3.2 Engine Stalling - Stumped

[wnsgc]

Techman1,

We have checked all the grounds, and then re-checked them by three different people. That is one area we feel confident about. Is it your belief the ground could cause the fuel pressure to spike the meter? If so, please provide more detail, as I don't understand how it could (not saying I'm an expert, actually just the opposite). This has been quite a learning experience for me.

Thanks,
Scott

[techman1]

Not sure, but a guess would be the normal flow of the injectors stopping would cause a pressure surge before the pressure regulator caught it.

Is the surge noticed in advance of the stumble/shutdown?

Ingo, where is the current coming from in the DME to drive the injectors? Are there any wires to the DME that provide an internal ground, for that purpose? Just trying to think out of the box!

Not in the field as a pro, but love fixing problems!

[Otto]

"At idle, the fuel pressure was 38lbs, when we took off it stayed at 38lbs, but then when the car went into that "funky state" where it appears to be running on 5 cylinders, the fuel pressure spike the meter at 100lbs. Could this indicate a bad fuel pressure regulator (as Otto stated last week), or is it a bad fuel damper, or both."

Glad you found your problem. It's unfortunate that you got persuaded into replacing so many
parts especially the rebuilt DME ECM and the "rebuilt" injectors. But that's what happens
when the shotgun troubleshooting approach is used.

So now you need to replace your fuel pressure regulator, as it's sticking causing the high
pressure which in turn kills the engine. When the engine is accelerating under heavy load
the fuel demand in high causing the fuel pressure regulator to allow more fuel. When the
load/RPM is reduced, the fuel pressure (amount of fuel) doesn't return to the normal value
since the regulator stayed at the high pressure setting. The accumulator is not the problem.

[wnsgc]

Greetings,

So with my new issue whereby the fuel pressure goes from 38lbs to 100+lbs under heavy acceleration (3rd gear, 5k RPM's), how can I tell if the Fuel Pressure Regulator (FPR) or the Fuel Pressure Damper (FPD) is the culprit. As a side note, when the car gets into this condition whereby the pressure exceeds 100+lbs, the engine does not stall, but runs erratically (too much fuel I guess), and as I idle, the fuel pressure s l o w l y decreases back to the high 30's of pressure.

Since I'm getting tired of buying parts w/o results, I want to make sure I order the right part. Also, I can only see the FPR for an 85 3.2, not the FPD.

Thanks.

[Flat Six]

Scott: The FPD function is to even out the hydraulic fuel pulses caused by the injectors switching on and off. Really doesn't have anything to do w/your fuel pressure.

Agree w/Otto it's a fuel pressure regulator issue. Before replacing, however, check FPR function using the procedure in the Bentley manual. I'd be willing to bet (50/50 chance or better) that you may have a vacuum issue. The FPR uses engine vacuum against a diaphragm to regulate fuel pressure in relation to engine load (low vacuum/WOT = high load; high vacuum [idle, closed-throttle decel] = low load).

Based on your description of symptoms, it's possible you're not getting sufficient vacuum to the FPR vacuum port under decel conditions to reduce fuel pressure following your high-load/low-vacuum condition. Check the vacuum hose (condition, split, etc.); might even want to put a vacuum gauge on the end of the hose to make sure. IMHO worth checking this before springing >$100 for a new FPR. If nothing else will give you some peace of mind if/when you do replace FPR.

Hope this helps.

Dale

[Otto]

"So with my new issue whereby the fuel pressure goes from 38lbs to 100+lbs"

This is NOT a new issue. It's the same issue you've been having from the
beginning with just slightly different symptoms, i.e. the engine either stalls
or dies after continued hard acceleration. All the wasted time and money
(DME rebuild & injectors) could have been avoided by just monitoring the
fuel pressure as was suggested and not following all the typical mis-guided
info!

"it's possible you're not getting sufficient vacuum to the FPR vacuum port"

More mis-info, as the vacuum only affects the fuel pressure by a few PSIs.

[wnsgc]

Otto,

You're on the left coast, and I'm on the right coast, I needed you over here....

Thanks for your help. I'm heading out on vacation for a week, during which the fuel pressure regulator should arrive, thus the week after next I'll install it and hopefully be done!!! Of course, I'll provide a status update afterwards.

