Compstall

iTrader: (5)

I know this guy on base here that has one of these trucks. He bought it new a couple years ago, and has had a few problems with it over time. What we've found out is that GM had bought off on the idea, backed up the warranty, but never followed through with training for the tech's at the dealerships they sold the trucks through. Every time he's taken the truck into the dealer they don't know how to work on it and have to send off for help.

We're hoping some of you forced induction guru's may be able to provide some insight. Here's the latest problem, in his words:

"What is it doing? When you turn the key to start the engine will go to roughly 300 RPM, hesitate, then go to 1000 RPM and stabilize out to 600 RPM. This happens on the first start everyday and anytime of the day. It has now gotten to the point that it will not start at all on the first attempt and sometime the second attempt. I did some experimentation recently and it would duplicate the problem every time regardless of how many times I attempted the start. Once the truck is started it works as advertised. But, even lately I've noticed some things that I didn't notice before. Example: Coming to a stoplight/stop sign it will seem to indicate a stall situation rpm will drop to 400 RPM and then recover. Also, if you go to hit the gas there will be a hesitation also indicating a stall situation.

A couple of side notes the problem has gotten progressively worse over the last couple of months.
The dealership was helpless for this situation; they never found a code so they say.

I consulted with Magnuson Superchargers, they told me it was the fuel regulator packing?

They also wanted the program S/N to ensure it was accurate. I have yet to provide this information. The programmer is Superchips.

When the vehicle warms to operating temperature it starts without any noticable hesitation. But there is a subtle hesitation. The problem was with the vehicle from the day I purchased it. I brought it back to the dealership several times without nothing positive. The classic saying from the dealership: "The other Joe Gibbs Truck does the same thing so it must be normal." I'm in a situation where I'm on my own to figure this out. The factory warranty is expired. I still have a warranty for the supercharger but the dealership from dealings with them in the past may charge me a lot of money to fix something they know nothing about as already proven.

I read an article recently of an SSR with a supercharger installation and causing damage to the sensor. Similar problem but don't know if it started and worked or not.

Anyone got any inputs on this situation? Greatly appreciated. TIA!

Poik

Vacuum leak? MAF? IAC valve?

WAHUSKER

iTrader: (4)

Damn, it sounds kinda like what my car just went thru....it was doing pretty much the same thing.

I had to enter the Seattle car show with 2 gal of gas in the tank. I was thinking the fuel pump didn't like it cuz the car ran like *** ever since. I tried changing plugs, seemed better until I tried dynoeing the car. Then it misfired like a *****. (if this gets too long, I apologize)

It said it was lean & was dumping fuel in. I pulled the plugs & all were black, 1 was wet, and 1 was shiny black (washed with alky) - I had turned the fuel & alky up for the dyno....it had been running a little lean before above 5k, like around 12.2 afr). The tune is back wwhere it was now.

So I replaced the coils with MSDs, the plugs with Autolite AR94s, and Taylor 8mm wires. A couple of the wires bad burned outter sleeves , and 2 didn't want to stay seated in the coils. The car is pretty much all better now. The O2 sensors are still reading a little erratic.

Not sure if the dealer can read those for him if he doesn't have a data logger. Anything low (under 200mV) for any length of time indicates possible problems. Mine are starting to come around now that everything up stream is firing properly. But they have to be dead before you get a code. Same with a misfire problem.

Anyway, it sounds to me like a fueling (& maybe a sensor) issue. He needs a tuner to hook his car up & see what it's doing. I doubt the dealer can fix this. And since it's out of warranty, why go there? So if he lived north, I'd send him to Ellis, mid town send him to Turbo Tech, south send him to TJ wong. But since you're in NM now....er....um....burn it?

Hope that helps some

Compstall

iTrader: (5)

Yeah, that's the problem around here - if you don't own a Mustang, good luck finding a GM guy. All the shops around here cater to Mustangs and imports.

Daredevil_TA

iTrader: (6)

I'm not an expert by any means, but to me it sounds like a sensor issure--if it was only doing this at stop signs i'd maybe say check your o2 sensors, but this may not be the case cuz its doing it at startup too which im pretty sure your truck goes into open loop mode meaning it takes readings from all other sensors to get the right AFR untill your o2 sensors warm up enough to do thier job. So it could be some other sensor, like maybe your MAP, or MAF. You could send a pm to Ellis, I'm sure he can be better help than me.

Ryan K

iTrader: (11)

Check the fuel pressure, make sure that the Fuel Pressure is staying up. Put the gage on it, turn the key to run, make sure the FP comes up to about 60 psi, after the pump turns off (about 4 seconds), make sure the Fuel pressure stays above 45ish psi for the next 30 sec.

Then start it and make sure he's getting good pressure with it running.

Ryan K.

NWDragRacer

If that dosn't work, replace the O2 sensors. It sounds like they are getting lazy and having a hard time tracking the AFR.