football4life

Guys, I had a issue where my car was falling on its face then jumping back to life then falling again. Got home and checked the fuel pressure. Here is a video of what I found.
Lt1 Camaro Fuel Pressure testing - YouTube

I am wondering if this is a pump issue or a FPR problem? I have a fairly new fuel filter. Both the Pump and FPR are stock its a 1994 with almost 100K.

I am not having problems starting just once it falls there is no power even with full throttle, but once it picks back up it feels like nothing is wrong.

I did pull off the vacuum line and there was no effect on fuel pressure.

Thanks for any help!

ACE1252

What is the pressure with the key on, but not running?

football4life

It holds 33-37 psi with the key on but engine not running

slick1hunting

Was there fuel in the vacuum line? When you pulled vacuum line was you at idle? You should see 5+ psi extra with it off at idle. Might be worth making some wot runs with guage on windshield as well as normal driving and see what it does when you experience your issue.


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slick1hunting

sorry if your video showed any of that my phone dont let me watch from most links


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football4life

No I did not notice any fuel in the vacuum line or any coming out of the fpr vacuum port. But there was no +any PSI when I removed the vacuum line. The vacuum line has good suck to it.

All the video shows is the fuel pressure skipping from 38-18-38 PSI at idle.

football4life

Well, I went ahead and picked up a new FPR from autozone today and put it on along with a new fuel filter. I put the filter on first and the car was still falling on its face just like before.

Then I put the new FPR on and the car seemed to be running great, the tack showed stable rpms, the trottle felt great, no more bogging down. I took it on a twenty mile drive: no Problems at all.

But I was still curious so I put the Pressure gague back on. Even though the engine seems to be running happily, the fuel pressure is still bouncing up and down just like in the youtube video I posted before .

Anyone have any thoughts here? and is it safe to be running the engine with the fluctuation in fuel pressure like I am having?

Should I consider replacing my fuel pump next?

slick1hunting

I am no expert but if you had a big drop while wot it would seem that could be very bad. If you change the pump and do not have the trap door I would definately consider doing it.


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football4life

Yeah I have been in the trap door on my last two camaros.

I was looking at the walbro pump kit from racetronix. How critical is it to get the hot wire kit along with the pump?

Also, how much hp will the stock pump support? I have a small cam intake headers 1.6 rr some port work and cat back. Would it be worth upgrading the injectors too? I am running stockers now.

football4life

Update:

SO I decided to throw the pressure gauge back on the car this moring just to see if the pressure was still fluctuating. And what do you know turn the key to on pressue reads about 38 PSI. Start the car Pressure holds 34 PSI at Idle pretty steady with no fluctuation. pull the vacuum line to simulate WOT, Pressure jumps to about 42 PSI. put vacuum line back on Pressure goes back to about 34 PSI. Rev it from idle and the pressure raises from 35 to 40 as I give it more throttle.

This car is puzzling me. Maybe the pump is just Weak shouldn't I be at 43 PSI? And can anyone explain why the fuel pressure is raising as I give it throttle?

RamAir95TA

The fuel pressure raises as vacuum increases pulling on the diaphragm to allow more fuel to enter the fuel rail. That's how it is designed.

While the fuel pressure readings may be close enough to allow the engine to run properly it may also be worth a look to scrutinize your fuel pressure gauge. Perhaps you could try a friends or rent one.

If the readings ARE accurate your pump may be getting weak.

sscott

I just replaced my pump with a Delphi unit and have an adjustable FPR and my fuel pressure reads 48, what is the correct pressure my Autometer fuel pressure guage supposed to read? I think 48 may be to high. Thanks.

Injuneer

With engine idling, remove the vacuum line from the fuel pressure regulator. Plug end of line to prevent vacuum leak. With line off the FPR, set the pressure to 43.5 PSI ( 3 bar ). That is the standard pressure GM uses to flow rate injectors.

When you reattach the vacuum line, pressure should drop proportional to intake manifold vacuum. A stock cam typically drops the pressure 8 to 10 PSI below the "no vacuum" reading. A more aggressive cam produces less vacuum, so there will be less drop, maybe as little as 5 PSI reduction.

What brand is your AFPR. What pressure did you tell your tuner you planned to run?

sscott

Thanks engineer. Will 48 psi hurt anything with my setup, GM performance parts LT4 kit top half kit Hot Cam, heads and intake I also have 30# SVO injectors. Mike Norris tune in PCM. Don't remember the FPR name but the pressure was slightly lower when the stock fuel pump was in the tank, it crapped out about a month ago and I replaced it with a Delphi unit and the pressure is higher from when the factory stock unit was in.

Injuneer

Running at 48 PSI causes the injectors to flow 5% more than the PCM thinks they will flow. The PCM will react in closed loop by lowering the long term fuel corrections 5%. If the LTFT's are already near being maxed out (they can only subtract up to 15.6%) due to some other irregularities, it gets harder for the PCM to precisely control A/F ratio, using the short term corrections as well.

Big problem is when you go into power enrichment mode (~WOT). Since the PCM was subtracting fuel, it will default to 128 LTFT's, and be over fueling the engine by 5%. For example, if you PE mode target A/F ratio is set to 12.8:1 in the tune, it will end up at ~12.2:1, probably resulting in a small power loss.