Skipping Hummer h2

[cathyiam]

So I posted about the bouncing rpms. Still no reply. I took the Hummer to a private mechanic today and he said that it is probably a coil. The Hummer jumps like it is running out of gas. It does not do it most of the time usually of the morning, but has got to where it does it some in the day- it mostly still only does it around curves but will also do it @ other times. It will do it of the morning and he explained that the humidity in the air of the morning and rain will make it do it worse. Has anyone ever heard of this and does anybody have any different ideas. I have already spent a lot of money on guess work. It does not say "service engine soon' so no code has been pulled. When it jumps the rpms will go up and down, but like I said-it does not do it all the time. I have drove it today and it has not done it at all,but some days it is bad. can someone please help?

[Yetti]

well I have to assume a lot here. first off is the engine making any odd noises when the skip/miss happens? if it just dies in corners and then re starts then I would be looking at a short of some kind. H2 are famous for having bad ignition switchs. like if it does it on right turns and not lefts the weight of your key ring could be causing it.

as for no engine codes I would look at fuel pump drop out or ignition. the best way to check your coils and plugs is to squirt water on them with a two liter pop bottle with a hole in the lid. water down each one while its running to see if it misses when wet. if you can pin point it you can probablly fix it easy.

[cathyiam]

Hey. Thanks for the advice. We have noticed over the past 2 days that if it starts doing it-it does it like I said mosly of the morning,but it starts when we hit 55 mph-it will do it constantly if you stay @ 55, but when you go over 55 it stops. the rpms jump the whole time it is doing it. We will check the key ring,but it doesn't die all together-it just skips like it's running out of fuel. It has been doing it for at least 5 months and has not got worse. We have had it to the Chevy place because the nearest hummer place is over 100 miles away- they changed the rear diff fluid and the fuel filter,but did not know what else to do. I will try wetting the coils and spark plugs. Another mechanic told us to crank it @ night and see if a spark jumped off the coil, but no luck.

[La.Swamp Lobster]

Sounds like one of the knock sensors is bad...had to have mine replaced last week...was running rough as a leaf licker on a republicans hairy butt...and had very little power. The H2 has 2 of them, and they are located under the intake..but this should show a code when tested...but then again it could also be a cad. converter that is clogged up!

[PaHumBug]

Mine did this the other day for the first time. Hasn't done it since. I got the feeling it was the tranny trying to shift in and out of OD. I gave it gas to make it down shift and it quit. Hasn't done it since. If yours is doing it at 55mph, maybe thats the same thing. My check engine light came on, but went back off the next time I started it. Since then the check engine light has come on every once in a while, but turns off soon after. Does the light need to be lit in order to get a code?

[PaHumBug]

Originally Posted by PaHumBug

Mine did this the other day for the first time. Hasn't done it since. I got the feeling it was the tranny trying to shift in and out of OD. I gave it gas to make it down shift and it quit. Hasn't done it since. If yours is doing it at 55mph, maybe thats the same thing. My check engine light came on, but went back off the next time I started it. Since then the check engine light has come on every once in a while, but turns off soon after. Does the light need to be lit in order to get a code?

Does the check engine light need to be on in order to get the code out of the computer?

[TXSUT]

Originally Posted by PaHumBug

Does the check engine light need to be on in order to get the code out of the computer?

No.

[trofeo16]

my h2 was doing the same thing. Between 42 and 55 mph the rpm's would be bouncing. Almost like you were slightly revving the motor. No check engine light no codes. Took it to the hummer dealer. They found an entire gm service belletin on the issue. Turns out there is something in the 4l60e tranny that is excentuated by exhaust,intake,maf spacers..etc. I removed all the after market and it went away for the most part. Replaced parts and it came back. If you ask hummer dealer to do a search on bouncing rpms within the service bulletins you will find the article. Hope that helps.

[H2Much]

I had a similar issue as well, ended up being a small air leak in the intake manifold. Once it was fixed, the problem was gone. Only way to check for it was a mechanic who had a smoke machine testing system. Sometimes the check engine light comes on, sometimes it doesn't. The error code just says that the air and fuel mixture is not right, usually hinting to the mass air flow sensor going bad, but this wasn't the case with mine.

[HUMTECH]

If you have an intake(vacuum) leak it will almost always set a lean mixture code and will turn on the ses light. Need a scan tool to force it into closed loop operation and monitor fuel trim levels while spraying air intake cleaner around the intake gaskets with the engine cold, if the fuel trim levels change dramatically the intake is leaking. Dont think this is your issue though. I will put some thought into it and see what i can find.

[HUMTECH]

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1899786&from=sm#ss1-1899786">Condition/Concern:

99 through 05 GEN III truck engines may experience any of the following:

1. <LI type=1>A cold rough idle that diminishes as the engine warms up. <LI type=1>Possible DTCS P0171, P0174, or P0300.
2. Random misfires at idle.

<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=1899786&from=sm#ss2-1899786">Recommendation/Instructions:

The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.

1. <LI type=1>If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
2. The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements.