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Topic: Sputters, Backfires, then goes (Read 1723 times) previous topic - next topic

Sputters, Backfires, then goes

I'm having drivability issues. If I drive the car right after I start it, it will not go over 30 mph without sputtering and backfiring. Usually until the rpms get to be around 2500, the car will move very slowly. Once I hit the 2500 range, it will take off. If I let the car warm up for at least 5 minutes, it still is bad but doesn't backfire unless I floor it. Then driving in traffic... If I'm going at 50 mph and have to slow down to 30 because of someone turning infront of me, when I get back on the gas, the car bogs down and backfires about 4 times and then starts to accelerate. I'm really pulling my hair out on this. It has been going on ever since the heads were changed in June. It's just a lot worse now. I have checked all of the vaccume hoses for leaks and have found none. I dissassembled the emissions lines off the air pump and plugged everything. It really made no difference from when all that was connected. The cap, rotor, plugs, wires and coil are all fairly new. I am still running off the stock 5.0 cougar fuel pump. I have installed an off-road h-pipe so cats are not a problem. The only codes I got were for the fuel pump wire which I didn't connect when I did the Mass Air Conversion and another for the thermactor air system. It seems very convenient that this started the moment I drove it after the heads were done. Is it possible that the intake manifold, upper or lower, is not properly sealed?  Any ideas?
Sorry for the long message, just trying to explain everything
Please help if you can...  My 5.0 won't go

Re: Sputters, Backfires, then goes

Reply #1 –
What firing order are you using?? A mass air computer requires the 13726548 sequence, do you have a HO cam??

Re: Sputters, Backfires, then goes

Reply #2 –
The firing order is correct. I've checked it many times but will again when I get home. The motor is mostly stock 1988 Lincoln LSC HO. Still is the original HO cam in the motor. The only thing to change were the heads and the Mass Air Conversion. I've had my conversion wiring checked and it is all correct.

Re: Sputters, Backfires, then goes

Reply #3 –
Sounds like you've checked about everything.. How about timing??? Set it to 10*-12* with the sprout jumper plug removed.

Checked compression??? Maybe some of the intake valves are just barely closingand leaking back into the intake(did the heads get a valve job? if so may need some shims under the rocker pedestals). Either one of these problems would likely be worse in colder weather.
 

Re: Sputters, Backfires, then goes

Reply #4 –
My timing is set to about 10 degrees and the compression is good. Didn't think about shims. I do have some detonation. Relationship there?