2007 GMC Medium Duty with 7.8L Isuzu Engine

[scooper]

Sorry I don't know how to fill out profile, but we live Regina, Sask, Canada.
We have to use ultra low sufur fuel @ 15ppm, and low ash oil, which we are doing. We run all over North America, fuel filters have been changed at 6 different dealerships in the U.S. and Canada still have the same problem.
It shows no codes, and until a code shows they tell us they cannot fix.

The truck will start off good, then at any time it will go into the low power mode, no codes, nothing.

Fuel pressure was tested, this showed no leaks.

We pull a 51 foot beaver tail and can't even make the hills in Minnesota/ Wisconsin.
With no codes showing up dealership said they can't repair.

[mr. monte]

we have the "Lemon Law" here in the States

maybe something for you to check out

[DmaxMaverick]

Welcome to the Forums!

To get your signature filled out, go to your User CP options, and select signature. Basic info is very helpful (use other's as an example), but your truck isn't as common around here, so more detail is better. If you can't figure it out, please email or PM (Private Message) me or a moderator, like Mark. I'll move the thread to the Medium Duty Forum. The Duramax Forum is intended for the 6.6L Duramax.

Now, as far as your problem goes, it doesn't sound really unique to the 7.8L. Most problems are Diesel engine related, and can apply to any Diesel engine. The Dealer can diagnose problems w/o codes, but many are too lazy (for lack of a better term) to do real technician work anymore. You need to find a good Medium/Heavy Duty GM/GMC authorized dealership to take care of you. Very few issues that cause poor running will cause no codes. Fuel quality is one of them. If you are not using an anti-gel additive, try it. It could be simple as that. Also, check the air filter. If it's getting any moisture in it (like an airbox leak), it will freeze up and block airflow. If it were a sensor problem, you'd certainly have DTC's (SES lamp) stored in the PCM memory, which will still be there after the SES lamp goes out. And, it could be a transmission issue, which will cause low power mode and the SES lamp, but needs to be diagnosed separately from the engine.

We'd like to help you, and will given the chance. At the very least, someone else will be helped by the experience. Please keep us updated often with any new information.

[Duramaster]

I work on 7.8's occasionally. Now more often than not since our 7.8 guy is off on injury. I will ask him a question or two.

[GregCrabb]

I know this is a totally different engine made in a totally different country and does completely different work from yours....but....my Volkswagen diesel was doing the exact same thing your Truck is doing....and it was my ECU simply telling my turbo not to boost. The engine would start fine, idle fine, drive fine until around 25 mph, then it was as though the bottom fell out and it would crawl. It took my dealership a month to finally figure it out, but after I got a new ECU under warranty, it has been fine since, knock on wood. Just a thought. Mine would always act up on my interstate drive to work in bumper to bumper traffic at 70 mph...and my car would be struggling to do 45. They first thought it was the EGR sticking, then the MAF sensor.

Like I said though, I know my engine is not like yours.

[scooper]

Thanks for the info about your volkswagon, but the engineers changed all the sensors, 6 injectors, two ECM's, two emission pipes, still doing the same thing, that is when they decided to give us a new engine. Our old engine only has 20,000 miles on it. Bucking, jerking, loss of power, basically from day one, not as bad, but got progressively worse. First oil change at 5000 miles, oil real black, secondary fuel filter really black in the vanes of the paper filter.
Alot of carbon, I would think.

[Mark Rinker]

Fuel filter really black? Ummm...where are you getting your fuel??? As I said in the first post - bucking/jerking sure sounds fuel related. Now you report your secondary fuel filter is black? A lot of carbon? In your fuel?

Better get that one figured out - before you feed a brand new engine the same fuel that killed the first one.