Hi guys, my mom has a 07' H3 with currently 101k on it. It appears she needs a new cylinder head I did my research before she bought it and confirmed hers had the redesigned head (12-06 build date) and that she should be clear of the leaky valve issue. A couple weeks ago, her check engine light started coming on and going off. The code would switch from a cylinder 1 misfire to a random misfire code each time I scanned it. The truck had almost 100k on it, so we did a set of AC Delco plugs in it. No change. I replaced the #1 coil (AC Delco) this past weekend...no change. Our family mechanic looked at it today and did a compression check. He said 2 cylinders were low. I know cylinder #1 was one of them, not sure which other one was low.

I called Chevy customer service tonight and they said before anything can even be started, it needs to be diagnosed by a Chevy dealer. I understand that and she will get it there in the next couple days.

Has anyone with a 07' had this same issue? Any hope of Chevy helping out? This is extremely frustrating since Chevy supposedly fixed the issue in April of 06', but hers is having the same problems.

Thanks for any advice/tips.

 

Did you do a leak down test?

 

From my understanding, the mechanic only did a compression test. I live in FL, she lives in GA. My parents drove it down here this past weekend to visit, which is when I replaced the coil for them.

 

A leak down or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss.

A leak down test requires the removal of all the spark plugs. The crankshaft is then turned so that each piston is at top dead center (both valves closed) when each cylinder is tested. Most people start with cylinder number one and follow the engine's firing order.

A threaded coupling attached to a leakage gauge is screwed into a spark plug hole. Compressed air (80 to 90 psi) is then fed into the cylinder.

An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.

The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.

A leakage test can also be used in conjunction with a compression test to diagnose other kinds of problems.

A cylinder that has poor compression, but minimal leakage, usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, bent push rod, etc.

If all the cylinders have low compression, but show minimal leakage, the most likely cause is incorrect valve timing. The timing belt or chain may be off a notch or two.

If compression is good and leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery (bad injector) or ignition problem (fouled spark plug or bad plug wire).

 

Hummerz


Thank you for the very informative post, well written.

 

Any Atlas motor can have a bad head. Any vehicle made can have a bad head.

What you need to grasp is...... The S/Ns affected is any 2006 H3 lower than 287591 .... the first one started with 100,001, your truck build date will be Nov. 06 or earlier. Not all have the problem, but some could. The head issue affected not only the I5, 4s and 6s were subject to the same issues.

Just in case you're gonna say, wow they didn't even build that many 3s? The VINs are assigned at the same Shreveport plant building Colorados and Canyons. Their VIN sequence unit #s are mixed in and subject to the same TSB re: the head/valve issue.

The recall and extended warranty was for very early 2006s, those with the 3.5L L52 Motors built before March 31, 2006. That is not to say some 3.7L LLRs have never had a valve or head issue. All the Atlas motors built since 4/1/06 have the new hardened valve seats.

So when a 07+ has a head issue, it is not the same issue that was the subject of the 2006 TSB. You could have a weak or broken valve spring, bad gasket, cracked valve...... and a bunch more stuff?????

 

I have a late build 07 that got the cel at about 55000, kept driving until 80K then got the hear replaced free from the dealer, been ok since. Currently 165K

 

2007 H3 Had the head done at around 35,000 miles. so far 63,000 and still ok.

 

So Doc Olds, is a 1/2007 H3 3.7L I5 engine significantly less likely to see the dreaded head related issues? I ask because I am currently working a deal to purchase a gem of a 1/07 production (base/adventure) 3.7L from Jacksonville Florida with 40,600 miles on it.

I have an 06 (151,000 miles, head replaced at 74K miles) at the moment with bad valve seals that leak oil into the cylinder(s) over night while parked and smokes like a freight train now and again on start up. It also throws the random misfire code if driven on the highway and it has the often discussed near stall when coming to a stop.

I hope that the amazing gem of an H3 from Florida with a 4-5K mile average per year life is a more trouble free beast. I know that the vehicle is in amazing condition, being that up here in the rust belt of Western PA all vehicles undersides are covered in rust within a couple years. This is like a barn find to me.... one of those vehicles that is amazing to behold.

So what are the troubles to be expected with a 1/2007 3.7L H3? I expect to pull the transfer case and swap the plastic fork out for the updated allow one, but that was my only planned pre-emptive strike.