I have a 1998 chev half ton 4wd with a 6.5 turbo in it. It has been a great truck but the other day it started to smoking when accelerating, I noticed even going up hills it never shifted down and now it does, i changed out the air filter,fuel filter and it was time for a oil change so that was done. Took it on the road and it still smokes. I looked in the air intake where the mass air flow sensor is and it looked a little dirty, does any one know how to clean out the sensor?

To my understanding, poor power and black smoke on acceleration are typical signs of low boost pressure. The IP is putting more fuel in the cylinder than there is oxygen to burn it, so it comes out black since it is unburned.

I suggest you check your vacuum system, since the vacuum system controls your turbo. At idle, check for 15" Hg at the wastegate actuator, and check for 25+" Hg at the pump itself. If you have low pressure at the pump, it is likely the pump. If you have pressure at the pump but not the actuator, then look at the wastegate solenoid, especially the connections. Although the signal is pulsed, it should still look like 12v to a Multimeter. If you have an electrical signal and the pump shows vacuum, then you have a bad solenoid. Replace it.

I did this just the other day, and it cured my problem.

Sincerely,

Rob :)

'98, Light Duty with EGR and MAF sensor......eeeww.

Vacuum system is a good place to start checking, check wastegate to see if its getting pulled closed at idle, just hope its not an EGR problem.

Do newer S engines replace the firewall mounted baro with the MAF or do they still have it?

I have a 94 6.5 the same thing happen to me. I had a vac. cap that come off. If you follow the big vac. hose that comes from the air pump you will find a cap see if it is craked or missing.

to me it sounds very much like an egr malfunction... take a BB or #6 panhead screw and plug the vacuum line to the egr valve and disable it... see if that cures your drivability issues... i had the same problems with my 6.5td tahoe... i "fixed" it with a blanking gasket under the egr and removed the SES lamp from the dash... i needed to do that to pass emissions testing, and never got around to fixing it properly [F intake and ecm]

Thanks for all of the ideas, this web site is realy cool

Well i looked for a cap for the air pump but was unable to locate it, so i went and wired the waste gate for the turbo closed ( i lifted the arm for the waste gate up) then i road tested the truck, the power is back and the black smoke is very minor, i was wondering what is the side effect of keeping the waste gate wired closed?, i am guessing that the problem is in the valve that controls the waste gate for the turbo. I found no cracked lines in the vaccum system

That's a good trick for determining if your turbo is still working, but you shouldn't leave it like that!

As I understand it, the wastegate allows the use of a smaller turbocharger to reduce lag while preventing it from spinning too quickly at high engine speeds. The wastegate is a valve that allows the exhaust to bypass the turbine blades. The wastegate senses the boost pressure. If the pressure gets too high, it could be an indicator that the turbine is spinning too quickly, so the wastegate bypasses some of the exhaust around the turbine blades, allowing the blades to slow down.

By wiring the wastegate to be closed all the time, then you will increase boost past safe levels and can spin the turbo too quickly. Either one is detrimental to the operation of your car - you could kill it.

Sincerely,

Rob :)

i was wondering what is the side effect of keeping the waste gate wired closed?,

side effect will be an out of pocket expense of $4,000-$5,000 for a new motor.....:eek: but pretty good power until that happens:D ..... you can go to a manual boost controller, but you absolutely MUST have boost and pyro gauges before you start monkeying around with boost pressure....it will save your engine and your wallet....good luck with it!:grd:

Do newer S engines replace the firewall mounted baro with the MAF or do they still have it?
They have a BARO, MAP and MAF sensors....and they can be a PITA to diagnose.
to me it sounds very much like an egr malfunction... take a BB or #6 panhead screw and plug the vacuum line to the egr valve and disable it... see if that cures your drivability issues... i had the same problems with my 6.5td tahoe... i "fixed" it with a blanking gasket under the egr and removed the SES lamp from the dash... i needed to do that to pass emissions testing, and never got around to fixing it properly [F intake and ecm]
Disabling the EGR to narrow down possibilities for diagnosis is a good idea, but because the later model 'S' engines have the MAF sensor, you can't leave the system disabled or you will get MAF/EGR codes.
The MAF sensor monitors the change in air volume with the EGR operation.
If its disabled, there will be no change and you will trip some codes.

One other problem that you could have is that your wastegate solenoid could be bad. The wastegate solenoid is located on the top of the motor, driver's side. You will see two vacuum lines running to it. It may be easier to find if you remove the turbo power cover.

On an S engine it's the foremost solenoid. The vacuum is split between it and the middle one (EGR vent) it then goes from the middle one to the rearmost solenoid (EGR) where the vacuum is metered to the EGR and baro. If the baro doesn't see ~20" Hg vac the system won't make boost right.

I just had something similar happen to me today. I came off from a stop sign and the truck wouldn't accellerate as normal, it felt like it was limited to under 2k RPM and wouldn't change gears either.

I looked in my passenger side mirror and noticed a huge cloud of smoke pouring out behind me.

I barely made it home. When I got onto the driveway I gave a few revs in neutral and it seems fine, but when put into gear and accellerate it just lets out black smoke.

