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Discussion Starter #1
I finally got this new to me truck running and it runs pretty well all things considered, except maybe some injector clatter once it warms up.
Can read that saga under my "94, no start" thread.
I now get no IP,OP related codes truck fires instantly if warm. Cold engine I have to crank maybe 2 sec.
I'm getting the above codes. The 33 will clear and then reappear after driving it. 44&45 must come back immediately, if I clear them, start the truck even once then re-check codes they're back.
Found one bad vacuum tee, replaced and no change. All the vaccum lines look new and checked them. All 3 vaccum solenoids look new as well, wiring looks good as well at least a ways down into the harness.
Vaccum pump is pumping good, no vac guage, but it sucks, in a good way!
Baro sensor looks old and leads me to believe it may be the culprit with these codes.
Also possibly related, I get no wastegate dtc's, but boost seems low. I get steady smoke at full throttle runs. Not alot, just a haze and it's black smoke. Boost also seems low, as in I can't feel or hear the turbo. I recall from my last '94 6.5 (15yrs ago) that I could hear and "feel" the turbo kick in. (Been driving modded Dmax and Cummins for a while so my view may be jaded now, haha.)
Read this in a previous thread "One thing that many will tell you is that it's just EGR codes & you can ignore them, I found with GMTD Scan that is not totally true. The EGR codes will default the baro sensor reading also when they appear & that reading is used by the computer to calculate yr boost pressure. With the boost being calculated incorrectly that will effect performance. Also if the the vent is stuck open it can potentially rob some of the needed vacuum that is required to correctly manipulate yr boost actuator."
This could be what I'm seeing with my preceived low boost problem I guess?
Sound like the EGR barometric sensor, or the solenoids?

I know I could get a "F" PROM and a TM and can the whole setup, but i'd prefer to get it running correctly before I go modifying anything.
 

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Sounds to me you have a Vacuum issue. Low vac either from a bad pump or broken cracked lines will cause low boost and EGR issues. Vac should be 21 hg at idle for proper operation of both wastegate and EGR system.
You are totally right about EGR codes affecting prrformance. i have been trying to tell people that for years here but i dont think it sinks in. Fix your system or get a F or reflashed PCM/chip to delete the egr.
Plugging the EGR and trying to fool the PCM is not the right way. Even if it throwns no codes with things plugged. Running without the egr operating can cause little problems like blown head gaskets.
 

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Discussion Starter #3
I need to round up a vac guage, but it has good vacuum. line off the vac pump will stick to my finger pretty hard at idle.
Question, should the EGR be seeing vacuum at idle, or does the PCM not send vac/open the EGR at idle? Because I have no vac on the EGR line at idle.
Lines are all good. Pretty much new. I inspected every inch of vac line and looks like it was all replaced very recently along with all 3 vac solenoids (easy to tell what's new on the truck by the lack of dirt, oil and sh!t on it) and they used one existing rubber tee that was all cracked. I replaced this tee to no avail.
Another question, why if I blocked the EGR (or plug the vac line to it as you can do on the OBD 1 engines) could that lead to a head gasket failure?
I've never heard of that on any diesel, it's one of the most common mods on any EGR equipped engine. More exhaust pressure with closed EGR cause an overboost? Are these 6.5's really that sensitive?
 

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Ok. IMO. Fooling the PCM into not throwing codes, by plugging/blocking the EGR is not good because.
The PCM on EGR engines is programed with fuel & timing curves set assuming the EGR is operating. With EGR functioning properly exhaust gasses are added to the intake air. They reduce combustion chamber temps and pressures. This allows the PCM to add more timing and cut fuel a bit to get better MPG and emissions. These settings are pre programed in the PCM and only change when EGR codes are thrown.
Running without the EGR will cause higher combustion chamber pressures and temps because of the advanced timing. Also uneven or pre detonation can occur. In a gas engine you can hear knocking caused by pre-detonation but in a diesel you cant. In any engine pre-detonation is not good.
You may think your engine is running great as you are motoring happily down the road. But you may be also destroying the head gasket or cracking heads.
There is a very good reason you saw changes in boost, and other operations, in the scan you did. Its to save the engine if EGR system fails. On my OBD2 I can only get 8lbs boost. Timing is cut back and more fuel is added when EGR codes are set. This is so the engine does not run lean. which is bad for any engine.
Yes I know. Many recomend the plug EGR method and say it works fine, runs great, and causes no problems. 6 months or a year later when they have to change the headgaskets they just write it off to being a common problem with 6.5 diesel and donr even think about the EGR.
I am not saying that plugging the EGR will blow the gaskets. But It just seems to me that the higher pressures and temps caused by no EGR dont do the HG or heads any good. Everyone knows the 6.5 is sensitive to both high temp and chamber pressures. The PCM is programed to run with a EGR and IMO should be ran that way. If you want to delete the EGR do it the right way with a new Chip or reflash. You will get a little more power that way too. Espically with a performance tune -EGR

Usually there is no vac or very little vacuum at idle. If EGR opens to much at idle it will smoke, miss, run rough,
 

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Discussion Starter #5
Great explanation, thanks.
Well the EGR valve seems to operate fine (removed it, pushed in the plunger) and the intake isn't that coked up, so I'll keep it in service once I get 'er running right.
So does it sound like the baro sensor or solenoids?
 

