H3 2006 H3 3.5 misfiring. Scratching my head concerning what to do.

[CaddyStrophic]

'06 H3 with 129k on the 3.5 (has a K&N cold air intake)

A few weeks ago I noticed the engine would start to bog down on any incline around the 1500 rpm mark when giving it gas. Before the 1500 mark it would run fine. Give it some more throttle to around 1800+ and it would run fine. No check engine light would come on.

I started to read online and saw the horror stories about the head starting to go bad, so I immediately found a replacement head from a 2006 GMC truck with the 3.5 (50k on motor when totaled).

I did a compression test and the results were as follows

From what I read online, the ideal number is 215

#1: 205
#2: 185
#3: 205
#4: 215
#5: 210

When I took the spark plugs out, the #2 plug was definitely not right. It looked like the tip broke off, and I thought i had found the culprit. So, I replaced the plug with a new one and drove the truck for the rest of the day with no issue.

It started having a misfire again within 2 days. I put a new oxygen sensor in and a new crankshaft positioning sensor. I drove it for a while and it seemed fine.

Well, it started doing it AGAIN this last week, now with an additional problem, it has a rough idle when sitting still now. Idles around 750 rpm. but dips to about 400-500 rpm.

So, I put all new spark plugs in it yesterday and cleaned the air filter. Ran fine for 30 minutes and then went right back to it.

Put a new MAF sensor on it today. Ran fine for about 30 minutes, then went right back to the bad idle/throttle.

Within the last year, I have replaced:

PCM
spark plugs
collant sensor
thermostat
cleaned the throttle body
water pump
radiator
and many more parts that are not related.

Any ideas what I should do next? This truck is turning in to a real money pit and it sucks.

Also, Should I have the head I bought from the GMC truck cleaned up or anything like that? I don't have any experience with those.

Thanks for reading.

 

[deserth3]

Concerning this there are smarter people than me so wait a little longer. I'd suspect too much oil on the k&n filter. Which will foul up the MAF.

 

[CaddyStrophic]

Unfortunately, i've had this problem before and after the cleaning/oiling of the filter and before and after a brand new MAF sensor. I always follow the instructions very closely regarding the oiling of the filter. I'm going to put 5 brand new coil packs on tomorrow with all new rubber um, "boot" or ? things for the spark plugs tomorrow and see what that does. I also picked up some dielectric grease for the new parts.

 

[scoreh3]

Ok you are one step ahead of me with your last post , I was going to say coil packs . I had a #2 misfire problem too and it was the coil lack .

 

[CaddyStrophic]

Argggg, I hope so much that the coil packs will fix this!

 

[scoreh3]

My son had a Colorado with a 3.5 and we had misfire problems too . That was fixed with new plugs , coil packs and TB cleaning . I would also say do a good cleaning with something like sea foam or BG44 to clean up all of the juck from the poorly burning plug(s).

 

[4speedfunk]

Any codes? You're pissing up a rope by arbitrarily replacing sensors. #2 definitely has an issue but it's within 10% of the other cylinders so I would try to nurse it along for awhile before a tear down. The electrode missing off the plug is often caused from detonation....also a sign something is wrong.
As always...CHECK BATTERY AND CABLES. Time & time again...a malfunctioning charging system often manifests itself in the strangest ways.

 

[CaddyStrophic]

I couldn't get it to throw any codes for the longest time, but eventually I found a huge hill in town and just crept up the hill until it misfired. I held it there and eventually the check engine light flashed a couple of times. read the code and I believe it was P0300 random misfire. The Check engine light has not come on since I cleared it, but still runs funny.

I will go through and make sure all of the wiring is tight and in good shape, thanks for the tip.

 

[SedonaBound]

Anything else odd about that bad plug? Deposits? Color?

 

[4speedfunk]

You might also have to re-calibrate the the IAC and TPS after cleaning the throttle body (clear & re-learn). Several guys have described idling issues after cleaning the throttle body. Apparently due to the PCM adapting to the coke build-up over time. I guess it can be so dirty that the PCM learns to compensate for it...then after cleaning it, the set-points can be way off from where they were when dirty. So the PCM freaks-out a little. I don't know this procedure but, I guess a lot of guys have to re-learn after a cleaning.

 

[alrock]

Hmm, interesting on the PCM relearn. I did have throttle position sensor issues a couple of months back (no codes, but recognized the symptoms) and it went away after about two days. Hasn't come back. Can't recall what I did beforehand that could have created those symptoms

 

[CaddyStrophic]

I have been driving my H3 for the last two days, after the 5 coil pack replacement. It seems to have gotten rid of the idle/throttle issues. Honestly, it feels like a brand new truck. I suppose maybe this is the time to sell it and get an Alpha. Thanks for all of the input, folks. Your help and tips are appreciated.