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View Full Version : Backfiring, please help


51timber
04-29-2012, 07:13 PM
Hi All,

I have a 2003 x30 200 hrs. I just had the tranny replaced. so the dealer had the engine out. I took it out yesterday and it ran perfect. Today I took it out ran it with the throttle open for about 3 minutes and it was smooth.

I shut it off to check the oil for the heck of it. All was fine. Started it back up with no hesitation and then at 2500 rpm's it would backfire through the spark arrestor intake. No power above that. In nuetral it would wind up fine but under load it was a no go. And now that's it always choking at 2500 rpm's??? Any ideas???

its a mcx

Jerseydave
04-29-2012, 09:29 PM
Check dist cap for carbon tracking. Remove cap and see if there are any carbon trails between the terminals. If the cap and rotor are old, you should replace them anyway and take another test drive. Also check your spark plug color to see if they look ok. Again, if they are old replace.

If none of the above helps, grab a fuel pressure gauge and test your fuel pressure. Try to duplicate the problem at higher rpm's. Will it rev up in neutral? Did you try filling your fuel tank? When was the last time the fuel filter was changed?

JimN
04-29-2012, 10:14 PM
Hi All,

I have a 2003 x30 200 hrs. I just had the tranny replaced. so the dealer had the engine out. I took it out yesterday and it ran perfect. Today I took it out ran it with the throttle open for about 3 minutes and it was smooth.

I shut it off to check the oil for the heck of it. All was fine. Started it back up with no hesitation and then at 2500 rpm's it would backfire through the spark arrestor intake. No power above that. In nuetral it would wind up fine but under load it was a no go. And now that's it always choking at 2500 rpm's??? Any ideas???

its a mcx

On any engine with a distributor, any time it runs rough, has a performance issue or backfires, the first thing to do is consider what was done to it before the problem started. In your case, the engine was removed for a transmission replacement and my first question would be "Was the distributor cap removed or were the plug wires removed from either the cap or plugs?"

The second thing to do is verify the firing order, then verify base timing. The fact that it's backfiring tells me that either the timing is way off or the firing order is wrong. After that, I would look at the plug wires- how old are they? If they're original, they're way past needing to be replaced. Bending old plug wires can cause problems that wouldn't occur if the engine had been left in place because the wires aren't metal wire and the material inside can crystallize. When it has done this and someone bends the wires, the material breaks and doesn't conduct as well as it should. If the easiest path for the voltage to travel is an adjacent wire, so be it- electrons don't care where they go.

51timber
04-29-2012, 10:15 PM
Well i am running on last years tank filled in november with stabil. I will check the plugs and rotor.
Could it be the mass airflow sensor?

JimN
04-29-2012, 10:28 PM
Well i am running on last years tank filled in november with stabil. I will check the plugs and rotor.
Could it be the mass airflow sensor?

If it didn't do this last year, I don't know why it would be the MAF. If you had a bad MAF, you would get a code and it may not even run as well as it does, but it wouldn't cause backfiring- it would default to a pre-programmed setting for fuel delivery. Check the firing order, then the timing. If these are OK, check the cap, rotor, plugs and wires.

When were these parts previously replaced?