RJP 951

I'm looking for a good description of what systems would be observed when the fuel pressure regulator and/or damper are going bad.

I've had a hesitation or pulsing type of response in my acceleration for several months. In general, this blip/hesitation happens in the mid-rpm ranges and under medium to heavy throttle. The pulse/pause can't be seen on the tach, but it feels like a series of momentary pauses (2-3 per second) in an otherwise smooth acceleration. It seems that the harder the acceleration, the stronger the pulse. It's driving me nuts.

I've replaced a number of items in trying to eliminate, but it persists, and seems to be getting slightly worse. So far I've replaced the O2 sensor, plugs, ignition wires, distributor cap and rotor, coil (MSD Blaster), throttle position switch. I've noticed incremental improvements in several areas thanks to all the new parts, but none addressed this issue.

I've also cleaned the air flow meter, and disconnected and cleaned/lubed every electrical connection within reach. Boost and vacuum hoses appear OK and I've replaced or tightened clamps. I get full boost using the BoostSciences enhancer, but prior to that it wasn't quite there (I'm assuming weak wastegate spring for now).

I'm starting to suspect something on the fuel delivery side of the equation. The filter was replaced not too long ago, and I've run several bottles of Techron through the fuel system, but to no avail. I've messed with the fuel quality settings on the DME but no help.

Now I'm thinking fuel pressure regulator and/or damper. How would a bad damper make itself known? What are the common symptoms of a bad FPR?

May be a long shot, but what about the cat? I.e., what are the symptoms if it's starting to clog up?

Any help greatly appreciated.

Thanks
Ron

Jason-85944

I had almost all of the symptoms that you described just a few months ago. Turns out that it was a bad FPR. It was a PITA to figure out.

Jason

Steve Lavigne

I have a similar problem. I've spent some time diagnosing fuel, spark, and vacuum and replacing parts. FYI, I have replaced the fpr and dampener.

After giving Porshche G96 a ride in my car, he is convinced that it is coming from the back of my car and not the engine. After I thought about it further, I realized that the frequency of the vibration seems to change primarily with speed, it does not occur below 50 mph, and the intensity seems to vary with the level of torque. Additionally, it does not seem to happen till the car warms up.

Based on this information, I believe it is something between the secondary shaft of the gearbox and the wheel bearings. I'm going to replaced both of my rear axles and hope that that fixes the problem (I also have a clicking from my left rear cv).

RJP 951

Jason - were there any other symptoms such as rough idle or other consequences of the bad FPR? My car runs fine except for that pulsing/hesitation while accelerating.

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Steve - based on your use of the word "vibration," I think you have a different problem. In my case the speed doesn't seem to matter either, but on a few occasions it did seem worse when the engine was warm (tough to tell since I drive gently until it's warmed up). In any case, thanks for the reply. Please post your results.

Thanks
Ron

RJP 951

Bump...

anyone know how a bad dampener would make the car behave, or if it's a potential culprit?

Thanks
Ron

Melchior

Are you getting any vibration from the engine at idle?

RJP 951

I do get some vibration at idle, more when cold, that I'm attributing to motor mounts. The engine itself runs smoothly at idle, and the rpms stay steady.

Ron

cheetah chrome

ive noticed an uneven exceleration w/ my car too....very similar to what your describing. it happens under normal acceleration when boost is just starting to build (from the .04 to the 1 mark on the stock gauge). very light on the peddle, like putting around town or in traffic driving. mine is most noticible in 3rd gear, not saying its trans related, due its longer lenght of time under said conditions. if i gas it harder and the boost builds rapidly theres a lil' bobble then its even hard excelleration. the issue has become more noticable since i installed my chips, fpr, and lbe....which i dont think are causes either.

in my newbie to turbo cars wisdom i would have to say the issue caused by either uneven delivery of the fuel/air or the burn/igition (im new to turbo charged cars so bare w/ me). it seems your thinking the same way. ive just replaced the fpr w/ a 3 bar bosch (supplied w/ guru chips) and im going after the damper next. after that im going after the fuel filter and the fuel pump (im thinking my fuel pump is probably tired...on cold starts it takes a few too many cranks for my liking to turn over which im thinking is low/no fuel pressure). anyone running a fuel pressure gauge...what type of readings are you getting at startup, idle, engine under excelleration (on a dyno maybe). could this possibly be an injector issue?

ive kinda ruled out uneven boost coming in, the lbe should be a cure all for the low pressure which my problems exist. otherwise theres not much there (again bare w/ me) charge comes out cold side of turbo into intercooler then into intake (pls correct me if im wrong) which ive checked tightened all connections.

ignition and vacuum is what im gonna hit last. eventually i'd like to replace all hoses in the vacuum circuit, ive purchased most of the large formed hoses now i just need the little stuff and time. ignition wise i replaced the plugs 5k ago but havent done cap or wires (hmmm maybe a crossfire issue....ill have to look under hood in the dark).

anyhow best of luck and keep us posted if you find the fix...i'll do the same

83na944

I'm positive that a failed FPR will flood the engine with gas becuase the fuel rail will be over-pressurized. Learned that the hard way.

Suggest you look for a leak in the small vacumn lines. The connectors get hard with age and crack.

triscadek

Depends on how bad, when the FPR was bad on my S, I was running about 65 psi and it idled roughly had the drop to idle shudder pretty bad and burned your eyes to stand behind it running it was so rich and blackened the bottom of the rear bumper.

Melchior

RJP951,
Try the simple stuff first.
It sounds like you have a vacuum leak. I was amazed how much better my car idled, accelerated, and started after I replaced the two $1.50 vacuum hose connectors that connected to the FPR and Dampener. The old ones looked and felt like they were in excellent condition but after swapping them out, the difference was amazing. Also, follow the plastic vacuum tubes from the FPR and Dampener and see where they connect: replace those rubber fittings as well.

RJP 951

Thanks for the advice.

I was hoping to get the new FPR and damper on Friday but they didn't show. Once I'm closer the putting the car away for its winter nap I'll replace all the vacuum lines. I plan to repaint the intake manifold, so its removal should make the work on the vac lines easier.

Ron

Melchior

If your taking the intake manifold off, then order new vacuum lines (~$30) for the in/out of the Idle Speed Valve. Also, clean the vacuum passage of the ISV with throttle body cleaner and follow it with a little silicon lube to keep the valve operation smooth. Also, you can easily reach the oil seperator and replace it's cheap o-rings that usually fail and allow oil to run down the side of the block.

Chris Prack

[quote]Originally posted by Melchior:
<strong>Also, you can easily reach the oil seperator and replace it's cheap o-rings that usually fail and allow oil to run down the side of the block.</strong><hr></blockquote>

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Not on a 951!!

Melchior

Sorry, I was thinking S2!