90 corvette cranks right up and then dies immediately. Engine runs fine no missing but just dies instantly. Started this a year ago. Took to dealer and they put computer on it. Run for a short while and started again. I changed fuel pump today and it still does same thing. I'm thinking the ignition switch but not sure. Mine has the key with the resistor in it for anti theft. Any ideas? Thanks a bunch.

 

lotsa parts, no solutions... sad...

Did anyone bother to check the fuel filter? What is the fuel pressure like at the rail?

How long does it run? 30 seconds or 10 minutes?

 

I had that problem when I put a new fuel pump in....it would turn on, blow out of a connection, then reset when pump went off....i'd put a guage on the rail while you start it to make sure you have pressure...

 

...AND...make sure the pressure is holding when the engine dies also.

Could be the oil pressure/fuel shut-off switch can be bad where if it is not detecting oil pressure.... the fuel pump will shut off to save the engine.

DUB

 

Wow thats a Good one I'd say pressure gauge up at the rails to see if it holds after it dies If so move on to Ing/spark Make up a test light from a 12 volts bulb with the socket with 2 long wires and start up at the dist. Take in to it to see if the test light turns off when the engine does. If so like I'm thinking, start with the low/no oil pressure cut off by jumping it the move on to the key/lock cyl anti-theft and the wires that go up to it.
You have to start crossing things out and then moving on to the next because quite a few things will do that.
Good luck and Keep us updated

 

If the car is starting it is not the resistor key pellet. I'm with the others for putting a fuel pressure gauge on it, and watching it hold pressure. Mine will only lose 10 lbs in an hour.

 

That's a popular misconception. The oil pressure switch is to turn *on* the pump if there's oil pressure. It's a backup as they didn't fully trust the electronics at the time.

 

It amazes me how many people believe the "save the engine" scenario. I have proved that this is not true by disconnecting the oil pressure switch and the engine ran just fine.

What I find interesting is that Corvette Central's resident "expert" Chris Petris stated in one of their videos that the fuel pump relay is only used to pressurize the fuel rail before starting and never used again. That's totally wrong, as the fuel pump relay is also turned on when the ECM sees DRPs (Distributor Reference Pulses), which the ignition module sends out whenever the engine is rotating.

 

WELL.

For the last time.

And this is a FACT...NOT my opinion. REPEAT...FACT

The fuel pump will run for 2 seconds when the key is turned ON...via the ECM. After that 2 second cycle....the ECM has nothing to do with the fuel pump running.

AFTER that 2 seconds...the oil pressure/fuel switch at the back of the intake manifold HAS TO recognize 4 psi of oil pressure to energize the FUEL PUMP RELAY and thus the fuel pump will run. Doubt me...look at the manual or CALL Gordon Killebrew.

If you remove the wire on this switch...the engine will DIE...IF it does not...you have a problem ELSEWHERE. REPEAT...You have a problem elsewhere

GORDON mentioned NOTHING about DISTRIBUTOR PULSE SIGNALS to turn on the fuel pump....EVEN when I SPECIFICALLY asked him about it.

If you doubt me...Call Gordon Killebrew and ASK him...you will see that what I am writing is HOW it is supposed to work.....EXCEPT for ZR-1's...and this goes for 1982 to 1996 Corvettes.

You can have a problem in the fuel sending unit where the wires connect to the underside to feed power to the fuel pump. I have seen these terminals melt many times....ESPECIALLY on 1988 and 1989 Corvettes.


LAST TIME ON THIS ISSUE...I am tired of it.

WELL...then tell me how on EVERY Cross-Fire/Tuned Port/LT! (4) engines I can disconnect it and the engine will NOT get fuel pressure...EXCEPT for the initial 2 second prime cycle....and I can not read fuel pressure. when I connect it back up....I get fuel pressure.

And as I have written before...DO NOT BELIEVE ME...GO AHEAD and call Gordon Killebrew and tell him that he does not know the system and how it works. I have had it confirmed by him verbally and also in tests at my shop.

THINK WHAT YOU WANT...and I bet many of you will not call....and if you do....I BET you will not come back and reply with what is a FACT...UNLESS you feel that Gordon does not have a clue.

This is pointless when some people will not do their 'homework' and call someone who KNOWS. BUT YET they KNOW EVERYTHING. COMPLETE IGNORANCE!!!

OIL PRESSURE/FUEL SWITCH IS NEEDED. And in turn ...if the switch is bad ....then the pump will not come on after the initial 2 second prime...as I have replaced MANY TIMES in the past to get fuel pressure and keep the fuel pump running....or I might have been dreaming that day. I have also seen this switch be bad and cause the fuel pump to run even with the key OFF.

They DID trust the electronics...because this switch is for safety....like you wrote....no oil pressure...the engine will not run. That is why it was installed.

DUB

 

Gordon Killebrew left GM 20 years ago. I doubt he remembers all the little obscure details on how these cars work.

