Stumble @ 2,000 r.p.m.

[rrausch]

My truck has developed an annoying problem and I don't know what could be causing it. Coming back from work I get on the freeway after about 15 minutes of city driving. I take it easy on city streets, and when I hit the freeway I drive a mile or so at about 60 and then take it up to 70. Many times within 2 miles of getting on the freeway headed home, the engine seems to stumble slightly at 70mph--2,000 rpm. It won't stumble under acceleration, only when I plateau it at 67-70. If I give it more gas the truck goes faster and sometimes stumbles and sometimes doesn't at the higher speed. If I don't give it more gas it seems to stumble a little longer. Irregardless of what I do it seems to clear up after about 3 miles at 70mph, and then it doesn't stumble any more the rest of the way home. It generally stumbles at about the same point on the freeway and stops at about the same point.



This is drivin' me nuts.



The strange thing is that it doesn't seem to do this during the daytime on my way to work, only when I come back home, about 11:00 p. m. I'm in L. A. right now, and temps are about 55 at 11:00p. m. Gas tank is full, but that doesn't seem to matter. (edit--I just realized that I go to work at 4-5 during rush hour and often don't get over 45mph on the way in to work. )



Truck is a '95, 2500, 12 Valve. 102,000 miles. TST#6. Stronger valve springs. Pacbrake--(Which is not working right now and I'm not sure why) Automatic, K&N, I use Stanadyne Lubricity Formula at the recommended strength. KDP has been fixed.



Any help & suggestions are appreciated.

 

[M Barnett]

I wonder if the fuel system could be pulling some air.

M Barnett

 

[illflem]

I've never had the problem you describe with my Cummins but have with other diesels. I always figured they just weren't warmed up.

 

[rrausch]

M Barnett, How could I check for sucking air? And where do you suppose it could be sucking from?



Illflem, interesting idea... what do you think would be happening in the engine, if it is not warmed up, to make it stumble?



I'm off tonight, but tomorrow night I'll drive around a little more and let it warm up before I get on the freeway.



Thanks a lot! Whenever this happens my guts about get sucked out my eyeballs

 

[R.ebel]

Stumble

I had a bad overflow valve on a 95 cause a stumble. You might start by checking fuel pressure.

 

[M Barnett]

I was just shooting in the dark at one thing it could be. If there is a line or fitting pulling a little air on the suction side of the injector pump it would probably be damp with a little fuel. Just look carefully at the fittings and hose connections for any thing wet. I've had this happen with big diesels around the fuel filters and its sometimes a little hard to find until it gets bad.

M Barnett

 

[BCFAST]

I totally agree with the air-sucking theory... I'm going thru it right now! I just replaced the rubber-coated washers on the banjo fittings and found the existing ones to be rotting! The nice fella at the Bosche pump shop told me how to test the overflow valve: If the spring isnt obviously broken, turn the thing over and stand it up on the bench. Put a tiny bit of oil in the hole in the end. If it holds the oil, the ball is seated properly.