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Low power, black smoke

P

pat dolan

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Martensville SK
I imagine every newbie arrives here with a problem to post...so I won't dissappoint.

'97 K1500, 200k kms, had an easy life as vet truck, parked until last year. The FSD was giving some grief last year, & what I thought was one symptom was losing boost. Had code for boost solenoid, so replaced that, as well as relocating a new FSD with SS diesel harness & heat sink. It runs better now - EXCEPT the one symptom did not go away.

If I use any more than a middling bit of fuel feed, it smokes (black only). Threw AE on it (I'm a newbie with that too) & went for a drive. Anything over 55 mm3 of fuel delivery & the smoke starts. I am getting 21psi absolute MP (which I think is right), & boost control shows over 95% duty cycle at full pedal position.

Getting only 15 inches of vac at the pump idling, but the 7 psi of boost SHOULD be enough to burn this much fuel...or is it.

Any suggestions most appreciated.
 
F or S engine? it might be a sticking egr. also should have closer to 20-22" vac so you might have some leaking lines
 
It's an "S". I can see it being low on vac, but how the heck am I getting 7 lbs. of boost? Also, please correct me if I am wrong, but isn't that all the MP I should get from this engine?

It is behaving as not enough air (and, unless the injectors suddenly grew a bigger set of holes, or there is a common failure that delivers a lot more from the pump than showing on enhanced diagnostics) it IS. Just need to understand where these numbers are coming from and what is right/tolerable/wrong for values.

Also: how would a sticking EGR give me too much fuel/too little air??
 
If EGR were open then too much exhaust gas would go back into the engine and not enough actual air.

21psi manifold pressure MP? So that would be about 7psi of boost should be enough, if you are actually holding that, or is it just popping to that? Then you might have a bad or wrong boost sensor just saying you have that much.

A failing IP could dump too much fuel, but if you could actually verify the boost with a mechanical gauge that would be best.

Also, did this just start happening or been a common thing, was IP ever changed before, timing ever set correctly?
 
EGR is `working` electronically, but no idea if it is mechanically. Any suggestions to check. I will eventually delete, but want to diagnose & repair first. I get EGR duty cycle of 0 with power, but is the EGR valve closed with vacuum or spring pressure.

MP from AE is right, but will have to mechanically verify. It is not peaking, but holding steady at higher power requests. Is there a handy port to tap.

IIRC, IP has not been disturbed, & would not expect timing to be spot on, but this has been an intermittent problem until last month.
 
If you pull the top of the intake off and see the soot build up...

Check the EGR gasket as this can fail or go missing and cause EGR bypass choking the engine.

EGR valves tend to work fine till they stick. The stick because the back pressure valve in them gets sooted up. Backpressure from the exhaust changes the amount the EGR valves opens. This valve failing will flop the EGR valve wide open at any vac signal instead of modulating EGR from back pressure.

The EGR is one part that it doesn't hurt to throw a part at - because they act up a long time before total failure.

To test it simply plug the vac line to the EGR so it should stay closed. Then do a quick test. After that you can decide to eliminate it or replace it. You can also put full vacuum to the EGR valve, bypass the solenoid. If the engine stalls or you watch the valve slam full open then you know the backpressure valve is stuck.

EGR will not open without a vacuum. The computer gives it full vacuum and lets the exhaust back pressure determine how much it opens.

Note:
Some EGR valves work without a back pressure valve in the design. I am 50% sure this one has it.
 
The EGR is def suspect ,but a dirty clogged airfilter produces black smoke as well.
What about the soot trap,is it still on there and fauled up maybe?
 
WarWagon: Thanks for the EGR description. Is there a drawing or other text floating around for reference. Which EGR gasket are you referring to for failure or missing status. (keyboard defaluted to French, can't find question mark!) I don't think it is a problem with the backpressure operatig the valve, as it is only a problem with zero duty cycle condition. If it IS an EGR issue, it would have to be constant leak, but the problem came, went for quite a while (cold weather) and returned along with spring floods - and I can't see a leaking gasket "fixing iteself". What is best way to eliminate EGR on this engine (q-mark).

