So I guess it's time for me to introduce my self and ask for some help/advice. My 95 OBS is COMPLETELY STOCK and new to me, a friend of mine used it as a farm truck and said come get it one day! So I rescued it from a horrible death as a yard ornament on his farm or worse, the junk yard! It has 256k miles and is throwing three codes 0107,0603 and 1211. The one that is getting on my nerves is the 1211, I've looked at the normal EASY stuff. No oil in fuel, reservoir full, no aeration. I have not pulled the VC and looked at the injectors or around their bores for leaks yet though. I've connected a manual high pressure gauge to the head. It reads around 485lbs-575lbs at idle, 1465-1590lbs at wot (no load in neutral) and that pressure remains constant suggesting no aeration in oil. I've also ran the truck with the gauge attached while driving but the pressure has never climbed above 1650lbs before the CEL set and lost power. We also looked at ICP and IPR with a scanner today (no road test). ICP confirmed above manual pressures, IPR was at 14% at Idle and 34% at WOT in neutral. It was getting late so we did not run scans while driving, however when driving it will sometimes set CEL at about 21-2300 rpms and loose power until you kill it and start over. But it will set the CEL if you accelerate hard right about 2300 rpms and looses power same as above. The truck acts like it wants to run strong right up to the point it sets the CEL. I just cant get it to run hard long enough to check the pressures and duty cycles under a load.

All the reading I've done (100's of threads) leaves a lot on the table to be discussed, I even found a thread that a fella solved a similar issue on a 99, his cause was rust in the tank. Don't see how' that would set a HPOS code but it proves I've done my homework!

I'm just wondering if any of you have had a similar issue on a NON chipped truck? I know that chipped truck can throw this code due to commanded pressures being higher than the PCM likes.

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Update:

I changed the oil today, Delvac 15/40 and Lucas oil stabilizer, It improved the the HPOP pressure to:
At idle:
750psi at start up
580-600psi at temp

WOT in neutral:
2700psi with brief WOT flicks at about 130*
1650-1700psi at temp (but that’s the highest it would produce even when cockroached)

Took it for a spin, while temp was at 130-150* it ran pretty well, would produce and hold 2800psi and never set the CEL. But it would not pull past 3000-3100rpm.

When temp reached full operating temp, it ran ok, but wouldn’t pull more than 20000psi, would pull to 2500-2800rpm before pressure would start to fall of to 1700psi and it would set the CEL and loose power. This a major improvement from what it was doing prior to oil change.

I haven’t pulled the VC’s yet but that is a must at this point since I only found 1 half *** working glow plug and it was 10ohms resistance, the others all showed infinite! There is also oil in all the connectors at the VC. So I’m sure there is another $300 for the gaskets, UVCH’s and glow plugs.

Which brings me to another point, the PCM is not sending the negative signal to the GPR to energize it. It is always hot on the A side of the plug. I’m thinking the BARO code 0107 I got from the scanner probably has something to do with it. It functions if I remove that terminal an manually supply a ground.

It would appear that the ICP and IPR are functioning correctly, So if you guys have any more suggestions please speak up. If you think I have been a dumb ***, and missed something, say so!

 

THANK YOU SO MUCH FOR ACTUALLY INVESTIGATING YOUR OWN PROBLEM AND NOT JUST COMING HERE SAYING YOUR TRUCK RUNS LIKE CRAP, WHAT DO I DO?


Sounds like you are going to need to replace your pump... At temp you are certainly having an issue holding ICP...

Also, glowplugs should cost you about 90 bucks. UVCH/gaskets can be had for like 60 bucks a side. So it won't cost you 300 bucks. And you can get it all at Oreillys...

For your GPR... I'm not sure which side you are calling the "A" side... But one of the large lugs should be a constant 12v..

 

Need to work that old oil out of the HPO system will take time/miles. Then, change it again.

Glow plug relay needs positive signal to energize. One side should always be hot, positive signal closes the switch.

 

What I call the "A" side is the small terminal that is controlled by the PCM, it should switch to a ground signal supplied by the PCM in order to energize the glow plugs. The other small terminal is the "B" side, it is always hot with the key on. At least that is what the workshop manual shows.

 

After reviewing your manual and one of my own, it appears you are correct. Two conditions must be satisfied to complete the control circuit that activates the glow plug relay.
condition one, the key must be "on" to supply +12volts.
condition two, the PCM must complete the circuit to ground.

The BARO sensor is one of the information inputs the pcm uses to decide for how long to satisfy condition 2 for, so, since you have the corresponding code, check the BORO circuit and/or replace the sensor.

Thank You, I learned something new.

 

You're welcome, i did what I could to make ya think! LOL I'm a decent mechanic, and I was a diesel mechanic before all the computer controlled diesels came of age, and believe it or not this is my first diesel truck since the late 80's (no carbon dating jokes!) I've been playing with gas stuff for a long time.

As far as the GPR issue I figured that is what it would take to fix it. I just wanted a second opinion befroe I dropped anther buck30 on the sensor!