I'm having problems that started recently. I have replaced the wires, plugs,
cap, rotor, and fuel filter. All these actions have improved the response of
the car but have not solved the overall problem. I have checked for trouble
codes - none. There are no exhaust leaks. When the car is cold, sometimes
takes time to start, and you can smell gas form the engine compartment. This
I found odd because it is fuel injected. It also can hesitate before it revs
up but when in gear will accelerate readily with sometimes a backfire from
about the area of the cat but its peppy enough. BTW it is MPFI. The problem
is once it warms up it will adjust the timing through the ECM and when you
accellerate it will sputter and miss, back-firing until you back-off the
pedal and try again where it will either go OK or do the same. It can also
run fine if you apply steady slow acceleration. Then again it can react as
if nothing is wrong and accelerate through the gears without a problem. When
you are driving along at high speed it seems to run without problem, good
acceleration and high end. At idle, running temperature, you can hear the
engine change rpm's. When it is at a higher idle there is no miss and it
rev's fine. At the lower rpm you get the hesitation in response to the
throttle change. I am going to do the compression test on the cylinders
next, but it seem to me that it would be constant through all circumstances
if I had a flat lobe or sticking lifter. Any suggestions out there?
Have you checked/cleaned/tested the Mass air flow (MAF) sensor? Common issue on
If you used a cheap air filter, the fine dust will settle on the hot wire and
cause it to insulate and it will cause some of the problems you described.
Good place to start barring that all other stuff is in order.
Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director
'80 Carousel Red Turbo T/A, 27k orig.
'79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig
'84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 143k and still going....
'91 S10 Blazer 4.3Z
I've got the same problem with my '89 Firebird 2.8L V6... only my backfiring
happens in deceleration. Not the mass airflow, tps, idle air, filters (air,
fuel), or even the decel valve. all new from dealer. It's not even the
timing, or the distributor itself (yes I replaced that damn thing too).
The curious thing is.... when you force it into "limp mode" your power and
all that sucks... but it doesn't hesitate, or backfire. So to me the engine
is normally running rich, but it's not even the injectors, or it would run
rich in limp mode too.
Anyone have the not-so-obvious.... although correct answer... that it's the
'89 Pontiac Firebird Red 2.8L V6 MPFI
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