Truck Running Rough...Sometimes...

[94_dieselpower]

Howdy,

This post pertains to a '94 F-250 IDIT. It is actually my fiancees truck (pretty awesome she drives one of these good ol' trucks ), so I don't get to drive it all the time. However, the time I get to drive it the most is when we take a longer trip to our hometown.

Here about a month ago, we were driving back to our apartment from her parents house (about a 3.5 hour drive), and it drove just fine at highway speeds. However, when we got to town, I got stopped at a traffic light and as I was sitting there idling, the truck was running rough, like it had a miss. It was also blowing some blue smoke. However, when I started driving again (in town now) it went away and the engine was running smooth as glass and there wasn't any blue smoke.

When we got to our apartment it was running rough again at an idle and blowing blue smoke again. It was late at night, so there wasn't much I could do. So, I shut it down and decided to mess with it the next day. I went out the next day to check the oil, of which was fine. I then started it, and it ran just fine. I let it idle for 15 minutes or so, and it was running great. Took it for a drive, and nothing. I couldn't get it to do it again...so I just thought nothing of it.

Well, my fiancee mentioned it was doing it again a couple weeks ago, so we took it down home for her dad to look at. He is a chief engineer on tugboats, so he is constantly working around diesels and knows a lot about them. However, this issue kinda has us stumped. He drove the truck for a week and his conclusion was...he didn't know what is wrong with it...

He could make the truck do what we were complaining of....but he couldn't make it do it consistently. He would go pull some hills with the truck, pourin' the coals to it, and could make it run rough. Then, he would try the same thing again and it ran fine. One thing he did notice was the truck has a lot more power running on the front tank of fuel compared to the back. We aren't sure what is going on there...but I imagine we are going to have to pull the tank to find out. He could let the truck idle for 30 minutes, rev the engine up to the rev limiter, let it start idling again, and it would run rough briefly. But after 10-15 seconds the truck would smooth out and run fine.

So, this past weekend him and I were messing with it trying to consistently make it run rough. We were suspecting the CDR might be the culprit, but we drove it without it hooked up and we could get the truck to run rough. He did show me there is a significant amount of blow-by when the truck is warmed up.

There was one thing we were able to do to make it blow blue smoke somewhat consistently. I am assuming what I have surrounded by the red box in the picture below is part of the wastegate. (Sorry for the big picture...I don't know how to make it smaller). He was able to push on this with a screwdriver while revving the truck, and it would put quite a bit of blue smoke. It wouldn't, however, make it run rough.

So, I was hoping someone would be able to confirm that what I have a red box around is part of the wastegate and why when this was pushed on with a screwdriver, it would allow the truck to blow blue smoke?

Also, any suggestions as to what else could be causing this problem would be greatly appreciated. At the present time, the truck is here at the apartment. So I can go out and take pictures/look at things if anyone has suggestions?

Thanks in advance for the help!!!

 

[sle2115]

Looks like the waste gate actuator linkage, pushing on it is changing the amount of air flowing through the turbo so to speak, causing it to make less boost. You may have leaking turbo seals or a fuel line sucking air somewhere, my guess would be on the rear tank, but it's hard to tell...sounds like a fuel issue though, or at least that's partially to blame.

 

[typ4]

where in oregon are you and I am guessing you future father in law is near coos bay?


Turbo looks like a hi miler, opening he wastgate will lower exhaust pressure on the turbo hot side and may let some oil past the seal ring.

 

[94_dieselpower]

Typ4 - I am located in Corvallis at the present time. I honestly don't know much about the truck, beings it isn't mine. I was told that the truck was "rebuilt" before they bought it. To what extent, I have no idea. I don't know what was done. Yes, my future father-in-law is near Coos Bay, and beings that he works on tugboats, he is gone for lengths of time, and then home for a length of time. So your thinking it is possible that oil is getting past a seal in the turbo...causing the blue smoke? Would that cause it to run rough like I described?

sle2115 - I thought it was interesting that there is a noticeable difference in power running between the front and rear tanks. I think one of our projects in the future will be to pull the rear tank and take a peek inside/try to figure out why we are losing power when running on that tank.

 

[94_dieselpower]

So, does anyone else have any suggestions. I am pretty new to diesels, and trying to learn what I can. But this problem just has me stumped.

 

[hesutton]

I agree with the above concerns/suggestions, and I'll add a few other things.

