Whattup, I have a 1984 fiero with the 2.5 out of an 1985 fiero

So I finally got my fiero running but it aint running right, and now it wont run at all. It just backfires out of the intake and wont start and I dont know why. Ive replaced the MAF sensor, ive set the ignition timing to 8 degrees (At least i thought i have), Ive preplaced the leaky injector and Ive replaced spark plugs. I checked all of the vacuum lines and they all seem to be fine.

It wants to run, you can feel it try to stay above 1k RPM but it just dies if you dont have your foot on the gas.

Issues that I am aware of right now is I do have really old gas and a bad fuel filter, but can bad gas really affect the preformance of an engine this bad? I think I set the ignition timing right, i heard its supposed to be 8 degrees advanced so I marked where I thought 8 degrees was on the degree thingy by the harmonic balancer. When I first started it initially it would run then die, so I got my brother to keep his foot on the gas to keep the engine as close to 1k rpm as possible so i could set the ignition timing, hoping it would help it run. It was a few degrees retarded so i advanced it to where I thought it should be at and it improved how it ran, but it still didnt idle properly.

I marked where I thought 8 degrees was on the degree thingy with silver sharpie so it would be easier to see when timing it.



but Ive tried to start it now it just backfires out of the intake which makes me think its either a gas or ignition issue

Help pls,
thanks much

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James Bird

quote Originally posted by BruhMans06: Ive replaced the MAF sensor...

There is no MAF sensor on your engine.

quote Originally posted by Patrick in your Previous thread: Make sure to have the ALDL jumper in place when using a timing light.

[This message has been edited by Patrick (edited 12-22-2023).]

Dump "all" the old / stale gas, fill up with high quality gasoline. Restart engine and get back to us.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

quote Originally posted by BruhMans06: Whattup, I have a 1984 fiero with the 2.5 out of an 1985 fiero So I finally got my fiero running but it aint running right, and now it wont run at all. It just backfires out of the intake and wont start and I dont know why. Ive replaced the MAF sensor, ive set the ignition timing to 8 degrees (At least i thought i have), Ive preplaced the leaky injector and Ive replaced spark plugs. I checked all of the vacuum lines and they all seem to be fine. It wants to run, you can feel it try to stay above 1k RPM but it just dies if you dont have your foot on the gas. Issues that I am aware of right now is I do have really old gas and a bad fuel filter, but can bad gas really affect the preformance of an engine this bad? I think I set the ignition timing right, i heard its supposed to be 8 degrees advanced so I marked where I thought 8 degrees was on the degree thingy by the harmonic balancer. When I first started it initially it would run then die, so I got my brother to keep his foot on the gas to keep the engine as close to 1k rpm as possible so i could set the ignition timing, hoping it would help it run. It was a few degrees retarded so i advanced it to where I thought it should be at and it improved how it ran, but it still didnt idle properly. I marked where I thought 8 degrees was on the degree thingy with silver sharpie so it would be easier to see when timing it. but Ive tried to start it now it just backfires out of the intake which makes me think its either a gas or ignition issue Help pls, thanks much

You probably mean the MAP sensor (manifold air pressure) sensor, which mounts to a little "L" bracket that sits off the side of the air cleaner, held in place by a big U-clip.

If you're getting backfiring, it's more than likely (in my experience) a bad timing issue... meaning that the coil is firing the spark plug while the intake valve is still open.

So this is definitely timing. Like Patrick said, timing needs to be adjusted with the computer set in diagnostic mode.

Per the Fiero Online Service Guide: https://www.pontiacperforma...cles/OSG/timing.html

"With the car running, jump pins A and B on the diagnostic connector (beneath center console cigarette lighter panel) to place the EST unit into base timing mode (electronic spark advance disabled)."

quote Originally posted by Spoon: Dump "all" the old / stale gas, fill up with high quality gasoline. Restart engine and get back to us. Spoon

quote Originally posted by BruhMans06: I do have really old gas and a bad fuel filter, but can bad gas really affect the performance of an engine this bad?

YES...

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Man i didnt even know that there was a diagnostic mode that needed to be on when the car was running, so i probably messed the timing up. Ive dropped he tank and im going to refill it weith new gas so ill see what happens.

Thanks yall

quote Originally posted by BruhMans06: Man i didnt even know that there was a diagnostic mode that needed to be on when the car was running, so i probably messed the timing up.

Which is why I mentioned it to you 12 days ago.

I agree. It's either gas or timing... or firing order or low fuel pressure or a valve hanging open.

quote Originally posted by phonedawgz: I agree. It's either gas or timing... or firing order or low fuel pressure or a valve hanging open.

Backfire from the throttle body can happen with a burn't or bent intake valve. Backfire out the exhaust may indicate a bad exhaust valve. A jumped timing chain or belt can yield the same results.

Try this: Hold a $1 bill an inch from the exhaust pipe and have a willing subject crank over the engine. Observe if the $1 bill repeatedly sucks against the tailpipe. It should not. If you don't have a $1 bill, a $5 may yield better results,, just joking.. but you could go high tech and pick up or borrow a vacuum gauge and observe it while cranking.

Spoon


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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

[This message has been edited by Spoon (edited 12-28-2023).]