I've had my '97 Sierra 2500 6.5 for about 10 months now and put almost 30,000 miles on it in that time. Recently I've noticed the thing has been drastically losing power. Part throttle is still alright, but full throttle there's nothing there. For a while it would pull alright until 2500 and then get very weak up until 3500, causing there to be a jolt forward when shifting into the next gear, but now it's just weak everywhere. I'm going to try replacing the fuel filter just since that's cheap and last time I did it was when I bought the truck 30,000 miles ago. When I plugged in the Snap-On scanner and drove around with it connected to check the boost pressure, I saw it peak at about 128 kPa and then it would start trailing off as the revs got higher, to as low as 119 but normally about 122 or so (I did several pulls to test this).


As a side note, I have a Heath Diesel boost controller which I put on about a month and a half ago, and I have a SES light with code P0236 Turbo boost sensor 1 out of range. The truck has 171,300 miles on it. I don't know if this is the original turbo or not. When I got the truck, the wastegate solenoid was malfunctioning which I didn't realize until about 2 months ago, which is when I ordered the Heath Diesel mechanical boost controller and put that on. Since then I've done roughly 8-10,000 miles of driving, a lot of which was with my trailer on back. Any advice would be much appreciated. I'm driving out to Indiana on Saturday with a full load (car on trailer + all my stuff for school), so I'd like to get this thing solved ASAP.

Just checked out the turbo for play. Zero in/out play, but somewhere ~1 mm side/side play. Guessing that means I'll be swapping out one of my spare turbos tonight.

Fuel filter is suspect. Diesels are much more sensitive to fuel filter pressure drop than gassers. Filters must be changed on a regular interval. I usually change mine every other oil change, which is about 6000 - 8000 miles.


On your turbo, what does "in-out" and "side to side" mean? Edited by: ronniejoe

Thanks for the response, Ron! I was planning on changing the fuel filter first and hopefully that will fix the problem for me. If you're supposed to change them that frequently on a diesel then I may very well be well over my limit. I hope that solves the problem!


"In-out" motion is when the impeller will move on the axis of the shaft connecting the intake and exhaust sides. If you were looking at the turbo inlet on the intake side it would be the shaft moving towards and away from you. "Side to side" motion is when the impeller is moving within the housing. Looking at the inlet on the intake side the motion would be up/down and left/right.

Checking turbine shaft axial and radial play is best done shortly after shut-down, such that full floating bearings have full-contact oil film.


When cold, oil has gravitated out of bearing assy, and increased 'play' will be noted.


If compressor blades do not touch scroll housing at any point when checking cold, turbo is functional.


Checking shortly after shut-down results in less 'alarming' clearance indication.

i had the same code, po236 and it started smokin a lot and loss of power. when i installed the heath turbo master it still had the exact same symptoms untill i unhooked the batteries for an hour or so so that the computer could reset itself. all has been great since then and no more codes or ses lights.


so i would suggest unhooking your batteries and reseting the computer before doin anything else drastic.


how long is your spring on your turbomaster?Edited by: steiner43511

Ok, I've reset the codes before but I haven't tried resetting the computer by disconnecting the batteries for an hour as you suggested. I'll try that tonight when I change the diff fluid, glow plugs, and fuel filter. The code has been on and off, though. It will go away, but then come back. It also has a P0717 (intermittant, hasn't popped up in a long while) which I believe a list member said is most likely a loose plug on the transmission.


I imagine the spring on the TurboMaster is too long, I put it in and I think it's 2", but it's probably closer to 2.5" which might explain the low boost. It is, of course, the light pressure spring. Do you notice on your truck that the boost will drop off at higher revs regardless of setting?

I sounds like you don't have Boost pressure gauge which I suggest you get. The factory programing will send the computer into limp mode if you get the engine too warm and until you clear the codes which I don't know how to do on a 97 you will not be able to pull full power. The other thing is you can get codes if your boost is too high with factory programing. The TurboMaster is great but the spring length adjustment is not that accurate. I adjusted mine ran it a week I thought I had it set at the 7 PSI level and low and behold it was 10PSI when I got the boost gauge installed. So you could be boosting the engine higer than the ECM likes and so your getting codes. Just a couple of thoughts.

