I have a 96 Diesel Suburban. After about a hour of driving I experience huge loss in power. The truck will maintain speed on the highway but when I try to accelerate the truck builds the necessary RPM and boost (12-14PSI)but does not go anywhere. If I shut it down for a few minutes it's fine and has plenty of power.
I've replaced the PMD and installed a heat sync.
Any thoughts.

I have a 96 Diesel Suburban. After about a hour of driving I experience huge loss in power. The truck will maintain speed on the highway but when I try to accelerate the truck builds the necessary RPM and boost (12-14PSI)but does not go anywhere. If I shut it down for a few minutes it's fine and has plenty of power.
I've replaced the PMD and installed a heat sync.
Any thoughts.

Tranny slipping?

Gary

Tranny is not slipping.
Everything works fine, just no power and a temp increase.

it's over boostin' for stock flash and it's goin' into "limp mode"....

it's over boostin' for stock flash and it's goin' into "limp mode"....


X2 sounds like the problem to me.

what do you suggest to fix that,

How bout filling out your sig. so we know more about your vehicle and what upgrades you have done to it. So we can further help you.

Signature can be filled out following the link in my signature

my truck (bought a few months back, still working thru some issues) had/still has a loss of power. i bought autoenginuity usb scanner. the TDC offset is wrong (need to adjust pump, will do this week). but, i bought a heath GLE computer. it immediately acted different. the fuel rate was way too low. turns out the old computer must have been in some type of limp mode. get IP adjusted, should be about fine. i cold have put a new ip in and still had a screwed up computer.
it would be best to use a scanner, boost and egt gages to see whats happening.
fill out your sginature and the checklist.
wheres your PMD? on a heat sink doesnt say where it is. what brand?
fuel pressure at t handle?
jon

Haven't check the fuel pressure at the t handle.
Problem only happens after an extended period of driving

Mine does that too after a long trip sometimes if im not just real easy on it. The problem is once it goes into limp mode it wont build the same amount of boost. I can hit 8psi most times but when it goes into limp mode im doing good to see 5-6psi. It will accelerate in OD but not in D. The computer cuts the fuel rate back too much, and once the R's come up there just isnt any fuel to keep going and i actually lose speed. Sounds like this is whats happening to you but I dont know why you still have so much boost. Which is btw too much. I run 8psi and thats really too much, too. (unless you have a performance ECM which i doubt you do since its going into limp mode). You could very easily be going into limp mode from a high intake air temperature also. That is the problem I encounter after extended driving periods. I imagine an intercooler would solve that problem.

I have a 96 'burb too (chevy instead of GMC, but its all the same thing anyways). Mine will not let me go over 12psi, atleast for more than about 2 seconds. It cuts me off and throws on the SES light. Limp mode from high boost turns on the SES light, limp mode from high IAT does not turn on the SES light. Do you get an SES light?

P0236
I'll have to see what I can do with that.

Boost too high. That code only sets when boost pressure is out of range. Too high or too low. Ive had it for both. The problem for you is too much boost.

do you think lowering the boost will stop this "Limp" mode from happening or should I get a performance ECM?

Boost is relative to engine load. If his trans was slipping he wouldn't be able to build that much boost as there's no load on the motor(turning the wheels against the pavement(friction) and against inertia). This is why revving the engine in neutral builds little to no boost.

That being said, 12-14 psi is too high a sustained boost for a factory PCM program. The PCM thinks the engine is in trouble, when its not, and usually dumps the boost via opening the wastegate.

If the PCM cannot dump the boost(no longer computer controlled- T/M comes to mind here) then it'll cut the fuel back, which in turn dumps the boost as there's not enough exhaust flow to maintain the drive pressure and create boost on the compressor side of the turbo.

Turn down your boost level to ~8-9 psi sustained and you'll be fine.

Lowering the boost may not stop it from EVER happening.... like i said it will happen if the IAT gets too high (doesn't happen all that much) or if the boost is too high or too low. Even when boost was low it would only give me P0236 in certain conditions (high % of throttle with a load) but man you hit 12 psi sustained for more than 2 seconds and it will get you every time. A reflash is the only way to get rid of the limp mode from high IAT or high boost, but i really wouldn't recommend that. Just find out why the boost is high. If you have a TM, turn it down, if its vacuum controlled still, maybe the lines are backwards on the WG solenoid.

Running a steady 8-9 lbs of boost was causing my truck to go into limp mode, so I added a boost fooler. Now it behaves until the IAT gets up to about 240F, then that will cause as defuel. So I drive by my EGT and IAT guages as my truck rarely goes anywhere without a trailer and up mountains. A better exhaust and an intercooler are on my wish list, but no matter how much I earn, more urgent problems always take the cash. So I learn to live with the shortcomings of the 6.5 cause it's really not a bad little engine in a nice driving truck.