oliverdeonarine

I have a 1995 Trans Am with 108k miles. Has ran perfect. While driving it made a loud backfire but didn't cut off. I continued driving and it would bog over 2500rmp. Drove to work and when I was leaving it would not start.

It will crank and when I let off the key it will sneeze threw the intake.
Replaced optispark 4 times just incase I got a bad one. opti is ok.
New plugs and wires all in correct firing order.
ICM is ok.
Coil wire is alright.
Opti harness has correct voltage and continuity.
Fuel pressure ok and injectors are firing.
No codes!
Please Help. It's been in the lift for weeks and we are having trouble diagnosing it. I'm going crazy.

Could it be the PCM?

TwoFast4Lv

iTrader: (8)

Have you checked the timing chain slop when you had the Opti out?

oliverdeonarine

Yes. There isn't any slack indicating it jumped or broke a tooth. At TDC the cam is at 9 o'clock. Pretty sure it's in time. I've been thinking about taking the timing over off

TwoFast4Lv

iTrader: (8)

Yes you should have 3 OC(TDC Fire) or 9 OC (TDC 180 out)

Injectors are firing?

oliverdeonarine

Yes. Taken noid light to all of them. Fuel pressure good also.

SS RRR

iTrader: (2)

It's a timing issue of some sort. When is the last time the valvetrain was messed with?

oliverdeonarine

I am not sure when the valve train was ever messed with. I bought the car not too long ago. Everything is stock and looks perfect. The car backfired through the exhaust randomly and the car bogged very hard. Completely out of no where.

I think I will check the timing marks tomarrow on the cam and crank. If timing is fine what else could cause a no start. I don't have any security issues.

oliverdeonarine

Is there any chance it's the PCM?

lt1slowz28

are you 100 percent positive the opti is good? if so, check it again.

maybe see if the injector and the plug go off when cranking. Plug the noid light in on say cyl#2 and check for spark at the same time @cyl#2.

also, for some reason ran into this problem with another LT1, it would NOT start unless you had all the sensors plugged in (ran like a brand new motor after scratching my head for a while). Never know with some of these cars, seen lots of botched jobs.

oliverdeonarine

I have went through 3 remans and a brand new Delphi. Unless they are just all bad. I dont really wanna get a $500+ opti.
I don't have the water pump on or radiator. But I did plug in MAF and water pump sensor while trying to check if it will start.
Does everything need to be plugged in?

When I crank it and let off of the key it will backfire through the intake a few times. When I turn the key it will not make any effort to start. Only when I let off the key will it attempt to start.

TwoFast4Lv

iTrader: (8)

It screams timing. Either cam or ignition

oliverdeonarine

When it is at TDC, the rotor fan on the opti is about 20 degrees or so past the #1 post on the cap. Advanced timing?

lt1slowz28

are you sure you stabbed the opti on the correct spot?


this whole issue you are having reminds me of when I have seen that happen. Common mistake and can be a pain in the butt sometimes.

oliverdeonarine

The opti is installed correctly

quik95lt1

iTrader: (7)

pull the valve covers.....may be something a bit more mechanical than the opti

lt1slowz28

Hopefully not timing chain issues. They tend to get pricey depending on the severity.

30696bird

iTrader: (4)

Have you tried another wiring harness going to the opti? I have seen issues that act just like the opti when it's the opti wiring harness.

quik95lt1

iTrader: (7)

shutty lol

oliverdeonarine

I'll pull the valve covers and check it out. I just want to know what's wrong. Not too conserned with what it will take to fix it. Just want to get to the bottom of this.

The opti harness is fine and has continuity as well as the correct voltages.
Give me ideas of things to check. It's at a performance shop I work at and I can do just about anything to it. I need my trans am back lol

30696bird

iTrader: (4)

I suggested that because I have seen it happen before. I too had continuity and and the correct voltage when my harness was bad. It only acted up when the engine got warmed up.