Every other start, it starts in "safe" mode

[spark3542]

97 K2500 Suburban 6.5TD.

I had crank position codes frequently, so I changed the crank position sensor. Now this is what I get:

Cold Start: A little bit excessive cranking, but it fires, after a few seconds running, the diesel knock gets loud and large blue cloud out the tailpipe very briefly, then goes away. Truck runs fine while driving.

Warm restart: If it sits for anywhere from 5 minutes to several hours, this is what happens...Cranks and cranks excessively then finally fires, but it is in this "safe" mode where power is significantly reduced and rpms will not exceed 2k, but engine runs quiet. Turn key all the way off to shut it off. Restart immediately and it fires without excessive cranking and there is clearly a louder diesel knock at idle, but truck runs fine. No blue smoke out the tailpipe after either of those restarts. Blue smoke is only at the initial cold start.

The codes seem to be mostly related to fuel and air metering (I don't have them available as I type this). About 4 or 5 codes come up, and sometime the crank position code comes up as well.

I haven't had much time to troubleshoot, so I've been living with this condition. My kids even think it's a joke now...Crank and crank until it starts, drive a few feet, determine it's low on power, pull over, shut it off, restart immediately and then it's fine for the rest of that trip until it's shut off again. "Dad's got to restart the suburban!"

Does this condition sound familiar to any of the wizards on this forum?

Thanks in advance.

Mark in MA

[spark3542]

Ok, freed up a little time last night to do some troubleshooting.

The SES light has been on for weeks. The burb sat for at least a day until I went out to troubleshoot. Before I started it, I hooked the laptop up to see the codes. This is what was stored from before:

P0216 Inj timing control ckt
P0251 Inj Pump Fuel Metering
P0335 Crank Position sensor A ckt
P0370 Inj timing Ref High Resolution Signal A
P0606 ECM/PCM processor

I cleared the codes, and started the vehicle. It started fairly easily, emitted the blue cloud, then it cleared up. Let it warm up to operating temp. Turned it off. It restarted easily. Turned it off. It restarted easily and the SES light came on. Code was P0335 Crank Position Sensor A circuit. Shut the vehicle off. It restarted easily. Shut if off. Reset the codes. Restarted, and it took excessvie cranking this time, and 2 codes were set:

P0236 Turbo Boost sensor A ckt
P0251 Inj pump metering control A (cam/rotor/injector)

Shut it off. Restarted easily and added a code:

P0370 Ign timing ref high resolution A

Shut it off. Cleared the codes. Restarted easily and code was set:

P0335 Crank Position Sensor A

As I mentioned, I just replaced the Crank Position sensor, but I'm now at a loss on what to replace next.

Does this sound like an actual sensor is malfunctioning, or bad wire somewhere, or ECM on the fritz?

Thanks

Mark in MA
97 burb K2500 6.5TD

[DmaxMaverick]

With the range of codes you are seeing, I'd suspect either a poor connection at/near the PCM, or the PCM itself. Rare, but they do fail.

Not likely with all the successful cranking you've done, but low voltage can cause the same issues. Just for fun, try cleaning and reconnecting all the battery terminals and grounds. Check voltage at both batteries, separately, while you have them disconnected. They should be within .5V of each other, and greater than 12V on a full charge, after sitting idle (no loading, no charging) for at least 6 hours. A fresh battery should be 12.8V+. If you have side terminal batteries (like OEM), check for cracks and/or leaking around the terminal lug.

[john8662]

Ok, freed up a little time last night to do some troubleshooting.

The SES light has been on for weeks. The burb sat for at least a day until I went out to troubleshoot. Before I started it, I hooked the laptop up to see the codes. This is what was stored from before:

P0216 Inj timing control ckt
P0251 Inj Pump Fuel Metering
P0335 Crank Position sensor A ckt
P0370 Inj timing Ref High Resolution Signal A
P0606 ECM/PCM processor

I cleared the codes, and started the vehicle. It started fairly easily, emitted the blue cloud, then it cleared up. Let it warm up to operating temp. Turned it off. It restarted easily. Turned it off. It restarted easily and the SES light came on. Code was P0335 Crank Position Sensor A circuit. Shut the vehicle off. It restarted easily. Shut if off. Reset the codes. Restarted, and it took excessvie cranking this time, and 2 codes were set:

P0236 Turbo Boost sensor A ckt
P0251 Inj pump metering control A (cam/rotor/injector)

Shut it off. Restarted easily and added a code:

P0370 Ign timing ref high resolution A

Shut it off. Cleared the codes. Restarted easily and code was set:

P0335 Crank Position Sensor A

As I mentioned, I just replaced the Crank Position sensor, but I'm now at a loss on what to replace next.

Does this sound like an actual sensor is malfunctioning, or bad wire somewhere, or ECM on the fritz?

Thanks

Mark in MA
97 burb K2500 6.5TD


You got's electrical issues there!

Well, let's hit the basics, cause they're related.

In decoding your codes you have stored, it would seem that maybe three different things are going on here.

1) You replaced the Crank Position Sensor, but have the codes been cleared? You need a scanner that can initiate a pcm clear. This problem may be solved already.

