H2 Engine Misfire

I have a 03' H2 with a Magna Super Charger (here's the web site for those who may be interested http://www.magnacharger.com/sc-hummerh2.htm) which has been working great for over 3 years. However just recently I started noticing a slight engine misfire when the engine is idling, and then today when I started the engine the missed fire was very evident. The engine RMP goes from around 1000 down to 350 and back up. I have a Hyper Tech on board (http://www.hyperpac.com/)   and when I check for codes it read P0300 which says "Radom/Multiple Cylinder Misfire Detected". Can anyone direct me to the most likely area to check out? Has anyone ever experienced this problem?

thats the same code that h3's get when they have to get a head replacement. not sure on your h2 but I would have it checked out quick.

Thanks for the tip, I hope thats not the case. I'm having a Tech look at this week. I'll let you know what we fnd out.

Maybe plugs or plug wires..

quote:

ORIGINAL: Dennis

Maybe plugs or plug wires..

 
HOPEFULLY!!!!

could be many different things that cause a misfire but that code just makes me cringe
 
Didn't mean to make you nervous with my original answer to you.

Spoke to a tech friend (top notch Hummer Mechanic) who suggested to start out with the most likely stuff, like changing out the fuel filter, plugs, wires and clean out the Air filter. I have one of those Ram Induction air filters which you clean and re-install.. The fuel filter makes alot of sense. Since I have a supercharger with duel fuel pumps the filter is working twice as much. By the way in addition to the supercharger I have also installed the Stage IIB kit from Breathless Performance which has really made the supercharger sweet. Here's the link to Breathless Performance http://www.breathlessperformance.com/products/Hummer%20Stage%202.asp.
 
After doing all that typical tune up stuff,  he said if I'm still having trouble have the injectors cleaned out. I will keep you all posted. Thanks for all the advise. 

Before you start fooling around with the injectors..run a couple of cans of this stuff through (1 can per tank full)...This stuff is phenomenal (pricey too, about $20.00 per can), But it works miracles..Google it to find a distributor near you.
BG 44K
 

Thanks. I heard about this awhile ago from a dealership that had once worked on my daughter's car which had an EGR problem. It seem to have help. I will give it a shot. How often do you think I could use it?

To start with one can per the next two tank fulls..let the tank go almost empty before refilling.

I use it in my Jag and Hummer, one can at every oil change (5000 miles) and Redline SI-1, one bottle every 1000 miles

I found some on ebay, 4 for $ 40.00, thats a deal. Thanks again for your advise.

Well as promised, here's what was discovered to be the problem with th engine misfire. (after giving up and taking it to the dealer, ouch!) On the rear of the supercharge intake there is a vacuum stem approx. 3/8" that the cap was missing. This is an extra vacuum outlet use for other applications, according to the Rep. from the makers of the supercharger. As a result of the open (unpluged) stem, (the plug somehow had fallen off AND it was located on very rear side of the intake), it caused the engine to run very lean and misfire. After the stem was pluged the tech also discovered that 2 of the NEW plugs were causing a misfire on #2 & #5 cylinder. After changing out the NEW plugs with another set, the problem was solved. By the way, prior to taking it into the dealer we did look for vacuum leaks with brake clearner however this plug was so far back under the fire wall we never hit that area with the spray.  So much for trusting new plugs. The first set of plugs were made by Bosch, called "No Gap" . They seem to be good plugs. Iguess we just got a bad batch.  Here's the link http://www.boschautoparts.com/Products/SparkPlugs/IrFusion
 
Thanks to all who offered advise.

Glad you got it fixed.

See..I told you it was plugs

quote:

ORIGINAL: Dennis

See..I told you it was plugs

 
lmao....thats like sayin...see I told ya it was something in the engine

No it ain't..I was specific..PLUGS or WIRES.........Pull my finger!

Hey, question. importkiller, where did you find  those girls? Are these your hummer hotties? The last hummer event I went to I had 5 hot hummer hotties. It was a blast!