Engine/Transmission (1998.5 - 2002) High idle test, faulty injector, but a question for you all...

[NPloysa]

Ok, so I have a missing injector. It does not want to fire at idle like the rest of them, which one it is I am not sure. It only happens when engine is warm and after a quick run, SOMETIMES, can't really predict it.



I decided to listen for it while I watch my digital tach. My truck idles around 860 rpm and after I bump the pedal, as the rpm drops, I can hear it from about 930 back down to 860.



So, I thought it could be fuel pressure, but it isn't, that all checked out good.



I decided to test it for sure by rigging up a temporary high idle. What I did was stuck a dime on the set screw on the control arm, this raised idle to around 1100. I did this with the truck on, taped the dime on, turned the truck off, restarted and the idle jumped to 1100. I drove around hard and pushed it and pushed it. Did not notice the injector misfire at all.



I then smashed a dime so the thickness was smaller and lowered it to around 975. I did this with the truck on also, and then shut it down. When I restarted the idle stayed at factory 860 rpm.



So, to me, it seems like there is some play in there, like the engine decides when idle actually moves. I may just order a high idle kit and set it at 950 to get rid of that miss, but how precise can I get it if there is that play in there? I'm foncused!



Nick

 

[mgoncalves]

Not exactly sure on this Nick, but it sounds like you are screwing with the APPS calibration by starting it with throttle applied





Matt

 

[NPloysa]

That would be a good guess. Probably why my 'check engine' light came on yesterday when I was messing with it. I wonder why though, only the small throttle increase makes a difference, while the big one does not?

 

[jrandol]

Just slap in a set of EDM 10's and call it a day Nick!! Oo.

 

[NPloysa]

Well, still a no go. I am going to get a high idle kit since I can't seem to trick the ECM into thinking 930 rpm is the new idle.



After I was playing around I put the idle screw back so my FMS read 850-860 and did the TPS reset. It stayed right around there. I turned on the truck and set the idle to 930. Last time I did that the idle would reset if I turned the truck off. I turned it off, then turned it back on, the idle jumped up right away to 930.



So, I took a drive, WOT and such, pushed in the clutch a few times coasting to see if the idle speed stayed, it did, right at 930. I thought that was it!



So last night I took it out for dinner, but idle had gone back to 850-860.



Guess I can't fool it.

 

[mgoncalves]

Are you trying to set your idle at 930, all the time?



Matt

 

[NPloysa]

I was going to try, although it may not work without a high idler. I don't think the ECM will want the idle that high and recalibrate itself down to 850 or so.



I did just dump in a 14 oz bottle of injector cleaner/diesel conditioner when I filled up today and it seemed to go away!



I hope its just a sticky or dirty injector.

 

[mgoncalves]

That's what I was afraid of. If you use an electronic high idler, like the one from practical solutions, it changes the way the throttle works when it is turned on. If you just barely turn it on without it changing the idle, it makes your throttle 100% different. Almost a dead pedal effect. It is useful for bumpy roads in the snow, but I don't think it would get you what you're after.



Matt