firebird904

I've been working on my car for a while now trying to get it closer to being driveable and slowly but surely it's getting there now the problem I'm having is my 2.8 backfires through the intake when given a little throttle.It also occasionally stalls when first started. When the engine is cold and you give it some throttle it will slightly bog down, backfire and then accelerate just fine after that. When I drive it it will do it under acceleration but other than that it idle's smooth so I believe it's only when the engine is under load. I've asked around and some people tell me it could be the ignition control module and others tell me it could be the maf sensor or the coolant temperature sensor. Before I go out and buy stuff I may not need does anybody know what could be causing this? Anything I could check for? Within the last 9 months I've replaced because I needed to:

1.Injector's
2.Maf sensor
3.distributor cap & rotor
4.sparkplugs and wire's
5.Iac valve
6.Air temp sensor
7.Air filter's
8.pcv valve

firebird904

I had a new coolant temp sensor in my fiero and I put it on the camaro to see what it would do and it still has the same issue. I know for sure I have no vacuum leak's I replaced them all already and checked em over and over to make sure I didn't miss anything. I was told it could be valves improperly adjusted but wouldn't it backfire every time that valve would open or close? I think I'll check the tps next to see what it does but any help would be greatly appreciated.

firebird904

I forgot to add sometimes there will be a kind of knock near the water pump and timing chain cover area. My dad thinks the chain could be stretched I had being when I checked the timing it was 10 degree's off. It's right at 10 degree's btdc now though.

ASE doc

The timing chain on the 2.8 is a weak link. The OE used a funky little tensioner with an even funkier little spring to keep slack out of the chain. Its very possible you have issues there and that the chian is climbing the sprocket teeth as you increase RPMs. Check for this by bumping the throttle while watching the timing marks with a timing light. The marks should move smoothly from idle spark to advance back to idle spark. Look for it to toggle at either end or jump around. Uneven timing is generally caused by a loose timing chain. Do not let this chain fail. It will take your motor with it.

Other things to look for:
Do you have a scanner? If you do, use it to check O2 voltage while you accelerate. It should go rich under load and lean when you decelerate. Check fuel pressure.

firebird904

Thanks ASE doc I'll be sure to check that out. Could this cause stalling when the engine is first started in the morning? What happens is I turn the key it starts right up then dies turn the key again starts up fine then dies after about 7 or 8 tries it will stay running.

firebird904

I've been reading around and all but the backfire through the intake appears to be a bad maf sensor maybe I got a bad one as I've heard the auto part store re manufactured ones are junk

ASE doc

I advised you to watch O2 voltage on datastream to see if AFR(air/fuel ratio) is correct. A lean AFR will cause your symptoms. Lean AFR can be caused by a malfunctioning MAF. Be aware though that while it is true that aftermarket MAFs vary widely in quality and reliability, the MAF system is a group of parts. Any of which can cause a MAF malfunction. You were instructed also to unplug the MAF and start and run the engine without the MAF. The ECM goes into Memcal fault mode with the MAF unplugged and if the engine and fuel system are sound, the engine should run decent though far from perfect. If the bacfire and stalling are gone with the MAF eliminated, then you have a MAF system issue.

If this is the case, you need to either have the system diagnosed by a reputable professional, or follow the diagnostic sequence for the MAF system. You could replace every part on the car and never fix it if you dont pinpoint the problem.

The place to start is by checking the engine mechanical health. Check for T-chain wear as I instructed. Check compression to be sure youre not dealing with bad valve(s). Turn the key on, does the Check Engine light come on with thekey on and engine off? If not you may have engine codes and not know it. Then connect a scanner and look at codes and data. You need to familiarize yourself with the various PIDs(parameter ID) and their meaning as well as their relationship to one another. The information available on datastream is key to diagnosing your vehicle. I suggest investing in a factory(Helms Publishing) manual. This manual is filled with valuable information and will help you greatly in understanding how things work.

firebird904

Well I put my old maf back on just to see how it would run and it ran a little bit better didn't stall when first started but idle dropped to around 500 then went back up to normal start up rpm's. Then I decided to check the tps sensor and wouldn't you know it the sensor was way off I set it to .54 volt's and It accelerates smoothly all the way from 900 on up no backfire through the intake. So it is running much better it used to smell like it was running pig rich as well.

ASE doc

Good news! Thanks for letting us know.