I don't have a boost gauge. I can clear codes on the '97 with my OBDII reader (I have a personal one as well as the professional Snap-On one at my work). Yes, I know you can get codes and reduced power if the boost gets too high. However, this is showing the boost to be LOWER than it was on the factory setup, and furthermore I'm seeing it drop off as the revs increase. This is all according to what the Snap-On scanner is telling me, i.e. it's what the truck's computer is seeing.


I do plan on adding a boost gauge, EGT, and tranny temp gauges shortly. However, at the moment my concern is solving this problem. I'll deal with gauges and such when I get back out to Indiana.

i would suggest setting your spring length at 2 1/8" and see how that feels. that is what the instructions say to be around 7 psi.


when i had the po236 turbo boost range sensor code, the light would come and go, untill i reset the computer.

Here's a question for ya: if you have a restriction in your exhaust (like a plugged up cat) will that reduce your boost pressure? You may be building up back pressure in your exhaust, and slowing down your turbo, follow my train of thought? Or am I just all together off on my thinking?

Correct.....you're on track.

Thanks for everyone's help so far! Last night I did some much-needed maintenance on the truck. Replaced the diff fluid (was about 25k miles old), replaced the fuel filter (same age), and replaced glow plugs (that was fun). Also adjusted the spring to 2 1/8" from 2 1/4". While doing all this, I left the batteries unplugged to reset the computer. Plugged in the Snap-On computer and went for a drive to Pep Boys to buy a tool box. 0-60 times down to ~11-11.5 from 12, and the truck felt back to its normal speed. Boost pressures were at about 138-141 kPa, holding up through redline. From a stoplight I raced my buddy in his Nissan 240SX and beat him by a truck length. He wasn't too happy!! http://www.dieselplace.com/forum/smileys/HiHi.gif Of course, then my clutch fan kicked in at the next stoplight and I didn't have a chance, but I still got a kick out of that.


Then this morning on the way to work the SES light came back on and the truck was back to no power, and no smoke under hard acceleration. P0236 had returned, and on a drive the Snap-On computer was recording ~128 kPa dropping off to 118 as redline approached. Reset the code, and the pressures went back up to 138-141 kPa holding until redline.


Now, I do know that the work I did made a difference because for a while my truck was just getting slow WITHOUT a code. Then the SES light came on and it got really slow. However, now the question is what is causing this light to appear, since that sends the truck into limp mode. I'm also somewhat confused as to how the boost pressures are being affected in limp mode considering the fact that I have the Heath boost controller which is 100% mechanical and completely independent of the truck's computers.


Another point of interest: The Snap-On computer pointed out that my desired and actual timing were set at 12.4 degrees, but desired timing should be 0 degrees. So this would indicate to me that I should adjust the injector pump to get the desired timing at 0 degrees.


As a side note, I gutted my cat about a month after I bought the truck and noticed a nice improvement in acceleration at the time. When I get back out to Indiana I intend to buy the Flowmaster crossover pipe and downpipe setup and then make my own exhaust (100% straight pipe) from there, and then set the spring to higher boost.


I appreciate everyone's help and hopefully I'll be able to get this problem solved in the next day or two before I head out to Indiana! I hate to think about having to make that drive in limp mode with a full trailer up the hills in Pennsylvania. Yick... Of course, I could always sit there with my mini-scanner and just reset the code every time it pops up. :) I think I'll try to fix it correctly.

Limp mode pulls back fuel, which will restrict boost because of less energy in the exhaust. You are probably overboosting with the TurboMaster to cause the out of range condition. The computer sees this and pulls fuel.


Where in Indiana?Edited by: ronniejoe

i would suggest setting your spring length at 2 1/8" and see how that feels. that is what the instructions say to be around 7 psi.


when i had the po236 turbo boost range sensor code, the light would come and go, untill i reset the computer.





I set mine to the 2 1/8 and it produced 10 PSI boost so again it's not excact so Until he gets a boost pressure gauge I would just keep back off the nut until he stops throwing codes. The factory programing is design so as to prevent over boost and over fueling so we don't melt the psitons into molten metal. GM doesn't like buying replacement engines.

if you lengthen the spring on the turbomaster little by little, the code might go away if it is sensing too must boost. the sensor could just be bad too.


another idea is to try quantum mechanics boost fooler. this should keep the pcm from seeing too much boost and maybe keep you out of limp mode.

