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Discussion Starter · #1 ·
Hello I have a 1995 6.5l 2500

I have a power loss issue that I’ve been fighting for a year now truck starts perfectly fine and sounds good. Blows some black smoke at startup then clears up. When I take it for a drive following the speed limits and driving very easy as far as acceleration there are no problems if it’s a short drive. If I take it for a 3 hour drive it seems to have some but not a whole lot of power loss. If I take the truck for a drive and I drive it pretty hard then is where it gets much worst and I have lots of power loss. If I cruise 85 on the highway for a few miles I have probably 75% power feels like. And if I’m really letting it eat and flooring it often and really pushing some fuel through it then it feels like 50% power and it barely likes to move but it still will do all speed limits fine just takes a long time for acceleration. So it’s a problem that gradually gets worse the faster I put fuel through it, not the longer but the faster.ALSO DOES NOT BLOW HARDLY AND IF ANY BLACK SMOKE WHEN IT HAS POWER LOSS.

I replaced the entire fuel system from tank to injectors including pmd

lift pump pressure
4-5 psi at idle
2 psi at about 35% throttle
.5-1 psi Anything past 35% throttle

I also cut in a tee right after the lift pump to get pressures to see if I had a clog and same data
I hard wired my lift pump (12v)to run a max effort to bypass the ops and same data
4” straight pipe so no issues there
Vacuum pump delete and manual wast gate installed
I run about 10-14 psi at max throttle
 

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Welcome to DieselPlace

Have you checked for any codes?
It sounds like you are going into limp mode due to an overboost condition..
The stock PCM settings for boost is a maximum of 12psi. Anything above 12 then the PCM will put the engine into limp mode and defuel to protect the engine.

Try dialing down your boost to a max of 10psi and see if things improve
 

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1995 GMC Suburban
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I agree, more than 12 psi in a stock engine with stock ECU will cause defueling which explains the loss of power.
 

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Discussion Starter · #4 ·
Welcome to DieselPlace

Have you checked for any codes?
It sounds like you are going into limp mode due to an overboost condition..
The stock PCM settings for boost is a maximum of 12psi. Anything above 12 then the PCM will put the engine into limp mode and defuel to protect the engine.

Try dialing down your boost to a max of 10psi and see if things improve
Hello, very sorry for the late response I’ve been so busy working I haven’t had any time to think.
The truck shows no codes for defueling or overboosting. I have turned my boost down in the past to see if it helped and jt didn’t. I’ll give that a try again when I recover from covid.
the truck has no engine light until I accelerate and the code is for egr(I deleted it🤫🤫)
 

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Discussion Starter · #5 ·
Hello, very sorry for the late response I’ve been so busy working I haven’t had any time to think.
The truck shows no codes for defueling or overboosting. I have turned my boost down in the past to see if it helped and jt didn’t. I’ll give that a try again when I recover from covid.
the truck has no engine light until I accelerate and the code is for egr(I deleted it🤫🤫)
Also this problem isn’t like and on it off swich type thing. It’s a very gradual loss of power from full power to what feels like 50hp.
It can be down on power not so bad if I don’t let her eat too much but when I let her eat more she looses more power and so on and so on. When I let the truck cool off for 30 minutes some of that power comes back but is soon gone again if driven hard enough
 

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If you are getting an EGR code you have not deleted it properly. It might be the cause of de fueling but I am not sure.
EGR codes tripped in my truck always made it run worse. Its programed in that way so you will get it fixed. Because its emissions.
How exactly did you delete it? You cant just un hook stuff. You should get a new chip for the PCM with EGR deleted.
But on OBD1 trucks sometimes you can get away with leaving the Baro sensor hooked up to the vacuum line. If you have done a vacuum pump delete. You need a new chip.
 

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Discussion Starter · #7 ·
If you are getting an EGR code you have not deleted it properly. It might be the cause of de fueling but I am not sure.
EGR codes tripped in my truck always made it run worse. Its programed in that way so you will get it fixed. Because its emissions.
How exactly did you delete it? You cant just un hook stuff. You should get a new chip for the PCM with EGR deleted.
But on OBD1 trucks sometimes you can get away with leaving the Baro sensor hooked up to the vacuum line. If you have done a vacuum pump delete. You need a new chip.
I bought a different intake horn without the egr valve port on the top and made a custom block off plate for the lower half of the intake. Other than that I havnt done any chip or bypasses. I’m going go slap the egr back on and see what happens. I really appreciate the input. Also I turned my boost down and no change in de fueling.
 

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This is how the EGR system operates.
When at a steady cruise above 45 MPH . The PCM commands the EGR valve to open and close 3 or 4 times in succession. As the EGR opens and closes. The PCM looks for vacuum changes in the line feeding the EGR. It uses the baro sensor on the firewall. Which is also hooked to the EGR control vacuum line, to sense the changes. If it does not see changes in vacuum. It lights the CEL.
Also I believe The PCM looks for small changes in the Boost sensor readings as the Valve cycles. In my truck I can see the PCM cycling the EGR in the boost gauge. It will go down and up a pound or two as the EGR cycles open and closed after I have been at cruise speed above 45 mph after a few minutes. If PCM sees EGR is not operating it throws the codes.
So The PCM is hard to fool because it uses redundant systems to check EGR operation. On OBD2 trucks like mine, they throw a MAF sensor in the mix. To sense changes in air flow . For further redundancy.
Best way to delete EGR is a performance tune with EGR delete. The performance tune will put a smile on your face:)
Just so you know. Deleting the EGR violates federal/ emission laws. So Joe Biden may come knocking at your door and tell you to. Get jabbed, put on your mask on, and hook up your EGR!

Getting the" F" lower intake to go along with the upper you have. Will help with air flow and power.
 

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Discussion Starter · #9 ·
How certain are you that the egr codes will cause de fueling.
I got my truck to de fuel earlier today at about noon. Parked the truck and got back in it at 7 and the truck seemed to still be down on power quite a bit. This has never happened until today.
I’ll be looking at the quad star 8 position chip if I end up getting one
 

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There is no code for defueling.
It just felt sluggish and loss of power.

Turbo pressure should be set at around 10 psi max intermittent, just to be safe.
Now, this truck is NOT designed to be a hot rod, it has power but no "oomph" to begin with.
 

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Discussion Starter · #11 ·
There is no code for defueling.
It just felt sluggish and loss of power.

Turbo pressure should be set at around 10 psi max intermittent, just to be safe.
Now, this truck is NOT designed to be a hot rod, it has power but no "oomph" to begin with.
The truck has plenty of power and torque when the truck is cold. Then I can take it for a 3 hour drive on the highway and if I keep it under 70 and never get on it. then it seems as if no power change and power is still good.
if I take the truck out cold and I am really on it flooring it then it seems to lose power after the first floor and as it gets floored it looses more and more power.
Or if I’m cruising 80-85 up and down hills on the highway it also starts to de fuel and it de fuels fast going that speed.
also there is no more black smoke and the truck acts like it’s starving for fuel
 

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One other thing that can make your truck act like yours does. Check the gas cap. Make sure it is the proper vented cap for diesel engines and the internal vent is working. The fuel tank must be vented or vacuum builds and fuel cant be drawn thru by the lift pump.
 

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Discussion Starter · #13 ·
One other thing that can make your truck act like yours does. Check the gas cap. Make sure it is the proper vented cap for diesel engines and the internal vent is working. The fuel tank must be vented or vacuum builds and fuel cant be drawn thru by the lift pump.
I replaced the cap and also tried driving with the cap off. No difference
Also My truck makes a weird noise on the passenger side interior when the key is turned on but not cranked
 
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