Levan

Hi guys!

Recently, my GT started bucking (backfire in the air filter) on low rpm's during acceleration, mostly when engine is cool. This also occurs when I shift gear from 1st to 2nd even when engine is wormed up.

Computer codes indicate that the EGR vale is bad. "EGR not opening...".

I have seen posts in which people say that the EGR valve can be safely removed or disabled at all and it will not affect engine performance, but at the same time I read official instructions that this valve helps cool combustion process and it is important for proper fuel/air mixture. I'm little bit confused and decided to buy a new one but I need your comments to be sure this is what I need. Last thing is, could it be a MAF sensor somehow related?

Thanks

mattdel

Misfires & bucks can present themselves in a lot of different ways. When I read your description, I think MAF problem, with a small probability of a dead coolant temp sensor.

EGR bucks are possible, but they're usually created when releasing the throttle after a period of steady RPM. Also, don't be so quick to buy an EGR. It's controlled via an electronic switch and a vacuum source. Either of those could be producing the code as well.

Levan

thanks

well, according to some docs, bad EGR valve even can overheat the engine, so I thought its an important part and can't be ignored. Why it could be a coolant temp sensor when the fan is operating?

What if I'll disconnect maf sensor and see if bucking is gone, will it be a sign of bad MAF?

mattdel

If the computer registered a full time, uncompensate-able problem with the coolant temp sensor, it would run the fan full time, so there's that.. But that's not to say that the readings it's giving out are accurate. It could still be within it's acceptable voltage range but still be wrong, which would contribute to backfires because of A:F ratio mixtures being off.

Unplugging the MAF will run the computer in a fuel-richened limp-home mode(which also negates most sensor feedbacks), which could produce its own backfires depending on the condition of the engine and ignition components, but yes it should help narrow down the issue.

EGR stuck OPEN would create an overheat issue if the cooling system was already weak, but if it's unable to open, it will not contribute to engine heat.

Check for vacuum leaks associated with EGR components, too. Vacuum leaks = lean mixture = increased engine temp = backfires

There's also plenty of other reasons for this, including timing chain. Stay vigilant, my friend. You'll find it.

Levan

thanks again for you help!

I'm just looking at this rockauto.com and think what component I need to buy, EGR Valve, MAF Sensor, Water Temp Sensor, or all together

Disabled EGR = Poor gas milage
Enabled EGR = Check engine light + maybe this backfire

Sitting and thinking....

Levan

We have checked ignition system and discovered spark illumination around ignition coil on high rpm's. What does it means? Do I need to change coil or spark plugs, or both of them or even wires? Could this cause a backfire through intake?

mattdel

Yes, it could.

Levan

thanks

2008saleen

I had a bad ignition coil cause this problem for me back on my 91 gt. That car had more mods than I can remember.

Levan

thanks a lot! I'll definitely buy a new one. Now the question is, which one. There are so many brands. Motorcraft is the best choice, right?