I was writing a test i did while you were sending yours--it's above yours---I'm multi-tasking right now--Tree fell through the sky light on my house --which ever one pi$$'S me off the most i go work on the other If there is another fuse block i have no idea where it would be

 

I don't kow how familiar you are with the aldl -more than I, maybe, but do NOT, not turn the ign to start with jumpers in it.
our next questin is to verify where fuses are. should be in owners manual, if not...have to do a google search, I guess.

I've beenon forums where this would have goten a lot of help, not sure what the deal is.

 

Didn't turn the switch on while testing (G)--I'm to scared to screw something else up. I only put the jumper on with key out. Removed the jumper when i got fuel then i started it ran till fuel was used up

 

didn't want it on my conscience...

the responses I got on the 87 FP fuse says it may be FR or CRANK. also said there was or may be one under or behind the display panel, 3A. I would verify all that before I spent an hour removing plastic parts. but it should be btm right corner, so they said, from their "memory." not the book. go figure.

circuit is interrupted, all we kow for sure.

 

One thing i stated in the begining of the thread is i had taken the battery out and cleaned the bat. comp. No water just rag and blow gun-Theres a bunch of fuseable links behind the bat. Do any of them send power to the fuel system???Maybe i disturbed one that was ready to go bad. I can't seem to find a wiring diagram for the fuel system for 87c4--not in my book or i just missed it. (HAYNES)

 

Go BACK to the "jumper terminal" and follow EACH hot wire past its fusable link and continuity test. Your loss of power is there.Which wire..? don;t know. They are all "hot" wires to the engine mngt, ecm, FP, etc. Obviously you disturbed one or the wire was rotted and broke internally,...that does happen alot on C4s.
Continuity ck all the fusable link wires.

Before you do anything, take a look at the low oil pressure switch and make certain that is seated on the plug well. Actually, you can jump that and test for power on one side. If there is no power, go back to the links. If there IS power, the car should start without the FP relay. Thats what the low oil press switch does, provides an alternate path for power to the FP in case of relay failure...it just makes the engine crank over longer building a couple lbs oil pressure before it will power the pump...
Also look at the ground bundle by the oil filter. There are 4-5 on one bolt. They are critic for operation.

because there are 2 ways of getting power to the FP....you have to dig a little deeper.

 

you confirm that your light has no power at the fuse terminals, yes? your owners manual, if you have one, will show more info than haynes on fuses. I have the haynes also.

I have seen all the fuse "cocoons" under the battery. they work by heat, I guess, so fiddling with them should not damage them. I have to stick with the approach if it were mine. Verify where the fuses are, and check them. My horn's fuse, example, was in another cluster, up under the knee board passenegr side. sent a question to another forum, since this one has two people interested in it. will pass on any info. until then, I am no help.
as for explaining what happened, anybody's guess. It may not be related to what you were doing -although the relay is out in that area, far as I know. Is this a correct assumption?

 

That car should still start with the relay in his sock drawer.

 

Checked the relay in the how to check section OK

 

LEESVET---I think your the winner. Low oil pressure sending unit i'm assumeing it's behind the dist. Well anyhow i unplugged that sending unit and replugged it. Turned the ign. switch on and heard the fuel pump come on. I didn't start it up yet but thats the first time i heard the pump come on since i started with the problem. I'm sure that did it. Time will tell. Have to walk away from it today. Now to fix the sky light on my house that a tree fell through.------Screw the sky light had to see if runs---(RUNS LIKE A TOP) now back to the sky lite---NEVER WOULD HAVE MADE IT WITHOUT THIS FORUM (THANKS)

 

Before you go ripping everything apart just take a step back and think about this logically.

Where did you work and touch when the car failed? The battery compartment and the related wiring around there. There are wires at the back of the block by the firewall that get real brittle and get tugged on when you are messing with the battery. Check them also. Unless you hooked the battery up backwords chances of fuses and relays being blown out else where in the car are slim imo.

So get your volt meter out and make make sure you have voltage PAST all the fuseable links and splices. They can look good and still be bad.

The reproduction Factory service manuals are easy to find for sale online. They have all the wiring diagrams and are specific to each year. They beat the crap out of the $12 Haynes manuals you get from autozone. If you had that you could divide and concur this fuel pump problem in 10mins

 

It's fixed--LEESVET was right--lose plug on the low oil pressure sending unit--pump came on and started right up

 

good info from leesvet! I read the posts since yesterday, and a guy posted last night at 750 or so, suggesting the oil sender behind the distributor might be unplugged, remember that? said it shut down the ECM.
now I'm confused, wondering how it could show plenty of oil pressure if that sender was unplugged. what am I missing here? more than one sensor, evidently. I learned something.

