No power, won't rev under load. Low fuel pressure.

[Roadster]

My car ran great until she sat for a while. Starts up from cold immediately but over about 2000 RPM or so under load it is undriveable. Car hesitates and acts like it may be starved of fuel.

The car will rev in neutral with some hesitation at first. I checked the pressure, normal running pressure is 20 at most, I know this is low. When I close off the valve to the CPR I get 70 PSI in the line from the top of the fuel distributor which should be fine. I've watched other people check pressure and close off the valve and the car stays running, when I do it the engine dies. It fires up again immediately.

If I'm getting 70 psi at any point doesn't that suggest the pump should be good? It's only a few years old. I'm thinking the CPR/WUR is bad which is unfortunate as I had it rebuilt a couple years ago. I know the heater element in it is broken but it hasn't been much of an issue.

Anything else you can suggest to check the CPR would be helpful. I'm hesitant to throw one at it with how expensive they are. Thank you!

[Bitsyncmaster]

That sounds like your fuel filter is plugged.

[Ron]

That sounds like your fuel filter is plugged.
I'm thinking you missed him saying it's getting 70 psi out of the FD??

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A restriction at the CPR will raise the pressure too high. So, if it's getting 70 psi from the FD and it never raises the control pressure above 20 psi, it's bad.

[Bitsyncmaster]

I'm thinking you missed him saying it's getting 70 psi out of the FD??

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A restriction at the CPR will raise the pressure too high. So, if it's getting 70 psi from the FD and it never raises the control pressure above 20 psi, it's bad.

My thought is low flow rate because of almost plugged filter when engine is under load.

[Ron]

My thought is low flow rate because of almost plugged filter when engine is under load.I'm with ya.
With the injectors not opening until ~55 psi and it having 20 psi left over (through the decoupling restrictor) at 2000 RPM, it would have to be just right tho....Good thinking!
~$20.00 would tell which.

[David T]

Do you hear the frequency valve buzzing? If not, that would make the car run very lean.

[Roadster]

Do you hear the frequency valve buzzing? If not, that would make the car run very lean.

I do not recall specifically hearing the frequency valve buzzing. The exhaust is so darn loud in the garage I may have drowned it out. I'll try to isolate the sound of that more tonight.

[Helirich]

The car will rev in neutral with some hesitation at first. !

When you say this, are you saying after a bit you can't even rev it in neutral? If that's the case, I would check the pressure after it won't rev in neutral. If the pressure is going down, Either a clogging filter or maybe the fuel pump is losing power. I had an issue where I didn't have 12V at the pump.

[Roadster]

When you say this, are you saying after a bit you can't even rev it in neutral? If that's the case, I would check the pressure after it won't rev in neutral. If the pressure is going down, Either a clogging filter or maybe the fuel pump is losing power. I had an issue where I didn't have 12V at the pump.

I can still rev it in neutral, there just seems to be a bit of hesitation at first. I just tried it again, fired up immediately from a cold start and settled at 24psi constant running. Shutting the engine off the pressure goes up to 39psi and holds. Frequency valve is still buzzing away while it runs.

I shut it off and tried again a few minutes later. Pressure was now down to 15 psi constant running. Shutting the valve on the tester to the CPR spiked the pressure up to 70 but stalls the engine quickly.

Pump and filter are not that old, but not out of the question. CPR has failed before which is why I suspect it again. Also after this is warmed up and experiencing the issue the car seems to be running crazy rich, hurts your eyes just to be back there checking it over.

[Ron]

Shutting the engine off the pressure goes up to 39psi and holds.
Then, at that point, the CPR had to be holding at least 39 psi. ...Bitsy's idea about the filter is looking very promising.

[Michael]

Those oe style pumps are ALL junk these days.

[David T]

If your eyes are burning and it is running very rich the plunger is stuck inside the mixture unit. The muffler also turns red.

[Helirich]

If your eyes are burning and it is running very rich the plunger is stuck inside the mixture unit. The muffler also turns red.

I agree with this, but I don't know why his control pressure is so low. If you must replace the CPR/WUR, they do sell rebuild kits on eBay. I did mine. I was not confident, but it works. There's no instructions and what printing there is, is German. But it's pretty straight forward replacing parts. There's also a video on Utube of a Porsche one.

[cdrusn]

FWIW when I was buying insurance damaged cars that had sat around for sometimes over a year or more in the hot sun, they would act like this because the gas had gone bad. Start ok, idle ok, but put a load on it like trying to accelarate and it would bog down. Take the gas cap off and give the tank a whiff to see if it might be bad or going bad.

[Helirich]

FWIW when I was buying insurance damaged cars that had sat around for sometimes over a year or more in the hot sun, they would act like this because the gas had gone bad. Start ok, idle ok, but put a load on it like trying to accelarate and it would bog down. Take the gas cap off and give the tank a whiff to see if it might be bad or going bad.

