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Discussion Starter · #1 ·
figured id bring this van question here for mopar elite to dissect, this b250 had no spark initially, checked asd power, good, went through tune up, plugs cap wires f filter, and got it fired up, no parts looked excessively worn, noticed this backfire accelerating, checked fuel pressure at 45 idling, up more as it revved up, thinking lean can be caused by vacuum leak, the intake came to mind, with magnum motors, when were they used in the van? with their history of  vacuum leaking, also o2 sensor can be suspect, but pcm crank sensor and dist pickup have been replaced, hoping someone has had problem relative that might chime in with some guidance.
 

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I'm not sure when they switched from TBI to Magnum motor in the vans, but they are very different-looking engines. TBI has the carburetor-looking injectors, almost like a traditional carb/intake appearance, and you should be able to tell immediately by looking at yours. And all the early Mag motors have the belly pan gasket problem.

Since you just changed the wires, etc, my first thought is wrong firing order or you have arcing from one wire to the next. My other thoughts include worn cam lobe, worn intake valve, loose timing chain
 

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1992 was 1st year of 5.2 magnum in van. 
Check for codes
check vacuum behavior with gauge
consider compression check
listen to toxic doc
 

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1992 was the first year of the magnum motor, so it should be a muiti port system. I've had those "pop" with low fuel pressure, but you've already checked that. The two things that first come to mind are ignition timing and cam timing. It could be as simple to check the ignition timing, or as mentioned before, a loose or jumped timing chain.
One problem is it's an OBD1 system, and there are not that many scan tools that read it anymore vs the OBD 2 that came out in 96. If you can find a scan tool that will support it, it may give a code or a direction to go.


Mark
 

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Discussion Starter · #5 ·
thanks, this is multiport injection, i sprayed either around manifold and vac lines engine idles smooth, ive got a legend showing ground locations, one is specified rear of engine, i cant locate any behind the intake manifold, someone have a clue?
 

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Discussion Starter · #6 ·
it did have code 12, then 55, probably from messing with wiring, compression or firing order was not a problem, it was idling perfect, i went through every sensor connector, ground, hot and reference connection, wiggling and stretching harness,  and changed something, started and drove up my hill, and it looks like it runs good, ill need a good drive on it this morning to confirm its not backfiring, if all is good, ill still be curious what the source of demise was?
 

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codes 12 is battery was disconnected OR pcm lost power 55 is end of codes .... so no codes if you had the battery unhooked ....  when you say backfires under load , does it do that like 1 cylinder , a constant pop pop pop or is it ONE pop when you depress the gas ?   

pop pop pop , crossed plug wires OR burned intake valve ........... 1 pop vac leak .. lean  my guess's
 

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Discussion Starter · #8 ·
finally got a 30 mile drive with steep hills and mixed start and stop loads challenging the failure, looks like a success, runs very well, still would like to pin point where things changed, i will continue around local driving to confirm dependability, thanks for your comments, hopefully in the next few months, ill be posting my restore progress on '74 cummins 6bt 3/4 ton ramcharger.
 
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