Stalling, PCM or IP stepper motor?

[94blazer]

Problem: Explain your problem in concise language (ie: Cranks but won’t fire). Cranks, fires, runs, and then dies at random. Throws a code 18 when it dies.

Demographics: The IP is a 5068, with a matching PCM. Its an 'F' engine with the 'GM Goodwrench Crate Motor" stickers on the valve covers. FTB done. Previous Owner says there are about 70k miles on the engine. I reproduced the stalling tonight, it was about 85 F out. Vitals on the truck when it died -
Coolant temp - 202.4 degrees, Injection timing actual - 25, Injection timing desired - 4, IAT - 103. I have my fuel pressure gauge teed in between the Filter and IP, Showing a steady 4.5 PSI and holds there even after truck stalls.

- Year: 1994

- Truck model and class (ie: c2500) Blazer (k1500)

- Automatic

- Mileage: (indicate miles or km) 215,000 Miles on the Odometer

- Replaced parts and mods: Again, according to the previous owner - 9k miles on IP, PCM as well at that time.

- Model: ‘S’ or ‘F’ engine, NA or Turbo, EGR? F, Turbo, No EGR

- Ambient outside temp: (indicate *C or *F) 85 or 90ish F it felt like, it was just after sun down here in balmy AZ

- What fuel are you using? #2 Diesel

- What fuel additives are you using? I havent driven the truck yet.... I can of sea foam in with the 10 or so gallons of #2 that were in the tank

- Where are you located? Coolidge, Az

General maintenance: inspect and evaluate the condition of each. When were they last changed?
- Air filter? New
- Fuel filter? New
- CDR Valve? New
- Coolant – last flushed/replaced at: just done
- Oil – synthetic/regular, changed at 15/40 shell rotella also just done
- Batteries – state of charge, (matched set) replaced at Matched set, New, 0 miles, showing 12.7 V with truck off

- Battery cables and grounds (removed, cleaned and tightened): New 00 cables, stainless bolts and jamnuts(no factory ends) New crimps and heat shrink ring terminals at the back of passenger head, also seconday 4 gauge ground from passengers battery to same head stud. new 4 gauge grounds replacing the flat braid cable from head to frame to body.

- Glow Plugs - how many miles on them? Unknown- but she starts like right now with only 4 plugged in. What type? factory G9 I belive
- Injectors - last changed at Unknown


History: (Describe how the problem first appeared.)
- What were you doing when it happened? Buying the truck from the poor broke bastard.

- How was the truck running fine before this problem appeared? Hasnt even been registered in a year.

- Has this problem ever happened before? Unknown

- Describe any related factors that might be part of the problem. PCM was mounted to the IP, I moved it to a intake mouned cooler from SS Diesel (yeah yeah price was right I know its not optimal)

- Have you checked for DTC (Diagnostic Trouble Codes)? (Y.N) Y as stated above. And? 18


Diagnostics:

1] Starting:
1a] Does the engine start? Yes
1b] Does the engine crank over?Yes
1c] Are your batteries fully charged? Yes
1d] Have you removed, cleaned, and tightened all battery connections? Yes
1e] Does your Wait to Start light come on for a time? How long? Isnt that the GP light?
1f] Does your glow plug light come on? Yes For how long? 5 or 6 seconds.
1g] Do you see smoke from the exhaust while cranking? What color? None
1h] Does the Service Engine Light Glow during Start/bulb check? Yes

2] Fuel Issues (if not running):
2a] Can you hear your lift pump working? Yes
2b] Do you get a steady flow of fuel from the water drain (T-handle) ? Yes
2c] Loosen the inlet line from the IP – is fuel coming out (Lift Pump on)? Yes
2d] Loosen an injector line and crank the engine - does fuel come out? Yes
2e] Do you hear a vacuum (hiss) when you remove the fuel cap? No

3] PMD / IP Issues
3a] Location of PMD (on pump, on intake, remote mounted) Intake
3b] Condition of Extension harness (if used) Vendor or Homemade? None
3c] Condition of grounds / ground wires to IP / PMD. Check Harness. Good
3d] PMD Make: Standyne
3e] PMD Age: Unknown

4] Stalling Issues
4a] Do you experience stalling only when hot? No
4b] Does it stall under particular circumstances? (ie hit bump, or on accel) It was sitting in the driveway idling last time it stalled
4c] Does pouring cool water over the IP seem to help with restarting? No need, starts right up.
4d] Is stalling momentary (engine recovers)? No, sounds like someone reached over and shut off the truck.
4e] Does SES light come on when engine hiccups? Yes
4f] Does cruise control quit working when engine hiccups? Unknown
4g] Does re-starting seem to reset engine, restoring cruise and power? If you key off then start yes. If you just crank without cycling to Off it goes limp mode.
4h] Changes to dash lights or instruments during stalling events? SES light