Bison: clogged air filter would not allow full boost (keep in mind I have yet to mechanically confirm MAP, but the electronic values from AE look right). Air cleaner is fairly new.

Soot trap (qm). now we are in strange territory for me. What is where is the soot trap (qm).
 
exhaust under the passenger seat aka catalytic convertor. partially clogged air filter would still allow boost but still be starving air,some rigs full boost is 10-12 psi
 
Put a solid 1/16 piece of plate under the EGR,problem solved forever,it don't cause codes.
Check the round gasket under the intake top,mebby it blew.
 
Have to go off on a job for a week or so, & won`t be able to work o Chevie. At least I can check in at night to continue my slow but I hope steady education.

Thanks for the direction so far, but I would like to take a side trip through EGR & ECU memory lane if I might: so far, everything I read says MAF starts with `98 model, but I have a `07 vehicle, S engine code, and it seems to have a MAF located at the air cleaner end of the duct to the turbo. It also has what appears to be a helmholz resonator that comes out near the tubro on that same rubber tube. Does this make any sense. I have also read that the MAF version does not take well to EGR delete.
 
If you can post a picture of it, that would be of help.
Plus, if you can run your VIN # to ascertain when the truck was built, it might help determine if you got one of those mid year builds where GM made some changes outside the norm for that build year. That's why I have a single T-Stat on my 96 and others, who's trucks were built later got the dual set up. Just an example and may explain the anomaly you seem to have come across. Just a thought.
 
Pavel: I will do that when I get back home, probably next weekend. BTW: It went from damn near totally gutless & super smoke back to it's approximate performance over the winter (which means visible smoke over 55mm3, but no longer a genuine, WWII destroyer size smokescreen) yesterday & set a new code (will read when am back as well. Does this ECU have adaptive learning algorithms (thinking it is unlearning what it saw during FSD failure).
 
Well, I am back (sort of, the one week job will turn into a two week one it looks like). While messages are flying back and fourth between Europe and here (time zones make it delay) I have a few hours off, so I took the Chevy for a wee ride with AE hooked up. I have some data (and some ideas), so I will tell you what I see and what I think I might be seeing, and request your comments.

This data (very rough) warming idle light accel heavy accel
Inj pump timing about 9 (down as warm) about 5.5 peaks at 20.4 degrees what is optimum?
Inj solenoid close 1.75ms 1.75 ms 1.55 ms same
fuel quantity <9.0 high 20s 61 - 62 mm3 smokes at 50 mm3 and up
wategate solenoid 80% high 70s 93 - 100%
vacuum at w/g actuator 3" 5" 11" - increases to 14" over time @WOT
boost (electronic) 14 psia 16-17 psia peaks at 19 psia today (had 20 and a bit last time)
EGR posit desired 69% 33% 82% (HUH???)
EGR duty cucle 0% 100% 0%
EGR feedback 4.59V 4.51V 4.51V (I think)

Can't pull anything apart to look into EGR (need truck constantly right now)...but I think is possibly a problem
I get really quick boost to 17psia or so, and seldom any smoke (except on tip in) on light accelwhere it runs well
..BUT goes to hell in a handbasket with any fuel delivery over 50mm3. Boost stops at 19 today, and it is clearly NOT enough to burn that fuel.
Add Cat to possible problem there.

Got a trouble code for EGR function, so suspect something there as above.
 
The boost you are looking at is likely the total pressure, so subtract about 14.5psi for atmospheric and you would have about 5psi, which is not much and may be part of the problem. Together with the low timing at idle will produce a lot of smoke if you get onto it. EGR vehicles have this very low idle advance, I guess it has something to do with port timing and pulses and what not. It makes them less responsive too, so that kind of sucks and a reflash of the PCM without EGR would make truck come alive.

Also, you should try timing it, by running the TDCO procedure. What does it think the TDCO value is now? If you havent run the TDCO learn it may not be right, so just need to run the TDCO learn to reset it.

