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I have a 1995 6.5 with a cold start smoking & stumbling issue I can't figure out?

I'm will Will L. On this one. It sounds like a glow plug issue to me. A amp clamp is hands down the best way to test them. You can watch total amperage pull and the amount of time they are commanded on. If you see low amperage then jump the glow plugs manually with a wire and measure your amperage again. If your amperage is still low you have a GP issue, if it's normal when manually jumped you have a module or power issue. If your amperage is good but your on time is too short, you have a module issue, or a bad sensor causing the glow plugs to short cycle. Manual jump them for and see if its start better. That will confirm a module or sensor issue.

Also you can watch the advance piston servo movement and see if its pulling up for cold start advance.
 
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Will L. said:
“Block heater or pulling the coolant temp sensor did the trick too. I pulled the sensor and it fired right off with the normal small puff.”

I missed the point that pulling the temp sensor allowed it to start properly. If that is the case- then the glows ARE working ok.
I am confused- there is something I am missing here and can’t see what I should. EVERYONE HELP please, I am not seeing the culprit but it is in this circuit,Focus on this - the problem is here. I want to say bad sensor, but it tested ok. Bad connection maybe? Faulty wiring after the sensor? Unplugging the 2 wire sensor basically sends the signal to advance time and maximum glow time right(?) so could it be longer glow? I'm going to check the connector side of this circuit... But I think that sensor plug is part of the New engine wiring harness that got replaced with the IP... The ECM was also replaced with everthing else... If I know the ambient temp and look at the chart should I see that value in the voltage lead at the ECM? With the engine on circuit charged... Observation: The glow plug light does seem to cycle longer or shorter giving the temp when starting. I'm going to see how it cycles with the cts disconnected.

Are you positive the advance is engaging when the 2 wire sensor is connected and it isn’t starting properly? I cant say, or see the advance? If I read right that advance is in the pump on the bottom of the DB4. All I have is, unplug the cts and it fires normal. Heat it up and it fires normal. Let it sit in the cold cts plugged in and no block heat, not so good!


After you replaced the lift pump and did 3/8” line all the way to the ip (great upgrade btw), are you still getting the bubbles? Yes, only after an overnight sit. It think the bee bees are micro bubbles gathering over night. At one point I made 2 loops hoping to see what side they were coming from? I forget which earlyer sequence this pic was taken but look close there are small bubbles on both sides. I'm going to set this up again just to keep an eye on things. That vinyl line does not last too long.pic of clear loops.jpg
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MrMarty51 said:
Might try cleaning every connector on the engine and behind the engine too. There is a bunch of them. It sure helped the way My truck performs.
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Yup I did that too looking for a intermittent short that left me broke down a time or two (that turned out to be air bubbles) messing with the cam reference and not tripping a code right away... That's also when all the grounds were cleaned.. This truck has been driving me crazy!
Can't thank everyone enough!
 
It is normal for a tiny amount of air to collect in the return line. The system was designed to do that and have a high point out the ip for the air to escape. That small amount of air won’t do anything.
Yes the colder the coolant the longer the glow time if the system is working properly. It also will trigger post engine start glow if needed.

I cant remember details on db4 vs db2. But on db2, two things happen. There is a an electric contact that moves a cold advance position and advances timing. There is also the solenoid that move the throttle slightly so the idle rpm is raised- same solenoid used for a/c system to bring up rpm at idle so added load of compressor doesn’t kill engine at idle.
 
Will L. said:
It is normal for a tiny amount of air to collect in the return line. The system was designed to do that and have a high point out the ip for the air to escape. That small amount of air won’t do anything. Good to hear, that puts air being the problem off the table. I was told there should be "0" air in the fuel system.....

Yes the colder the coolant the longer the glow time if the system is working properly. It also will trigger post engine start glow if needed. I did observe longer heat times the colder it was with the CTS plugged in. The temp range 35 to 50 in the garage... Yes the problem started at 50deg...