Now it's time to slip into a dry martini and forget the week!!!
Enjoy all,
Scott

[rick-l]

Hey Otto,
Do you really think those injectors were functioning correctly with the waveforms they presented? Is there always only one thing wrong with the cars you work on? This one so far has had wiring issues, injectors and now fuel pressure.

The only thing I worry about your pressure regulator is a restriction in the return hose that flows the volume at idle but won't flow the reduced amount when you get on it.

[steely]

While I would've encouraged a bit investigation prior to the purchase of all 6 injectors, I still think Scott made the right move. The stalling has stopped and presumably there is no more flat-lining of the drive signal. And there was the issue with the short in the relay socket, so I don't think all of the problems were/are related to just one cause (FPR).

[rsscotty]

Here we are at post #188 and the fuel pressure regulator problem gets found.

I did suggest this in post#68 since I worked on a car with identical symptoms.

Then, once again the same suggestion came up on post#14.

[wnsgc]

***** NEWS FLASH *****

After one year, countless part swaps/installs/replacements, diagnosis's, missed diagnosis's, re-diagnosis's, my 1985 Porsche 911 Carrera Targa is fixed. Tonight we replaced the Fuel Pressure Regulator (what a b*tch that was to get to...), cleaned up the vacuum lines between it, the Damper and the throttle area, and took it for a spin. The car was very responsive, and plowed thru the gears, shifting at 6k RPM's. We drove it for a while in a very "spirited" movement, and no problems, no stalling, no rough idling. It drove as it should and probably better than it's ever driven before.

I want to thank everyone who followed this thread, who provided suggestions, encouragement and perseverance, as this got me thru this very very long learning experience, something I don't want to repeat, but am the wiser for going thru it. I have not added up the costs yet, and I just may leave it that way, but over the year, I ended up doing quite a bit of "preventive maintenance..." if you will. I now have about 2 hours of clean-up work to do, and then I'll be ready to wash, wax and polish the car. I may even treat it to a new set of tires in the spring, as this years Porsche kitty has been spent...

Thanks to all!! I could not have done this without the Pelican forum members.
Scott

[Tippy]

Congrats! So in a nutshell, there must have been a groove that developed in the FPR that would cause the diaphragm to stick, fuel pressure building up, and then the motor would be given a good dose of 100 PSI of fuel pressure causing it to die.

Good to hear you're back on the road.

[BoxsterGT]

For those who may need this, I have the correct fittings to the fuel rail to test fuel pressures using either hose..........



or Polyamid tube.......



or as part of a complete Fuel Pressure Tester assy......



The Poly line shown above is long enough to bring up front to the pass compt to monitor fuel pressures while driving.

Please email me for info.

Thanks, Have a great Porsche day everyone.

Len

[Pyrenee2005]

Hi, I found this thread about your issue you finally got resolved, incredible. I have an issue that I have not been able to resolve and it’s a bit different than yours. My car is a dedicated 1985, 3.2, race car, with open exhaust. About 4 months ago I developed a partial loss of power only at full throttle, can happen from 6000 to 7000 RPM, when it happens you feel the car stop pulling as hard and hear the pitch in the exhaust change, when it happens sometimes after a second or 2 it will clear itself out and if it doesn’t 50% of the time lifting the throttle and going back to full throttle will clear it, sometimes I have to lift off the throttle a few times to clear it. When it happens I can also lift off the throttle say 400RPM and hold it there and it clears out and then going back to full throttle also clears it out 50% of the time as well. It can happen once a lap to several times a lap to not happen all day to happen all day, it can happen in the first session of the day or the last session of the day, it can happen if the air temp is 60 degrees or 100. Very hard to isolate because it is so intermittent and won’t happen on the dyno.

I have a fuel pressure gauge and when it happens the fuel pressure is unaffected.
The DME has been checked out and I have tried a different DME,
I have also replaced: coil, fly wheel sensors, temperature head sensor, throttle position sensor, air meter, DME relay, spark plugs, plug wires, rotor, cap

Not sure what to try next, but feels full related as the loss of power is smooth, does not miss and stutter like an electrical miss might. Any input would be great.