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LOL well here I do contradicting my self. But to eliminate the EGR system. Try clearing the codes and plugging the EGR and running the truck. If the smoke and other problems go away. then the EGR system is to blame. You may have a stuck solenoid bad baro, or something like that.
If the problems are still there Then the pump may not be putting out enough vacuume.
? Can you move the wastegate arm when the engine is at idle. It should not move or take a lot of effort to move it.
If you can move it there is not enough vacuum.
 

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Discussion Starter #7
LOL well here I do contradicting my self. But to eliminate the EGR system. Try clearing the codes and plugging the EGR and running the truck. If the smoke and other problems go away. then the EGR system is to blame. You may have a stuck solenoid bad baro, or something like that.
If the problems are still there Then the pump may not be putting out enough vacuume.
? Can you move the wastegate arm when the engine is at idle. It should not move or take a lot of effort to move it.
If you can move it there is not enough vacuum.
After I fixed the vacuum tee, there was less smoke at full throttle.....maybe. Still a light haze, but it never was thick smoke. If I hadn't read anything about the 6.5's I would have called it normal other than my perceived lack of boost. No where near rollin' coal.
I'll ck the WG arm. It moves freely (relatively) with the engine off, so not stuck open, but haven't tried it at idle. Which way opens/closes the WG? Forward on the arm = open?
I ran it with the EGR vac line plugged and connected. Same codes, same light smoke, same performance or lack thereof.

Wouldn't a bad baro or solenoid throw the codes whether the EGR line is plugged or not, since the PCM is only monitoring the operation of the those parts and not the EGR itself?

Oh, on OBD1 trucks, do you just depress the throttle&brake once to clear codes? That's what I think, but read here about depressing 5x to clear codes.
 

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I have never cleared codes by depressing the brake/accelerator.
Have to disconnect battery power or pull the PCM fuses for about 5 minutes to clear codes without a scanner. Cant rember if its ECM1 or ECMb so pull both to be sure codes are cleared. If it were me i would disconnect the batterys for a while. That will clear the codes and reset the PCM so it will relearn. Maybe that will clear things up. at least it will get rid of any stored codes so you are starting with a clean slate.
 

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Discussion Starter #9
ICBW, but I think what you're describing is the procedure for the OBDII trucks, 96? and up. Or clear them with a scan tool.
OBD1's do clear by depressing the pedals simultaneously. I've been clearing codes for the last few days while working on it and I can get them all to disappear after clearing except the 44 and 45, so either those are thrown as soon as the engine fires or I need to do a different clearing process.
 

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If I read all the details correctly it would suggest you have either a bad solenoid or the wiring signal to one or both is foobar or... Are you sure that all the vac lines are hooked up per OEM schematic located on the fan shroud? The only line that can be plugged in OBD1 to effectively isolate the EGR without coding is the line that feeds the EGR valve itself, the others must remain connected.

The wastgate is closed with the arm pulled all the way in towards the front of the truck, if you have any doubts unhook the supply vac with the truck at idle & then hook up the vac direct from the pump, you should see the gate get sucked in and you should not be able to move it. Take it for a short ride see if it performs any differently with the full vac on the gate.

Now an aftermarket chip or most any chip from a non EGR OBD1 6.5 should eliminate all the EGR BS.

I also suggest you do some reading on OBD1 code clearing unhooking the battery or...Clearing OBD1 codes may be accomplished by simultaneously depressing the brake and accelerator pedals fully while the PCM is in diagnostic mode (terminals A and B connected). It will not appear that you have cleared the codes until the next time you power up in diagnostic mode, however.

EGR on any diesel is just plain and simple WRONG!!! Friggin tree huggers

PS I know the gent that wrote yr quote above LOL!
 

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Discussion Starter #11
Haha yeah I've read a bunch of your posts. Very helpful.
So I'm gettin no vac to the WG actuator w engine running. Think I have f d up solenoids for the WG and egr. As there's strong vac off the pump.
I'll try the wd40 trick on all the solenoids and hook the vac pump up direct to the wg actuator to make sure it's not popped then is a few new solenoids maybe.

Oh well, after running fine for 2 dAys except the egr codes and low boost I got fuel codes again. I need to repl the rubber fuel lines and hopefully clear up the stalling first.
Then I'll tackle the egr stuff.
Good thing I only gave a grand for this truck cause I forgot about all the pos ancillary things with these engines.
 

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PS I know the gent that wrote yr quote above LOL!
Crankme..........
You mean my "Earth First We will mine the rest of the planets later" quote ?
The guy must be old as the hills like me LOL I first rember seeing it on bumper stickers around my parts about 20 years ago. I would like to meet the guy. I work in the largest open pit gold mine in North America.

ICBW, but I think what you're describing is the procedure for the OBDII trucks, 96? and up. Or clear them with a scan tool.
I described the only procudures to clear codes for OBD1 That I have ever used. I have heard of the pedal method but I dont think it clears all the hard cods set. Only the soft codes. But i may be wrong on that. Cutting power to the PCM is the best way I know to clear codes.
With OBD2 the only way to clear codes is with a scanner. Cutting power to the PCM will not clear codes.
 

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Dog here's an easy cheap interim fix I have used in a pinch before buy a wooden screen door spring at Ace hardware and attach it to the bottom of the waste gate arm stretch it tight towards the front of the turbo and attach it to hold pressure on the gate. I had to use this spring from my bros cabin up north to get home. This setup on my truck netted me about 8lbs boost at WOT and cruise was running at about 3 lbs. I keep the spring with me now in the truck along with my spare PMD and few extra fuses. Kinda like a 6.5 emergency travel kit.
 

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