3.2 FPR fuel pressure regulator died. Ran lean for some time, how cooked am I?

[thisisgoodnews]

Engine fully rebuilt (stock internals, SW chip, Fabspeed exhaust + cat bypass) this past spring at a reputable aircooled Porsche specialist shop. Everything went well for 3k miles. Went for a last autumn ride before winter hibernation. Made some power runs up until the redline and noticed unstable power delivery at around 4-5k rpm, difficult to reach redline. Repeated several times, 4/5 runs were bad, 1/5 was ok. Scratching head.

At home, did some diagnosis, checked the FTO switch, appears to be working. Disconnected O2 sensor, went for another drive, pressed harder, no changes.

Couple of days later, went for another, now calm, highway drive. Now notice, that power delivery is unstable even at lower rpm, difficult to climb uphill ant 2nd gear at 3k rpm, slight vibrations noticeable when climbing uphill.

Left it at the shop. Shop reports low fuel pressure, FPR and diaphragm damper needs replacing (was not replaced during reassembly). Makes sense.

Now, it is obvious, that it wasn't getting enough fuel, thus running lean. Am I correct guessing, those vibrations could been engine knock? How screwed am I doing between 120 and 180 miles, since noticing first symptoms? Reading horrible things, high combustion temperatures and oil washing down by unburnt fuel. Oil temperature never went above middle mark.

Besides the compression test, what else should I be looking at? I realise, this did nothing good, but how likely I (badly) damaged this 3.2 engine?

Also, show me your most discreet AFR gauge installations.

BONUS pic as a thank you for attention.

[proporsche]

If the shop said you need the FPR have you or them replaced it yet?
Also do you have CAT or straight pipe?
Ivan

[boyt911sc]

What are the fuel pressure readings (with and w/o vac) with just the FP running? This is a simple test that will determine the condition of your FPR. To test run your Carrera 3.2 fuel pump, bridge fuses #16~#17 (counting from front bumper). Do not replace parts unless tested and confirmed defective.

Tony

[thisisgoodnews]

Originally Posted by proporsche

If the shop said you need the FPR have you or them replaced it yet?
Also do you have CAT or straight pipe?
Ivan

New parts are yet to arrive and to be replaced. As for CAT, it has been replaced by pre-muffler cat-bypass pipe, which is what you probably call straight pipe?

Originally Posted by boyt911sc

What are the fuel pressure readings (with and w/o vac) with just the FP running? This is a simple test that will determine the condition of your FPR. To test run your Carrera 3.2 fuel pump, bridge fuses #16~#17 (counting from front bumper). Do not replace parts unless tested and confirmed defective.

Tony

Fuel pressure has been tested by the Bentley manual procedure. With engine running and it showed just over 1.5 BAR. Disconnecting vacuum did nothing and pinching the return line rapidly increased the pressure. All this point to the FPR.

[BoxsterGT]

Following this with interest.

We have a Fuel Pressure Gauge......



....that is easy to connect to evaluate the Fuel pressures. PLEASE NOTE: This gauge is for test purposes only and not for permanent installation. There is no support to stop possible vibration when driving.

We also offer a Modular FPR and Damper set....



.... that is very reasonable in price (MUCH less than factory) and available as individual parts, including the Fuel Damper.

For information please email me. NO pm's as my box is FULL.

len.cummings @ Verizon.net but without the spaces.

[thisisgoodnews]

Len, thank you for the offer. I might be interested in a pressure gauge - do you have it in BAR?

Here, due to lack of aftermarket options locally and wanting to fix it asap, to calmly put it in winter storage, went with OEM parts. Shop replaced the regulator and damper and the fuel pressure went to spec - 2 BAR at idle and 2.7 BAR with vacuum disconnected.

However, now we bumped into another wall - with fuel pressure now correct, engine starts easily, but seems to be running overly rich, unevenly and fuel smell from exhaust is felt immediately. Mechanics made a little test drive, power is not consistent, and it becomes undriveable when warmed up.

I didn't like them making test drives in this condition, also their approach to start throwing parts at everything and see what sticks, and tear it all apart while without making all the necessary checks of sensors beforehand. Therefore, I parted with them.

Now I will be having the car at home for coming several months before I will get it to the (distant) aircooled 911 specialist who built the engine. I kinda wanted to bring the car to him for a checkup after a engine rebuild, so now it will make more sense.

