dieselfuelonly

My 96 started doing this cold weather stumble, maybe at the beginning of the winter this year.

I start the truck up, rest my foot on the pedal so it runs at about 1100 RPM for about a minute, then go.

If I go above 1500 RPM or so, the thing will studder, stumble, whatever you want to call it, and blow some bluish/whitish smoke.

After a little bit of driving, it will clear up just fine and run great and has great power.

The truck does not burn an abnormal amount of oil, it ALWAYS starts right up with just a few (if not one) revolution. It does not stumble at idle more than 1-2 seconds after starting.

Here's as much information as I can give:

1. It only occurs when its chilly out (maybe 45* or below) and the truck isn't plugged in. Plugged in it doesn't do it at all, even at colder temperatures.

2. It only occurs for a little bit after start up - once its been driving for maybe 2-4 minutes, it all clears up and runs great.

3. I have not tried winding the truck way up to see if it would clear up sooner as I HATE revving a cold engine way up.

4. If it is warm outside, the problem is nonexistant. Once the truck is warmed up, I can shut it off and start it back up later on and the problem does not occur.

I did some searching and it seemed like there were a lot of different responses I got, some of which I've listed here:

a. Timing slipped - I've never had the truck timed, don't have kit to do it myself.

b. Overflow valve - I've heard this is related to fuel mileage too - I get about 16-18MPG, and I drive my truck pretty easy. Compared to what some 12v's get, I know this could be a little higher.

c. Air in the fuel lines - if this was the issue, wouldn't it occur when it was warm out too?

d. Injectors - if it were an injector issue, would it occur just at start up?

e. Fuel filter - maybe this is where I should start. As far as I know it doesn't need to be replaced yet... but maybe it does?

Any ideas on where to start troubleshooting?

THANKS.

Dennis

Wicked500R

My truck is the same EXACT way! I chalk it up to the cold air causing an inefficient burn in the combustion chamber.... compression ignition... If I rev up when cold, it'll start dumping white smoke and my EGT's start to climb. I warm up at about 1100-1200 rpm after I get full oil pressure.. Soon as it warms up... it's fine...

wyododge

Just as an experiment try adding some power service or stanadyne to the tank on your next fill up and let it set over night unplugged and see if it does it again. I see that your are down in NC and they may not treat their fuel for colder conditions. I have read on this site that ulsd gels at a higher temp than lsd. I own a 2nd gen so I am not sure if you have a fuel heater, but it kinda sounds like your fuel is a bit thick, not gelled, and it just needs to circulate a little. The ps experiment will only cost five or so bucks, and if that is not it it wont hurt anything. Just a thought.

Mt Ram

Fuel won't gel at 45*, and if it did, the problem would get worse the more you ran it and plugged the filter more. Your problem is most likely an injector that is not atomizing the fuel properly. The reason it gets better as the engine warms up is because the fuel is ignited by heat (caused by compression of air) and the longer the engine runs, the warmer it gets, thus the poorly atomized fuel ignites easier. I would suggest you have your injectors tested.

turbo246

check the fuel heater...mine did the same thing! my fuel heater went bad giving me blue/white smoke and a stumble arounf 1800 rpm if it was cold. get a meter and shop book and it shows you how to test them.

Wicked500R

So, then this is a problem?? I always thought it was normal

Dartmouth 12V

It is going to be a problem on any stock engine when t gets cold. The best way to get it to go away is to advance your timing a little. With advanced timing the engine won't start quite as easily but it will let you rev up more once started. Basically, the higher the engine rpm, the more advanced your timing should be so at idle, you don't want advanced timing but at redline, you want it advanced a lot more. A 12V has static timing so you have to set it to balance cold start ability and the rpm that you are most likely to run at.

dieselfuelonly

This is different from the grid heater, correct? I will have to check into that, thanks!

It can't be completely normal, because my truck didn't used to do it as far as I remember... unless the auto really kept the RPM's that low that I wouldn't notice it (since I build more rpms before I shift with the 5spd now then the auto did).

infidel

I don't think you have any problem at all.
The ring to piston tolerance is loose on most diesel engines until they warm up and expand.
You are just experiencing typical cold weather warm ups.

Install a fuel pressure gauge anyway. Great for troubleshooting and will pay for itself by eliminating just one unnecessary fuel filter change.
Instructions> How to Check 12 Valve Fuel Pressure

Buckshotram

mine does kinda the same thing when its cold has a real rough idel maybe even a miss for about 15 seconds when its real cold. Ive got a fuel press guage as well. I think its just the nature of the beast.

Tate

Does your truck get quieter before it starts studdering and blowing smoke? My 24v has done this ever since I have done the p-pump on it. Went from jammer injectors to brand new DDP's, same thing. Timed and reverified that it was at 15.5 degrees. Overflow valve is ok, still at 30+ fuel pressure. If I had air in the lines, it would be hard to start. It sat for about 3 months, and other than the solenoid not pulling up, it fired up on the first or second revolution.

I don't think it is completely normal, as my 12v doesn't do this to near the extreme my 24v does, or by the sounds of it, the OP's truck. My 12v only does it for maybe 10 seconds, and thats when its -15 to -25. My 24v will do it in +15C.

KHoffman

My truck does the same thing when it's cold. If you are very slow withthe throttle you can rev it higher and it won't do it, but you can't rev it normal until it warms up.

Lil Dog

Mine does it too.. If I am shifting 1-2 and 2-3 on the street as soon as it crests about 2K Rpm it starts sputtering and blowing blue. If I give it a good shot of fuel, it will not.

Even after having the engine heated with the Espar, it does it for the first couple of revs, then its gone.

Diesel_Dan

[QUOTE=infidel;2378244]I don't think you have any problem at all.
The ring to piston tolerance is loose on most diesel engines until they warm up and expand.
You are just experiencing typical cold weather warm ups.

Exactly, I live in northern michigan, while it may not be as cold here as some of extreme cold some on here live in. I have the same "problem" and infidel is spot on. If your truck is plugged in, it doesnt do it, if it is warm outside, you don't have the problem. So basically when the cylinders, rings, pistons and everything else is warm because of a block heater or warm outside temps it will have complete combustion and rev right up. Now when the engine is cold it can not heat the air in the combustion chamber to an adequate temperature to burn all the fuel. There is a lot of iron in our motors and it will take a few minutes to build enough heat to make everything combust completly. I hope my ramblings help.

Wicked500R

[QUOTE=Diesel_Dan;2379231] Precisely what I thought... Thanks !