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‘94 Suburban Stalling w/ Codes

Big T

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No you aren’t. No way I ever change one unless it is proven bad. WarWagon was not exaggerating one bit. Timing covers get damaged once in a great while removing them.

Plus they can be really hard to get to depending on rig and accessory lay out. Some hummers HAVE TO remove the power steering pump.

Glad for BigT he seems to get his out no problem because he is just - No big deal- so cool.
Thanks Wil, but I was looking for answer on the mifires at high rpm, not celebratory back slaps for removing a CPS.
 

Will L.

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Haha, yeah just saying for him. I know you knew the story from your last time.

So did the cps fix it?
The optic sensor is about an hour fix and cheaper than ip, but if you don’t mind 2 more hours and more nickles, a new ip is my preferred IF it is old and issues.

What is fuel pressure when misfiring?
What was fuel volume at idle then at high rpm?
How many miles on timing chain? If over 200,000 there is a strong likelihood that is it. Leroy calls timing gear drive a “time keeper” for a reason.

Can you crack any injector lines and get different results on different cylinders at idle? If so swapping the “bad” one for location of a good one tells if it is the injector- however they all may do ok at idle and be failing high rpm as AK mentioned. Imo testing them in high mileage is pointless. Just get a new set from Leroy and be done if in doubt. New injectors vs worn usually gives about 1 mpg gain, so they pay for themselves in a while.
 

Big T

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Haha, yeah just saying for him. I know you knew the story from your last time.

So did the cps fix it?
The optic sensor is about an hour fix and cheaper than ip, but if you don’t mind 2 more hours and more nickles, a new ip is my preferred IF it is old and issues.

What is fuel pressure when misfiring?
What was fuel volume at idle then at high rpm?
How many miles on timing chain? If over 200,000 there is a strong likelihood that is it. Leroy calls timing gear drive a “time keeper” for a reason.

Can you crack any injector lines and get different results on different cylinders at idle? If so swapping the “bad” one for location of a good one tells if it is the injector- however they all may do ok at idle and be failing high rpm as AK mentioned. Imo testing them in high mileage is pointless. Just get a new set from Leroy and be done if in doubt. New injectors vs worn usually gives about 1 mpg gain, so they pay for themselves in a while.
Injectors have 47K Miles on them. Unknown miles on timing chain, but assume it’s original. Unknown miles on IP, but I assume it’s second one as they typically go like 120K miles.

What is the optic sensor fix? Do I have to crack open the top of the IP? Last time I did that on the ‘99, the optic wheel was broken and I replaced the IP. Lot more time than 2 hours.

It’s starts like normal every time, so the CPS seemed to improve that. Not my truck, so I’m not driving it and do not have a benchmark.

I’ll hook up the scanner when he gets back from Big Bear late Sunday.
 
Last edited:

WarWagon

Well it hits on 7 of 8...
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Any smoke at the high RPM misfire? Keep in mind more fuel flows at higher RPM so keep an eye on the clear return line when revving up.
 

Big T

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Started up the truck and hooked up the GMTD Scan Tech. Puff of black smoke at start up but engine ran smooth, but still has the misfires above 3200 rpm. DTC codes 17 and 18. Clear them and they come back.

GMTD Scan Tech screen was not reading on injection timing screen. I shut down each injector at 3300 rpm and it did not change the misfires. And no I don’t have the clear hose on the IP but I will install that tomorrow.
 

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Big T

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OK hard to start today. Took a bit to catch and light. Once running, checked the misfires at high rpm and I get puffs of black smoke on the misfires.
 

Big T

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Would be nice to have some answers here. Yes puffs of black smoke on the high rpm misfires.

Sounding like an IP replacement. Will the IP from the '95 work on the '94?

I go in for surgery on my right ankle Tuesday, so I'm down as far as truck work for at least 2 months.
 

Will L.

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Need the numbers from the two ips to make sure. iirc 5068 is the number that won’t swap over. It might help for a while, how many kiles on the other ip.
Mega stretched chain, dropped compression, and yes the ip all being tired it might be better to swap ip than optic.
The smoke is unburned fuel, but little puffs at high rpm could be weak compression, the valves mentioned, timing off, or could be burning engine oil.

