I am working on a 2003 WD2500 with a hemi in it.I have run into a problem when i have a multiple cylinder missfire. when I check the missfire counter I see that cylinders 1 thru 4 are missfireing big time at idle through 2500 rpm.When you go over 2500 rpm then it stops missfiring and the engine runs smooth but as soon as you drop under 2500 rom it is missing again. I have put in a new PCM with the newest software updates. The compression is good, the fuel pressure is good, the cam and crank sensors are in sync, the coils and plugs are good, the asd relay is functioning, the injector pulse is good, the vacuum is holding steady, and I seem to be lost as to what may be the proper repair. Just seeing if anyone has possibly heard of this condition.

thankyou

 

Under load? No load? Doesn't matter? Sounds like you've covered the basics, so we're gonna need as many details as you can provide to help out.

 

no load sitting in the shop with the manual transmission in neutral as well as when driving under normal conditions until you get above 2500 rpms.

 

Are you absolutely sure you have the plug wires right? If you are misfiring that bad I would double check the plug wires, then check again. Have a buddy check them because sometimes we do not see the obvious and it takes an outsider to notice something we could not. It sounds almost 100% thatyou have the plug wires in the wrong places.

 

i agree with pirata.... it has to be something along those lines with that bad of a misfiring problem...

 

YO could swap out the plugs with cylinders that you know are not missing.
That way you have eliminated the plugs.
You canunfortunately buynew faulty plugs.
Also, do the same with the coil packs and the wire.
See if the missing cylinders change when you move this hardware?
That's if you haven't already done this stuff.
It's always worth re-going over this sort of thing.
Sometimes you "can't see the wood for the trees" if you know what I mean????
Al

 

ok thanks for the tips guys, i have swapped coils andplugs and the same cylinders missfire. I have checked the wires and had someone else check the wires as well. the wires are labeled for which cylinder they go to right on the wire so they seem to be in the right place. the plugs look good so I am still stumped. also i have good injector pluse so in theory I have everything in place so that this should run right. I must still be missing something little.

 

Hi..Plugs "look good" but they can and do, missfire/breakdown.
I know it's a PITA, but do a plug swap with known good cylinder plugs and see if the fault follows the plugs.
Al.

 

So is it running like crap or is it just pulling the code?

 

I swapped and regappped plugs and no change. Still missing on front 4 cylinders. It not only pulls a code but runs terrible.