Working on my first H3 and need some advice.

It is an 2007 H3 with 120,000 miles
Sticker in the door says 01/07 so early model 2007 then

It started as a hesitation or misfire at idle. Not much of one but a little. My friend had it towed 3 hours north of where we are to her hometown. Her dad had the dealer look it and they said it needed a cylinder head. To the tune of $5000+. I said bring it to me and if it truly did need a head I would do it for way way less but I highly doubted that it needed a head.

2007 H3 120,000 miles
VIN: 5GTDN13E578189149
Hesitation at idle/ misfire
P0301 misfire cylinder 1 code.
No white smoke or coolant usage.
No overheating

I did some research on this forum and found out about the coil issue causing people to suspect Head problems.

She then drove it back to where my shop is 3 hours no overheating or coolant lost. Upon start up after sitting for 2 days there was no hesitation.
I drove it for 15 minutes with my scan tool hooked up and the check engine light never came on but I did feel the slight hesitation(which is only noticed at a stop sign). I scanned the truck anyways and got the P0301 code. I went back to my shop and took the coil off and swapped it with the coil on cylinder 4. Drove it in town and on the interstate and cannot get it to send a code or even pending code and do not feel the hesitation.

 

Also this is the 3.7L engine

 

Just to update. I've spent about 5 hours on google researching the PIP3935D service bulletin. I am going to go to Karl Chevrolet and have the VIN checked to see if it has had the head replaced before. Seems likely because most of the heads went bad prior to 85,000 and this H3 has 120,000 miles.

I pulled the plugs and it had autolite cheapies in place.

So far:
1)swapped in a set of AC Delco iridium OEM style plugs gapped to .043 as spec
2)swapped #1 and #4 coil. Misfire stayed at cyl #1
3)cleaned throttle body and intake with intake cleaner.
4)cleaned all sensors in the intake with electrical cleaner.
5)cleaned cyl #1 coil plug male side. Engine seemed to be very well detailed and wasn't sure if a small amount of corrosion had formed causing a little resistance.
6)bought ZMAX engine and fuel additives poured those in and filled up with non ethanol gas.

I haven't drove it since the intake and electrical cleaning. Going to let it sit over night before I fire it up since I hosed the throttle body off pretty well. 25 mile drive to work should let me know where I stand as far as the misfire coming back.

The last 6 of the vin are below the magic serial number effected as per the TSB. But the door jam build date says 01/07. Would I still fall under that TSB? Or does the serial number not come in to effect since it is a build date of 2007?

 

Heads probably shot.

Sadly as most Hummer owners know, it's almost a dealer to dealer situation on who will warranty & what they will warranty...

Try a compression check

 

Head problem was on the 3.5L only and I haven't seen a case with the 3.7L, I'm over at 355 nation 2 years now and not once seen a 3.7L head problem but anything can and will go wrong. I had the same issue you are talking about due from E3 plugs burning out my #2 coil. ONLY at a stops/idle it had a nasty hesitation then are taking off good as new.

I think your on the right path and should be working fine after all you have done, I would have taken the same steps but also check and clean the MAF sensor. Good luck and keep us updated!!!

 

OK I lied I have found a hand full of 3.7L 2007 with head issues but not many, still looking info for the VIN that are affected.

 

The TSB is for 3.5L, not 3.7L I5s.

From an old post of mine regarding the paranoia surrounding the "I must have a bad head cuz I read it on the internet."

"Service bulletin? Closest thing for anything post 06 is the dirty fuel injector bulletin.

Atlas motor misfires: 1) bad valve spring (weak or broken); 2) worn or bad valve seat; 3) broken valve retainer; 4) cracked/bad valve; 5) bad head gasket; 6) bad spark plug; 7) bad coil pack; 8) dirty or clogged fuel injector; 9) PCM fuel management program glitch; and, 10) even a a bad valve oil seal if worn enough. All can all cause a misfire from negligible to violent at idle or under load.

A dirty MAF, dirty Throttle Body, bad O2 sensor, or bad cam position sensor can cause similar symptoms with a rough idle or false stall sometimes mimicking a misfire and can be read by the PCM through knock sensors as a misfire .... which usually shows up as a random misfire P0300 rather than cylinder specific.

#2 was the subject of the 06 TSB (the S/Ns affected is any 2006 H3/Colly/Canyon lower than 287591) for all L52 motors built before March 31, 2006.

So, you do the easy stuff, and if that doesn't clear it up, go to the dealer.
If you have a local shop that has the time to put the vehicle on a scanner and allow it to reach operating temp, you can watch all the sensor, fuel and spark data to see if you/they can spot something not like it is supposed to be.

Good luck."

 

Doc:

I've got a MAC tools OBD 2 reader with data maps on like 47 or so sensors. Do you know which ones I should look at for my issue and what the reading should and should not be?

 

we had a random multiple misfire code early on. ended up to be a dirty Throttle body. From the sounds of it you probably did not remove the throttle body to clean it properly did you? I'm just guessing that from what you wrote that you soaked it good and want to wait to start it up. You need to take it off of the car so that you can properly clean both sides of the throttle body. That is the only way to do it right. The back side that you can't see is just as dirty if not dirtier than the part that faces out. So before going anyfurther if you didn't, take it out and clean both sides. Let it dry. It takes just several minutes to dry. install it and you will be on your way.

 

Pic one MAF ground. Spec around 12v
Pic two MAF power. Spec above 12.3
Pic three MAF at idle. Spec 2.2-2.5hz
Pic four MAF at 1500rpm. Spec 3.6-3.7hz
Pic five MAF at 2000rpm. Spec is 3.9hz

I'm thinking bad MAF??