5] Running Issues
5a] On cold start, does upper rad hose get hard before engine warms up? No
5b] Any bubbles or oil film in coolant overflow tank? No
5c] Any white slime on oil surfaces (dipstick, CDR, oil Fill cap)? No
5d] Excessive white smoke from exhaust on cold start? No
5e] Excessive black smoke from exhaust under hard acceleration? No

6] Performance Issues
6a] Do you have gauges (boost, EGT) ? Just my laptop and fuel pressure gauges.
6b] Maximum boost under load? not driveable
6c] Have you added a performance PCM (reflash) or Chip? no
6d] Have you changed exhaust / downpipe / crossover? Downpipe
6e] Wastegate – mechanical or vacuum (OEM)? OEM

7] Temperature-related Issues:
7a] Single or dual thermostats? Single
7b] Have you replaced them lately? Manufacturer of replacements? New, stealer
7c] Have you pulled and cleaned Radiator and coolers lately? Yep
7d] Have you replaced the fan clutch? Manufacturer of replacement? Nope
7e] (winter) Have you tested your antifreeze? Good to what temp? 0 F
7f] (winter) Are you using a winter grille cover? Nope

List and describe any other factors which are not addressed in this checklist. We can’t see, hear, smell, or touch your truck, so the more descriptive information you can give, the more likely it is that somebody can assist you.

 

[buddy]

Edit.... DTC18 is an Optical Sensor (OS) code. The PCM thinks the OS in the Injection Pump (IP) is not correct compared to the Crank Position Sensor (CPS) .

That doesnt necessarily mean its the problem, but first off try unplugging the CPS, it has a pigtail up from drivers side timing cover to around the thermostat. Start it and check your timing again. Your timing was way off. It should not be a desired of 4 degrees, and should not have 25 degrees ever on the measured. Be careful that you are reading desired and measured injection timing and not the "actual injection pump timing". The "actual injection pump timing" is set at idle by IP position and TDCO value, and referenced against Crankshaft degrees, compared to the desired and measured injection timing which is referenced by stepper motor position and in camshaft degrees.

If you have an actual injection pump timing of 25 degrees that must mean the TDCO value is like +1, when it should be a negative number. What is the TDCO value? When the CPS or OS is bad, or installed wrong you cant trust any of those numbers though.

It could be the CPS is installed backward, or it could just be youre getting air in the fuel lines. Check lift pump operation real good, what is the pressure at the drain at idle? Look for rusted lines on top of the fuel tank. There should be some vacuum when you pull fuel cap off, after using several gallons of fuel driving, otherwise must be a hole somewhere. Is fuel filter clocked correctly and seated right? Air in the fuel wreaks havoc on the OS and will throw all kinds of timing and fueling codes.

You should not have a 5068 IP in a blazer, but maybe we have been through this before. Open up the glove box and pull out PCM to check the code on the EPROM within it.

When done with that, compare results to running it with CPS plugged in and the OS on top of the IP unplugged, which should produce combinations of DTC 17,18 and 19

 

[94blazer]

Well, DTC18 is a crank position sensor (CPS) code. The PCM thinks the CPS is not correct compared to the Optical Sensor (OS) in the Injection Pump (IP).

Ok, I was having trouble finding what code 18 was, as '18' is to short and is excluded from searches.

That doesnt necessarily mean its the problem, but first off try unplugging the CPS, it has a pigtail up from drivers side timing cover to around the thermostat. Start it and check your timing again. Your timing was way off. It should not be a desired of 4 degrees, and should not have 25 degrees ever on the measured. Be careful that you are reading desired and measured injection timing and not the "actual injection pump timing". The "actual injection pump timing" is set at idle by IP position and TDCO value, and referenced against Crankshaft degrees, compared to the desired and measured injection timing which is referenced by stepper motor position and in camshaft degrees.

I believe I was reading "actual injection pump timing". Will follow and report.

If you have an actual injection pump timing of 25 degrees that must mean the TDCO value is like +1, when it should be a negative number. What is the TDCO value? When the CPS or OS is bad, or installed wrong you cant trust any of those numbers though.

GMTDScan reports TDCO as -1.41

It could be the CPS is installed backward, or it could just be youre getting air in the fuel lines. Check lift pump operation real good, what is the pressure at the drain at idle? Look for rusted lines on top of the fuel tank. There should be some vacuum when you pull fuel cap off, after using several gallons of fuel driving, otherwise must be a hole somewhere. Is fuel filter clocked correctly and seated right? Air in the fuel wreaks havoc on the OS and will throw all kinds of timing and fueling codes.

