runs good then warms up then no fuel pressure

[rdrive]

1986 corvette manual w/overdrive sat for 12 years with blown head gasket. so here's what Ive replaced:
had engine rebuilt (bored new pistons etc..)
replaced 1 head and had both rebuilt (aluminum)
new radiator
new fuel pump (twice)
new clutch and master cylinder
new injectors
fuel pressure kit
new cap, rotor, wires, plugs
new tires
new ignition key
new battery
The engine starts right up and runs good until it warms up then fuel pressure gets erratic then drops then will only idle
until I turn key off for a few seconds then it starts and runs another 30 seconds then same.
I have a Gage on fuel rail on window so I see it go down.
also if I turn key on (without starting) it goes up to 4opsi then I hear a click and it goes down. but it stays up at 40psi (when running) until it warms up. I replace the fuel pump twice.
It didn't seem to have this problem until a repair shop said it had 60psi fuel pres. so they put a fuel reg kit in it but
at that time I was fighting a injector problem which is solved but I don't think it was dieing after warm up until then. I just am sick and tired of taking off the plenum.
one last thing there is a round vacuum thing that I see in the manual but it's not clear how it hooks up but it has no vacuum leaks.
So my plan is to replace the fuel filter then go for the fuel reg.
anyone have any advice I'm open and would be grateful

 

[Schrade]

also if I turn key on (without starting) it goes up to 4opsi then I hear a click and it goes down.

Start here.

Static fuel pressure (motor off) should STAY at 40 longer than you describe.

Don't care about motor-running fuel pressure (dynamic fuel pressure) right now.

Get pencil + paper, and write in 15 sec intervals how much static pressure drops, then post it here.

If it drops as fast as you describe, you have leaking injectors, or FPR bladder failure, or fuel line leak, or combo thereof.

Post leakdown time, nothing else right now.

 

[rdrive]

I appriciate your fast response

Start here.

Static fuel pressure (motor off) should STAY at 40 longer than you describe.

Don't care about motor-running fuel pressure (dynamic fuel pressure) right now.

Get pencil + paper, and write in 15 sec intervals how much static pressure drops, then post it here.

If it drops as fast as you describe, you have leaking injectors, or FPR bladder failure, or fuel line leak, or combo thereof.

Post leakdown time, nothing else right now.

doing as your requested turn key on it jumps to 43psi then drops to 0 in 3 seconds. when i turn key off then back on it stays at 0 until I wait for a minute. I just put in new injectors and o rings and that's what got it to run good. I'm going to go play around trying to find some answers.
(little update)
well I left my manuals at home but if your standing at the back of the car looking down at the gas tank I pinch the bottom right line and the pressure went to 60psi when i turned key on and when I turn key off it stayed up and slowly was coming down looks like it holding around 40 looks like it would take about 1/2 hour to go down. I'm thinking it is the return line telling me it's the fuel reg. what do you think?

 

[Schrade]

doing as your requested turn key on it jumps to 43psi then drops to 0 in 3 seconds. when i turn key off then back on it stays at 0 until I wait for a minute. I just put in new injectors and o rings and that's what got it to run good. I'm going to go play around trying to find some answers.
(little update)
well I left my manuals at home but if your standing at the back of the car looking down at the gas tank I pinch the bottom right line and the pressure went to 60psi when i turned key on and when I turn key off it stayed up and slowly was coming down looks like it holding around 40 looks like it would take about 1/2 hour to go down. I'm thinking it is the return line telling me it's the fuel reg. what do you think?

STOP

Stop there. No more info necessary at that moment. (I'm not even reading further...)

Separate the return line at the Fuel Pressure Regulator. Cap it; re-test EXACT SAME TEST.

Post results.

 

[Schrade]

No can do on a TPI .
Have to remove and cap the return hard line at front of intake

Typo.


"STOP

Stop there. No more info necessary at that moment. (I'm not even reading further...)

Separate the return line a-F-t-E-R the Fuel Pressure Regulator. Cap it; re-test EXACT SAME TEST.

Post results. "

 

[rdrive]

STOP

Stop there. No more info necessary at that moment. (I'm not even reading further...)

Separate the return line at the Fuel Pressure Regulator. Cap it; re-test EXACT SAME TEST.

Post results.

well I replaced the fuel regulator kit before I read your message but the good news is now when I turn the key on it goes straight to 40psi and holds. after about 5 minutes it start creeping down slowly. The bad news is when I start the engine and drive down the road when it warms up the fuel Gage starts shacking and goes down to 15psi then if I idle it goes back up until I give to gas then it repeats. if I turn it off for 10 seconds it come back up solid for a couple of minutes. So I'm still lost.

 

[Schrade]

Good job on static test.

Dynamic test is idle, motor warm, vacuum line OFF of FPR.

Note the reading.


(gimme' 5 here, to dig up the testing article...)

ed.:
from TPI diagnostics (LT1 is ported fuel injection, so it doesn't matter that the article is L98). Tests are the same, SPECS of pressure MIGHT be a little different.
(I think CAC servers are resizing with limits)

 

[boomdriver]

Has anyone looked at the inline fuel filter lately?