Yea, it couldn't hurt to drain the gas for your lawn mower. Fresh gas for the car.

[Roadster]

The gas isn't bad, only sat for about two months while waiting on parts.

I have sent the CPR/WUR out for a rebuild, as knowing this is good will eliminate a big unknown right now. I'll report back once it's rebuilt and installed.

[Roadster]

I got my CPR rebuilt and installed. This solved my apparent fuel starvation as the car will now rev under load. This exposed a new problem, where it is now extremely hard to start and does not seem to be running right, chugging a bit at low RPM and generally lacking power. It takes usually takes numerous tries to crank, walking away for about ten minutes, then coming back and it will fire.

I've been attempting to diagnose the fuel injections system as we want to know the fuel mixture is right. Using the guide on the CO mixture I've started with using a dwell meter on the frequency valve. I don't get a reading anywhere that I should, it sits at 84.5 with the meter set to four cycle, four cylinder as instructed. Jumping the RPM relay the frequency valve does buzz, but I get no normal reading. Pressing the full throttle switch does change the tone of the frequency valve but not the reading. I've even had others try to make sure I'm not missing something on the connection. Even with small copper wire around the ends between the pin and the probe I get nothing.

If I'm unable to get a reading with the dwell meter on the frequency valve, is there another component that logically I should check to restore this?

[Bitsyncmaster]

Reading 84 deg. says your lambda ECU is faulty. The most common problem is a missing ground going to the lambda ECU. Check that the two grounds running through the bulkhead connectors are attached to the engine block.

[David T]

Exactly where are you hooking up your dwell meter? You do not hook it up to the frequency valve. You hook to a wire in the diagnostic plug and ground. Messing with the mixture screw and reading dwell is the LAST thing you do. Before you can do that you must make sure the entire fuel and electrical systems are PROPERLY adjusted and working correctly. You CANNOT "adjust" your way out of this by twiddling the mixture screw. If the tamperproof plug is still in your mixture unit the mixture screw is probably very close to where it should be. ANY vacuum leak is going to make it impossible to correctly set your duty cycle (dwell). If the mixture screw is way off there is a procedure to get it close by seeing when the injectors start spraying. If the fuel plunger is stuck or is sticking you will never get it to run right.

[Roadster]

Understood, right now I'm not adjusting anything until I go through basic tests of the components that I can. I have the dwell meter hooked up to the two pin connecter on the passenger side of the engine bay. I was given some pretty clear instructions and am fairly certain I am checking correctly.

Given that I am unable to get a reading other than 84.5 on the dwell meter for the frequency valve connector but the valve does buzz along and change tone with the full throttle switch, is there a next logical step to check that would prevent me getting a normal reading? I'm having trouble understanding what component would prevent this if it appears to be operating.



Exactly where are you hooking up your dwell meter? You do not hook it up to the frequency valve. You hook to a wire in the diagnostic plug and ground. Messing with the mixture screw and reading dwell is the LAST thing you do. Before you can do that you must make sure the entire fuel and electrical systems are PROPERLY adjusted and working correctly. You CANNOT "adjust" your way out of this by twiddling the mixture screw. If the tamperproof plug is still in your mixture unit the mixture screw is probably very close to where it should be. ANY vacuum leak is going to make it impossible to correctly set your duty cycle (dwell). If the mixture screw is way off there is a procedure to get it close by seeing when the injectors start spraying. If the fuel plunger is stuck or is sticking you will never get it to run right.

[Ron]

I'm having trouble understanding what component would prevent this if it appears to be operating.
Follow the suggestions Bitsyncmaster gave you in post 18.

[David T]

There are other things that can prevent the engine from producing full power. Check the timing, vacuum and mechanical advance. The motor may also need a tune-up if it has worn spark plugs or bad ignition wires. Vacuum leaks are also very common and will lean the fuel mixture out and "starve" the motor for fuel. Vacuum leaks will prevent the vacuum advance from working properly too. Getting back to the fuel system, dirty injectors that don't open and close at the right pressures, or have bad spray patterns will affect how the motor runs too.

[Roadster]

Reading 84 deg. says your lambda ECU is faulty. The most common problem is a missing ground going to the lambda ECU. Check that the two grounds running through the bulkhead connectors are attached to the engine block.

I appreciate all the suggestions. This seems likely but I've spent the past couple weeks carefully going over every ground and connection I can find and I am still not certain where the physical ground locations for this one are located. Does anyone have a photo or description of where I might find the Lambda ECU ground mentioned above? After every check I still get the same reading from the frequency valve with the dwell meter.

6687866879

[Bitsyncmaster]

Here is the bulkhead wire list. I fixed the original because it did not state the two grounds that are used by the Lambda ECU. Look at wire #22 and #23.