Hey everyone. New member. Don't have a corvette my self but need some help diagnosing this thing. My buddy has an 86 vette (tuned port injection, which I believe makes it multi port injection???). It cranks fine, but will not fire up and stay running, it will turn a few times with no fire, then starts to sputter likes it's gonna start but dies as soon as you let off the key, not sure if its from lack of fuel or lack of ecm. I believe this is because the oil switch is powering the pump once it starts cranking. What I've found so far... The check engine light will not come on, not even when trying to jump a to b in the dlc, but the bulb itself is good, comes on if you jump a ground wire to it while installed. The fuel pump can be hot wired from the relay or from the dlc and it will kick on. But it doesn't prime. I don't know how much fuel pressure there is at this time, don't have access or funds to do a loan a tool on a gauge, but not convinced it's a fuel pump issue with the other issues at hand . Sufficient fuel has been verified in the tank. Ive been leaning towards ecm issues but im not sure how to pinpoint the source of the problem and don't want to start throwing someone elses money at it. I tried checking the grounds but g104 seems to be the main grounding point of the effected components, but the only thing I can find in that spot is a ground strap that goes from the engine block to the chassis near the battery, no actual wires. I've checked for voltage at the ecm and have voltage, and I think continuity with very low resistance on the grounds (not sure if all of them have been located). Most recent replacement parts are new maf sensor (code 34, hard starts and rough acceleration), and oil pressure sending unit (bad leak). If anyone has some input, or could help point me in the right direction it would be greatly appreciated. I don't have a fsm as I don't own the car, but do have access to all data. Sorry if this is a duplicate buy after submitting first thread I couldn't find it again

 

You need factory manuals and diagnose no ses light 1st. Fuel pressure gauge to see if ecm sends fuel pump prime signal and if there is over 43psi and holds.

 

most likely a fuel problem...the ONLY way to start is to put a fuel pressure gauge on the schrader valve on the fuel rail and monitor....they aren't that much and I think you can borrow one at auto stores...pump should run for 2 sec at key on....should get 36#...at least my 85 does....fuel pressure should drop but slowly after pressurization..If you have pressure, check the fuel pressure regulator...pull hose and see if you smell gas....also the fuel filter could be your problem...good luck

 

, start with the basics - FUEL, spark, timing....

 

Thanks for the replies folks. I won't get another chance to look at it til later this weekend. I understand about the importance of the fuel pressure but my concern is this, the command to prime the fuel pump comes from the ecm and it's not priming. I also can't get the check engine light to come on even though I've tried putting it into diagnostic mode. That's enough for me to believe there are ecm issues. The guy that was driving it when it dies said that when the cel/ses light is on the car will run, then it would begin to blink and start cutting out, and once the light turned off so did the engine. So what I think I really need is help figuring out if the ecm has lost a ground connection or if one of the quad drivers in the ecm have failed. Only descriptions I have of the ground locations are short half sentence descriptions. Thanks for your time!

 

your post said the fuel pump would kick on but not prime........

 

The only time the fuel pump gets power without manipulating the circuit is after cranking for a few seconds. It's my understanding that the oil pressure sending unit will by pass the fuel pump relay in the event the fp relay fails and I believe this is what's powering the fp during the brief time it does come on. The relay has been replaced.

 

The ecm will turn on fuel pump for 3-5 sec. When key is turned to run. With the check engine light flashing, now it is out. Have you checked bulb? When jumping aldl do you hear relays cycle, ecm should cycle relays it controls. You should check power and ground at ECM.

 

So, not sure what I've done now. So After rechecking ground and power to the ecm i then ran a jumper wire to the individual ground and hot wires. The ecm has slowly come back to life. After applying 12v to the power feeds to the ecm the ses light has started working and somehow after checking continuity for the diagnostic circuit I can get a code 12, and the fuel pump now primes on its own but not it won't even sputter, and has a strong order of gas. I did find on the green/white wire for the fan relay someone had spliced a ground wire to it in what seems to be an attempt to hotwire the fan so that it runs constantly in the run position. Not sure if it began correcting itself after disconnecting the splice. But giving it time to unflood if its flooded itself. There is spark but the plugs that were removed were wet.

 

So, if I hold the pedal down all the way, it will start, as long as I don't let off the throttle for a minute or two it will idle and hold and we managed to drive it around the block. After checking now have codes 15, 32, 33, and 36. Also noticed even not hot wired fan still come on when key is in run, the ecm is considerably warm, and the fuel pump and ran relays both are hot to the touch, not sure if this is normal, or possible indication of a bad ecm. Finally got it to run but not convinced I'm ready to hand the keys back. It doesn't seem normal to have to floor it to get it to fire up.