black smoke,truck slows

[farmerherb]

Under hard acceleration pulling(6000lb)trailer first geart no problem 6-7lb boost. Shifts into second when rpms reach 2300-2400 black smoke boost drops to 0 then below 0, -5psi. Let off the pedal some boost comes back up. Checked wastegate act. vacunm good. Is the boost sensor on the firewall or mounted on the intake? This seemed to start when I installed a Hypertech chip, so I put the old one back no change. Also the original chip is blue with no GM marking or numbers is that a factory chip?

[MTTwister]

Farmerherb I love the hour/min you posted - My B-Day!
on my '96 - no EGR, the boost sensor is on the intake - a little black dealie near the front.
If you don't have a 'boost fooler' I believe the ECM will pull back fuel if it senses too high a boost level.
However, you're really dropping boost to neg #'s and Black smoke indicates too much fuel. So, No real help here :rolleyes: - 'cept the location of the Boost sensor.

If you put your rig's configuration in the Sig area of your profile, you won't be asked the question all the time - What's the year, configuration of the outfit?
GoodLuck - somebody will have some clues for ya, soon.

[markrinker]

With those kind of miles, sounds like your turbo might be shot. I'd pull the air intake (WITH ENGINE OFF!!!) to examine the turbine blades, free shaft rotation, bearing endplay.

Another idea could be restricted or plugged exhaust - i.e. catalytic converter.

How does it run unloaded?

[farmerherb]

Runs fine not towing, I don't push it as hard. I have a 98 turbo, I may put that one on it.I have the aftermarket downpipe with straight exhaust. Its been awhile but I checked the endplay on the turbo, hardly any.

[G. Gearloose]

Sounds like the rubber elbow is collapsing.

[farmerherb]

I have been watching the boost gauge and the tach today. The magic RPM is 2500. At that RPM the boost heads down adding more fuel makes it move faster down.

[markrinker]

Try removing the elbow and running a short test run - (in a relatively dust-free location).

[kowsoc]

The wastegate solenoid is known to fail on these engines and when it does it can dump the vacuum to the turbo intermittently causing loss of valuable boost. If you can hook up your vacuum gauge where you can read it during a test drive then you can check if vacuum is getting lost when the boost drops. You can also physically tie the wastgate closed with wire to test but remember that the boost will no longer be controlled by the PCM and boost will rise high.

The elbow collapsing is definitely quite possible also. Good luck, keep posting. smile.gif