I cant remember details on db4 vs db2. But on db2, two things happen. There is a an electric contact that moves a cold advance position and advances timing. There is also the solenoid that move the throttle slightly so the idle rpm is raised- same solenoid used for a/c system to bring up rpm at idle so added load of compressor doesn’t kill engine at idle. I'm not sure but I think that is all internal on the DB4 from looking at the info on the pdf I posted. I have a call into John at Quadstar, but he is yet to get back. Good thing he's not the fire department! I'm guessing he has his own fires right now, busy filling orders before he leaves for vacation. QS keeps him pretty busy from what I can see from being his pain in the ass neighbor. The clues are there...? I'm going to learn how to check the harness side of that CTS to the ECM. There must not be that much advance needed (where ever it is) Because the truck fires off just fine with the CTS disconnected? Its been pretty cold in the garage. I'm going to put a thermometer in down there today to see exactly what the air temp is?

So when connected, the CTS must be sending improper/unexpected signals???? Unhooked the default allows a clean start??

Thanks for your time and input Will!
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The DB2 and DB4 use a HPCA solenoid to control cold start advance. The advance piston uses transfer pump and housing pressure to operate. There are no electronic parts in the advance system technically. The HPCS just opens to allow housing pressure to drop to 0psi. This allows the transfer pump pressure to overcome the housing/spring pressure and advance the cam ring. Once the engine warms up the HPCA closes and housing pressure is returned to normal and the piston retards timing. There is also a light load advance that uses the mechanical lever of from throttle movement to advance the timing under low transfer pump pressure situations.

The DS4 uses a stepper motor to control the servo piston position which in return directs transfer pump pressure to either advance or retard the cam ring.

I was thinking about your hard cold starts last night. Two things I would do. I know you ohmed the coolant sensor. But what reading did you get on your scan tool? I've gotten in the habit of scanning all my pressure and temps sensors with a cold engine to confirm they a read correctly when performing any diagnostics. Secondly I would still manually jump your glow plugs to see if it helps. It sounds like they worked when you unplugged the coolant temp sensor. But they could be short cycling with it plugged in. If that all test good I'd say ak diesel driver has the right idea about a possible advance piston issue.
 
If the advance piston had a sticking issue then it would instantly trigger a timing DTC when desired and actual timing didn't match up. The DS4's pre-position advance spring is only used until the motor is running, then the stepper motor takes over and the computer is controlling timing.

If desired and actual timing match up when it's running and your closure time pulse width isn't above ~1.9ms on cold start, then there's most likely nothing wrong with the pump as far as startup goes.

Your #1 tune is mostly stock for diagnostic purposes, but #3 has advance at idle. There should be a difference in how they react to startup, so if they behave the same, I'd say it needs more glow time. Reason being-disconnecting the ECT sensor will give it full advance as well as full glow time.

There's also a bunch of OBDI trucks floating around that never escape this issue and have the ECT sensor on a switch for this exact reason.

If you have time to send your chip back, we can get wild with glow time and advance on cold start to see if it behaves. The risk will sill be there that it doesn't respond and you have to put the ECT on a switch.
 
Too many DB2 references in here! The DS4 has full control over its timing advance at all times the engine is running. The small pre-positioning spring in the advance bore of the DS4 just sets the piston in a slightly advanced position when the engine is shut down so it's already advanced on re-start. Reason being - the pump can't determine advance position until the engine is running and the optic sensor is providing feedback. There's not much guess work here either as you can see Desired/Commanded and Actual timing advance values directly on the scan tool anytime the motor is above ~300 Engine RPM
 
Not trying to argue here but I have had a pump behave like this as well as bison(Simon) and the fix was a new IP. That was on my 96. I actually considered doing the switch but didn't want to confuse my wife who drove it once in a great while.
 
Never had any codes either, but on the 6.5 that doesn't surprise me too much. Alot of things don't seem to show up even on a scanner. For example I had a 94 that wouldn't run right and I was thinking the CPS but the scanner didn't show any missed counts. Did the CPS/OS test and proved it was the CPS. Ran fine after we changed the CPS. The truck had been to several mechanics that couldn't figure it out.
 
When these issues happen and the pump is the cause then you'll typically see c-time (closure time) out of spec. It doesn't throw a code because the diagnostic routine doesn't run until the engine is warmed up. Thus why I mentioned it.

ak diesel driver said:
It's usually an indication of of the advance piston sticking in the IP. At the very least ohm out your sensor though.
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You specifically mentioned a stuck advance piston and I specifically addressed why that can't possibly be his issue. Could it be something else pump related? Sure.

