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Discussion Starter #1
Under high manifold vacuum, high spark advance, low throttle setting on highway (i.e. flat, level road) van will sporadically "misfire" by getting wrong air/fuel mixture, generally say 20 to 40 times a minute. Not immediate, it takes some time of driving on flat road, for it to "build up" where it becomes a problem If incline of road increases so have to increase throttle, the "misfire" goes away. So, gas mileage suffers. If unhook egr valve, it stops "misfiring" at 70 mph, but it still does it at slower speeds. No codes occur.

Have had to several garages and by them or self, replaced spark plugs, wires, coil, filters, tps, air sensor, camshaft and crankshaft position indicators, fuel injectors, first oxygen sensor, and egr valve system. Had to Dodge garage twice. First time they submitted to 19-point test, took $80 and said was in great condition. Second time, they said was due to worn motor mount allowing torque of engine to rotate pull on wiring harness causing bad connection and took $720. I don't understand logic as it seems to be when pcm is in closed loop and pcm is trimming fuel to be economical (could always hear engine strain in such condition when driving for fuel efficiency but can't drive that way anymore, as it just misfires away).

So is problem due to bad air-fuel mixture first, as determined by ???? in closed loop mode at highway speeds (generally >40 mph) and first O2 sensor corrects it.

Or is it the second O2 sensor correcting it?

Could it be a bad second O2 sensor that is messing the first one up causing bad air-fuel mixture.

Or is it coolant sensor or any other sensor?

Why does it not do it when unhook EGR and run van at 70 mph (I think gas mileage still suffers. . . .)

Dodge garage says bring it in, but the still feel problem is due to bad wire or bad connection. . . but they don't seem to be playing in the right pond.

Can feel this "misfire" in 4th gear in lockup, but can also feel it, if have it in 3rd gear and it's more noticeable due to higher engine rpm, but again, road has to be flat, with minimal throttle setting.

Thanks
 

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Since in the 4 cyl section, I assume you have a 4 cyl, but would be a 2.4L in 2002.

I doubt an O2 sensor since that should throw a code. Also, I think the only way it can operate is close to stoichiometric O/F since your O2 sensors are simple on/off switches. They can lean it slightly with a few tricks, but not much. New cars are just starting the get the "wideband" O2 sensors that tuners use.

Why do you think it is a fuel problem? Could it be a spark mis-fire? My 2.4L was missing bad under WOT. I lowered the spark plug gap, per a Chrysler TSB for turbo engines and no more problems. Yours is opposite. A marginal spark ability is felt more at high cylinder pressure (low rpm, open throttle). Could also be a bad coil pack, crank sensor, or wiring. I don't know that the cam sensor affects sparking in a "waste spark" system like ours. It seems it is only needed for sequential fuel timing. But some say does affect spark. Anyway, a bad cam sensor can draw down the 8 V power that the crank sensor also needs.
 

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Thanks for response.

Early in attempting to diagnose, one garage w/ Chrysler meter said it was not an electrical misfire; I thought in might be until that gentleman said, "No."

No codes show. We have replaced spark plugs, wires, coil, fuel filter, air filter, MAP, throttle position, and crank shaft position sensors, fuel injectors, front oxygen sensor and EGR valve system.

Also took a generic meter and at 65-70 mph on road w/ moderate incline and down hill elevation changes, read meter when “misfiring” started (flat or slightly down grade) and when it ended (getting into throttle going upgrade).

Engine conditions for “misfiring” were:
~40 degrees spark advance and higher
MAP hg 17-to-19 range
<20% engine load
22% absolute TPS
O2-sensor output that fluctuated wildly except under heavy-throttle, seemed to be driven even lower during periods of “misfiring.”

Thanks
 
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