2) You appear to have a grounding issue somewhere, causing multiple codes, and perhaps your aggravated Crank sensor code. Check the back of the engine near the firewall on the passenger's side, There should be a stud in the intake that has electrical connection going to it. There should be two wires there, make sure they're present. It's possible one's missing in action, probably the good ground needed for the PCM and engine components.

3) Your pump is having issues in the cam/optic sensor department. This can be for several reasons. I'd take a stab in that it's an electrical connection issue somewhere. Disconnect the harness going to the top of the injection pump (optic sensor) and verify it's connection. Sometimes a filter harness is also connected to this sensor, verify it's connection before and after the initial engine harness. It could be just loose. Next, air in the fuel also causes optic sensor readings to be off, posing codes. Check for air in the system (the clear tube out the return trick).

How are the battery connections?

Post back!

J

[spark3542]

You got's electrical issues there!

Well, let's hit the basics, cause they're related.

In decoding your codes you have stored, it would seem that maybe three different things are going on here.

1) You replaced the Crank Position Sensor, but have the codes been cleared? You need a scanner that can initiate a pcm clear. This problem may be solved already.

2) You appear to have a grounding issue somewhere, causing multiple codes, and perhaps your aggravated Crank sensor code. Check the back of the engine near the firewall on the passenger's side, There should be a stud in the intake that has electrical connection going to it. There should be two wires there, make sure they're present. It's possible one's missing in action, probably the good ground needed for the PCM and engine components.

3) Your pump is having issues in the cam/optic sensor department. This can be for several reasons. I'd take a stab in that it's an electrical connection issue somewhere. Disconnect the harness going to the top of the injection pump (optic sensor) and verify it's connection. Sometimes a filter harness is also connected to this sensor, verify it's connection before and after the initial engine harness. It could be just loose. Next, air in the fuel also causes optic sensor readings to be off, posing codes. Check for air in the system (the clear tube out the return trick).

How are the battery connections?

Post back!

J

1) I have AutoEnginuity software on my laptop. There is a single button on the screen to clear the codes. This is what I did in my last post to clear the codes. Is there anything further that needs to be done to clear the codes for the crank sensor?

2) I'll check the engine for proper grounds.

3) What is the function of the optic sensor, and exactly which code would it set if it were failing?

I'm 90% confident the battery connections are good. They are clean and well maintained. Voltmeter on the dash stays about 14 for the most part, so I'm fairly confident the charging system and batteries are good.

Where is the ECM...in the passenger kick panel I assume? I'll check it for solid connections.

You know, One thing strange I recall, (now that you guys are talking about electrical), is once when I reset the codes a few weeks ago, the clock reset to 12:00 when I knew it was accurate just minutes before.

Thanks

Mark in MA

[john8662]

"I'll check the engine for proper grounds."

Your Clock reset when connecting the scan tool and doing a rest is suspcious, like you've got a grounding issue.

Check grounds underneath the dash (there should be at one point a ground to the main bar of the dash). The more important ones are the ground connections that go from the engine to the chassis. These are located starting at a grounding strap at the rear of the engine (already mentioned) and traveling to the cab and to the frame, you'll find these on the same side as the turbo and starter, you'll have to access these from below. Suggest verifying connection, then renew connection with some contact cleaner and sand paper, then re-install.



3) "What is the function of the optic sensor, and exactly which code would it set if it were failing?"


The codes 251 and 370 point towards the optic sensor being at fault, in this scenario of course.

One thing to keep in mind while troubleshooting these codes, is you start at the top (first code) and work your way down. I didn't believe it either, but it does happen.

The PCM is behind the glove box in the inside. Remove the glove box (depresse tabs when open, and it'll come right out), then you have access to the PCM and it's connectors, stuffed in the upper right hand corner (approx) of the glovebox.

Good to have the Autoenginuity, I'm gealous!

J

[spark3542]

Found a single ground wire on the intake manifold stud. Heavy gauge wire...maybe 14 gauge or even 12 gauge, but only one wire. No others dangling nearby that I could find.

Inspected battery terminals, look good.

Found the PCM behind the glove box. Removed all three connectors to it. All look clean and dry, and none of the wires to the connector were frayed or cracked.

Noticed the label on the PCM said "remanufactured by GM", so I'm immediately suspicious that the PO had electrical issues as well.

Put everything back together and truck started normally.

Drove it to work this morning (12 miles) as a test drive. No issues so far.

I suspected with me moving around wires and harnesses, I may have temporarily fixed the problem.

Mark in MA

[john8662]

Since you have a scan tool, you have the ability to watch sensors live. For finding an intermittant just watch each sensor while moving the harness, until you find the bad harness. That's about all I know to do to find something like that. Well, besides replace every harness.

J

[spark3542]

Since you have a scan tool, you have the ability to watch sensors live. For finding an intermittant just watch each sensor while moving the harness, until you find the bad harness. That's about all I know to do to find something like that. Well, besides replace every harness.

J


I can actually watch individual sensors live? I knew I could watch certain variables like engine temp, rpm, vehicle speed, etc in real time, but I didn't know I could see something like crank position sensor live. I'll have to check the manual.

From what I could understand, OBD-II got better each year...meaning '06 models you can read many more items than '96 models. The software didn't give me many choices on data that I could see on my '97.

I need to read the whole software manual.

Thanks

Mark