Real Fiero Tech

And all the fly bitches come to ME!

Until the backfiring blew out my muffler.

Has anyone else with a catless 2.8 had this problem? I'm wondering if the TPS is flaking out so the ECM isn't giving decel enleanment (does the Fiero ECM even have that?), but I haven't hooked up my scan tool to really look at it, though. The backfiring is exclusively on coast down from high RPM. I ran out to 100+ the other day and lifted and it backfired repeatedly coasting down.

New ignition components as of last fall... offroad pipe, EGR blockoff at manifold, TB coolant lines removed... anything else I ought to be checking? Common failure modes for the cold start injector?

Backfiring through the intake? Or do yuo mean the exhaust is popping really loud?

I am guessing second since the muffler blew out.

The fiero does have enleanment when you let off the gas after going WOT and leave it in gear. It dumps no fuel. Confirmed with my wideband

However you could be running so rich, that the fuel is puddling up in the exh or muffler and after going WOT its hot enough after letting off the gas and enough unburnt air pumping through to ignite it.

When I was running 19 lb injectors in my 2.8 DTB setup, I could get it to pop(backfire) on command. I would rev it up to around 3k a couple times then take it to 5k or so and on the way down it would pop and ssometimes shoot flames out the back. A couple times it would just shoot flames, but sometimes it wuold pop like a backfire, just really loud. I am guessing its because of way too much fuel untill it got enough clean air to ignite.

I was no cat as well.

If the cold start injector (or anything) is leaking you will see your fuel pressure drop immediately when you shut off the motor. Put a gauge on the rail and see what it's doing.

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SappySE107 wrote:cold start injector?

GM decided it was too hard to just add cold start enrichment on the Fiero ECM. Instead, they put a temperature sensitive switch on a hot-in-start wire that leads to the special cold start fuel injector in the lower intake manifold so that it sprays fuel during cold starts.

my old 3.4 pushrod swap I took to virginia tech would pop and sometimes throw fire if i shot up to speed and then coasted it down out of gear. If i engine braked then it would just gergle all the way down.

I tried using the adjustable FPR to tweak it but no help. the CAT was apperantly empty.

Will, try advancing your timing to get a more complete burn, this may solve your problem. Then again it may not. Its only a 15 min job.

a cracked exhaust manifold will cause off throttle back fires, as well.

I thought ALL fieros popped on decel :scratch:

It doesn't just pop... it fires HARD. It blew open the muffler, after all.

I know I had a manifold leak. I had to pull the manifold when I did the clutch, and one of the flanges came off. I had it welded back on, but in extremis I couldn't get the best welder in the shop and the guy I did find warped the stupid thing... and now it leaks again.

I'll put "check fuell pressure drop at shutoff" on my list of things to do this weekend.

New ignition coil helped, but did not cure, problem.
All other ignition components are new as of last September.
Fuel rail retains fuel pressure. 1 hour+ after priming it still had 30 psi in it.

As I said, I do have a manifold leak. I'll have to pull that off (damned front manifold) and fix sooner rather than later. I'm getting tired of it being loud and NOT sounding good.

Another possibility is that the EGR may be introducing air into the exhaust via the cracked tube. Anyone ever encounter that?

my buddys 2.8 had a cracked mani, and it ran rich which = flames up over the decklid.

Nice.

The Dark Side of Will wrote: Another possibility is that the EGR may be introducing air into the exhaust via the cracked tube. Anyone ever encounter that?

not likely, an air making it in should be sucked into the intake. cant see it going into the exhaust.

Except that a block off plate is cheaper than a new tube. Air can't get sucked into the intake.

FUCKING FIERO OWNERS. you can make 2 block off plates from a miller high life can for less than 5 cents. Go do it, report back.

won't work, has to be a Mountain Dew can

What I'm saying is that I already installed the EGR blockoff plate at the intake manifold, but the tube is cracked, so air could enter the exhaust that way under low pressure conditions like overrun.

And I used .040 stainless for my blockoff plate. I'm not your average Fiero owner. I know when to throw down.