wruiz

Facts: 1990 TPI 350 5.7, new fuel pump relay, new fuel pressure regulator, old fuel pump (over 140k miles), fuel line clears, fuel pressure idle 30-32 psi.

Question: What could cause low PSI? Should I replace pump? Thanks

keykey

Are you measuring without vacuum to regulator? How's the fuel filter? How is the fuel pump relay harness connector?

wruiz

With vacuum to regulator. Filter is new, relay harnes is ok.

keykey

Maybe nothing is wrong, the fuel pressure is supposed to be lower at idle, and that is done by vacuum raising the diaphragm in the pressure regulator to relieve some tension from the spring against the outlet seat. If you want to measure the full pressure you should temporarily remove and plug the vacuum line when measuring.

wruiz

Thanks key,

I replaced the pump anyway, it had over 212k miles on it. I figured it was time to do so already. PSI remains the same around 32 with key on engine off. This time I did remove the FPR vacuum and it went up to near 43 psi. So I guess that's ok. This is what the engine is doing: minor engine missing at idle, when I increase RPMs you can notice lack of power, like engine needing more air and/or fuel. This week I'll check vacuum for leaks. Then go from there. I wonder if I have to replace the FPR, but it is new. Also the fuel injectors are Bosh reman (yellow ones) from ebay.

jacksobe

Do you have an update? My car is coughing and chugging like it is starved for fuel, so I think it may be a fuel pump issue. I am going to swap out the FPR tomorrow since that is easier than replacing the pump, and I think it is the original relay. My 88 Firebird has 391,000 miles on it. These message boards are very helpful to me. The fuel pump probably has about 200,000 miles on it, which is about what the last one lasted.

wruiz

I replaced the fuel pump and it did not fix the problem. I don't think it is the regulator since I don't see any evidence of fuel coming from the vacuum line. I'll check for vacuum leaks this weekend. I've been so busy with other things I have not had time to work on these issues. Also, I will re-set timing and IAC. I hooked tuner pro and have a good 6-7 minutes of data, on idle. Tuner pro shows OK for displayed codes. I'd like to post the data but don't know how to do it. I'm curious on correct parameters for IAC counts, IAC motor position, O2 reading, etc.

wruiz

While I'm getting ready to give another try this coming weekend, I decided to post the most recent data from tuner pro. I'd appreciate any input.


TPS % - 0.00, going less than 2.00 when rev up

Coolant temp – 95.75

Start-up coolant temp – 80.75

Battery voltage – 13.30

Voltage at fuel pump – 12.70-12.80

Engine speed – 675-700

NV ratio – 255

MAP volts – 1.54-1.56, 2.25 at 2% TPS

MAP kPa – 39.50-40.24, 52.79 at 2% TPS

MAT – 65.71

Target AFR – 14.73

O2 – 256 – 800, going back and forth

O2 cross counts – 0 to 246, then back to 0

Integrator – 126-133

BLM – 156

Block learn cell – 4

Injector base pulse width – 2.33-2.46

Desired idle speed – 687.50

IAC motor position – 71-65

Spark advance related to TDC – 17.23-24.96

Spark advance related to ref pulse – 11.50-13.71

Time between ref pulse – over 21000.00 less than 22000.00

Knock count – 2

Knock retard – 0.00

EGR duty cycle – 0.00, EGR removed in chip, but EGR set upstill there

Charcoal canister duty cycle – 0.00

Loop status – closed

O2 rich/lean status – switching between lean and rich continuously

Lean control – enable

)2 sensor status – ready

Shift light – off

Codes 12, 13, 14, 15, 21, 22, and 23 – OK

100ms old CCP purge – false

Air controlled – false

Air switched to port - false

riche

When you did the fuel pressure test did you watch the fuel pump prime before you started it? Did it slowly drop to a lower psi and hold or drop down consistently to bellow 20 psi before you started it?

wruiz

It did prime, but I cannot tell you whether the psi dropped/held or not. I can check tonight.

riche

Ok, The idea is for the pressure not to leak down fast. I like mine is doing right now. Mine will pressure up to 45 and drop to bellow 20 psi in 10 to 15 seconds! I believe my injectors are leaking if yours holds pressure then I would look somewhere else. It is normal for the pressure to drop, but it should be slowly not fast like that. The less it leaks down the better your system is.

If yours is not leaking I would say maybe check the timing? Does your car have the small cap computer controlled 8 pin hei distributor?
I would check the timing with timing light and rev to over 3500 rpm and make sure the computer advances the timing off the timing tab. If it doesn't then the HEI module, wiring or ecm could have issues.
And watch the light if it is not strobing/flashing consistently then that could indicate a weak hei module or coil.
Take my advice at face value, I don't own a thirdgen, I have an aftermarket setup in an old truck. Just sharing some of the things I have learned.