The reg needs a new diaphram. The system needs a new filter. Possibly a new pump w/strainer.

At least do the 1st two things...

 

[Schrade]

well I replaced the fuel regulator kit before I read your message but the good news is now when I turn the key on it goes straight to 40psi and holds. after about 5 minutes it start creeping down slowly. The bad news is when I start the engine and drive down the road when it warms up the fuel Gage starts shacking and goes down to 15psi then if I idle it goes back up until I give to gas then it repeats. if I turn it off for 10 seconds it come back up solid for a couple of minutes. So I'm still lost.

So we're NOT ready for dynamic FP tests...

Exactly WHAT does it bleed down to?

You've got to cap the line A-f-T-e-r the regulator, and check for injector / regulator / line leakage.

NOTHING else right now...

 

[rdrive]

Well I got my pressure back but still want to send over a cliff please help

The regulator and fuel pump got my fuel pressure up to 40 and it holds for hours. But still had problems with missing. Then I found the shop that rebuilt my motor put cast plugs in my aluminum heads so I thought I had it. It idles pretty good down to 600 almost smooth but when I accelerate it feels like it's missing a cylinder especially on freeway or any load it shakes. But it sometimes feels OK then as soon as I load it it shakes unless I give it 3/4 throttle then it smooths out and moves but I may be getting faked out because it is a lot of power. I took it to Corvette specialist and wasted $200.00 he told me it failed a leak down test on #2 cylinder so I took it back to the shop that did the engine and I saw the leak down test and it was fine so is the compression and every spark plug wire I take off one at a time and each one reacts so I'm lost again . What ever it is I'm tired of it. I have an 1986 FSM with wiring schematics but I need some wisdom and or experience to point me on the straightest path to fixing this please.

 

[vigman]

So the car's running more or less ok ?

I would measure the TPS.. I assume it's the original one?

Mike

 

[John Robinson]

I would measure the TPS.. I assume it's the original one?

Mike

Right and with all the on again off again of the connectors I would suggest he check all the wires for brakage or bad connectors or bad grounds

 

[Schrade]

but still want to send over a cliff please help

Read what I post, and if you don't understand what I post, then post back, that you don't understand. Otherwise, we're wasting time (and your money, which we can get back, unless you're rich, and you don't need it)

The regulator and fuel pump got my fuel pressure up to 40 and it holds for hours. But still had problems with missing. Then I found the shop that rebuilt my motor put cast plugs in my aluminum heads so I thought I had it. It idles pretty good down to 600 almost smooth but when I accelerate it feels like it's missing a cylinder especially on freeway or any load it shakes. But it sometimes feels OK then as soon as I load it it shakes unless I give it 3/4 throttle then it smooths out and moves but I may be getting faked out because it is a lot of power. I took it to Corvette specialist and wasted $200.00 he told me it failed a leak down test on #2 cylinder so I took it back to the shop that did the engine and I saw the leak down test and it was fine so is the compression and every spark plug wire I take off one at a time and each one reacts so I'm lost again . What ever it is I'm tired of it. I have an 1986 FSM with wiring schematics but I need some wisdom and or experience to point me on the straightest path to fixing this please.

SERIOUSLY; we need to work BACKWARDS on this. NOT FORWARD.

FIRST:
told??? THE CORVETTE SPECIALIST TOLD ... ??? WORDS GO AWAY WHEN THE SOUND STOPS. YOU TELL HIM THAT YOU'RE FROM MISSOURI, THE 'SHOW-ME' (NOT TOLD-ME) STATE.

Do you have the receipt, with THAT IN WRITING, THAT #2 CYLINDER IS A FAIL - CAN'T HOLD THE SQUEEZE???

SOMEONE IS SHOVELING THE BS, AND YOU DON'T NEED A WRENCH FOR THAT - YOU NEED BOOTS, OR WINGS:

Oh, man. The bullshit piled up so fast in Vietnam you needed wings to stay above it.

SECOND:
How long did you see the squeeze guage on cylinder #2, at the shop that did the engine???

I think we need to address that, and NOTHING else at the moment...

 

[Schrade]

You've done STATIC fuel pressure tests, and you say the pressure holds for hours. Right?

Great.

If (and ONLY if) you're sure about that, NEXT, AFTER GETTING TO THE BOTTOM OF THE #2 CYLINDER PROBLEM, you need to do dynamic fuel pressure tests. NOTHING ELSE.

DID YOU READ THE TPI PAGE SECTION THAT SHOWS THE DYNAMIC FP TESTS??? If you cannot read it, give me your email address. YOU HAVE TO DO THE DYNAMIC FUEL PRESSURE TESTS NEXT. NOTHING ELSE.

(they are not called dynamic fuel pressure tests in the article. dynamic FP test means 'with the motor running', with vacuum off of, AND ON, the regulator, and also with the FP guage ON THE WINDSHIELD, HAMMER PEGGED. YOU HAVE TO DO THIS TEST)

 

[vigman]

Just puttin this out there

There's an OH BY THE WAY in the newer style fillerneck assy's/wiring. There is a little white plastic RF trap in the fuel pump power line that FAILS and I cant remember when that started ( Year ) but the fix is easy... CUT THE BASTARD OUT!