n2jmk

Hi, Did you get the popping / backfiring problem fixed? I have the same problem with my 90 GT. Under a heavy load, it will backfire through the MAF. Does happen every time I give it moderate or full throttle. Any info would be appreciated!

aode08

what happens to combustion if the intake valve is open too long?

It comes out the intake.


Adjust those valves and check for proper timing

n2jmk

Thanks for the reply aode06. I should have given you more details.

I have a 90 GT with stock ET7 heads and stock stamped steel non-adjustable rocker arms. You may be right about the TFI module being faulty - I'll replace it andcheck the timing again. If I can find a fix for this, I'll post it back here. The problem doesn't happen everytime I try to accelerate with moderate to full throttle though; so maybe it is igntion timing-related? Except a cold air intake, and equal-length shorty headers, the engine is otherwise stock.

Hey, I'm open to any other suggestions or thoughts while I check into this.

shaners90lxhatch

I say lean all the way. Intake backfires are the product of a lean condition or a cam timing issue (given your plug wires are routed properly and base timing is not too retarded). Why it is running lean will be your PITA without the right equipment.

n2jmk

I got it resolved. The TFI module was bad. When I checked the timing, it would fluctuate (yes, I did have the shortout plug disconnected). Foolish me, I never though about ignition timing! Thanks all

aode08

what were your timing readings doing as you read them

n2jmk

At first, the timing was at 14 deg, then it changed to 10 deg after I
revving the throttle. I revved it a couple of more time and it
was at 12 deg. Then, the timing mark was actually walking while I
had the engine idling, even though the distributor hold down was
tightened.



I changed the TFI module, reset the timing to 14 deg and it stayed!



I have since:



-Swapped on a set of AFR 185 heads (large chamber)

-FRPP F303 cam with new roller lifters

-FRPP true roller timing set