I am halfway through trouble shooting a no start issue on my 91 - 305 stock.

Driving yesterday it just died - no notice, and wouldnt start back up. Just cranks, but doesnt actually run/start - car delivered home.

Background - Fuel pump was replaced about 3 years and less than 2,000 miles ago - so I doubt its the FP, but want to rule it out 100%.

I checked the fuse by the battery - its good, Replaced the FP relay just to be safe, Checked to see if I have 12V at the relay - I do. And when when I jumper the Orange and grey wires I can hear the pump kick on - Given this is it safe to rule the FP as Good - 100%.

Just want to go through the process of elimination and ensure there are no other checks before I certify the pump as good and move onto something else.

Thanks,
DK

 

Another thing you can check to see if its fuel related. Spray starter fluid in the intake and start the car, if it fires up and immediately dies, you have a fuel issue. If it does not start its a spark issue. Driving down the road and it instantly dying coule very well be fuel related thats for sure but do the easy checks 1st. What about fuel filter? How old is that?

 

You maybe onto something, I never thought about the filter. I tried the Quick start, and it did run for a bit....so I wil likely just change the filter since its cheap and easy, and I will report back.

It would be really nice if thats all it was - I am dreading a fuel pump replacement.

 

Test fuel pressure using a gauge. It should be about 45 psi with the pump running and engine off.

 

Checked Fuel pressure today - its about 42ish with the pump priming and the engine not cranking. Key off - then the gauge drops slowly (over 2-3 min) down to about 10PSI - is this normal?

DK

 

That sounds fine. Check spark and fuel injector pulse. To check injector pulse, you can buy a noid light that connects to the injector plug.

 

I am now thinking that it maybe something electrical related, as it seems like sometimes the injectors are sending fuel, and sometimes not.

I have gotten it running a few time until it stalls out, but half the time when I crank it over and it does not start the plugs are still dry - where I would have expected them to be wet since I have 42ish PSI at the Fuel rail.

My next step is the noid light I guess.

Any other suggestions.

Thanks all for your help!

 

Check fuses. Check the fuse by the battery and the INJ fuses in the under dash fuse panel for good contact. Check the ECM grounds at the rear of the heads for looseness. Check the connectors at the distributor and coil.

 

Check ALL your grounds, testing for continutity would be a good idea too. It would also be a distributer problem, check cap/rotor. cheap and easy fix. Next step is a noid light

 

The fuel pump should only drop a few psi and not go down to 10 psi. Check the fuel pressure again but this time pinch off the return line. if it holds at 45 psi then the fuel pump is good , if it drops even a pit you fual pump is bad.

 

Hi Guys, all fuses are ok - Both all in the fuse block and the 1 by the battery.

Checked grounds at back of the block, all look good and none look to be in bad shape.

I replaced coil and ignition control mod today since they are relatively inexpensive...it started and ran for a bit...but then died and same issues - so it didnt solve anything.

I will try pinching the return line - FP was done about 3 years ago and less than 2K miles ago - but I wont rule it out.

picking up a NOID light tomorrow after work - seems like sometimes its spraying fuel, and sometimes its not.

DK

 

Fuel pressure dropping to 10 psi over 2-3 minutes is not ideal, but it does not point to an issue either. It is best for the system to hold pressure for 20 minutes, but as long as it does not drop more than 20 psi in 1 minute, it is not the cause of the no start. If fuel pressure is not dropping below 35 psi at idle while the engine is running, it not the cause of the engine stalling either.

 

Need to monitor fuel pressure, injector pulse, and spark when this issue happens. I suspect that either the fuel pressure is falling off due to an issue with the fuel pump control circuit or, possibly, the pick up coil is suffering heat related failure killing the crank reference pulse to the ECM, which shuts down both spark and injector pulse.
Knowing what the car is losing first will be helpful. Once the car stalls and won't start, knowing what is missing will tell us what to look for.

This is a VATS passkey car also. Therefore, it is possible that that VATS module is failing and dropping the fuel enable signal to the ECM. It could also be the ECM, but that would be a rare occurrence.

 

push the gas pedal all the way and turn the ignition, does the car start? (dont let go of the gas) if the car runs but shakes alot then we have the same problem, mine (1984 trans am 305) started fine yesterday but today I had to put my foot all the way down and it started but ran low rpms even though I was giving it full gas, if I let go of the pedal it shut off.

 

bumping this thread i have the same exact same problem, only my car dont turn on at all

 

It might have been mentioned, but I didn't see it. Both of you should ohm check the injectors. The factory injectors are known to fail and cause problems like this. Ohm test them all. It only takes one shorted injector to prevent the whole bank from firing.

 

Well I dropped the car off last week, and picked it up yesterday Fixed.

Car rolled into the garage and the cylinders were full of Fuel which hydrolocked the engine - likely from all the attempts I had at trying to get it to start.

They tracked the key problem down to the ECM - Which at first I thought was total BS...but when they could get the car started if they tapped on the ecm it would stall out, and if it wouldnt start a little tap on the ecm again then it would start - weird electrical noise coming from it also.

Replaced the ECM...oil change and it ran well. Have about 100 miles on it since, no issues to report running well - fingers crossed it stays that way.

 

That is a strange diagnosis. But you can't really deny the tap test. What's odd is with the ECM having failed, you would expect not to have injector pulse at all, unless the Injector drivers, one or both was shorted and causing the injectors to hang open. This would be very rare. I've never seen it on any make or model of car.

At any rate, great news!

 

I have a question how which wire is it that power goes to the fuel pump? I got a purple, grey, and black. I am getting power to my relay but my pump don't turn on and i just replaced about 6 months ago

 

The gray wire is power to the pump. Black is ground.

 

Thanks i found the problem. It was in my alarm

 

Well, let me toss my name into the hat of those having problems with potential FP issues. I recently got my 1990 IROC Z painted, and had repaired brake issues (had to replace both front disc brake assemblies, and the master cylinder). Then, after a jump, the car started up and ran fine. I went to the store, then to a gas station to fill up. After the fill up, the car did not start. It would turn over, but sounded as if it was not getting fuel or a spark. I had some carb cleaner, and after spraying it into the throttle body, the car would catch, but then quickly die. After several attempts....the car finally started and ran rough for a while, then sounded like it started running normal.

Well, I drove it around a bit....and while I was idling in a parking lot at a mall....it died again. Again I could not get it started...sounded like no gas getting to engine. I would spray carb cleaner and it would fire up, but then die. After an hour sitting in the parking lot and thinking ill thoughts about my car.....I sprayed carb cleaner on one last attempt and it fired up and ran....got me back home.

Yesterday I fired it up while sitting in my driveway. It started up and ran for about 15 minutes...then died out.

I have purchased a fuel filter, and will replace that tomorrow. However, I am leaning toward an intermittent fuel pump as the problem....had a similiar issue in another car I have.

Is there anything else I can check on this? Where does one get a meter to measure fuel pressure....how does one go about doing that?

 

Fuel pressure gauge is available at most any parts store. To verify that it is the pump, monitor power to the pump and watch fuel pressure as the problem occurs. If power and ground to the pump are good and pressure falls off, the pump is bad. This is of course after you've replaced the filter.