Rough Starting 6.9idi

[Stu Bailey]

So here's the new concern. When I go to start the truck in the morning it cranks up right away but then if I don't give it throttle after start for about 5 seconds or so, it starts to idle roughly, almost sounds like the engine is choking, bogging out. Sounds like a bad smokers cough with the shakes. It is usually pretty cold here, below freezing, but the truck is always plugged in to the block heater. After I give it throttle she runs fine for the rest of the day. I was going to start with water/fuel separator drain. I have already installed new fuel filter, new air filter too, it was due. She is an 86, 6.9idi, with 153,000 miles. Always appreciate the help gents.

 

[WAID]

Someone more knowledgable should be along but I would suspect air intrusion. How are the fuel return lines?

 

[franklin2]

I suspect air intrusion also. Do you always run it everyday? If you have a minor air intrusion problem, the longer it sits before you run it again, the worse the problem will get.

For instance if you start it everyday and it runs a little rough, if you don't drive it one day and start it the next, the roughness should be worse. If you let it sit for a week, if it's air intrusion it will start, and then actually quit. And then you have to do the crank crank crank till it finally starts and then it runs fine after that.

 

[Cubey]

My 85 was like that this morning at around 27 degrees but eh, it could have been a glow plug or two. I really can't complain, considering. Not starting is what is upsetting more than a few seconds of rough idle.

 

[Stu Bailey]

Yeah I run it everyday. She is my daily driver. But air intrusion is starting to make sense, I had the in laws stay over the weekend so we drove a rental around. Then Tuesday when I started her up it was definitely rougher than during the week and it is started every day. The truck is old and it looks like all original hoses. Probably about time to replace them.

 

[Stu Bailey]

Fuel return lines have to be original as well...

 

[Cubey]

Yeah I run it everyday. She is my daily driver. But air intrusion is starting to make sense, I had the in laws stay over the weekend so we drove a rental around. Then Tuesday when I started her up it was definitely rougher than during the week and it is started every day. The truck is old and it looks like all original hoses. Probably about time to replace them.

I had to replace about a foot of hose right after buying my 85 RV before I could even start it to drive away. The short piece between the return lines output end, and the steel line heading back towards the tank. The seller went and fetched the new 5/16 hose for me. It was visually leaking/bubbling out of the hole when cranking it. Being a van chassis, it was pretty easy, just extremely dirty from the leaky, rotten old hose. After many cranking attempts, with breaks for his engine starter to prepare, it finally fired up. I need to go in and replace all the fuel hose like that. Although that piece had a hard life, near the dog house cover on a turboed engine, with a fairly hard bend where it drops down. The hard bend is where the leak was.

 

[Stu Bailey]

Yeah upon getting off work and actually inspecting the lines, many of then are soaked in diesel. I'm going to replace them this weekend. Here's a pic showing the contrast between a soaked one and a dry one.

 

[Stu Bailey]

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[IDIBRONCO]

That's just another part of maintainance for these trucks. Too bad that a lot of people don't realize this. At least we try to educate people here.

 

[franklin2]

Dampness around that area is usually the o-rings leaking, they are more of a problem than the small lines. The o-rings are under that black plastic piece that the lines go to.

Since they are wet, they are definitely leaking air. The whole top of the engine, all the little return lines and the injection pump are all hooked together and there is a return line running down the back of the engine back to the tank. This system works like you putting your thumb over the end of a straw in a drink and pulling the straw out of the drink. As long as you hold you thumb over the end of the straw, the drink stays in the straw.

That is how the fuel system works in this truck. Every little fitting, line and o-ring in the fuel system has to be sealed. When it's air tight, the fuel stays up on top of the engine. If there is any little place where air can get in, then that lets the fuel run back to the tank, and the top of the engine ends up dry. It will start on the fuel remaining in the hard steel lines, but quickly stalls when all that air hits the injectors.

 

[david85]

Those hoses might not even need replacing by the look of them. I sourced some viton O rings the last time I did mine and so far they are holding nice. I put off replacing mine for many years and they were obviously cracked and heat damaged by the time I dealt with it.

 

[Cubey]

Those hoses might not even need replacing by the look of them. I sourced some viton O rings the last time I did mine and so far they are holding nice. I put off replacing mine for many years and they were obviously cracked and heat damaged by the time I dealt with it.

Yes, those hoses dont appear too bad. Mine were obviously splitting the ends, in addition to leaking O rings on my truck. My RV's don't appear to be leaking at all right now from what I could see without a good flash light, but I think I have left over viton orings from doing my truck. I kept the truck's old caps as spares.

 

[Stu Bailey]

Hell yeah. Thanks guys. I'll post back with an update once I get some new o rings on and fire it up. Cheers!