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1998 6.5 shuts off past 170° f

If it very consistently shuts off at 170* and you can get it to start by unplugging the ECT sensor on the thermostat crossover housing, then it's shutting down for the fail-safe mode of TDCO being too far out of spec when it tries to learn. Fix is to mechanically adjust the pump into an acceptable position or repair the fault that's causing the learn to fail (Optic sensor, crank sensor, wiring, etc.)

You can verify if it's too far out of spec by performing a "TIME SET" Command with the proper scan tool. Desired timing will command 0* and Actual Timing will read back to you how many * the pump is advanced from TDC. If this procedure doesn't work, then one of the sensors or wiring is bad and the computer can't determine the crank/cam position relationship.

Unplugging the ECT (engine coolant temp sensor) tells the computer the engine is still cold and kicks it out of the learn procedure. The OBD II 6.5 PCM automatically goes into re-learn every 50 warm up cycles. That's what the book says, but it's a bit more random in real life. Same reason many OBDII trucks will go into idle lope randomly from a missing or #9 PMD resistor because the only time the computer actually adjusts the fueling calibration per the resistor is during a TDCO re-learn.

OBD I trucks don't behave like this so this reply only applies to 1996+.
 
Head and rotor wear was mentioned in one of the previous replies...A DS pump will idle and run all day with an extremely worn head and rotor because the computer can just command a higher fuel rate. Head and rotor wear on the DS only shows its face during a heat soaked start up scenario where you crank and it won't fire. When the engine cools down and the tolerances tighten, it'll start and stay running.
 
Rockabillyrat said:
Two things, do you have tools to do a pin drag test? The terminals on the extension harness might be making poor contact. As they heat up it may turn into a open circuit long enough to cause the engine to stall.

Also do you have a lab scope? Scoping the power, ground, signal, and control wires at the PMD might be a good way to catch what's going on. The great thing about a lab scope is you can see the issue on a graph. Takes away any guess work. I've fixed many unfixable vehicles that way.
Click to expand...
Unfortunately I do not own a lab scope. I'm working with a power probe, multi meter, and a test light. I have tried installing the pmd without the extension harness and have gotten the same result. I've gone through and cleaned the electrical connectors on the harness with electronic cleaner and a wire brush I use dielectric grease as well. The connectors look ok and seem to make a good connection I've tried wiggling the harness with the truck hot and cold and I cannot duplicate the problem. I think I'm going to try and double check my grounds. There are 3 I know of for sure. Driver side intake manifold, passenger side intake manifold, and back right of the engine by the firewall. All seem to have a good ground per my power probe, are there any grounds that I am missing? It this where the ECM grounds?
 
quadstar87 said:
Head and rotor wear was mentioned in one of the previous replies...A DS pump will idle and run all day with an extremely worn head and rotor because the computer can just command a higher fuel rate. Head and rotor wear on the DS only shows its face during a heat soaked start up scenario where you crank and it won't fire. When the engine cools down and the tolerances tighten, it'll start and stay running.
Click to expand...
Would a worn head and rotor cause the truck to shut off on its own even while idling?
 
quadstar87 said:
If it very consistently shuts off at 170* and you can get it to start by unplugging the ECT sensor on the thermostat crossover housing, then it's shutting down for the fail-safe mode of TDCO being too far out of spec when it tries to learn. Fix is to mechanically adjust the pump into an acceptable position or repair the fault that's causing the learn to fail (Optic sensor, crank sensor, wiring, etc.)

You can verify if it's too far out of spec by performing a "TIME SET" Command with the proper scan tool. Desired timing will command 0* and Actual Timing will read back to you how many * the pump is advanced from TDC. If this procedure doesn't work, then one of the sensors or wiring is bad and the computer can't determine the crank/cam position relationship.

Unplugging the ECT (engine coolant temp sensor) tells the computer the engine is still cold and kicks it out of the learn procedure. The OBD II 6.5 PCM automatically goes into re-learn every 50 warm up cycles. That's what the book says, but it's a bit more random in real life. Same reason many OBDII trucks will go into idle lope randomly from a missing or #9 PMD resistor because the only time the computer actually adjusts the fueling calibration per the resistor is during a TDCO re-learn.

OBD I trucks don't behave like this so this reply only applies to 1996+.
Click to expand...
Yes it is consistent at 170° the truck may not shut off on its own every time but you can hear the engine rpm fluctuate from 700 to 670 and back up. The truck starts pretty well cold a d I have been able to get it to start before after stalling by unplugging the ECT sensor but I have to play with the pedal a little while cranking and it takes a bit longer before it fires. After it shuts off it sounds like it is attempting to fire but doesn't have enough to get it going. TDCO last time I checked was -0.46 and while commanding "TIME SET" the desired timing was 0 and the actual timing was anywhere from 3.5 to 3 to 3.9 as it would fluctuate. I'm wondering if it is a timing issue. Once time set is commanded the truck runs rough and wants to die. I can only command time set above 170° ECT. Above 170 the truck wants to die so I am forced to keep the truck at above 1000 rpm. On the scanner I saw that my cam and crank reference missed would occasionally show 1 on the chart. I installed a new CKP a few weeks ago just to be sure. I had brought the truck to SMR diesel to verify timing was correct when I had my 2nd diesellogic.com IP and they found that timing was set in spec and that the truck would loose cam signal past 170°. They ran through the testing procedure and determined the optical sensor was defective. The truck now has an AC Delco reman pump and ac delco included pmd with a #9 resistor installed. Still having the same problem.
 
