Hello, I have been trying to diagnose a lack of power problem with our 1997 GMC 6.5 turbo. Here are the symptoms and what we have done so far...

Lacks power, not real bad when driving with no load on, but when you add a skidster on a flat bed behind the truck it takes 3-4 miles to get up to 55, it will not shift into a passing gear under these conditions even if you put it to the floor. At about 1/4-1/3 pedal it strats dumping a ton of black smoke, more than i've seen before. If you manage to get up to 55mph even the slightest incline, even one thats barely noticeable to the naked eye will drop the speed down to 30mph. and started getting the code from our obd2 scan tool P2563. I also noticed that the air filter and housing were unusually warm almost hot when I pulled it over to take a look.

So far we replaced the entire turbo unit, and the Turbo Boost sensor.
That caused a noticable difference for about a month but durring that time we never pulled a load. Now its right back to the same issues again, I put a load on it, and cannot get up to speed for a LONG time, getting black smoke again and getting the Boost sensor code again.

I started to think that it was lacking air in the fuel mixture, so I tried removing the filter and the housing which made no difference.

I am turbo stupid, I am learning as I go, and not liking my results so far, lol. Could someone please give me some idea of what I can try next? I would love to take it in and have someone do it for me, but cannot afford a bill in the $1,000's. Any help would be so appreciated! Thanks in advance.

I know its bad when I can get passed by all the collage kids on there mopeds =(

First fill out your signature with the details for your truck.

Then do the diagnostic checklist and post the results.
http://www.dieselplace.com/forum/showthread.php?t=42248

Sounds like your turbo wastegate is staying open and not building any boost. check the linkage with it running the rod needs the be pulled up in to the vacuum diaphragm for the wastegate to be closed. you can push down on the lever to see if the vacuum is holding!

sounds like lack of boost, which shows up as lack of power and black smoke. A boost guage is one of the most important things you can add to your truck, also EGT and trans temp if an auto. 97's have a vacuum actuated turbo wastegate that is controled by an elec/vac solenoid that is controlled by a ECM that gets inputs from your throttle, boost sensor and IAT sensor. The ECM is programed to save GM from engine warranty problems. Anything from a simple vacuum leak or loose wire to a failed part can cause the turbo to not supply boost. Hook up a guage and then go to the checklist at the top of the forum to find your problem. If that doesn't get you fixed, post your results back for more ideas.

I have checked the Wastegate and the actuator they seem to be in fine order, the acuator holds vacuume and the rod moves up and down with no restriction from anything except some vacuume pressure. I also closed the wastegate and started the engine, slightly reved her up a bit and saw the wastegate open slightly by itself, so from what I can tell it seems to be working.

Could it be possible that when we first encountered the problem and it started smoking bad that it could have plugged up the EGR valve, and would that be a reason the the problem has reaccured now even with a new turbo and boost sensor in place? Altho I took a glance under the hood last night as did a buddy of mine and neither of us could find the EGR, do the 6.5 turbos even have 1?

I am going to replace the boost sensor again and see if that makes any difference, but my gut feeling says its not the sensor, because the one thats in it now is less than 2 months old.

I am getting tired of dealing with this thing, I live in minnesota, and we have had a very snowy season so far, this is a plow truck and and needs to work or I dont make money...

Uh, when the engine is idling, can you move the wastegate by hand? (you should NOT be able to)

I have checked the Wastegate and the actuator they seem to be in fine order, the acuator holds vacuume and the rod moves up and down with no restriction from anything except some vacuume pressure. I also closed the wastegate and started the engine, slightly reved her up a bit and saw the wastegate open slightly by itself, so from what I can tell it seems to be working.

You need gauges... a boost gauge will tell you a lot about your turbo and wastegate system, and an EGT gauge will tell you about your Exhaust Gas temps - which are gonna be VERY high if your turbo isn't working right.


Could it be possible that when we first encountered the problem and it started smoking bad that it could have plugged up the EGR valve, and would that be a reason the the problem has reaccured now even with a new turbo and boost sensor in place? Altho I took a glance under the hood last night as did a buddy of mine and neither of us could find the EGR, do the 6.5 turbos even have 1?

2 ways to tell if you have an EGR valve:

a) look on top of the intake plenum, under the plastic 'TurboPower' cover. Your EGR looks like this:

http://www.dieselplace.com/forum/attachment.php?attachmentid=34034&d=1171828781

b) check the 8th digit of your VIN. If it is an 'S', you have an EGR. If it's an 'F', you don't.

Yours is a K3500 - I'm betting it's an 'F' engine, which makes the EGR thought wrong.


I am going to replace the boost sensor again and see if that makes any difference, but my gut feeling says its not the sensor, because the one thats in it now is less than 2 months old.

