I was driving my Cummins Excursion today and it was having dead spots while accelerating. It would surge and then very slowly speed up then surge it would do this over and over again from 10mph to 65mph. Any one have any ideas? Any help would be appreciated.

John

 

Sounds like a leak in the AFC diaphram located at the rear of the injection pump.

 

So what do I have to do now? I am 400 miles from home on vacation with my family. Can I make it back? Is it an easy fix? Thanks for your reply

John

 

its an easy fix if thats your problem just have to get a new diaphram, its not a fuel system prob is it? if you're concerned about the air getting in the pump then just plug the line off of the intake it would be like running in valet mode though.

 

The surges and dead spots always happen at the same speeds. If I drive like a grandpa then I don't really notice anything, but even at moderate acceleration, there is a dead spot at around 10-20mph then I get a surge of power from 20-40mph then it's dead from40 to about 53mph and then the surges and dead spots come and go more frequently until I reach cruising speed. I don't notice anything after the cruise is set its only when I am getting up to speed. Is the diaphram on the outside of the AFC housing? I left my shop manual at home so I feel kind of lost.

Thanks again.
John

 

its in the afc housing, its what the boost air from the manifold pushes on to move the lever. you'll have to take the afc off and take a look.

 

I already have a fuel filter so the first thing I will do is change that. I will wait until I get home to take the afc off. What is valet mode?

John

 

Blocking boost signal to the AFC. A good way to control your power (& EGTs) with large injectors and/or deep fuel plate

 

I changed the fuel filter and that seemed to help until the engine got up to temp and then back to the same problem. I drove it home the 400 miles as it was. The dead spots were not as consistent as they were on the first leg of our trip. This time the dead spots were much longer and the power surges shorter. Driving through the city in stop and go traffic it stalled a few times and while trying to keep with the slow flow of traffic. The accelerator pedal would hop back and forth and I would have to put it into neutral and rev the engine to keep it from stalling. Is this part of the same problem? Does anyone have the part# for the diaphragm?


John

 

I'd take the AFC off and remove the leg. It will take the AFC out of the equation, so if it continues, you can rule it out. If it stops, then you've narrowed down without spending a dime. Whatever tools you need to get the AFC off, and a 10mm wrench to pull the slide pin out, foot just drops out. Two minutes tops.

 

I'm thinking fuel delivery. Have you replaced the over flow valve and/or checked the fuel pressure recently? Possibly a lift pump getting weak

 

now that sound like fuel prob. hence the good running after fuel filter change cause you more than likely had the canister full of fuel when bleeding it. check your suction side of the fuel system lines for cracks or kinks. or even could be trash in the lines from the tank

 

I tried to take off the back of the afc housing but could not get one of the screws out. Is there a break off screw on the back of the afc as well? Tomorrow I will replace one of the fuel lines.

John

 

Yes, there is a breakoff screw in the back of the AFC. You will need to take off the AFC to access it.

 

I found a very small leak on my return line and replaced it. I also cleaned the prefilter screen and took the Excursion for a test drive. I did not notice any more of the dead spots but boy did it feel like I had power like I had not seen in awhile.

The idle is too high now but it might be because I was moving the throttle arm in order to get to the clamp and take off the return line behind the pump. The prefilter had some junk in it but I did not think it was too bad. Where did all this extra power come from? Was the screen dirtier than I thought? Or could it be the little hole in the line?

John