On the wife's Excursion with 255k on the clock, it has a random knock that comes and goes every once in a while. It only occurs with the truck in drive and not moving...like sitting at a stop light. I can move the gear shift selector to neutral and it will go away...when I give it some go pedal to start moving it also goes away. This probably happens every couple of hundred miles...not consistently all the time...but when it does happen it will do it at a couple stop lights. It's hard to tell exactly where it's coming from, but I'm guessing around the firewall area. My first thought was the possibility of the flex plate starting to crack, but to me it would get worse...I've been through that with my F350 years ago. So now I'm thinking it might be injector #8 as they are original and I'm sure need to at least have the armatures shimmed. I've also thought about a loose rocker arm but I'd think that would be more consistent. There's no loss of power or any smoke, and it seems to run fine. It really doesn't sound like a fuel knock, but could be the beginning of a faint fuel knock. Only other thing I thought about was the fuel pressure regulator sticking every once in a while bleeding off some fuel pressure.

 

I'd run thru a tank of fuel with Power Service Diesel Kleen, see if it improves.

Did you change the oil recently?

 

The oil is due to be changed, so it will get done in the next couple days.

 

I second this. Also adding 2-cycle oil to the fuel makes a huge difference, too.

 

Does it sound like your torque converter has marbles in it? The flex plate bolts might be loose.

 

I try to run fuel that has some bio-diesel in it...used to make it and run it straight. I'll have to mix in some 2-cycle oil as I have some sitting over where I store my boats.

 

No, as stated I had that happen years ago in my F350, and it was all of a sudden. I was thinking this could be the start of that, but I only recall it was all or none when it happened with the F350...

 

You don't need much. 100-1 is plenty. I'll put 8 oz in my VW TDI and fill it with 12-14 gallons and that's all that is needed to make a difference. The Ford, I'll get a gallon of cheap 2 cycle oil and pour it into the 98 gallon aux tank and that's all I need for the whole fuel supply, and it also feeds the 35 gallon main tank.

 

what does adding 2 stroke oil into the fuel do for a diesel?

 

Lubrication.
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Years back the sulfur was pulled way back out of diesel fuel...much like lead was pulled out of gasoline in the 70's...which is the lubrication. When this happened we were getting nothing but ultra low sulfur diesel fuel which was causing premature wear on fuel system parts...mainly injectors. I was making and running biodiesel at this time and many were adding some 2 stroke oil to add the lubrication back into the fuel. Biodiesel...according to several studies...was the best lubrication alternative, plus it's a great solvent for cleaning your fuel system...tank, lines, injector tips, etc. really good. Because of it's great lubrication properties, this is probably why you now see it at the pumps in percentages around 5%-20% added tot he ultra low sulfur dino diesel. I can still find a local guy that makes and sells biodiesel straight out of the pump...it's a little more pricey and a drive across town. So I'll mix in some 2 stroke for now and maybe pick up some bio diesel when I'm over that way...

 

Interestingly, the trend towards blending biodiesel into regular diesel has now brought lubricity and a mild cleaning effect back to the fuel we use. Biodiesel isn't so great for the newer common-rail diesel engines but we here in 7.3 land don't care aabout that. In MN, the mandate is for a minimum of B20 now.