Crank and optic sensors can be scoped fairly easily, same as any other EFI vehicle. Don't rely on codes to tell you the issue as diagnostic routines are often not running in real-time. Live data, however, is much more useful.
 
quadstar87 said:
If the advance piston had a sticking issue then it would instantly trigger a timing DTC when desired and actual timing didn't match up. The DS4's pre-position advance spring is only used until the motor is running, then the stepper motor takes over and the computer is controlling timing. This is above my pay grade but I'll try to keep up!

If desired and actual timing match up when it's running and your closure time pulse width isn't above ~1.9ms on cold start, then there's most likely nothing wrong with the pump as far as startup goes. Check the closure time pulse and see where it is. I saw that on the scanner

Your #1 tune is mostly stock for diagnostic purposes, but #3 has advance at idle. There should be a difference in how they react to startup, so if they behave the same, I'd say it needs more glow time. I will try a start in #3 I know what #1 does. Reason being-disconnecting the ECT sensor will give it full advance as well as full glow time. That makes sense and puts glow time back on the table..

There's also a bunch of OBDI trucks floating around that never escape this issue and have the ECT sensor on a switch for this exact reason. This may be another one! Thanks John let me know when you get back and dig out from vacation

If you have time to send your chip back, we can get wild with glow time and advance on cold start to see if it behaves. The risk will sill be there that it doesn't respond and you have to put the ECT on a switch. Thanks for the input John! let me know when you get back and dig out from that much needed vacation.

Thanks everyone!
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WayneB said:
Had a chance to check this after work today.
Parameters:
Ambient temp = 48
ECT sensor temp = 70.4
Started with tune #3
If desired and actual timing match up when it's running. Those numbers seem to stray a bit + or - 0.3 but for the most part the same.
and your closure time pulse width isn't above ~1.9ms on cold start. If closure time pulse is the same as "injection pulse refrence" it was 2.36 at a 70.4 start temp. I took pictures of the screen as the temp went up, the number did to. It also bounced down to 0.17 then back up, back and forth.

I checked it yesterday but didn't log the temps or take pictures it was colder and the "injection pulse refrence" was 1.99 tune #3

then there's most likely nothing wrong with the pump as far as startup goes. Would this point to that piston sticking?

Your #1 tune is mostly stock for diagnostic purposes, but #3 has advance at idle. There should be a difference in how they react to startup, so if they behave the same, I'd say it needs more glow time. They both start the same. Not pretty!
Thanks John
Thanks Everyone!
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I'm back!

The advance piston is not sticking since actual & desired timing match up. That's an easy one to diagnose.

Is DTC 35 or 36 triggering at all? Will give you a call because the numbers are a bit high for injection pulse width and could contribute to the issue.
 
quadstar87 said:
I'm back!

The advance piston is not sticking since actual & desired timing match up. That's an easy one to diagnose.

Is DTC 35 or 36 triggering at all? Yes it tripped 36 (see below) Will give you a call because the numbers are a bit high for injection pulse width and could contribute to the issue.

Well to close this one out.

OK talked to John at QST the other night and he said it looks like the IP is the problem from the out of spec Injection Pulse Reference / C-Time. What did I learn? It looks like the "Injection Pulse Reference / C-Time" should be one of the first things look for in the troubleshooting process.

To add, I took the truck for a short drive "before John and I talked" and it tripped DTC #36. (mentioned above) Which also points PMD, IP and electrical. So I checked both of the PMDs I have here. The Main harness and the PMD extension harness are new along with the PCM when the IP was changed. The connector to the PCM was just cleaned and all 34 pins re-tensioned into a new / replacement connector. Went through every single ground on the truck from the dash forward, including the splices in the firewall harness. Both PMDs produced pretty much the same Injection Pulse Reference on start. First start was 1.99 and quickly jumped to > 2.35 > 2.42 > 2.55 (I read DTC 36 will trip at 2.5ms) Again pointing to the IP
I have to say, no wonder these trucks are confusing to the novice like me... Injection Pulse Reference (94-95) also called C-Time (96 on) same thing, only different name and number. Pump Mounted Driver also called Fuel Solenoid Driver..

Here is what I have on DTC 36 from the GM 1994 Diesel Supplement. Perhaps it will be helpful to someone.P1 code 36.jpg
P2 code 36.jpg

Thanks everyone!
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