6.5 black smoke

[blkhead48]

I have a 97 suburban with a 6.5 turbo diesel. Recently the engine started surging while driving and upon acceleration alot of black smoke. I checked for air restrictions, and checked boost, I had no boost, checked turbo and it had no play in bearings and fins looked like new. I then checked vacum, No vacum. I replaced the vacum pump and the surging went away and the smoke was cut in half. It still however while accelerating constantly black smokes. I have plenty of power, Idles good, starts good, No codes logged, and once you reach desired speed and let off accelerator, no smoke. Only when you accelerate constantly does it black smoke. Could this be a overfueling problem? I thought blueish gray smoke was fuel, and black smoke air restriction. HELP ! Nobody seems to know the answer at the garages I have been to. Any help would be appeciated Billy

[M.Novak]

We need to know what the vehicle actually is- 1/2 ton, or 3/4 ton and VIN letter "F" or "S". It makes a difference when troubleshooting. A VIN "S" will have in addition to the waste gate an EGR valve with two more of those solenoids in addition to the wastegate solenoid. The vacuum lines and solenoids can couse a lot of grief. Check all of the vacuum lines from the pump to the wastegate and EGR if equipped. If any of the plastic lines are cracked they need to be spliced with a rubber hose or rubber run completely to the component. Check any and all rubber vacuum lines for deterioration and replace as needed. The solenoids usually set a code and turn the SES light on when they go bad, but not always. If you need to replace any of the solenoids, they are ALL DIFFERENT, so don't let anyone tell you they are the same. That's why they have different colored dots on top-so you can tell them apart and correctly place them back on the bracket if all are removed for some reason. The center one even has a different electrical plug than the other two. You should have about 12-13" of vacuum at the wastegate cannister, unplug the hose and check with a vacuum guage and engine idling. Check these things and let us know what you find. Mike

[blkhead48]

Thanx for your help, It is an F in the vin number. I did find the hard plastic line joining the rubber hoses from a solonoid on the right hand side of engine broke. I replaced it with a rubber vacum hose, It ran from the wastegate diaphram to the solonoid. No difference in smoke. It is also starting to surge a little again. Again thanx for all your help. Billy

[M.Novak]

Some other things you might try just so you're sure the wastegate is actually working is to temporarily tee a vacuum guage into the line from the solenoid to the wastegate cannister. Get enough hose to run the guage inside the cab then go for a drive. Make sure the guage is keeping around 15" or more of vacuum at highway speeds. If it drops lower than that for more than a few seconds check the wiring to the solenoid for a bad connection or broken wires near the plug, or change the solenoid. Even if that isn't the problem, it's not a bad idea to have a spare on hand because they do fail every few years. I recommend one from GM because I don't really trust aftermarket sensors for emissions equipment. Make sure the new one has a green dot on it, or it is the wrong one. Also open the water in fuel drain valve with the engine idling to make sure the lift pump is working. The engine will die in about 30 seconds to one minute after opening the drain valve if the LP is not working. You shouls get a strong stream of fuel from the drain hose if it's good, place a catch pan under the front of the engine at the PS pump to catch the mess. Believe it or not I've seen an engine starving for fuel make black smoke, so it's worth a look. Mike

[blkhead48]

Mike, Vacum at idle is 13, I teed into the line like you said and went for a ride, Up to 45mph the vacum stayed at about 13, after that it dropped to zero and the engine started to surge, almost like the fuel was being shut off for a millisecond at a time. I also opened the bleed screw and fuel just dropped out, no steady stream, but the engine did not cut out. it sounds like it has an electric pump, I don't know if that makes a difference. I really apreciate your time, The nearest gm diesel shop is almost 80 miles from us. The local garages have no clue as they do not work on diesels often. They have scanned for codes, but could find none past or present. If you think it is that solonoid, I will order it today. Thanx again Billy

[M.Novak]

Originally Posted by blkhead48

Mike, Vacum at idle is 13, I teed into the line like you said and went for a ride, Up to 45mph the vacum stayed at about 13, after that it dropped to zero and the engine started to surge, almost like the fuel was being shut off for a millisecond at a time. I also opened the bleed screw and fuel just dropped out, no steady stream, but the engine did not cut out. it sounds like it has an electric pump, I don't know if that makes a difference. I really apreciate your time, The nearest gm diesel shop is almost 80 miles from us. The local garages have no clue as they do not work on diesels often. They have scanned for codes, but could find none past or present. If you think it is that solonoid, I will order it today. Thanx again Billy

I think I would try the solenoid, you should have vacuum all the time as that is what keeps the wastegate closed, thus boost supplied to your engine. Without a Tech 2000 or equivilent scan tool, you can't manually controll the solenoid to see if it is working or not, so the vacuum guage is all you have to diagnose with. Unfortunately the guage leaves something to be desired as to a good diagnosis. If the solenoid doesn't fix it, then you probably have a wiring problem near the plug for the solenoid. My '94 had problems with the EGR a few months ago. After me fiddling with it for a month, I took it to the dealer and they messed with it for 3 weeks before proclaiming the wiring connector "bad" at the center solenoid (which you don't have). It turned out not to be the connector or plug, but one wire to the plug was broken about 2 inches from the connector. I decided to change the connector and cutting into the original pigtail I accidentally found the broken wire. The new connector comes with about 10" of pigtail wire, so don't be afraid to cut away from the connector when repairing if you have to go this far. The LP should have a good stream of fuel squirting from the drain hose. The LP can get weak and won't supply enough fuel to the IP at speed, this will cause a miss and or a loss of power. Some trucks will run with a completely failed LP and some will not. You should have 5-7 PSI fuel pressure at idle and never less than 2 PSI at full throttle. The LP is on the frame rail under the driver's seat. Some people replace it with an aftermarket or even a different kind of pump. Yours should be powered by the LP relay (only while key is in the start position), then the OPSU sends power to the LP along with the ECM after the engine is running. The OPSU is under the fuel manager or filter on the driver's side of the intake valley. The OPSU goes bad on some engines and causes problems, but I've found that on mine I always used the more expensive AC Delco LP and have never burned up the OPSU in my truck with over 420K of service. In my opinion the aftermarket pumps ( AZ, O'R, ETC.) draw more current to operate and the OPSU can't handle that and burns up. It has one set of contacts for the oil pressure guage and another set for the LP, so the LP side burns up and the guage keeps on working. I don't think the OPSU is YOUR trouble because you get some fuel from the drain hose confirming that it is pumping, but maybe is too weak to pump enough fuel under all conditions. Just a heads up as to potential troubles down the road if a cheaper pump is used. Figure out why the vacuum goes away at speed first, then decide if the LP is too weak to fuel the engine at speed. The WG solenoid has a vent in it that could be causing the vacuum to go to zero, so it could be failing without giving a code. Mike

[blkhead48]

Man Mike, I appreciate your expertise and advice, Thank you very much for the tips and tommorrow I will try putting the solonoid on and take a fuel pressure reading, Hopefully it will do the trick. Again my deepest thanks. Billy

[M.Novak]

Originally Posted by blkhead48

Man Mike, I appreciate your expertise and advice, Thank you very much for the tips and tommorrow I will try putting the solonoid on and take a fuel pressure reading, Hopefully it will do the trick. Again my deepest thanks. Billy

Don't talk me up too much, this is only an online guessing game and I could be completely off base, maybe even out of bounds as to my guess. My truck has been mostly trouble free for it's entire 420,000 miles when compared to others, so a lot of this is new to me also. I'm only going on what has fixed it in the past when I've had problems and what I've picked up here on this site. You can do a search of similar threads and find the problems others have had and fixed with info from here. Mike