6.2L & 6.5L Performance Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines Related to Performance and Longevity

Newbie to turbo diesel and needs help.

Old 04-18-2017, 01:00 AM
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Default Newbie to turbo diesel and needs help.

Hello, I am a newbie from Australia with a factory converted í98 Chev suburban with the 6.5l diesel. I have owned it for about 18 months now, its the first diesel Iíve ever owned and Iím no mechanic, so has taken me a while to understand your lingo. I have been on this forum many times and gained valuable info as I try to iron out little problems with my truck.
This is a subject that seems to have been covered many times. I have power loss issues, Iíve replaced the lift pump with a new one from a í94 as suggested (higher PSI than the factory í98), also the wastage solenoid, the fuel pump drive module was already relocated to the front for better ventilation.
The turbo seems to be set up like Iíve not yet read on your forum. (It maybe a Turbo master set up?) It has two gauge's one is for pressure & the other maybe temperature? in its own little housing with a control **** in the centre & when I turn it anti-clockwise, the turbo gets more boost and I get more power. the previous owner said he had set it up to ďtrick" the turbo to have boost when ever required, along with wiring the wastage actuator shut. (his words, not mine) Does this sound right?
I lose considerable power when towing, the pressure gauge goes no higher than 5 PSI, although I do recall the previous owner saying it can reach up to 25psi the way it is set up (I have never witnessed this). Blows black smoke also.
It seems fine when not towing (still only 5 psi max)
I have looked through this forum looking for answers, I have checked all the turbo lines for cracks or holes. The only things I haven't replaced that maybe causing it is either the vacuum pump or wastage actuator, Does that sound right?
Do not like the sound of replacing the vacuum pump, sounds difficult as I don't have tools to remove pulley. So hopefully there are some other suggestions first?
Also, it has an 'F' in the series number. I believe this is important. And what is a EGR valve?
What does EGR & WOT stand for?
Have also replaced the MAP sensor, fuel filter and fuel cap.
Could it be injectors, they have done 100k?
Only mod's I know of are relocation of PMD, straight through 3" exhaust, K & N filter & the turbo set up mentioned in previously.
Help anyone?
Old 11-22-2018, 03:21 PM
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This thread is over a year and half but others who find this.

If you have mechanical spring operated waste gate on a 98 OBD-II engine someone hacked a mess and that is one reason it is running right.

Since you still have a PMD-you have a DS4 electronic IP on an F motor which should. Not have EGR

LONG story short make the vacuum pump is working, put the vacuum waste gate and a new waste gate solenoid back on and make there no vacuum leaks and it start running right again

The PCM does not handle timing adjustment properly to the DS4 when system is missing

Once the engine gets warm do the KOKO timing procedure

Lastly get a positive displacement actual lift pump that will put and keep spec inlet pressure to the IP

The OEM solenoid lift pumps do not wo*k or for long at spec pressure even new I use the 6.5 Sure Cure Lift Pump and ended all ridiculousness of poor performance hard starting and blown PMD"s which are all related

I had all the problems the OP described and in my case it was a melted poly vacuum line on the manifold, a rusted waste gate solenoid due to condensation moisture being sucked in that melted line, a weak vacuum pump wearing out, and a loose Josť on it too, and the timing being out 1 degree which the KOKO procedure corrected

One cannot run mechanical waste gate and over boost the 6.5 an expect it to run right

In short put it back stock or you are fighting the PCM computer and you will not win

The limp home mode burns more fuel, has crap performance, and runs hotter EGT"s and it will stay that way and likely never throw a check engine code

See also https://www.dieselbombers.com/6-2l-6...d-its-own.html at post 4

Last edited by Unioncos; 11-22-2018 at 03:30 PM. Reason: Link

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