I've looked though the forums and haven't found exactly my vette’s systems, so here goes. I need help.

I have an 86 Auto Coupe (w 65,000 miles) with an intermittent no start/dying problem.

The first time it just died and wouldn't restart (cranks). I tested the fuel pressure (40 psi) and it holds for over 5 minutes. I also had good spark. At that time I had a Code showing a bad MAF sensor and the MAF relay. Change the MAF sensor. The car started. I thought I had it fixed. Wrong...

After that I started it up backed it up 8 feet, let it idle (maybe 2 minutes) and then it died and wouldn't re-start.

They next day it started for the mechanic, I've called Dealer's Vette mechanic (he moonlights) and he's come over several times, hooked up his equipment (pressure gauge, tester and spark tester), turned the key and its started. But this time there was no codes.

Fast forward to last week... running great...Went out to start and no start. Vette mechanic came over and hooked up equipment and no start. There were still no codes. He's been using the factory service manual and followed the No start and no codes flow chart, and has tested everything twice to include wiring, still no start. He's used the nodes to test the injectors (all) and there are no pulses to them. We’ve checked spark every time and there’s always been spark.

When its cranking it will catch on what seems like one or two cylinders once and the tach will register briefly 5-600 RPM, but only the first two attempts. After that, no catching on anything.

We've changed the ECM, Mass Air flow Sensor, MAF relay, and ignition control module (the old one tested good). All the parts were new GM Delco parts.

Also the Vats system has be defeated...meaning there is a resistor in place of the steering column sensor.

Not sure where to go from here. Any suggestions?

 

Did you change the coil pack and the distributor spark module?Or did you change the electronic spark control module located on the passenger side?I wasnt sure which one you meant.

Did you change both MAF relays or just one?Theres a power and burn off.

Also,if the car cranks and wont start,unplug the MAF sensor and see if it runs.Just wanted to see if that makes a difference,even though you changed the part already.

I also wonder if the pick up in the distributor can be going bad.Just something else to check.

 

I bought both relays, but in my dignostic process, I replaced the burn off as just replacing the MAF Sensor didn't fix anything (Willing to bet the MAF Sensor wasn't bad) and the burn off relay got the car going and replacing the other one (with the new one) caused a no start. I even brough the old relay in to Chevy to match it up. I changed one started the car...changed the other w/new one and no start. So currently we have a new relay and an old one.

Haven't thought about the Coil pack as i've always had good spark

We have upplugged the maf sensor and no change. I've even uplugged the TPS without postive results. (Ive checked the specs on the TPS and its within specs without any spikes)
I changed the ECM on the passenger side(Engine Computer...used old prom on new computer) and the distro spark module (seven spade connectors).

I'm at my wits end.

Thanks!

 

Are you running out of fuel? Did you or the mechanic leave the FP guage on the car when it was running?Have you tried to change the fuel filter in case it might be clogged?

Just something cheap to try.The engine needs air,spark and fuel to run.
I forgot earlier you said the tech...

"He's used the nodes to test the injectors (all) and there are no pulses to them. We’ve checked spark every time and there’s always been spark."

Since you have spark,and air,sounds like the fuel isnt getting in there,from what you stated.If the injectors arent pulsing,youre not getting fuel.That would explain alot of cranking over but no full starts.

Im really curious about this and the FP readings when the car runs and dies and wont start.

Im sure the others will check in here soon.I gotta go to bed soon,but will see if I can think of anything else to check tomorrow.

 

I think this comment pretty much sums up why it's doesn't run.

1) I would ohm test each injector to see if one maybe has shorted out and playing havoc on the ECM injector drivers.

2) check terminal B5 on the ECM and see if the ECM is receiving the reference signal(1.3V) from ign module, during cranking. It needs this to fire the injectors.

3) Are both banks of injectors getting 12V on the pos side of connector.

 

I agree the reason why its not running is the injectors aren't getting pulsed. the question is why?

The other thing we've checked is the ground wires--By the starter. All good and tight with no signs of corrosion, damage etc...

The FP gauge has been on the car while running, but never been on the car when its died. Its been on the car while troubleshooting...FP pressure never been below specs while cranking...Fuel filter changed last spring/Pump sock changed two weeks ago.

I'll check the injectors today...we've checked some of them and the checked out good.

Not sure on 2 and 3. I'll ask when he come over tonight.

Thanks for the help.

 

You might want to check the grounds on the block, above oil filter. That's where the ECM gets ground.

 

I've checked this. This is the ground down by the starter. Checked the connection and for continuity. Every thing checked out good.

Thanks!

 

Also, the injectors all ohm out between 15.9--16.2 Ohms/

Thanks again for the help!

 

Thanks for the help. It turns out the new (reman) computer I got from the dealer was faulty. We swapped computers and it fired right up...put the old one back in and no start.

Thanks again!