Running rough when cold/lots of smoke

[dan brooks]

Over the past few months I've noticed the truck will run rough when started first time for the day. It normally clears up after a few seconds, but when I started it tonight it felt like it was running on about three cylinders, and when I gave it some throttle it really started shaking. It was also belching out TONS of smoke. It smoothed out some after 30-45 seconds, and once I drove about a mile it was fine.



The temp when I started the truck tonight was around 45*, but the WTS light didn't kick on and the grid heaters didn't cycle. They are working, though, because they cycled yesterday when I started it the first time for the day. It seems like it runs fine if the grid heaters kick on, but without them it runs a little rough. Tonight was the worst it's been - normally it isn't very noticable and is only for a few seconds.



Any ideas?

 

[BushWakr - RIP]

Dan, the first thing I'd check is your idle. We are now in the season were most fuel outlets are selling winter fuel. It is, to be blunt, really poor grade... so much so that on my truck I loose about 75'ish RPM when compared to summer fuel.

I always run a good fuel conditioner in my truck, summer and winter. This helps lube the pump, and also raise the cetane rating of the fuel. The result is I gain back nearly all of my "lost" RPM, I get less smoke, better (stable) idle and better all around performance. Remember our pumps are lubricated entirely by the fuel as it passes thru the pump so additives are a real good and, cheap insurance policy to help extend the pump life.



pb... .

If your idle is under 775-800 then tweak it up.

Also, even if the "wait to start" heaters don't kick in on start up, you can still get some cycling of the heaters/fuel heater when running.



Did this problem happen to relate to a new tank of fuel ???

Did you do any tweaks/mods that might have cause this??

 

[JLEONARD]

Dan,

Ditto what Bob said... but I'm surprised it's that rough when started at 45*.

Mine's a little rough for a few seconds when its in the 20s and lower but when it's a balmy 45 its smooth.

It does idle down during the grid cycles, and makes the truck shake a little... . it's worse if I don't "wait to start" for a few cycles till the manifold temp comes up a bit. .

Jay

 

[dan brooks]

Bob - Idle seems good. I don't have a tach but I'm not getting any wobbling in the mirrors when idling in gear (once it's warm, that is... ). I run the Power Service fuel additive with each tank. The heaters definately weren't cycling last night - none of the familiar clicks or dimming of the lights.



The problem actually started a few months ago - when I'd start the truck the first time each day it would run rough for a few seconds, then clear up and be fine. If it was a gas engine I'd think the choke was too tight and it was loading up - it acts just like a couple plugs were fouled by too much fuel.



Haven't done any tweaks or mods in quite a while, well before the problem started. I've been buying fuel at several different stations so I don't think that is the issue since it has been starting rough for a while.



Jay - I'm not sure why the grid heaters didn't kick on since it was 45* outside, but the only thing I can think of is that the truck only sat for about eight hours - maybe there was still enough heat contained in the block that the intake was above 59*? It was cloudy and raining most of the evening, and it probably didn't drop below 50* until an hour or so before I started the truck.



I'm wondering if I have an injector that is leaking down when the truck sits for a while, or maybe it's sticking open when cold and dumping too much fuel when it first starts? Not sure where else to go, and I don't want to (and can't afford to) spend money on injectors unless I know for sure that is the issue... .

 

[dan brooks]

Problem fixed. Turned out to be a bad temperature sensor for the KSB solenoid. Picked up a new one (Cummins PN 3921642, Chrysler PN 4713521) and swapped it out about a week ago and it's starting up fine now. Glad it was a cheap and easy fix this time... .

 

[JLEONARD]

Question...

does the same temperature sensor/switch control BOTH the grid heater and the KSB?



Jay

 

[dan brooks]

Nope, different switches. They are both on the intake manifold to the rear of the intake tube (on intercooled models, that is - can't help with the earlier ones). The far back one controls the KSB solenoid, the one just in front of it controls the grid heaters.



Best I can tell there are no aftermarket manufacturers of the KSB switch, so its either dealer or Cummins. The grid heater sensor is available from Standard Motor Products and is part number AX-36 (around $20 from the local parts house).

 

[JLEONARD]

Thanks Dan.