Did you address the plenum gasket issue?
http://www.hughesengines.com/Index/p...p?partid=27091

 

platinum bosch plugs and I do believe the original crank sensor. has no problem starting up and driving under 2000rpm. its only under heavy throttle above 2000rpm does the miss fire come into play.

 

update #5 97 dodge ram 1500 with 5.9 magnum. miss fires mainly on cylinder 2 but I will also get the p0300 and cylinder 6 miss fire according to AutoZone and a snap on scan tool. The miss fire only happens under heavy acceleration and idles just fine. Just did a fuel pressure test and did a resistance test on my injectors. all injectors on the passenger side at least tested 11.8-11.9 ohms of resistance. unable to test the fuel pressure while driving because I bought a cheap kit with the wrong fittings but I made it work while parked. testing only the fuel pump side of the system the pump gets up to 46psi of fuel pressure before I'm assuming the pressure regulator kicks in. sprayed starting fluid around the heads. throttle body and intake checking for a vacuum leak. had no change in idle. tested battery and tested good, replaced both the spark plugs with napa platinum bosch plugs and wires with no change. resistance tested coil and was within specs. Had a lot of work done to the truck within the last year, new heads, new tps, new distributor cap and rotor, all new gaskets for everything, new transmission with sensors and a new timing chain. Miss fire only recently started happening. Been chasing this miss fire close to a month now. Truck is also slow under heavy throttle (75-90%) really slowing down around 3,000rpm and wont shift up unless I let off the throttle, assuming this problem is occurring because engine doesn't have enough power from the miss fire. Truck accelerates better under medium to light throttle but sure does suck trying to get onto the freeway. No rich or lean codes, MAP sensor at idle running 1.2V average while upstream sensor at idle running bouncing up and down from 0 to 1 volt. Don't know if any of this information is of any help to anyone. My brain is melting trying to figure this out and buying a new truck or engine isn't a option for me.

 

plugs are a week old. and ignition wires a day old. still has a miss fire and slow acceleration.

 

gasket is brand new, replaced it with my engine heads.

 

I wonder if the fuel pump is getting weak or possibly the filter and pickup screen is full of Gooky Stuff. (<------fancy technical term) Retricted fuel flow can cause a great idle but poor load conditions.

 

I tested the fuel pump side of the system and the pressure would read 46psi before the pressure would be relieved Id assume. Unable to test it on the road yet because the kit i bought wasn't the greatest. But I bought the right adaptor hopefully and will be here Monday to do a on road test.

 

First, get rid of the platinum plugs. These engines just don't like 'em.

Will your scanner read misfire counters? Would be interesting to see what the numbers look like.

 

Couple of things:
- Replace the platinum plugs with simple copper plugs. Plenty of anecdotal evidence these engines don't like them.
- Compression test
- How do the fuel trims look ?

 

I was unable to look at the fuel trims, and I will be doing a compression test here soon. And I will look into replacing the plugs with copper plugs but this makes me really sad considering all that money will go to waste. I don't think napa will accept them back since I don't have the box and I dont have the money to be throwing this much at my truck at once. Im probably going to keep the plugs. for a bit