Not being able to see what’s up on a scanner doesn’t help verify.

I am not, and I think others are not answering with options right away because everything points towards everything being worn out and we dont want to say live with it or throw a bunch of money and time at it. Kinda hoping someone else steps in with a magic idea here. Either that or Megan Kelly is e-mailing folks to keep their secrets-

Unplug the new cps to see if the optic is working? That could be why you aren’t seeing desired vs actual on the scanner. Usually hard starting is a major symptom, but it could be the cause still.
 
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If the IPs are both from Burbs not likely one is a 5068. The 94 would be the one to have it if it did. Even if it did if you still have the PCM from the 95 it should work on the 94 as long as the gear ratios are the same.
 

WarWagon

Well it hits on 7 of 8...
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Black smoke is not enough air to burn the fuel. ( White that hangs around is fire out unburned fuel, White that fades away is coolant, blue is oil and black is over fueling for the air.)

Listening to the video it may be that the IP missed firing a cylinder and the ECM dumps more and more fuel, as the engine slows down from no fuel, to speed the engine back up until the IP actually delivers fuel and you get black smoke. ECM asking for fuel, not getting fuel it asked for, engine slows even more, ECM askes for even more fuel, finally gets it and black smoke as ZOOM! happens. Also possible timing is going way out for the actual fuel delivery resulting in smoke. Timing one way or the other - I forget - gives you both white smoke and black smoke the other way. Advance takes care of white smoke cold.

With the codes still active it looks like the IP, wiring to IP, and with 290K on the chain I agree with @ak diesel driver 's guesses above. CPS and OPS don't agree could be from the chain hammering the valves and bouncing around. I am still shocked and reminded of what any slop in the valvetrain can do to valve stem tips...

DTC 17 - High Resolution Circuit Fault
DTC 18 - Pump Cam Reference Pulse Error

With the high blowby maybe swap entire engine rather than just the IP.

With the scanner I did not read where you disconnected the OPS connector to verify if it runs any different. Then swap IP. Then troubleshoot electrical. Last, I just look at all the scrap metal chains I have tossed or exchanged at 30K miles let alone the high miles ones and yeah, it may be chain elimination time.
 

Big T

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Black smoke is not enough air to burn the fuel. ( White that hangs around is fire out unburned fuel, White that fades away is coolant, blue is oil and black is over fueling for the air.)

Listening to the video it may be that the IP missed firing a cylinder and the ECM dumps more and more fuel, as the engine slows down from no fuel, to speed the engine back up until the IP actually delivers fuel and you get black smoke. ECM asking for fuel, not getting fuel it asked for, engine slows even more, ECM askes for even more fuel, finally gets it and black smoke as ZOOM! happens. Also possible timing is going way out for the actual fuel delivery resulting in smoke. Timing one way or the other - I forget - gives you both white smoke and black smoke the other way. Advance takes care of white smoke cold.

With the codes still active it looks like the IP, wiring to IP, and with 290K on the chain I agree with @ak diesel driver 's guesses above. CPS and OPS don't agree could be from the chain hammering the valves and bouncing around. I am still shocked and reminded of what any slop in the valvetrain can do to valve stem tips...

DTC 17 - High Resolution Circuit Fault
DTC 18 - Pump Cam Reference Pulse Error

With the high blowby maybe swap entire engine rather than just the IP.

With the scanner I did not read where you disconnected the OPS connector to verify if it runs any different. Then swap IP. Then troubleshoot electrical. Last, I just look at all the scrap metal chains I have tossed or exchanged at 30K miles let alone the high miles ones and yeah, it may be chain elimination time.
Thank you sir. As this is now a much bigger job, it will have to wait until spring when my foot has had time to heal. We'll do IP, timing chain, and add a Fluidamper. The engine runs well and we'll run it until it has a permanent life in the carnage thread. Then we will put the engine harvested from the '95 wreck into it.
 
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