Showing 4.5 PSI at idle, my gauge is between the IP and the Filter, not at drain. I believe the filter is installed correctly, can manually jumper the lift pump into operation and don't get fuel seepage. I haven't driven it anywhere yet, so I can not report on tank vacuum. Hard to drive when it stalls every 3 or 4 minutes. Will have to check on the lines between the tank and lift pump.

You should not have a 5068 IP in a blazer, but maybe we have been through this before. Open up the glove box and pull out PCM to check the code on the EPROM within it.

Yep, that was the PO, its definitely a 5068 pump, and has 5068 painted on the Eprom clear as day.

When done with that, compare results to running it with CPS plugged in and the OS on top of the IP unplugged, which should produce a DTC 17,19 and 42.

Will do. Thanks for the direction Buddy.

 

[buddy]

Get the actual code on the EPROM, a 4 letter code. And in the dashboard view of GMTDScan at the top left see what it reports as the PCM cal ID:

Post those so I can tell you if its correct. I would not trust something painted on the EPROM

 

[ak diesel driver]

Showing 4.5 PSI at idle, my gauge is between the IP and the Filter, not at drain. I believe the filter is installed correctly, can manually jumper the lift pump into operation and don't get fuel seepage. I haven't driven it anywhere yet, so I can not report on tank vacuum. Hard to drive when it stalls every 3 or 4 minutes. Will have to check on the lines between the tank and lift pump.




Just because you don't see any seepage doesn't mean your not getting air in fuel. You could have a pinhole pre lift pump and it will suck air without leaking. Put a piece of clear tubing on the return line coming out of the IP. Any air in system will show up there.

 

[94blazer]

Get the actual code on the EPROM, a 4 letter code. And in the dashboard view of GMTDScan at the top left see what it reports as the PCM cal ID:

Post those so I can tell you if its correct. I would not trust something painted on the EPROM

Eprom reads : 4244
BMSD
0152

GMTDScan shows PCM Cal ID : 145


With the crank sensor unplugged I am showing desired timing 0, measured timing 6.1

With crank sensor plugged in I am showing desired 4.5, measured bounces between 4.1 and 5.1

Installed a clear vinyl tube on IP return, no sign of air in the line. Although it has not died yet either.

 

[94blazer]

with the optic sensor unplugged I am getting codes 17 18 and 35. Showing desired timing of 14 and measured of 4.5

with CPS unplugged was only showing code 19.


when I shut down I do get a 1/8" or so air bubble in the injection pump return line, dont see any with it running.


Update- got it to die, no air in return line, would crank start and die within seconds. unplugged the CPS and now its running good. going to let it sit and idle 10 mins or so.

I am thinking crank sensor yes?

 

[ak diesel driver]

buuble in return line after shut down is normal. sure sounds like cps IIRC there not reall expensive can be a real pain to change. just luck of the draw some come right out others come out in pieces

 

[94blazer]

So after idling for 20 mins and no stalling with cps unplugged, I am guessing its a safe bet its bad. Will see if I can chase one down. NAPA here told me its listed as obsolete part and they cant get me one, guess I need to check with the stealer.

 

[buddy]

Oh, sorry, 19 is the CPS code, 17 and 18 are the OS timing reference codes.

You need to get the desired and actual timing to be the same. With CPS unplugged what is the timing showing.

If your measured timing never comes off 4.5 degrees with increasing rpm then the stepper isnt working. And could be as simple as its not latched. The stepper is external on the IP and it hooks. 4.5 is high for base timing. If you run the timeset or TDCO what does it go down to when the desired is 0?

 

[ak diesel driver]

try rockauto

 

[94blazer]

Oh, sorry, 19 is the CPS code, 17 and 18 are the OS timing reference codes.

You need to get the desired and actual timing to be the same. With CPS unplugged what is the timing showing.

With the crank sensor unplugged I am showing desired timing 0, measured timing 6.1

If your measured timing never comes off 4.5 degrees with increasing rpm then the stepper isnt working. And could be as simple as its not latched. The stepper is external on the IP and it hooks. 4.5 is high for base timing. If you run the timeset or TDCO what does it go down to when the desired is 0?

Let me go plug in and fire it up see what she says.

I sure wish my internet worked clear out in the driveway where its parked... ):h

 

[94blazer]

When running timeset, desired goes to 0, measured drops to 2.8

On a side note, now it wont run more than 2 or 3 seconds at a time with the crank sensor plugged in. Measured timing changes as I increase RPM with crank position sender unplugged.

With optical unplugged it runs great, but measured timing sits at 2.2 regardless of engine speed.

 

[buddy]

It sounds like we can't really believe any of the timing sources. In this situation I typically think of air in the fuel system. Or maybe the person that installed that 5068 IP, which a Blazer should not have, screwed with the OS, like the "optic bump".