Anyway you can put a fuel pressure gauge on the truck to see what the fuel pressure is doing when it acts up. If you are having a power difference between tanks and it runs rough when pushed hard, there may be a fuel supply problem. A fuel pressure gauge will help you find this out. Also, if there are a few questionable injectors (intermitant leakers), it will run rough and smoke. Same is true for a worn out IP, it will not run at it's best.

Heath

 

[redneckaggie]

kinda sounds like a worn out fuel system. the revving up and the truck stumbling as it returns to idle could be worn ip, the intermittent blue smoke and running rough kinda seems like fuel starvation, is there any wet spots on any lines

 

[94_dieselpower]

Heath - I will pass this on to my father-in-law to be, and see what we can do about putting a gauge on there. I have always felt like the truck is lagging in power. But, I was told the truck was freshly rebuilt before my fiancee got a hold of it, so I wrote is off due to the bigger tires on the truck. I am questioning what was actually done during this "rebuild".

redneckaggie - thanks for the suggestions. This is great info for me. Definitely learning a lot. I can't say as I have noticed anything unusual as far as wet fuel lines or anything of the like. I will say, I wasn't really looking for it. When my fiancee gets back, I will check the truck out and see if I can't see anything like that.

I had told my father-in-law-to-be that the common denominator I keep coming back to is injectors/injector pump. However, he feels it is something different. Reason being that when the truck doesn't have an episode, it does run very smooth. He feels it runs too good to be having an injector/injector pump issue. He is a diesel mechanic, and claims everytime he has had injectors bad on the tugs, the engine just runs like crap the whole time. Not intermittent like this. So, could it be the injectors are just starting to get worn out? We did put some ATF in the fuel this last fill-up. Just to see if that helps anything.


One thing he wanted me to ask was does the wastegate act as an exhaust brake in anyway? He was telling me that when he was letting the truck ride on compression coming down a hill and then gently put his foot on the accelerator, it would blow a lot of blue smoke and run rough. But it would clear up shortly there after. Just curious if someone could explain to me how the wastegate actually works and if it is related to what Typ4 was explaining to me?

Sorry for all the stupid noobie questions, I am just trying to learn more about these motors...considering I got a diesel project of my own to have fun with!

 

[hesutton]

The canister on the turbo controls the gate. Think of that canister like this.........a spring and a diaphram. Once the pressure from boost overcomes the spring pressure it begins to open the wastegate by moving the rod in the photo. It is connected to an actual gate in the turbine housing and allow a portion of the exhaust gas to bypass the turbo completely. It simple exits into the outlet of the turbine where the downpipe (exhaust pipe) attaches. This prevents the turbo for over boosting/spooling and will keep the boost at a maximum set by the spring in the canister. It doesn't act in any way as an exhaust brake.

The blue smoke you decribed above...... costing then throttle...... is common with leaking injectors. Oil consumption can cause that too, leaking past the valves, bad oil seals on the turbo, bad rings, a bad CDR, and so on.... But, if you are NOT using a good bit of oil between oil changes, my money is still on a fuel issue.......

Heath

 

[94_dieselpower]

Thank you Heath for that explanation. That really helps. I just asked my fiancee if her dad has mention anything to her before about the truck using oil, and she said he has never mentioned anything about it. I have not noticed it using oil either.

It is interesting you mentioned the CDR. If the CDR is bad, can this cause the running rough issues?

 

[TahoeTom]

Maybe the cap on rear tank isn't venting properly. Try swapping caps.

 

[94_dieselpower]

That is a good idea! I will just swap them on the truck and see if rear tank will run better than the front. A free and easy test! I like it.

 

[redneckaggie]

First thing i would check is to test pressure at the schrader valve on the filter head, if you have a mechanical pump(stock) then you should get at least 2 psi, recommend more like 4 and a minimum volume of one pint in 30 seconds of cranking, the fuel coming out of the schrader valve should be a constant stream shouldnt be any air escaping

 

[gingrass179]

ok your tanks can get crap in the lines real easy especially if your tank already goes empty around 1/4. the hoses that used to be onthe pickup tube rot and fall off and can cause partial or complete blockage just take off the lines at your valve and blow them back into the tank

 

[94_dieselpower]

Thank you everyone for the replies! This is all great information, and I will pass it on. I really hope to get this problem nailed down, and I will suggest to my father-in-law-to-be the things ya'll are tellin' me.

I think we are going to pull the rear tank and take a look in there. See what we can see. I have read some things about the infamous "shower head", and will be taking a look into that.