chck4342

I'm trying to diagnose hard starting issue on my 90 coupe. Hard starts both when cold or hot. Fuel pressure guage reads 46lbs with key on. holds 36lbs with engine running but drops to 0 within 10 seconds when shut off. FSM diagnostics says injectors or fuel pressure regulator and to pinch off return line to test regulator. Vacuum line has no smell of fuel. This is a 90 and has NO soft section of hose to pinch off, unless its back behind the tank somewhere where I cant access.
Anbyone know how I can determine fpr or injectors. Injectors have been ohm test and check ok. Yhanks

LT1 Spirit

Mine did the same thing. It turned out to be the fuel pump.
I took off the gas lid and the rubber part that covers the tank. That's where I pinched the lines.

65Z01

Remove the fuel filler cap and pull out the rubber surround to reveal the flex fuel lines; of the two to the right side, one is pressure, one is return.

Wrap a rag around the tubing and use vice grips to clamp it. Turn on the ign switch. If pressure holds when the return line is clamped the FPR is ok.

Have somone turn on the ing switch and immediatly clamp the pressure line to check the FP check valve. If pressure holds the check valve is ok.

If both test pass, the leak is either in the injectors on fuel lines.

cwyates4

[QUOTE=65Z01;1566379113] If pressure holds when the return line is clamped the FPR is ok.
QUOTE]

I thought that test ruled out injectors, not the regulator...?

FICINJECTORS

if fuel pressure drops to zero its 1 of 3 things. the FPR the injectors or the fuel pump check valve. If you are loosing pressure and you clamp the return line, you are taking the FPR out of the loop back to the tank. Therefor, if pressure holds it is the Regulator that is no good. If pressure does not hold then its probably injectors since you have multecs, But don't rule out the check valve.. you can test it by finding a piece of the rubber section out of the tank of the pressure hose. Have someone turn the key to pressurize the system. Quickly pinch that hose to eliminate the pressure from releasing back to the pump. If pressure does not hold it is for sure an injector or several injectors. It only takes a little leak in an injector to release pressure.

chck4342

Thanks LT1spirit and 65z01, I was able to get to the soft hoses to clamp it. After starting engine pressure did hold but at about 62 lbs which is high. According to chart 7 page 2 of 2 (6e3-A-29), the high pressure indicates bad fpr. Any body agree or disagree? ( No restrictions in the line BTW)

cwyates4

Whatever it is, the pressure is dropping rapidly! from 36 to 0 in 10 seconds is alot faster than my 21 minute drop was with two leaky injectors.

65Z01

Sorry but pp 6e3-A-29 in my '88 FSM is about Code 15...

Anyway I don't think high pressure is an indication of FP failure with the return line clamped. Since the FPR cannot releive the pressure back to the tank it should go to the max of the FP, IMO??

Since pressure held with the return line clamped, sounds like you have a FPR issue, with injectors, FP check valve and lines being ok.

chck4342

I think your correct and
i may have got lost in this darn diagnostic tree. I'll start over and post again. I think I need to get a degree in reading the FSM!

schrade

Picture help?

This is '94; I think Mr. Shaw might have L98...

cwyates4

Here you go, this might help you out:

http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf

Some slight differences, but basically the same.

chck4342

OK ...I've run the diagnostics again and this is what it leads to. 46lbs with key on, pressure drops to 0 as soon as pump stops running. Pinched off return line and pressure holds at about 62lbs. According to FSM this leads to faulty pump. Any comments? thanks. BTW this is on a 1990 L-98...vin8 Diagnostic chart is acually 6E3-A-23, not what I stated in earlier post. That was chart for vin J. Thanks

chck4342

Yes this chart is basically the same as I'm going by...seems to indicate fuel pump...Yes???

schrade

Yes? UNLESS there is a check valve between the pump and the FP guage itself. Then, THAT is what is wrong, but it does not show in Mr. Shaw's pics.

I don't think bad injectors wouldn't let the pressure off that fast, even if the car was running!

FICINJECTORS

I must be missing something? The fuel pressure holds 62psi when the return line is pinched.. How is that the fuel pump?

chck4342

Jon...thanks for pointing that out.I ran the diagnostic wrong again. Here is the latest run. ignition on...pinched off PRESSURE line...did not hold...ignition off. Ignition on...pinched off return line...pressure did not hold. So this indicates (according to FSM) leaking fuel injectors. Guess this is your department! I really didnt think that an injector issue would allow the fuel pressure to bleed off that rapidly. The pressure drops from about 45 lbs to 0 almost immediately. The car does not run THAT bad after it starts

schrade

I agree. There's no way 8 bad injectors would allow immediate drop to 0psi.

If the fuel was 'dumping' out of the injectors like that, it WOULDN'T be spraying into a mist, and it wouldn't run. AND, I think you'd be getting a hydraulic cylinder lock from gasoline dumping into a cylinder when it was not running. Then the crankshaft would stop turning when you're starting the motor.

Isn't that right Jon?

FICINJECTORS

they can absoulutly bleed pressure that quickly.. think about it. liquid does not compress. so any size leak will will release the pressure almost instamatically.

chck4342

I guess I will be calling you in a couple of days about a set of injectors