I'm wondering if it's my glow plugs, I've had the truck for 4 years now and haven't changed them yet. It's a 98 with 140k km on it.

Before I go checking EGR and vaccum lines, does this sound like something the glow plugs would cause?

...Its definitely nothing to do with your glowplugs, when they go bad you get hard/rough start cold.

So now we have another '98 LD with EGR and MAF sensor.

I have some advice for you guys, I just finished fixing a customers '98 Z71 LD 6.5 today. We sent them a new injection pump and when they put it back together it was pouring out black smoke, so of course they called and said that the pump was bad.

Not the case, They brought us the truck and I found a dirty air and fuel filters, missing EGR gasket, non functioning BARO sensor, broken intake manifold, and the TDC Offset was wrong.

When I replaced the broken manifold, I decided to try something. Now normally, if it were a pre-'97 model without the MAF sensor, I would install the HD manifold gaskets with the EGR plates still in to block the EGR passages and the problem would be permantently solved. But in '98-up you can't do that because the MAF sensor will pick up on it and trip an EGR code. So, I installed one gasket with the plate and one without, to limit the amount of EGR flow and hopefully not upset the ECM. Seems to have worked out perfectly, drives just like HD now, puff of black smoke when you romp on it and it dissappears almost immediately.

So just a though for you guys with the MAF sensor blues. Its also a good idea while you got everything off to clean the upper and lower intakes. And, take a cutoff wheel or grinder to remove the extra casting on the upper intake, makes it a lot easier to clean the gunk outta there, and frees up a LOT of intake restriction.

and don't forget that often forgotten little EGR gasket

Never do ;)

I was really hoping I wouldn't have to do much mechanical work on this truck. I can take apart a small block and know every piece, but looking under the hood of my truck gets me a little intimidated.

Texas Diesel Guy,

Where do you work? I have connections when it comes to auto mechanics, but nobody will touch by truck, nor will I let them. If I can't seem to figure out the problem, would you be able to have a go at it? I use this truck to run my landscaping business, so I'm kinda stuck right now because it just started acting up late this afternoon.

I don't know if it makes a difference or not, but after letting it sit for a few hours and driving it again it seems to be running ok, maybe a little black smoke but at least it seems to have full power again.

Pulled the vaccum hose off the EGR and the truck runs excellent, connect it and it smokes/less power.

I've gone through every post I could find but I'm stilled confused.

What's wrong with running the truck without the EGR vaccum hose connected? I understand it will set off codes, but will this cause any other immediate problems?

I'm just concerned because I have a long road trip this coming Thursday so if I can get away with it until next week, that would make me feel better.

it will set the engine light but you should be able to drive it like that if it doesn't bother you.

Z71, I'd be happy to help, where are you right now?

I just went ahead and made a metal block plate for the EGR. So far no codes.

Texas Diesel Guy,

I'm in Toronto. I'm a little concerned that it's going to happen again at the least expected time (ie. 400km from home!).

I'm wondering if I should replace the solenoids just to be safe, or does it even matter anymore since I blocked the EGR?

Now that I think about it, I've been on a few road trips this summer and after a couple hours of driving, going up a steep grade with the pedal to the floor it wouldn't downshift and felt sluggish, but eventually it would go back to normal.

But disconnecting the EGR vaccum hose made it 100% better and as soon as I plugged it back in it ran like crap, so I'm going to assume it's ok for now. (fingers crossed!)

But I'd rather be safe than sorry, should I replace the wastegate solenoid just in case is wasn't totally the EGR?

Bring it to Oakville Next week sometime.

1015 Industry St. Exit QEW at Trafalgar, turn left(south) on Trafalgar, left again on South Service, Right on Chartwell, Left on Industry St, first building on the left.

Bring it to Oakville Next week sometime.

1015 Industry St. Exit QEW at Trafalgar, turn left(south) on Trafalgar, left again on South Service, Right on Chartwell, Left on Industry St, first building on the left.

Thanks!

Is Monday ok? Who do I ask for?

Thanks!

Is Monday ok? Who do I ask for?

Just Ask for TDG, The Diesel Guy, :lol:

Ask for Travis, but even if you don't, Rudy will send me anyway ;)

I disconnected the egr valve and plugged it off, took the truck for a test drive no difference, i bought a manual but it mostly relates to older model engines, i am not sure where to go from here, i dont want to take to the local chev garage, i dont trust them with my nabours weed eater, any tips or ideas would be most welcome

My 1997 6.5 did the same thing. I replaced the vacuum pump and bingo!! No more black smoke and instantly more power. The check engine light even went off by itself!!

Wow...Today...the same thing for me...I have a 2000 6.5 "f" with 68,000 miles on it. I would sit at a light,,,hit the peddle and choke the guy next to me. I noticed when that happened that my boost gauge was at zero. Then all of a sudden it would kick in the turbo and the smoke cleared. Then when it shifted into 2nd, it did the same thing with 0 on the gauge and then all of a sudden the turbo would kick in again and smoke was gone...I noticed then as I rode down the freeway that my turbo came on and off periodically...I'm stumped.

WG solenoid for you 2000 I'd bet

Yes ...I'll try that.Thanks