I think you should check your BOOST before you play with the sensor. Hell, if nothing else, wire the wastegate shut (pull the lever all the way up) temporatily (I MEAN temporarily, too !! -Don't blow stuff up unless you want to)


I am getting tired of dealing with this thing, I live in minnesota, and we have had a very snowy season so far, this is a plow truck and and needs to work or I dont make money...

Personally, if it's a work truck, I'd put on a Turbomaster in a heartbeat, and scrap that cruddy vacuum system.

For that matter, I'd also want to put on a Heath PMD Isolator and an HP4 reflash, and then never worry about the college kids anymore.

This is a Work Truck: you owe it to yourself to call Bill Heath and ask about stuff that you can do yourself that will make a HUGE difference to the driveability, longevity, and reliability of your truck. Bill specializes in 6.5s, and will give you the best advice, even if it means he doesn't make a sale... that's important, too.

I am having similar problems. The truck seems to run ok with no load but even with a empty single axle rinky dink trailer (under 2000lbs total weight) I can barely hold 65 on the highway. I have pulled this same trailer with a v6 gasser with more authority. I do not get the black smoke just no power. I have the turbomaster for the wastegate so I do not think that has anything to do with it. I do have boost and EGT gauges. my boost is runnning 9-10 psi when hard on the pedal and 4-6 psi at cruise. The EGTs seem to get high (1200) when going up a slight grade. As my sig shows I have 4" exhaust from turbo back (3.5 downpipe) marine injectors, SS cold air intake, EGT probe is pre turbo. also just finished installing new IP. With the cold air intake I can clearly hear that the turbo is spooling and the boost gauges kind of proves the turbo is working ..right? I am not getting any codes and other than the lack of power when towing the truck runs good. it is almost as if when I hook the trailer up I flipped a switch it is that much of a diffedrence. again this is a dinky trailer and is not even as heavy as the 17' skiboat I usually tow. SOmeone anyone plaease help

I am having similar problems. The truck seems to run ok with no load but even with a empty single axle rinky dink trailer (under 2000lbs total weight) I can barely hold 65 on the highway. I have pulled this same trailer with a v6 gasser with more authority. I do not get the black smoke just no power. I have the turbomaster for the wastegate so I do not think that has anything to do with it. I do have boost and EGT gauges. my boost is runnning 9-10 psi when hard on the pedal and 4-6 psi at cruise. The EGTs seem to get high (1200) when going up a slight grade. As my sig shows I have 4" exhaust from turbo back (3.5 downpipe) marine injectors, SS cold air intake, EGT probe is pre turbo. also just finished installing new IP. With the cold air intake I can clearly hear that the turbo is spooling and the boost gauges kind of proves the turbo is working ..right? I am not getting any codes and other than the lack of power when towing the truck runs good. it is almost as if when I hook the trailer up I flipped a switch it is that much of a diffedrence. again this is a dinky trailer and is not even as heavy as the 17' skiboat I usually tow. SOmeone anyone plaease help

Kinda sounds to me like the computer has cut the fuel back (for some unknown reason) or maybe there is a brake or wheel hub hung up on the trailer. If you can pull the skiboat just fine then you know somethings wrong with the other trailer.

High IAT from too much boost and you could be defueling, or high boost pressure period seen at boost sensor, can you put a scan tool on it to see what your IAT is and what boost pressure PCM is seeing, I had a boost sensor go bad (high) once and PCM thought I was making 35psi boost and kept clipping fuel to max 50mm fuel, so you have a power reduction & no change in smoke.

Clipping fuel is tier 2 of defense for PCM, tier 1 under any out of range condition is to clip boost, your puter can't cause you have taken away control of boost with a TM.

How much boost by gauge you running, if too high, IAT is going high as well;

High IAT can contribute to high EGT, especially if you are trying to keep APP (fuel) to floor to make up for the power loss from the defuel protection. There is no code for defuel and it will reset when you shut off truck until you hit the out of range condition again, you need to be looking at a scan tool to know you are in defuel mode.

But if IAT or overboost is being seen by PCM those should be logging a problem in those areas

The boost gauge I have will make it to about 10psi briefly usually hits around 9 when holding it hard up a hill/grade. I am not sure about the IAT, I am guessing that is osmething that I owuld need the scanner connected while driving to find? I have a friend who can bring over a tech2 but hate to keep asking him to. I have seen a program from enghmotor for laptop anyone know if this program will monitor the IAT. If the IAT are high any suggestions how to lowedr them or is it usually just the sensors lying to the puter. Thanks for your guys help.

I have AutoEnginuity with the GM add on pack. Best $400 I ever spent. I think the OBD2 tool would perform the same functions, but I don't think they have a dedicated USB version. I like the USB, since the anti-piracy codes for the software are linked to the USB dongle. I can use it on any computer I choose.

Without the GM add-on pack, a scan tool is pretty much useless on these.

Scan Tech will monitor IAT. Leo