it went. it's definitely behaving as though I have a vacuum issue. I'll try to re-read the manuals' diagram of the distributor/mixture section; in the meantime, if anyone has any leads as to where each of the o-rings to be replaced are in the mixture unit section, and which one i might have missed, that'd be great. thanks!

[David T]

From the many posts in this forum concerning the Primary Pressure Regulator, it would seem, once you mess with the "O" rings, there is a high failure rate. I don't know if it is due to the replacement "O" rings not being the correct size, something about how the new ones are installed, or what, but once you touch that regulator it seems to become a problem if it wasn't before. IMHO the primary cause of loss of rest pressure is the fuel accumulator. Next would be the check valve at the fuel pump. Leaks are a possibility but they are very noticeable. The PPR is the LAST likely suspect unless it has been tampered with. Then it seems to become the #1 cause. Bottom line, unless you can rule out all other possible cause you should not touch that PPR.

[Bitsyncmaster]

From the many posts in this forum concerning the Primary Pressure Regulator, it would seem, once you mess with the "O" rings, there is a high failure rate. I don't know if it is due to the replacement "O" rings not being the correct size, something about how the new ones are installed, or what, but once you touch that regulator it seems to become a problem if it wasn't before. IMHO the primary cause of loss of rest pressure is the fuel accumulator. Next would be the check valve at the fuel pump. Leaks are a possibility but they are very noticeable. The PPR is the LAST likely suspect unless it has been tampered with. Then it seems to become the #1 cause. Bottom line, unless you can rule out all other possible cause you should not touch that PPR.

I disagree. The PPR o-ring is the first thing you check. Takes about 10 minuets. The problem with the replacement o-rings was one vendor seemed to get some faulty ones.

The o-ring that makes or breaks the PPR is the little one on the end of the little piston. You remove the large hex cap carfully and you will pull a spring and some washers (used as shims). Then you have to pull the piston that remains in the distributor hole. The o-ring is on the bottom of that piston. Check for missing chunks and or splits on that o-ring.

[NckT]

I disagree. The PPR o-ring is the first thing you check. Takes about 10 minuets. The problem with the replacement o-rings was one vendor seemed to get some faulty ones.

The o-ring that makes or breaks the PPR is the little one on the end of the little piston. You remove the large hex cap carfully and you will pull a spring and some washers (used as shims). Then you have to pull the piston that remains in the distributor hole. The o-ring is on the bottom of that piston. Check for missing chunks and or splits on that o-ring.

I agree with Dave. For what it's worth, I've setup the primary pressures back to spec on many D's now by adding additional shims to correct the preload of the aged spring to correct the primary fuel pressure to spec (or increased for performance exhaust) when setting the k-jet up, and by doing so have removed and re-fitted the same primary pressure parts and O rings and have never had a problem. It must be technique or something then. ..

A running engine with the fuel pressure gauge in the correct position with the isolator valve closed so the gauge reads the fuel pressure from the top fuel line of the fuel distributor, 44 psi (3 Bar) is still short of the 5.2-5.3 bar (75 to 76 psi) is still too low for the primary pressure so is either the regulator in the fuel distributor, blocked fuel filter/ constricted / blocked fuel pickup or knackered fuel pump.

Good luck sorting it