502 backfires
 

checked compression 150 all 8 fuel pressure 34 psi timming ok engine is a 1995 mpi plugs cap and rotor new back fires worst at 2000 rpm help?

Re: 502 backfires
 

Was this a previous problem or start after plugs, cap, & wires??? Firing order correct???

Re: 502 backfires
 

firing order is correct engine has set for 8 months ran fine before

Re: 502 backfires
 

Run a can of merc fuel treatment and also a quart of MMO in the crankcase .....

Re: 502 backfires
 

whats mmo? i PULLed injecters to have cleaned and flow tesed will install in the morning

Re: 502 backfires
 

Is the backfire coming from intake or exhaust?

Re: 502 backfires
 

exhuast does drive oil moniter not hooked up cause fuel cut ?

Re: 502 backfires
 

mmo=marvel mistory oil, red and black quart can.

Re: 502 backfires
 

Is backfire coming from both exhaust banks?

Re: 502 backfires
 

both banks

Re: 502 backfires
 

This motor ran fine then all of a sudden this started?
Its most likely ignition or fuel.

Recheck your firing order.
Check ignition timing.
A merc Scan tool would be nice.
Whats your fuel pressure?


While holding the throttle at 2000rpm pull a plug wire
then put it back. See if you can get the backfire to stop out of that bank. See if you can narrow it down to what cylinders.

Re: 502 backfires
 

installed new injectors cap and rotor rechecked timing and codes none tach needel bounces at idle and engine surges at midd range engine speeds up from 2000 rpm to3000 but tach doesnt still back fires. runs fine no load above 3000 rpm doesnt with load

Re: 502 backfires
 

Yes it could!
If the drive oil monitor is not hooked up and one of the leads is grounded, or oil level is low, the engine will be in "Power Reduction Mode" which will limit revs by not firing injectors above a certain RPM (i think 2000).

Dave

Re: 502 backfires
 

Try unhooking the tach, i have had that problem before and it turned out to be a bad tach.

Re: 502 backfires
 

Did you ever get the problem fixed?