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Backfiring / Skipping on Fuel Injected Engines

1994 Grand Caravan 3.3 - skips and backfires

KOG wrote that his Grand Caravan 3.3 ran fine one day, but not the next. He checked for a dirty throttle body and vacuum leak; there were no computer codes set. It acted like it was lean when he hit the gas. The fuel pump sounded normal.

Possibility One: Fuel Issues

Tech Man suggested checking the fuel pressure and filter. He noted that the 3.3 is distributorless, otherwise checking the timing would make sense.

James wrote: When my 3.3L wouldn't run good enough to get me out of the parking lot I tapped the fuel tank and somehow the pump engaged and got me another 70 miles before going out for good. Usually they have a different sound when on the last leg.

Possibility Two: Ignition

BG wrote: -- Wednesday, 27 September 2000, at 11:54 p.m.

It could be coil blocks and wires after 6 years that's about the time they start showing lower performance at least in some other cars I have been working on lately, in particular the Cavaliers. Just a thought!

Jerro O. added: Jerry O. -- Thursday, 28 September 2000, at 5:06 p.m.

Check the secondary wires and the coil pack. Bad wires can cause a burn-through in the coil pack, wherein the spark, due to resistance in the wire, goes through the insulating marerial to the nearest ground.

rcx6 said: Two years ago mine was experiencing the same symptoms and it was one of the coil packs was bad. Mine would skip and backfire causing the check engine lite to come on eventually. The code was for the O2 sensor which was replaced and did not help the coil pack. It really ticked me off when I realized the coil pack has three separate coils but they are all in the same assembly. I think it was about $125 for the coil pack.

Backfiring on a 2.2 liter engine

The air pump / diverter valve

A 2.2 liter engine was backfiring; the owner suspected the air pump, and Rocky2 suggested taking the belt off the air pump to test it.

John Auto Tech warned: The main reason for the air pump is to pump air into the exhaust to help the converter burn any unburned gasses coming from the engine . With the valve removed you will more than likely end up with a clogged converter due to it not being able to do its job completely and getting loaded up

John Wood asked: Could this be a switching problem between upstream and downstrean air? I've never seen one of those vacuum switches go bad on the thermostat housing, but I am suspicious. I never had the back firing problem, but twice I had the upstream check valve go bad to where hot gases melted the diverter valve. Replacing those items is not a fun job.

"Chrysler Tech" wrote: Eric, the valve is bad, but cause of the bad valve is the aspirater tube. It's a short tube coming off the exhaust manifold with a valve made on the tube,when the valve goes bad it let burnt gases and unburnt gases back into the air pump. Which in turn cause a backfire or melts the diverter valve and lock up the pump. If you remove the belt for a long period of time it will lock up the pump.

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