The truck (93 D250) has been running flawlessly for >2 years. Suddenly I go to start it and crank crank crank and it sounds like an old chevy missing on many cylinders. You know the sound, like it's trying to fire up on all cylinders but missing on half of them. The last time this happened was about 4 years ago and was due to the KSB wire broken. When repaired, it fired right up. Now it's back.

Once it starts it belches smoke for a half minute and then runs fine. Doesn't seem to happen when warm, only on startup when it has sat 8 hours or overnight.

I put the volt meter in the truck. Next time it happens I will check voltage to KSB and I have a jumper wire I can put in place if necessary. Any other things to look at if that doesn't pan out? Does the KSB take a full 12 volts to activate?

 

Air in the supply side of the fuel system, gets my vote.

 

x2!!!

 

X3

Inspect the two short sections of old brittle hose; one at the tank and the other between the lift-pump and frame.

 

x4 or someone stole the cummins and put a powerstroke or 6.5 in there.

 

Could it be the lift pump itself? Cracked diaphram?

It comes and goes. Started fine twice yesterday.

 

YES

Put a fuel-pressure gauge on it.

If you suspect a ruptured diaphragm, keep an eye on the dipstick and smell of it for diesel.


Did you inspect those rubber lines ??

 

I am fairly certain the KSB gets full voltage.

Have you checked it's wire for voltage ??

There are two completely different KSB systems used on these trucks and I keep getting confused on which years worked which way.

I think that the I/C engines use the KSB that only activates when the intake is cold, the current turning off once the intake temperature warms; these engines have a temperature sensor screwed into the top of the intake.

When the engine is cold, there should be voltage at the KSB connector and none when the engine is warm.

No voltage could mean a problem with the sensor.

That type of KSB can be rewired to a manual switch and activated on demand.

Since you had similar issues in the past caused by the KSB, I would not rule it out as the problem.

 

I'll crawl around under it tomorrow. I did smell diesel but couldn't find any drips and my oil level hasn't risen. May be time for a piston pump upgrade.

started ok the last 2 days. odd, but I'll do the exploring Sat morning.

 

The steel "hard-lines" that run inside the frame back to the tank can also rust through.

The way the Dodge fuel-tank obscures the left inside of the C-channel, it traps all of the road-salt, mud, and whatever and sooner or later will even cause the frame to rust through.

To compound this situation, both the un-protected steel brake-line and fuel-line are routed inside and through all of this rust-causing mess.

Therein could also lie your mystery air leak.

 

More times than not air getting into the supply side will not show a fuel leak. Best way I've found to track it down is to take a shop rag and a blow gun and wrap the rag around the blow gun and get it to "seal up" you fuel cap. Then apply 8ish psi to the fuel tank. While your buddy(wife in my case) does this, start looking for leaks at all the connections and lines. The fuel heater is also a big suspect in these fuel systems. 1 of my trucks ended up being in the tank but that was an easier find because it would only do it when I had less than 1/4 tank of fuel. My other truck was the connection between the supply line from tank to the lift pump. But this only showed fuel leaking with my wife blowing the tank.....um did that sound right?

 

Well I crawled and peaked and twisted. Far as I can tell all the fuel lines prior to to lift pump are some kind of hard nylon. no sign of seepage but my wife is gone so I don't have anyone around for a bit to man the pressure hose. maybe next week.

I'm tempted to replace the lift pump with a piston pump just to be sure it isn't the diaphram.
The KSB is getting about 11.5 volts. Not sure where the other 1.5 volts from the battery went. The KSB sensor pins are a little corroded. I'll clean those just for good measure. I'll find the prob eventually.