Extrememly Random "Power Reduction Mode" with a 2007 Hummer H2

[E.A.]

Here is the stats on the truck

2007 Hummer H2, stock other then a Magnuson Supercharger.

Installed the blower, loaded Magnuson tune that came with supercharger kit. As well very well truck drove great other then two issues.

- Horrid gas milage around the city.
- Randomly would go into power reduction mode (pull over, turn key off for 30sec, fixed)

The owner came to me to fix it, and I said that it shouldn't be an issue.

However.....

It has no codes in the ECU or the TCU, other then a Class 2 Data whatever error.
I was really expecting to see something like a MAP, or MAF, or ETC code of some sort to put the truck into a power reduction mode so many times.



Anyways, I tuned the ECU to pick up the milage (which worked big time) yet I couldn't find ANYTHING out of line in the Magnuson tune as far as something that would cause the power reduction mode. (Not that I expected to, their base tunes are always nearly spot on if the cars/trucks are in fact stock, with no issues) So I figured it was a fluke and let it go.

Guy calls again, says its still doing it. Talk to GM about it, they said it was a throttle pedal problem, and they could fix it. Well it gets the new pedal and its still having the issue.

Finally I told them to have GM flash the truck to the latest stock OEM GM program, and I would build a complete base tune from that. Well, I did that..... and you guessed it... .same result.


Whats fustrating is the following..

1) This thing can go weeks on end without going into that mode. Then sometimes it will do it 3 times in like 15min. There doesn't seem to be any rhyme or reason to it, and its gonna make me pull my hair out.

2) NOOOOO CODES to even help figure it out, other then that Class 2 Data Bus.


The truck has an Aftermarket Radio in it, so I figured that was the issue with the Databus? Is that correct?

Has anyone had this issue....?
Is he going to have to pull the blower off, and see if it does it stock?



Thanks in advance.

[Sid447]

The only thing,

I may be able to help you with is the data link code.
If it's U1000 "Class 2 Data Link" I have about a dozen logs from an H2 Hummer that show this code on every log yet the truck runs great without the problem you are having; this vehicle is also fitted with an after-market sound system.

Could it be the fuel system? The trucks are fitted with 24lb injectors and also the stock GM fuel pump wouldn't be sufficient to feed a blower engine, though it's only a guess.

[eficalibrator]

Have you independently calibrated both the MAF and speed density airflow models? If these two disagree, it's going to set the stage for all kinds of unhappiness with ETC controls. Some aftermarket supercharger companies make a habit out of just cal'ing out the safety checks (which are what cause reduced engine power) instead of taking the time to properly dial them in after getting both airflow models right.

[E.A.]

Have you independently calibrated both the MAF and speed density airflow models? If these two disagree, it's going to set the stage for all kinds of unhappiness with ETC controls. Some aftermarket supercharger companies make a habit out of just cal'ing out the safety checks (which are what cause reduced engine power) instead of taking the time to properly dial them in after getting both airflow models right.

Not until this truck have I had an issue with power reduction like this, let alone something that will put the truck into power reduction mode with the engine not even running. YES, if the key is left on in the truck for a lone period of time, you can come back to it and sometimes its in power reduction mode. Just sitting there, not even running. (Still no codes) So whatever causes this is pure random.... cause I can't think of anything (not even a broken wire) that will cause an issue with something not moving, and not running.

So the MAF/MAP correlation issues are kinda ruled out on that one.
Sorry I forgot to mention that in the first post.

Something has to be a total miss here, for three tuners to have the same issue.

- Magnuson tune has the issue
- Local KC shop tuned it, and had the issue
- I started from scratch and have this issue.

[ScarabEpic22]

Id try a new ECM and see if that fixes it, if 3 separate shops have played with it and the ECM is still throwing a fit it might be something is damaged inside. Long shot, but E67s are cheap so it wouldnt be a bad idea to have an extra around anyway.

Sid has an interesting idea too with the fuel system, what are the injector duty cycles when you're in boost? How is the fuel system setup, a boost-a-pump style setup?

[E.A.]

Id try a new ECM and see if that fixes it, if 3 separate shops have played with it and the ECM is still throwing a fit it might be something is damaged inside. Long shot, but E67s are cheap so it wouldnt be a bad idea to have an extra around anyway.

Sid has an interesting idea too with the fuel system, what are the injector duty cycles when you're in boost? How is the fuel system setup, a boost-a-pump style setup?

Truck has never had the issue while in boost, or under load of any sort. The only times it has happened to me are the following.

1) With Cruise set on highway at about 70ish MPH (flat ground)
2) With the key in the "on" position, but engine off, while I was pumping gas
3) Sitting at a stoplight, just before I went to take off. (then your "that guy")

The fuel set up, is the injectors that come with the kit, I don't think a BAP if I remember right. This is just the low boost kit, so its only 6psi tops. Really not a rocket ship by any means. Fuel trims are nearly perfect...like -1.8 or something close. No vacuum leaks, nothing out of the ordinary.

I have done plenty of other Maggy trucks and cars, and never have had this issue. Heck I have never had this issue on anything I have ever tuned before. And if I have an issue, its usually something I can figure out how to repeat, and from that I can always find whats causing it, and later the solution. The randomness to this event, is what makes it so darn hard.

PS: Its a standard LS1 ECU, they didn't swap the hummers over to the E38's until 2008, when they went LS3. Hummers are a bit slow to get the goodies.

EA

[ScarabEpic22]

Ah brain fart, they would use the E38 being based off the new fullsize platform.

What OS is it running, a 2 Bar or stock OS with a 2bar MAP tricked into being boost friendly?

Random problems are extremely hard to track down, thats part of the reason I suggested a PCM swap. LS1s are even cheaper than E38/67s.

I wonder if there is a test of some sort the PCM is running while cruising or at a stoplight, maybe a systems readiness test is triggering it? Throwing ideas out there.

[E.A.]

What OS is it running, a 2 Bar or stock OS with a 2bar MAP tricked into being boost friendly?

Stock OS, stock MAP. No reason to change it with such a low power application.

I wonder if there is a test of some sort the PCM is running while cruising or at a stoplight, maybe a systems readiness test is triggering it? Throwing ideas out there.

Thats my thinking, but I can't find a test that would run with a engine rpm value of "0"
Most tests require at least 400rpm and then other temp and map conditions to be met.

[joecar]

That's very strange... maybe the PCM has a problem detecting whether engine is running or not (does the RPM pid show correct values)... or might be a bad PCM as mentioned above.

[E.A.]

So after doing some digging, another buddy I believe has found the solution.

After basically agreeing that it HAD to be something with the throttle body, he pulled back the harness that was covering the wires going to the throttle body.... and guess what, there is a RANDOM butt connector on the power wire, leading to the throttle body.

Wiggle the harness, and guess what.... you can hear the throttle blade moving.


So, basically I am "thinking" that this has been the issue all along. I however am not going to say that its 100% fixed, until some time goes by. (cause this issue is so random)



So that begins the question. How did the butt connector get there, and why? The truck has never been anywhere other then the purchasing dealership, and the blower kit doesn't have you extend any Throttle or MAF wires. Hmmmmmmm


Thanks all for your help, it did get me thinking, and poking around again.
EA