Now, I have an opportunity to test by swapping a known good DME, but from a 1984 US model. Everywhere I looked, says, that they are compatible. Right.. right? Can anyone confirm? Or should I dig more? Here a the pictures for actual units: own, left, 1986 / borrowed, right, 1984.



What else can I easily check when the car is with me? I came upon a very extensive and very well documented diagnostic process in another thread I will replicate some tests of, but maybe there is something I could be directed to from the data we have now?

Would love to get out this issue of the back of my head for holiday season

EDIT: litereally, after making this post, and seeing both pictures next to each other, notices that one the ECU repair companys label, field ECU is the part # and it's the same, so I'm pretty sure they will be compatible..

[thisisgoodnews]

Swapping DME's and DME relays did not make any change, so can be ruled out.

Next onto the list are CHT, IAT, rpm and reference sensors. Static test's all checked out.

CHT


IAT


rpm (speed)


reference


Then, I tried to use my toy oscilloscope for starters, to get the signal generated by reference and speed sensors, and this is where things got interesting:

speed sensor data


ref sensor data


According to this result, signal is way too weak, both generating 0.4-0.5V peak to peak, instead of 2.0V for ref and 2.5V for speed sensors.

I guess my next step is to acquire a more trustworthy scope to verify the results for flywheel sensors. If confirmed, the main suspect is obvious.

Has anyone faced similar sensor data? Would this cause the symptoms my car is experiencing?

[BoxsterGT]

thisisgoodnews-

Yes we have this pressure gauge in bars.

Please email me for info.

len.cummings @ verizon.net but without the spaces.

Thank you.

Len

[thisisgoodnews]

Connected the scope over the weekend to read signals from reference and speed sensors.

Signal checked out OK and strong, so this means the problem is elsewhere.





Seems like it's hands down for me at my underground parking and the car will have to wait for the warm season, when I will be able to send it to the the aircooled specialist in Poland.

I entered this prompt below to Gemini, and it doesn't give me many suggestions what I could do at home.

My Porsche 911 3.2 1985 has a rough idle problem, misfires, smell of unburned fuel. For diagnostics, here's what is known and what steps were already taken:
- engine fully rebuilt in May 2025, 5000 km done since then;
- injectors have been tested for function and proper spray pattern during rebuild;
- mileage for first 5000km after rebuild was spotless. The power hesitation at high RPM was spotted, folowed by a slight misfire (popping) and later by erratic idle;
- fuel pressure regulator (FPR) and diaphragm damper were replaced, fuel pressures now checks according to spec;
- compression test is OK, 11 BAR across all 6 cylinders on cold engine;
- leakdown test of a cold engine is OK;
- cylinder Head Temperature (CHT) sensor resistance is OK;
- plug wires connected in correct order;
- disconnecting O2 sensor brought no effect;
- Air Flow Meter (AFM) has been refurbished during rebuild, contact track replaced;
- Intake air temperature sensor resistance OK;
- to check for DME faults it was swapped to a another known good unit with no effect;
- FULL THROTTLE and IDLE switches tested;
- no vaccuum leaks detected with a smoke test;
- flywheel speed sensor and reference TDC sensors are OK showing correct resistances and generating correct sinewaves;
- ignition coil resistance has been checked, is OK, both primary and secondary coils;
- spark plugs and spark plug wires replaced to new during engine rebuild;
- ignition cap and rotor were not replaced and have around 30000 km on them;
- GROUND connections checked and cleaned;
- valve clearance has not been adjusted since the rebuild;
What are possible next steps for diagnostics?

As it's a simple shot, I just ordered a new distributor car and rotor, as they haven't been replaced after the rebuild.

[76FJ55]

Have you changed the fuel filter? Or have you performed the flow rate test for the fuel system? the flow test should provide a min 850 cc/30 sec.

[thisisgoodnews]

Thank you for the hint. Fuel filter was replaced to new during the rebuild back in May, and with fuel pressures now OK, I excluded it out of the equation.

Will test it, and report back as soon as I will gel the similar hose with an elbow.

[76FJ55]

Originally Posted by thisisgoodnews

Thank you for the hint. Fuel filter was replaced to new during the rebuild back in May, and with fuel pressures now OK, I excluded it out of the equation.

Will test it, and report back as soon as I will gel the similar hose with an elbow.

Don't get caught up on the specialty hose shown in the manual. the return line off the bottom of the FPR is actually just a slip-on hose with a hose clamp. n this is low pressure since it is just the return line back to the tank, and you are just diverting it to a catch can to measure the amount of fuel delivered in those 30 seconds.