Engine/Transmission (1994 - 1998) Missing/Rough running at high alt, high RPM

[RyanStewart]

I was up in the mountains of Colorado recently, and while winding up a few grades at 9000+ ft my truck would start running rough and smoking white (missing?) as I pushed close to 2500 RPM. It seemed the higher I was, the sooner this would happen. Above 10000 ft it would start stumbling at 2300 - 2400 RPM, and by the time it got to 2700 I'd be belching a thick cloud of white smoke. As I descended back down, the RPM that it would start acting funny got higher and higher. By the time I was down at 6000 ft it wouldn't start acting funny until I got over 2700 RPM. Now I'm back at sea level and everything seems fine.



Is this normal or is it a sign something might be starting to go wrong? I have the stock governor spring turned 2 clicks tighter, by the way.

 

[Vaughn MacKenzie]

That's kind of odd, but maybe you are sucking a bit of air into your fuel which is exacerbated by thin air? I was in New Mexico/4-corners area not long ago up to 7700 feet and my '98 ran perfectly fine other than it made more black smoke than at sea level.

 

[JWashburn]

I saw this when towing heavy here at 7800 ft elev, but not when empty. I surmised a fuel restriction, and changed the fuel filter. Problem gone, but that was on the third gen.

Its got to be not enough fuel for the air going in. Its either fuel restriction or an air leak into the fuel supply to the P7100.

 

[RyanStewart]

I thought it might be the fuel filter, so I changed it while I was up there, and it didn't seem to have much effect. If I had an air leak, wouldn't I have trouble starting after its been sitting for a while? I never do.

 

[JWashburn]

Anything unusual with the boost back at sea level. It is normal to see a significant boost drop the higher you go, and when it was rumbling you couldn't make boost.

Another possibility: a leak in the boost line to the AFC or a leak in the AFC. At higher altitude there may be enough pressure difference to spring the leak. At lower altitude the pressure difference is lower perhaps not enough to spring the leak. This kind of leak might cause the AFC to back off on the fuel while the engine demands more air.

AFC connections tight? Any damage to the air line? All the turbo to air manifold connections tight? Any damaged boots?

On the '97 I had a cut one the passenger side intercooler boot caused by sheet metal crimp. I was still seeing normal boost in spite of a nearly 1 inch cut. Then suddenly one day I was only seeing 2-3 lbs. I went searching the boots and found the cut. Replaced all the boots with the Nomex BD kit, and bent the sheet metal away from the boots. I still only saw 2-3 lbs. Turned out to be a kink in the boost gauge plastic tube. I don't know how long the boot had been cut. Maybe since before I installed the boost gauge.

 

[dpuckett]

White smoke the higher you went up sounds like timing to me. If it is still stock, you wont get optimized timing for 9-12K ft elevation. Retarded timing will make gobs of white smoke. Couple the timing vs elevation difference with the distinct possibility of slipped timing, and it is compounded.



Daniel