 

went to the garage to check my own oil sender, and suddenly remembered something. there was never once voltage at the fuse panel, the question is why not? the oil pressure signal to the ECM would be 0 psi with key on, not running. the key on should have activated the pump, without the oil signal, if I understand the system. that's how mine works. but there was no voltage until you replugged the sender. (??)

does not follow logically, does it? I ask the question.

my understanding was that the ecm looked for oil pressure above 4 when engine was running, not before, because there isn't any pressure.

the question still is, why was the fuse dead, multiple checks? what I learn today will help me on my own vette, as it has already.

thanks

 

Don't know what your missing. I'm just learning this stuff. All i know is i pushed on that plug and everything seems to work ,starts,runs, fuel pump works. It did show oil pressure when cranking 4lb. At this point i don't care. Maybe tomorrow i will, but i'm happy as crap right now. I don't have to pull anymore hair out,can't spare them. MAYBE IT'S A FLUKE--all i know is replugged it and everything works

 

All i know is i replugged that plug hit the key and everything works--now i have to find Hudini to put that plug retainer on

 

KEn, you know I/m tickled your engine is runnuing. Could be me someday. But we have not found the root cause.

1. your FP never presssurised the rails since yesterday, until you jumped the G terminal. turning the key on should initiate the FP, regardless of the low oil sender unplugged. That's the way I read a tech bulletin, from "Ggrumpvette." Think about it: if the system needed to see 4 lbs pressure before starting the FP, you could never pressurise the rails on a dead engine.

2. the engine started and ran until that fuel was exhausted, meaning the ECM saw pressure, and pulses from the rotating distributor, OTHERWISE the injectors would not work. If the ecm saw no pressure, it should have cut off the fuel pump and the injectors, the way I understand it.

3. if your FP fuse was not showing voltage, you eventually have to explain that, because the oil sender cannot affect it. yet, you never heard the FP when turning the key on, so the fuse was dead.
4 last question is, was the plug disconnected, visually, or did you just reseat it?

I direct these questions to leesvet and ConnecticutJunkman rather than to you. Maybe someone can show me where my logic is flawed. My guess is that you rattled something to fix the problem, when trying to check the fuse links and such.
I said I was old school, remember? Not ECM educated.
regards, jc

 

I did have 4lb.oil pressure during cranking I never got to the fuse links i went directly to that plug ,touched nothing else. Hope it's not a fluke,but it runs now. Plug was not off but very lose so i unplugged it and plugged it back in hit the key and had fuel pump running. Sorry it's messing with your brain. If you find some logic in this let me know so i can learn some more about this. I'd like it if you kept this going . You said your old school, well i'm older school. The last car i worked on had points and condencer

 

You must have 2 problems. One you fixed but the other problem is the fuel
pump relay is not operating under the control of the ECM.

Pull the fuel pump relay out of its socket and the fuel pump motor will still
operate which tells you the fuel pump motor is operating off of the oil
pressure switch and not from the fuel pump relay.

There are 3 ways the fuel pump motor can receive 12 volts.

1) When the ECM provides 12 volts on the Dark Green/White wire of the
fuel pump relay socket Pin C.

When you turn the ignition on the fuel pump relay should energize for about
a second.

If the engine is cranking or running, the fuel pump relay should be energized
all the time.

When the relay energizes a set of normally open contacts closes. 12 volts from
Pin E an Orange wire, travels thru the relay and out on Pin A a Red wire that goes
to the fuel pump fuse. From the fuel pump fuse 12 volts then goes to the fuel pump
motor.

2) When oil pump pressure reaches 4 psi or more, 12 volts from the oil
pressure switch goes to the fuel pump fuse and passes thru the fuse to
the fuel pump motor. (The fuel pump relay is bypassed).

3) Applying 12 volts to pin G of the diagnostic connector. 12 volts
is applied to Pin D a Red wire. Goes thru the normally closed contacts
of the relay and comes out on pin A a Red wire which goes to the fuel
pump fuse then to the fuel pump motor.

What you need to verify.

Since the engine is running off of the oil pressure switch, with
the engine running, do you measure 12 volts on the Pin C
a Dark Green/White wire at the relay socket?

No 12 volts = bad ECM or wiring from the ECM to the fuel pump
relay socket.

If there is 12 volts on the Dark Green/White wire = bad fuel pump
relay or bad connections on the fuel pump relay socket. Bad
ground wire which is Pin B a Black/White wire.

Here's the schematics.

Red color shows operation of the oil pressure switch.

Dark Blue color shows operation when 12 volts is applied to Pin G
of the diagnostic connector.

Turquoise color shows operation when the fuel pump relay is controlled
by the ECM.

Gray color shows the wire the ECM monitors when the fuel pump relay
is closed.

Yellow color shows 12 volts from the ECM to energize the relay.

Code 54 will set if the voltage at the output of the relay is less than 2
volts for 1.5 seconds since the last reference pulse was received. The
code is designed to detect a faulty relay, causing extended crank time
and the code will help the diagnosis of an engine that cranks but will
not run.

If a fault is detected during start up the Service Engine Soon light will
stay ON until the ignition is cycled off.

 

excellent post! experience speaking.

the relay -or its wiring- may have been out of circuit a long time. dislodging the sensor plug revealed it. that expLains why it only ran when rails were filled by jumper to G, also why they both "failed" at same time.
but, he said after connecting the plug, he heard the FP prime when he turned key? if I follow it, the oil sensor would not prime the FP until engine is turning.

OR, HE PULLED/CHANGED SOMETHING NEAR THE RELAY WHILE WORKING ON THE OIL SENSOR

the test would be to see if the FP primes today when key is turned on.