Loss of Power in the heat

[cjones]

After looking on other threads, I wanted to see if anyone else had experienced this set of symptoms and had some advice as to where to proceed.

The 99 Suburban is losing power when the ambient air temperature exceeds approx 90 deg. This doesn't happen all the time just under load, like going up hills and it doesn't happen at all speeds just when I'm going say 50-60mph.

To give an example I live in Lewiston and from Lewiston to Pullman there's the Lewiston grade which is 6miles of 6-7% grade (I'm guessing). This morning, the air temp is approx 78 deg. I can drive the grade at 65mph with no problems. Using my code reader I can see that the Intake Air Temp IAT goes from 150-190 as I head up the grade. In the middle of the grade I can accelerate with a very scant amount of black smoke.....I would say this has been normal since I've owned the rig.

On the other hand, last week the air temp was 98 deg at 3:30 in the afternoon. Before I even started up the grade the throttle was very sluggish to respond and after the rig responded it billowed a large amounts of black smoke. I took the grade at about 55mph but had to slow to 45mph because of the black smoke. If I were to stay at 45mph it would drive fine but I had virtually no acceleration.

The Suburban starts without any problems, idles fine, and in the cooler temps runs as good as it ever has. I haven't noticed any missing or 'fishbiting' when I drive. I do have two codes that pop up only when driving in the the warmer temps: P0236 and P0251. The turbo code 236 comes up more often and like last night it occurred without the 251 (injection).

The air filter, vacuum pump, wastegate solenoid, and vacuum lines connecting them are all new as of last March. I have a vacuum reading of 17-19 at the wastegate actuator during idle. The wastegate actuator is loose with the engine off and stiff during idle. I changed out the lift pump a couple weeks ago with the fuel filter a week before that.

From my reading it seems my next step is Cat Converter, PMD relocation, Compression test, Injection Pump. Any suggestions?

Question: Can the turbo code P0236 set an injection code P0251? or are these related?

Thanks for the insight and help, Chris

[rabfan]

I had a P0236 as well. Caused a lot of black smoke and a rapid rise in EGT's. Wired my WG closed and the code hasn't come back but I'm suffering with low boost all the time. I have the PMD relocation 4" exhaust and AFE intake. If any of that helps you with you upcoming troubleshooting.

[Robyn]

the vacuum waste gate system likely is having issues.

Fix that and the smoke and lack of power should go away

Make sure the vacuum pump is capable of pulling 22++ inches of steady vacuum at the pump.
Make sure you are getting good vacuum to the waste gate actuator.

The waste gate controller solenoid may be going south. (sits on LH valve cover)
Make sure the plastic tubes that feed the system are in good order.

The vacuum systems on these can get a leak, then all manner of crap happens.

you can redo the tubes with vacuum hose

Place a vacuum gauge on the pump directly, if the needle is low (in the teens and or wobbles) the pump is junk.

Missy

[cjones]

Robyn, I think you're on to something. Today the temps were up to 102 deg and the rig was again losing power so I decided to test the vacuum. Sure enough I have 23 between the pump and the Wastegate Solenoid, but only 4 at the actuator.

The solenoid is new as of this spring but I swapped it with a solenoid (that has been working) off another diesel suburban and I got the same results. Both of these solenoids are bought within the last year so I'm hesitant to say that they're both bad. The vacuum tubing is also new and I couldn't see any holes. I felt the arm on the actuator, with the engine on, and I could move it down easily.

Is this simply due to low vacuum or could the a faulty actuator cause the low vacuum? Also, is there another electrical component that controls the solenoid that could be effected by the heat?

[DmaxMaverick]

The vacuum to the actuator is modulated (by the solenoid), NOT on/off. The pump should indicate a steady 20-26", and the actuator at idle should see a steady 13-16". 4" at idle is a bad solenoid, vacuum leak, erroneous sensor data, or a poor/intermittent connection. Most often, any of the above, except a leak, will cause a wastegate fault code. Leaks are most common, followed closely by a failed solenoid. The solenoid can be cleaned and lubricated with a couple squirts of WD40. This will often help it to work normally, at least until the replacement arrives. If the solenoid fails electrically or loses connection, it should set the appropriate code.

[cjones]

So the AC Delco solenoid that I put in the rig from my other diesel needed a nights rest because I haven't had any issues since. I tested the vacuum at 100 deg ambient temp and all checked out good and drives fine. It still feels a bit soft when the temps get really high and when the fan clutch kicks in the rig bogs down but overall it'll work.

Yesterday, I switched out the stock muffler with a straight pipe and the difference that made in power was noticeable. Thanks for the help, Chris

[Warren96]

That solenoid's electrical connector gave mine the intermittent smoke problem that sounds just like yours.Replacing the plug cured mine. With the type of driving I do, replacing the stock muffler, or even removing the cat had absolutely no effect on power or mileage.