More Power
04-21-2005, 09:38
I received the following email message from member Bill Parker, who had a problem with P0234 after installing a free-flowing exhaust system and other mods in his LLY. I thought it was important information so I asked and he agreed to allow me to post his message here. Bill says the folks at TST deserve a round of applause!
MP
I wrote you two weeks ago to describe a problem I was having with a P0234 code on my Duramax. I think the problem is solved but it may come up for other Duramax owners under some circumstances.
The problem is not the CPU or the MAP sensor. Rather it is the program which runs in the CPU whereby the GM computer tries to anticipate or predict what the boost pressure will be based upon throttle position, barometric pressure, engine RPM, etc. If the boost pressure is higher than the predicted level for 30 seconds, we get a code or the fuel is cut and the computer remembers the information without turning on the diagnostic trouble code light. Under some circumstances this happens in less than 30 seconds, and perversely can often go on as you crest a hill and power requirements drop but the turbo is spinning pretty high. The problem does not occur at really high boost levels, but seemed to commonly occur at levels non-threatening between 14 and 24 psi.
Conditions which contribute to this problem are 1) aftermarket low restriction exhaust system, and 2) towing with a heavy load (a 13,000 lb fifth wheel trailer in my case). Without the heavy trailer, the boost levels never get into the 14 to 24 psi level or stay high enough to trigger the "over-boost condition". The problem will occur without any aftermarket computer; the exhaust alone seems enough to drop the backpressure and spin the turbo to boost levels not expected by the GM CPU.
I am told that the GM turbo is somewhat more fragile than some of the competing brands, and can actually destroy itself at pressures like 40 psi. That doesn't sound too high in the overall scheme of things, but it apparently worries GM. Consequently, they seem to have gone to extra trouble and effort in their software to guard against that eventuality. Ford and Cummins don't seem to worry enough to try doing this "predictive" function within their CPU's -- hence they don't have the problem I experienced. I have heard from other exhaust system manufacturers that this problem is more prevalent with the 2004.5 LLY Duramax, so it appears that the software thresholds used by GM Powertrain may have been tightened up a bit for the new higher output motor.
Using the GM documentation to learn more about this trouble code, and dyno testing with my truck, the boys at TST sorted it out and engineered a fix. The sophistication and the effort put forth by TST were truly impressive. I doubt that most of their competitors would have sorted it out and been able to quickly engineer the fix. TST is a class act and they should be mentioned if you ever treat this subject in your newsletter.
Sincerely,
Bill Parker
MP
I wrote you two weeks ago to describe a problem I was having with a P0234 code on my Duramax. I think the problem is solved but it may come up for other Duramax owners under some circumstances.
The problem is not the CPU or the MAP sensor. Rather it is the program which runs in the CPU whereby the GM computer tries to anticipate or predict what the boost pressure will be based upon throttle position, barometric pressure, engine RPM, etc. If the boost pressure is higher than the predicted level for 30 seconds, we get a code or the fuel is cut and the computer remembers the information without turning on the diagnostic trouble code light. Under some circumstances this happens in less than 30 seconds, and perversely can often go on as you crest a hill and power requirements drop but the turbo is spinning pretty high. The problem does not occur at really high boost levels, but seemed to commonly occur at levels non-threatening between 14 and 24 psi.
Conditions which contribute to this problem are 1) aftermarket low restriction exhaust system, and 2) towing with a heavy load (a 13,000 lb fifth wheel trailer in my case). Without the heavy trailer, the boost levels never get into the 14 to 24 psi level or stay high enough to trigger the "over-boost condition". The problem will occur without any aftermarket computer; the exhaust alone seems enough to drop the backpressure and spin the turbo to boost levels not expected by the GM CPU.
I am told that the GM turbo is somewhat more fragile than some of the competing brands, and can actually destroy itself at pressures like 40 psi. That doesn't sound too high in the overall scheme of things, but it apparently worries GM. Consequently, they seem to have gone to extra trouble and effort in their software to guard against that eventuality. Ford and Cummins don't seem to worry enough to try doing this "predictive" function within their CPU's -- hence they don't have the problem I experienced. I have heard from other exhaust system manufacturers that this problem is more prevalent with the 2004.5 LLY Duramax, so it appears that the software thresholds used by GM Powertrain may have been tightened up a bit for the new higher output motor.
Using the GM documentation to learn more about this trouble code, and dyno testing with my truck, the boys at TST sorted it out and engineered a fix. The sophistication and the effort put forth by TST were truly impressive. I doubt that most of their competitors would have sorted it out and been able to quickly engineer the fix. TST is a class act and they should be mentioned if you ever treat this subject in your newsletter.
Sincerely,
Bill Parker