The EGR is normally closed and is opened by vacuum, so just unplug the vacuum to it and plug the line to start with. It will cause a code, but thats fine, it doesnt hurt performance one bit, just disables the EGR system. If vacuum is always to it then you would have an issue and it would go away. Or the gasket between the lower and upper may be gone. Its not difficult or time consuming to pull the upper intake plenum. Get a frost plug to fill the lower EGR tower, 1-7/8" plug should do it. And then have a new upper plenum gasket and just keep the EGR valve mounted on top, or make the block off plate to finish it off.
 
buddy said:
The boost you are looking at is likely the total pressure, so subtract about 14.5psi for atmospheric and you would have about 5psi, which is not much and may be part of the problem.
Click to expand...
Thus why it is expressed as psia (absolute). But, yes, it looks as if the first few psi comes in quickly, but after that, the MAP won't follow fuel delivery (i.e. boost tops out too early & too low).
Together with the low timing at idle will produce a lot of smoke if you get onto it. EGR vehicles have this very low idle advance, I guess it has something to do with port timing and pulses and what not. It makes them less responsive too, so that kind of sucks and a reflash of the PCM without EGR would make truck come alive.

Also, you should try timing it, by running the TDCO procedure. What does it think the TDCO value is now? If you havent run the TDCO learn it may not be right, so just need to run the TDCO learn to reset it.
Click to expand...
OK, that sent me scurrying over to the sticky in tech ref library (fantastic, BTW). I will look for TDCO value on AE menu when I drive to town today.

The EGR is normally closed and is opened by vacuum, so just unplug the vacuum to it and plug the line to start with. It will cause a code, but thats fine, it doesnt hurt performance one bit, just disables the EGR system. If vacuum is always to it then you would have an issue and it would go away. Or the gasket between the lower and upper may be gone. Its not difficult or time consuming to pull the upper intake plenum. Get a frost plug to fill the lower EGR tower, 1-7/8" plug should do it. And then have a new upper plenum gasket and just keep the EGR valve mounted on top, or make the block off plate to finish it off.
Click to expand...
I will kill EGR, but some farm, some industrial, some tax & some family obligations will shut me down again for a while. Was hoping for definitive diagnosis before ripping anything off.
 
Because you expressed the pressure that way and not mentioned having a low peak boost, I was assuring that you realized what that value represented, because not everyone would necessarily catch that it was absolute pressure, and how to extract actual boost pressure. You should get up to 9psi of boost easy enough. What is the EGR DTC that you had? Was it vacuum loss and your turbo still runs on vacuum actuator?

The TDCO value will be a constant after setting it. So you can look at it with the Ignition on, but then find the TDCO learn procedure in AE, should be a selection for it somewhere to run and ensure it is set correctly. Otherwise you have the Key-On-Key-Off (KOKO) method to intiate the relearn and verify the value on the scanner.

Good luck, hopefully its an easy resolution
 
buddy said:
Because you expressed the pressure that way and not mentioned having a low peak boost, I was assuring that you realized what that value represented, because not everyone would necessarily catch that it was absolute pressure, and how to extract actual boost pressure. You should get up to 9psi of boost easy enough. What is the EGR DTC that you had? Was it vacuum loss and your turbo still runs on vacuum actuator?
Click to expand...
I have to warn you: I am the techonazi to a bunch of young engineers & engineering technologists, so I tend to be correcting that kind of stuff or getting all preachy or testy out of habit. I was getting 7 lbs. last week, but this week I can not seem to pull over 5. The first 3 or 4 comes up as normal, but it runs into a brick wall at 5. The wastegate duty cycle keeps on going up, as does vacuum measured at the actuator, but the boost just stops. Either getting drowned by EGR, or bunged up from plugging converter - most likely both.

The TDCO value will be a constant after setting it. So you can look at it with the Ignition on, but then find the TDCO learn procedure in AE, should be a selection for it somewhere to run and ensure it is set correctly. Otherwise you have the Key-On-Key-Off (KOKO) method to intiate the relearn and verify the value on the scanner.

Good luck, hopefully its an easy resolution
Click to expand...
TDCO value is -0.44. I am getting something like `EGR function not normal` or such DTC (dark, couldn`t write a note). I can imagine a plugging kitty blowing the EGR open with high EMP (can`t measure on this engine). ALL resolution is easy....once you understand with what you are dealing.
 
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