Loganshaw_6 said:
Yes it is consistent at 170° the truck may not shut off on its own every time but you can hear the engine rpm fluctuate from 700 to 670 and back up. The truck starts pretty well cold a d I have been able to get it to start before after stalling by unplugging the ECT sensor but I have to play with the pedal a little while cranking and it takes a bit longer before it fires. After it shuts off it sounds like it is attempting to fire but doesn't have enough to get it going. TDCO last time I checked was -0.46 and while commanding "TIME SET" the desired timing was 0 and the actual timing was anywhere from 3.5 to 3 to 3.9 as it would fluctuate. I'm wondering if it is a timing issue. Once time set is commanded the truck runs rough and wants to die. I can only command time set above 170° ECT. Above 170 the truck wants to die so I am forced to keep the truck at above 1000 rpm. On the scanner I saw that my cam and crank reference missed would occasionally show 1 on the chart. I installed a new CKP a few weeks ago just to be sure. I had brought the truck to SMR diesel to verify timing was correct when I had my 2nd diesellogic.com IP and they found that timing was set in spec and that the truck would loose cam signal past 170°. They ran through the testing procedure and determined the optical sensor was defective. The truck now has an AC Delco reman pump and ac delco included pmd with a #9 resistor installed. Still having the same problem.
Click to expand...
Have you tried another PCM yet? That'd be a lot easier than some other options to look at first.

We've also had a couple that refuse to time properly or have errors like this so what we do is swap in a PCM from another truck that already has TDCO set on it. This prevents it from hunting for a new value on the first warm-up cycle, and often will be fine. Obviously it's recommended to properly set the timing but if "TIME SET" is telling you it's in a good spot and you need to get your truck running, you do what you need to do sometimes and make it comply.
 
quadstar87 said:
Have you tried another PCM yet? That'd be a lot easier than some other options to look at first.

We've also had a couple that refuse to time properly or have errors like this so what we do is swap in a PCM from another truck that already has TDCO set on it. This prevents it from hunting for a new value on the first warm-up cycle, and often will be fine. Obviously it's recommended to properly set the timing but if "TIME SET" is telling you it's in a good spot and you need to get your truck running, you do what you need to do sometimes and make it comply.
Click to expand...
 
I purchased a used computer from a salvage yard that I was told came off of a running truck. That truck was a non EGR truck a d I'm assuming no MAF either since my truck doesn't show anything on the scanner for the MAF voltage with this computer. Same problem with both ECMs.
 
I checked some grounds and added more grounds today and ran the truck without the PMD extension harness. The truck shut off at 170 degrees. I unplug the ECT sensor and the truck hesitated but started. I ran it for about half an hour got in the truck gave it throttle and it died immediately after I let off the throttle. I plugged the sensor back in and the temperature was at 195. while cranking the truck after this it didn't even attempt to fire there is no smoke
 
JMJNet said:
Reiterating Post #34 and #36?
Click to expand...
Somehow I completely missed a large quantity of responses on the forum. I dumped about 4 gallons of water on the pump and I got the truck to start back up. Truck was running and died at 186 degrees. I'm going to attempt to dump water on it again and see if I can get it to start
 
Doing the water test sounds dumb but tells a very important story...
Once I know I have no air and I have incoming fuel pressure, i try spare pmd, then after that dump water.
 
Swapping to a db2 is a more work and more expensive right now, but long term win imo.
So long as your dmv & smog laws allow it.

Maintenance goes like this: every 30k miles, advance timing a hair. Repeat but check timing because once timing chain stretches to max, no more adjustments needed. Unless you have gear drive. Then set it and drive forever.

Still add lube to fuel even if you get the hardened parts unit. The injectors like to live also.
 
Will L. said:
Swapping to a db2 is a more work and more expensive right now, but long term win imo.
So long as your dmv & smog laws allow it.

Maintenance goes like this: every 30k miles, advance timing a hair. Repeat but check timing because once timing chain stretches to max, no more adjustments needed. Unless you have gear drive. Then set it and drive forever.

Still add lube to fuel even if you get the hardened parts unit. The injectors like to live also.
Click to expand...

Does DB2 have less failure rate than DS4?
Do we still have a good supply of good DB2?
 
Judging by your original post it sounded like you had the timing right. So I didn't bother to question that. So I figured it had to be something with the injection pump. Just because a H&R isn't common doesn't mean it cant happen on a DS4. Glad we could lead you in the right direction!!

Personally I would DB2 swap every 6.5. The DS4 is a headache for most people that run them. Got one in the shop today with a stalling and timing issues.
 
JMJNet said:
Does DB2 have less failure rate than DS4?
Do we still have a good supply of good DB2?
Click to expand...

Yes and no on reliability. The DB2 had issues with the advance piston bore wearing out and causing a loss of transfer pump pressure. Most rebuilders ream then out and install a oversized advance piston. The better fix is to sleeve the housing which is less prone to wear out. That makes them last alot longer. The low viscosity fuel parts found in the military pumps are a must in my opinion with today's ULSD fuels. But a good additive can help with that. The govener weight retainer and a few other parts got upgraded over the years so if you buy a new pump from stanadyne it will have the upgrades and increase the life expectancy. I just dont know if stanadyne addressed the advance piston bore issue on the new pumps or not. The DS4 has a sleeve so I would have thought they would but I haven't disassembled a newer DB2 yet.

But with no electronics to worry about they are more reliable in that aspect. Plus they can be modified to push more fuel than a DS4.
 
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