limp mode still

[brad carlin]

my 2004 chevy duramax LLY & allison still has a fault when it gets to normal temp just under 100 cel usually on a hill it goes into this limp mode 2000 rpm only, by shutting the engine down it will reset but only for a short time ecellerator programer & scann tool saying no dtc problem started at 5000km now reading 12000km i have change fuel filter twice, accellerater postioning sensor, asm-p/sn module, turbo control valve. disconnected battery leads several times. with no change at all. problem does not accere as much on cooler days. i have imported this truck myself into australia and have no dealer backup .this is my 4th truck in 12 years and virtually no problems with the others can we have some more ideas cheers brads

[madmatt]

I fried a engine control module w/ a programmer. it had similar symptoms. it would idle fine but any sort of a load would set it into limp mode. it was setting a code though.

[More Power]

Problems like these can at first appear to be overwhelming, especially when dealing with a conversion (i.e. like your left to right hand drive). Try to eliminate one system at a time, to narrow down the possibilities.

I'd concentrate on the fuel system or the boost/turbo system first.

For fuel system, first make sure there is adequate fuel in the tank, that there isn't excessive vacuum or pressure being generated (loosen the fuel tank cap), and that the fuel filter isn't being contaminated soon after a replacement. kennedydiesel.com sells a fuel pressure/vacuum gauge that connects to the quick disconnect port near the alternator, that can be used to measure vacuum in the fuel supply when the engine is running.

Once you've eliminated a fuel supply problem, connect a Tech II scan tool or programmer so you can read the commanded and actual fuel rail pressure while driving (ideally, to get the numbers before, during and after the problem presents itself). If the fuel rail pressures are in the normal range, move on to the turbo boost pressure system.

Try to do a turbo position learn, to evaluate whether the turbo variable nozzle and position sensor are operating correctly. Then, do another test (as above) with your scanner on the highway to see if commanded VNT position is reflected by actual position.

With a little imagination, you can go through many additional tests for other systems, sensors and so on... to learn whether there's an anomoly...

MP

[madmatt]

I know this may be hard to do in your area but if you can check everything MP said and then try to find a like vehicle to compare it to. This would greatly help you w/ diagnosis.