Today I went by the local GMC dealer that we have a good relationship with and I asked one of the 6.5 techs there what he thought. He said that 9 times out of 10 it's a bad wastegate solenoid, because even if it's not actually doing anything, if it's bad it will throw the wrong resistance values at the computer and then the computer will throw the code. Makes sense.


I seriously doubt that it's an overboost code. Reason for that being that when I had the spring set at 2 1/4" (producing less than factory boost), it still threw the code. I'm going to try throwing on the new wastegate solenoid as recommended by the guy at the dealer and see if that does the trick.


Any suggestions on what to do about my timing? I'm guessing that means I have to rotate the fuel distributor. Whee... fun.


Ron, during the school year I'm in Terre Haute, Indiana (student at Rose-Hulman). Pretty close to Martinsville.

Combo Vacuum\Boost gage 20 bucks at jcwhitney.com - absolutely no reason to keep guessing at this.


Overboost sets DTC under power - PCM pulls fuel, for no power.


DTCs will also be set at initial crank if MAP sensors are defective, un-plugged, or intermittent connections.


That means at idle - don't have to be flogging it to get the code.


OBD-I sets real overboost after ~20secs.


Manuals indicate OBD-II sets within 2secs - could be misprint for 20secs.


Sproing-boost controllers usually have two springs - one low-boost for non-charge-air cooled, one higher-boost for vehicles with charge-air cooler installed.


Tends to indicate hi-boost runs hot - PCM pulls fuel when IAT is hot, for no power.


Hi-boost requires offset to MAP sensor output, to prevent DTC with stock GM flash.


Hot flashes defeat codes thru firmware.


Also, possibility your MAP Sensor is defective or failing.


You don't need a turbo - you're about to spend money without knowing why.


Don't guess - put a mechanical gage on it.Edited by: gmctd

My son is looking at Rose-Hulman for next year. He will be a senior in high school this fall.


I looked at Rose 21 years ago, but went to General Motors Institute (Kettering University, now) in Flint, MI instead. What year are you?

Can someone translate:


kPa = what in psi?

Multiply Kpa (Kilopascals) by 0.145 to get psi. Or if you really want to be accurate, multiply by 1.450370E-1. Edited by: ronniejoe

Going into my junior year @ Rose. Great school, love it. Contact me off-list (eMail jag_pushrod@softhome.net or AIM in my profile) to talk more about the subject since it's not exactly diesel-related. :)


GMCTD, you're right, I will go ahead and get the gauges when I get back to Indiana. However I'd like to point out that with the Snap-On computer I know exactly what readings the computer is seeing, which if anything is probably more useful. So, using Ron's conversion factor, here's some food for thought:


The computer was reading a max (according to my buddy in the passenger seat) of 141 kPa. That makes for 20.445 psi absolute. Subtract 14.7 psi (atmostpheric) and you have 5.7 psi boost. So, according the computer I'm only running a piddly 5.7 psi of boost. No wonder my truck feels so slow now at full throttle. I will confirm these readings with a proper boost gauge, of course, but the MAP sensor would have to be drastically off in this situation for this to be an overboost code.


I have already realized that I don't need a turbo (I tend to get panicy about such things, but am glad that I can last longer with this one), thanks. This isn't about me being cheap, it's about me not having the time right now to obtain the gauges and then install them in the truck. After I head back out to Indiana and then return from Texas I'll have a week and a half of basically free time. I will take care of all of these items then.


As an update, I drove about 100-150 miles last night and this morning after putting in the new wastegate solenoid, and the SES light hasn't come on. Recall that before it came on after roughly 40 miles of driving, so it appears that the dealer tech's suggestion was correct. Once I get out to Indiana I plan on putting on the boost, EGT, and tranny temp gauges, along with the straight pipe exhaust and start doing some real performance modifications to bring this truck up to where it's supposed to be.

Scanner info is only as accurate as sensor output - mech gage can verify readings. My jcw Boost gage is right on with MAP output.


The mech Boost gage would let you monitor the important parameters with the scanner - Wastegate Duty Cycle, Intake Air Temps, Fuel Rate, etc.


PCM cannot sense solenoid faults - it is a simple open collector driver, with solenoid connected to +12v.


Only feedback is when PCM drops Duty Cycle to reduce Boost, MAP Sensor output should change accordingly.


If not - Hi Boost DTC.