What is the idle fuel rate and RPM?

To summarize...It ran with all things hooked up, but occasionally stalled and would show the DTC 18 OS code. With CPS unplugged it wont run long. With OS unplugged it runs great.

The OS is the thing that has to see through the fuel, and if there is air it will manipulate the timing reading, and throw codes and stall the truck.

How about leaving it all hooked up and getting a snapshot at idle and posting it up here?

 

[ak diesel driver]

he said it was the other way around rand good with the cps unplugged

 

[buddy]

Eprom reads : 4244
BMSD
0152

GMTDScan shows PCM Cal ID : 145


With the crank sensor unplugged I am showing desired timing 0, measured timing 6.1

With crank sensor plugged in I am showing desired 4.5, measured bounces between 4.1 and 5.1

Installed a clear vinyl tube on IP return, no sign of air in the line. Although it has not died yet either.

I missed this post, BMSD is indeed a 5068 IP EPROM and has the correct cal ID too. Attached is your timing curve, or similar from another 5068 chip that does indeed have a desired 4.5 degrees idle timing. That is way low for turbo trucks though, probably slow off the line and slow spool up.

So it seems as though the CPS is working just fine. And the OS is finicky, although easily caused by air in the fuel, or if you recently dumped a gallon of used motor oil in or some harsh fuel system cleaner or an odd solid lubricant additive. Anything that can darken the fuel, make it less clear, or in some way increase its opacity you will have issues.

 

[94blazer]

Its about 10 gallons of year old #2 diesel with a can of seafoam in it.
I Have a clear vinyl tube on the IP return line, and I dont see any bubbles. Fuel looks a little yellow. Not dark or opaque.

Removing the filter on the optical harness did nothing. It runs with either the Optical OR CPS, but not both.

With crank sensor unplugged :
Engine coolant temp: 197.5 F°

Engine speed: 731 RPM

Fuel temperature: 109.7 F°

Intake air temp: 106.1 F°

Actual injection pump timing: 3.7 Deg °

Cam reference missed: 0 Counts
Crank reference missed: 8 Counts
Fuel calibration: 145 Counts
Fuel rate: 11.25 mm³
Fuel rate - Cruise: 0 mm³
Fuel rate - Idle: 11.56 mm³
Fuel rate - Maximum transient: 40.31 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.96 ms
Injection timing - Measured: 6.1 Deg °
Injection timing - Desired: 0 Deg °
TDC offset: -1.41 Deg °



I dont have a snap of it running with both plugged in. It appeared to have a fuel rate of 15.0 mm³, if it still displays correctly once the truck stalls out.

 

[94blazer]

Heres a snap of current run, everything plugged in.

Snapshot created 6/7/2010 7:40:11 PM
__________________________________________________________________
ENGINE SENSORS
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Engine run time: 00:37:28
Boost pressure (MAP): 13.61 PSI
Desired EGR: 15.23 PSI
Desired idle: 600 RPM
EGR pressure: 13.78 PSI
EGR duty cycle: 0 %
Engine coolant temp: 204.4 F°
Engine speed: 581 RPM
Glow plug relay feedback: 0.1 Volts
Glow plug voltage: 0.2 Volts
Ignition voltage: 13.1 Volts
Wastegate duty cycle: 81.6 %

__________________________________________________________________
INFORMATION SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
PCM Calibration ID: 145
Current DTCs: 0
Accel. ped. pos. 1: 0.67 Volts
Accel. ped. pos. 2: 4.35 Volts
Accel. ped. pos. 3: 4.04 Volts
Barometric pressure (BARO): 12.86 PSI
Battery voltage: 13.1 Volts
Fuel temperature: 127.7 F°
Intake air temp: 114.1 F°
Throttle position: 0 %
Turbo boost (Calculated): 0.75 PSI
Voltage reference sensor: 1.3 Volts

__________________________________________________________________
INJECTION PUMP SENSORS
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Actual injection pump timing: 26.22 Deg °
Cam reference missed: 0 Counts
Crank reference missed: 0 Counts
Fuel calibration: 145 Counts
Fuel rate: 8.12 mm³
Fuel rate - Cruise: 0 mm³
Fuel rate - Idle: 8.12 mm³
Fuel rate - Maximum transient: 35 mm³
Fuel rate - Throttle requested: 0 mm³
Injection pulse width: 1.94 ms
Injection timing - Measured: 4.5 Deg °
Injection timing - Desired: 4.5 Deg °
TDC offset: -1.41 Deg °



Truck ran fine for 45 mins, only thing I changed, was I got frustrated with the truck, yanked the steering column out, and pulled the dash to replace it.
Put the column back in, and ran it with the dash plastic out today, and couldn't get it to die.