Okay so I just picked up this truck for $3100, my plan is to fix it up back to daily driver shape so I can sell my cummins, I've missed my 7.3 ever since I sold it...

Anyway this one has what seems to be a weird idle problem, and it only seems to happen when warm. It's not hard to start, and the truck is not short on power, it runs great. However seems like when it gets warm the idle will dive and then come back up, almost seems like it pauses for a second, but like I said only at idle. If you press the pedal it will stay smooth. Any ideas what this could be??

Video of the weird idle:

Video of it idling fine:

 

Since the videos I have replaced the icp sensor and pig tail, it has not seemed to help, if I unplug the sensor while it's running nothing changes at all. Also since replacing the icp sensor the check engine light has come on, and it wasn't on before. Could it have turned on because of me unplugging the icp? Also the check engine light is on but there is no codes.... Weird. After changing the icp sensor sometimes the rpms won't stay steady if I'm sitting on the throttle, sometimes it will dive for a second like the idle...

 

Your check engine light will come on when the ICP sensor is unplugged. at least mine does.

 

any idea what your high pressure oil pressure is? my old 6.0 had a similar problem and what was happening was when the oil got warm and thinned out a little, the hpop couldn't keep enough pressure at idle to fire the injectors right. when I got on the throttle the hpop would turn up the pressure enough that the problem went away. I'm no expert by any means but it's something to check. a lot easier to change on a 7.3 than a 6.0 too if need be.

 

Scan tool/gauge of some sort?

 

I do have a Scangauge, hardly know how to use it though lol

 

Anyone else have an idea of what's going on here?

 

Is it possible that you have loose injector bolts. Rich (Tugly) and many other on this site are very familiar with this issue. Some of the sounds in that video sound like my idle when I had loose bolts. You could also have one bad injector that is dropping HPOP pressure intermittently depending on it's "mood" which could cause the rpm drop. If the injector has a cracked o-ring or is loose, the injector can move. This can cause the injection timing to jump around. Rodeo riders rely on timing, so do these trucks. Look at Tugly's threads-he has two links for troubleshooting injector problems from some very smart folks. Your repair project will require that you get more "eddicated" if you want to save money, sanity and the project. Larry

 

The phone microphone is very muffled, I think I do hear the distinctive "Tink Tink Tink" of an injector rattling around in there. Do you have a better video camera, and can you put what you have under the truck somewhere behind the front wheel?

If you have a loose injector, the ICP will do some weird stuff - and cold startups are usually a total fog at the tailpipe.

 

Will you get the "Tink, Tink, Tink" with bad internals on an injector even if it is fully bolted down and good o-rings?

 

I haven't yet, but that's not to say it can't happen.

 

Bkuzz, the important thing to remember when you are trying to solve problems is to:

Do not ask dealerships or shops for their opinion at first, they will almost always tell you that you "need a/some/all new injectors".
Try the least expensive, but likely repair first.
By taking this approach, you can most likely rule out those causes.
Certainly if you have the injectors replaced you will solve a loose injector problem, because they will properly torque the new injectors. But you could be out a lot of money for unnecessary repairs.
If you read up on tightening the injectors, take your time, and use patience you can certainly do the job. Hey I have done a couple of them, so anybody can.
If some of your injectors are loose, the sooner you tighten them up, the less chance of hammering that all important copper sealing washer (the one that seals out the combustion gases) into oblivion.
In conclusion, because of the noise of our older diesels, there can be many of them running around with this problem of loose injectors-so many that we start to believe that the sound is normal. Larry