As I have mentioned in the past, I DID THE TEST!!! I unplugged the oil pressure switch and the engine ran just fine using just the fuel pump relay. Is there anybody else out there brave enough to do an empiric test to see if this works?

We went through this in the past with quotes from the FSM. The ECM turns on the fuel pump whenever it sees DRPs from the ignition module. Some year FSMs were kind of vague on the wording, but for some years it was quite specific.

I'm in the hospital right now for a chemotherapy session and I have my new laptop. It doesn't have the electronic copy of my FSM on it, so I can't quote chapter and verse...

 

Fuel supply systems and function is NOT an 'obscure' area of the car.. GET REAL!

Kinda funny how this switch is connected to the fuel pump relay electrically.. And WHY would GM do that???? And if it MEANS NOTHING and serves no purpose.....why waste the money on it???

And as I remember...you did not want to call him for reasons that are yours...and you were trying to do things to your ECM without knowing any of the internals specifically. I CLEARLY REMEMBER YOU.

ONCE AGAIN...BELIEVE WHAT YOU WANT. I DO NOT CARE. This is like beating a dead horse.

And for the RECORD...Gordon is SHARP AS A TACK!!!! You have NO CLUE on the extent of his knowledge...and how he knows it and can recite it WITHOUT having to rumble through books like the rest of us.

Remember...HE was one of the people who wrote the service manuals.

It still amazes me on how people can argue how 'their' Corvette runs and operates perfectly....but in reality....may not be the case.. ( NOT implying anything DIRECTLY at YOU Cliff)...especially when they do 'things' to their Corvettes....such as wiring, and messing around with intricate electrical circuits...And will not CALL someone who knows how it was designed....and to verify that what 'they' plan on doing will work because 'they' know what the end result is supposed to be....BECAUSE MUCH of this detailed electrical information was not put in the service manual...BUT 'someone' knows this information. AND I have to wonder...like I have experienced....the wire from the ECM that energizes the fuel pump for 2 seconds is STAYING grounded...thus allowing the relay to keep the fuel pump on.

DUB

 

The fuel pump relay is turned on by putting 12 volts on the relay pin C, which comes from the ECM pin A1. The oil pressure switch is a backup for the relay. This diagram shows the connections:



I monitored the fuel pump relay voltage from the ECM pin A1 with my oscilloscope and it plainly shows that the ECM turns on the fuel pump for 2 seconds and then again when it sees DRPs from the ignition module:



See this link for the full explanation of the above waveform:

http://home.earthlink.net/~cliff_har...waveforms.html

 

Cliff.
YES...IF you crank the engine WITHIN the first 2 seconds of the key being on...the reference pulses do come into play....I DO NOT DENY THAT FACT...Becasue I can read and understand the dynamics of this system....BUT...

If you wait longer than the initial prime sequence (2 seconds)...the ECM stops applying power to the relay...and then the pumps cuts off. AND the ONLY thing that gets the fuel pump running again is the oil pressure switch closing when it get 4 psi of oil pressure.....PERIOD!!!!!

SO if your car is CORRECT...and the engine is running...you can disconnect you fuel pump relay and the engine will keep running due to the oil pressure switch (depending on year model ...it is the 2 wire or 3 wire switch)..is CLOSED and supplying power to the FUSE that goes to the fuel pump. And if you CAR IS CORRECT...if you remove the oil pressure switch connector (2 or 3 wire)...the engine will DIE...and that is that. If it does not...you have problems elsewhere....as I wrote before.

I checked a C4 that came by my shop today ...and when I removed the oil pressure switch connector....the engine died.

Call Gordon and tell him what you have going on and them tell him that he is wrong.

DUB

 

I'm sorry DUB but you're wrong, at least for '87s. The fuel pump relay is the only thing running the pump. The oil pressure switch will enable the relay, but power still goes through the relay

 

OK THEN....I will call Gordon...have him look at this and then comment on it.

BUT I have to disagree with you. 12 volts is going through the oil pressure switch when running....because you can disconnect the relay and the engine will keep running...as long as the oil pressure switch is correct. SO the oil pressure switch is NOT enabling the relay....and has NOTHING to do with the relay working at all.

DUB

 

If you look closely at the waveform that I posted, you can see that I waited FIVE seconds after the 2 second prime before I started cranking the engine, just to make sure that I was outside the 2 second limit.

 

The oil pressure switch and the relay are in parallel. That means that you can disconnect either one and the engine will continue to run.

 

O.K. This is working Right? Then after that

 

So ur problem is exactly this. The fuel pump relay is energizing and going into it's run mode just like its designed. Your motor runs for the 2 seconds, Then it Dies. So it's going into the Run Mode and it's not working. So what is the run mode? Is its suppose to or it needs to see dist pulses? to and through the ECM to trigger the Injectors? and it's not doing that?

 

So maybe When the fuel pump energizes the system of a second or 2, then cuts off and wants to see reference signals from the Dist to begin triggering the Ignition and Injectors it may then Simultaneously, once those are seen, it throws a leg to the run side of the pump relay through the ECM. So I'm thinking jump the relay to run