I haven't been on here in a while, but I just bought another truck and have a few issues I thought you guys might be able to help me with. I bought a 93 dually with manual transmission. The truck had sat up for about two years, so I dropped the fuel tank, cleaned it all out, replaced the fuel filter and cranked it up. When I test drove it, it was running rough, so I figured the fuel was bad (I had already drained the fuel filter and it was full of water and gunk). So when I cranked it up, it was slightly better, but still not running right. When you mash the pedal, it falls on it's face, then starts missing and bucking real bad. When you drive it, once you get it past a certain rpm, it smooths out somewhat but you can tell it's down on power and missing. I cracked all the injector lines, seems like pretty good fuel flow. So my questions are: 1) Do I need to pull the injectors? and 2) What is that plug on top of the manifold? It is the one closest to the firewall. I tried uploading a pic but it was too big. It has been disconnected and the harness has a jumper wire to bypass it. Does it have anything to do with timing and could that be causing the rough running? It idles fairly good, but not perfect. Thanks in advance.
Rick

 

I try to go from simplest to complicated, so I recommend that you check for air leaks first. Pressurize the fuel tank and see what leaks out. I know from my gas mechanicin' days that the most common cause of rough running is a vacuum leak, probably same for diesels except it's air leaking into fuel supply system, good luck...Mark

 

http://s1216.photobucket.com/upload Here's a pic of that switch...hope it works

 

The link doesn't work, just re-size the photo to 1024x768 pixels and you can post it. Any photo editing program can do it...Mark

 

Here it is, I hope

 

If I am looking at the pic right.
That is the manifold temp sensor.
It should have a wire that runs to the KSB to advance timing for cold starts on the '91.5-'93 12Vs.

I would get it running, then crack each injector [just enough to get it to leak diesel] line at the injectors one at a time and make sure that there is no air in the line.

When you say "drained the fuel filter", did you just drain it, or replace it with a new one?
I would replace it if you just drained it.
Fill the new filter with diesel before installing it and bleed the line again.
It should be good to go after that.

 

Sorry, my first post was a little rambling. I originally pulled the petcock on the filter and drained it into a mason jar to check it and it was full of water and gunk. I then replaced the filter, filling it with Sea Foam cleaner instead of diesel, cranked it and then cracked all the injector lines one by one. Would that manifold temp sensor affect how it runs even after it's warmed up? I'm just trying to narrow it down to either a fuel issue (like sucking air, or crap in the IP or injectors) or a timing issue. When you drive it, when you mash the pedal it will first fall on it's face, then catch and go, then it will reach a point where it starts bucking real bad, almost like you're at too low an rpm, then once you get it past that point it will smooth out somewhat, which will allow you to shift, then it will do it all over again on the next gear.

 

The temp sensor / KSB not working, shouldn't make the engine run like you describe.
It just is there to tell the KSB when to advance the timing a little.
Sounds like it is staving for fuel, or getting air in the system.
Does it smoke white when it is acting like it is starving for fuel?

I have never used Sea Foam, is it recommended to run it straight in a diesel?
I usually use fresh diesel or even fresh ATF ,as I have it handy in the shop, to fill my fuel filters.

In neutral can you stand on the skinny pedal and get it to run cleanly and smoothly up to the rev limiter?
Or does it sputter the whole time?

 

You filled the filter with Sea Foam? Probably wasn't a good idea, it has no lubricating properties. You may have damaged the injection pump. At the least, any junk in the system after the filter in now stuck in you injectors.

 

The filter full of Sea Foam sounded, scary to me too.

 

Yeah, fuel, oil, anything but "snake oil"! But then again, it could have been parked for the same problem, too.

 

This is from Sea Foam's website: To clean and lubricate diesel fuel injectors and pumps, prime the engine’s primary fuel filter with Sea Foam instead of Diesel fuel.

The engine will run on straight Sea Foam. Sea Foam will slowly re-liquefy the old fuel varnish residue deposits that block the fuel injector’s passages. Cleaning these passages will return the injector’s spray patterns to factory spec. Injectors can also be cleaned by adding 1 oz. of sea Foam to each gallon of Diesel fuel.
I've been using it for years. I do it every time I replace the filter, my other truck has 430,000 miles on it with no issues. It has lubricating properties, it's used to lubricate the upper valve train. Been around for 60 plus years. The only other thing I would add to my fuel is 2 cycle oil for lubrication. The truck had sat for two years before I bought it, p.o. had health issues, which is why the fuel looked so bad. It doesn't smoke white, just a puff of black smoke when it "catches" and decides to go, which is normal. In neutral it runs rough as well, at just about any rpm. Sounds like it's missing.

 

Pull your injectors and have them flow tested. You'll find them plugged.

 

I've been using it for years as well and that is exactly why I will never run it straight in anything. Chemtool is worse.

 

Did you have issues with it? I didn't mean to turn this into a post about Sea Foam, but if someone has had issues with it, I'd like to know what they were. You mentioned that it has no lubricating properties, but according to the MSDS it is about 50% pale oil, which I'm guessing is a light oil similar to mineral oil. It also contains Naphtha, which I guess is what does the cleaning. I guess if there is junk in the system, I'd rather it end up at the injectors than destroying my IP. I'm leaning towards pulling the injectors anyway, I was just hoping someone might have a better suggestion.