Idling blues

[jarsong]

Vaughn,

I would check all grounding straps that you can find on the motor/Body to frame/Even the hood. Loosen the scews and re-tighten. If you got a CB installed kill the power source. Do you notice any difference in Wet weather? It almost has to be interfference from a sensor/wiring or the ECM's inability to detect and deal with said "Line Noise". Since it smoothed out with the scan tool hooked up it almost eliminates any "Mechanical" problems and in my mind means the tool is acting as the noise filter. Having said that the VA and other modules are amplifying the noise. That's why it missed worse with these attached. I've seen some bad vehicle/trailer grounds do some very wierd things in my day that defy all logic. I hope we fix this.

Jarrett

 

[Vaughn MacKenzie]

Well thought I would update, although I can never seem to find the time to "go after" the rough idle issue and check wiring/sensor grounds, etc. , so I haven't really made any "progress. "



I was in Las Vegas and paid a visit to Diesel Dynamics to see what Lawrence thought. After listening to it for a few seconds he goes "it idles terrible!" He threw on his scan tool and ran a quick injector shutoff test like I tried to do before, and he concluded the miss was random and all the cylinders are even. Also, just like when I hooked up the scan tool, it idled very smoothl for a couple seconds every time he exited the injector shutoff mode. He didn't have time to investigate any further and only could make suggestions such as the CPS (cam position sensor) or IAT (not likely he feels). I want to thank Lawrence for taking a few minutes for me last Monday even though he had work stacked to the hilt to get done.



The fact this problem is temperature sensitive became very apparent in Las Vegas. It was really idling bad. Now that I'm home and it's 10 degrees cooler, it still seems to idle bad. I think it is gradually getting worse, so if I never get around to troubleshooting it, the problem may manifest itself on its own with some component failure. We can hope at least.



Vaughn

 

[Sean Flanagan]

I've had the same rough idle problem for quite some time now. I've been re-flashed, have a new TPS, and replaced the injector connector tubes (all while I still had a warranty). I was contemplating doing an injector swap, but it sounds like that doesn't help. I have given up and just live with it. The truck runs great otherwise. The warranty is long gone. I'm anxious to see if anyone finds a cure.

 

[Alan Reagan]

I would think that the Camshaft Position Indicator might be a good target for change on this. It's too bad the VP-44 has to go back to Bosch (not a Bosch certified shop) for problems. On the P700s the fuel pressure for each line could be measured and recorded. If their is uneven pressure at idle, that would cause this problem, also.



Back when I drove big trucks, we could always tell if we had a fuel system leak after filter change cause the engine would surge at idle. It wasn't a rough idle, it would just continue to change idle speeds in slight surges. These idle problems sound more like skips than surges.

 

[jarsong]

Thinking more about this it seems that it must be a sensor that the truck can run "Without". I'm not sure what the list would look like on our trucks. For instance with a gasser your vehicle will run with out the O2 sensor even pluged in. In some cases it won't even set a check engine until the engine has detected a "Lean" condition for a predetermined amout of time. (Had this happen) The test tool must provide some interrution to a sensor giving "drivability data" navigating in the menu's. I would guess if a cam sensor failed the truck would just die and set a check engine light. I'm thinking a IAT, Coolant Temp Sensor, There may be more than one of these, One for the Dash guage and another for the ECM. My old 6. 9L had 2. Isn't there some temp sensor on trucks with the snow plow prep package for the trans or transfercase??

Jarrett

 

[Swayse]

I changed the IAT sensor, idles the same. Mine seems to getting a little rougher too. Runs perfect in every other way. Thanks for the update.

 

[Vaughn MacKenzie]

Well I did some calling about he CPS, Cummins has a new part number for it but availability is very limited right now.





CPS (crank position sensor)

old pn 4001906

new pn 3408430



It is $33 from Cummins. I am trying to decide whether to wait for awhile and spend $33 or just take it to the dealer and force them to fix it