problems with WTS/IAT/ECM

[wakerc]

I have searched all over for days and cannot seem to find anything to help that applies to a 3rd gen. Issue: When I try to cold start (after truck sitting all night and it below 40 degrees out) the truck simply wont turnover unless I leave it plugged in all night. i'm talking NOT AT ALL. then I figured out that the WTS light is only staying on for a max of 3 seconds when cold so the grid heater isn't cycling long enough to warm up. it will stay on for the regular 10 seconds but only when the truck is at operating temp and shut it off and immediately turn it back on. What I have done: installed new grid heater, installed new IAT, and monitored IAT readings with scanguage. I found out that when the engine is cold the IAT reading is saying 115-122 degrees. after starting the temp slowly drops down to what is an expected temp. All this was checked when it was around 30 degrees out. Ideas: possible short in wiring harness? dying/confused ECM? Any and all help would be appreciated

[Mopar1973Man]

http://articles.mopar1973man.com/3rd-generation-dodge-cummins/60-obdii-error-codes/277-p0112-intake-air-temperature-iat-sensor-voltage-too-low http://articles.mopar1973man.com/3rd-generation-dodge-cummins/60-obdii-error-codes/278-p0113-intake-air-temperature-iat-sensor-voltage-too-high You might read over the error codes and it will explain how to test the wiring for issues. Still in all you should not need grid heaters at 40*F start. I don't even bother with the WTS light at all on my truck with temps above 32*F. But since this is a 3rd Gen I would see about having those injectors looked at. It really common to see injectors that have failed and CP3 can't build rail pressure up to fire the injectors because one or more injectors are leaking.

[wakerc]

Thanks, Ill try this. two questions, to check the ohms using a multimeter, which setting would be best? also, is it normal that this is happening but yet i havent had any codes come up?

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Thanks, Ill try this. two questions, to check the ohms using a multimeter, which setting would be best? also, is it normal that this is happening but yet i havent had any codes come up?

[AH64ID]

You said it was 30° out, but was the truck plugged in?The IAT reading on a scan gauge comes from the MAP sensor, not the IAT sensor near the air filter.

[wakerc]

no it wasn't plugged it. if I leave it plugged in over night it'll start just like it's 70 out. I ended up wiring up a switch to manually turn the heater grid on that still allows the ecm to turn the grid on also. Even after that the problem still exists; if It's below 40 degrees out and the truck sits for more than 4 hours with out being plugged in it will not start even with the heater grid workin properly. EX: left unplugged lastnight, went to start this morning (30 degrees out) and nothing. have to leave plugged in for atleast 40 mins till it will start. :banghead: MoparMan: you said it could be a leaky injector. is there any way to narrow it down to a specific injector or do I just have to pull them all and go get them tested? local shop charges $68 per injector to inspect, test, and clean. Im not noticing any white smoke ever like a couple people have said to look for but also I have dual 6" stacks so its hard to tell. Thanks Yall

[Mopar1973Man]

Either pay the dealer shop rate to do the test or pull them out and have them test it your choice of shops. Some guys like using rail caps and cap off one line at a time and see if the starting issue goes away. But if its more than one injector its going to be tough to test this method which return back to pulling all and bench testing.Common rail injectors are known for having a issue with building rail pressure after the injectors got wore down.

[AH64ID]

It is possible it's an injector, but the ECM also varies crank timing based on IAT and if your MAP sensor is reading wrong (which it sounds like it is) then your crank timing will be off and it may not want to start.. as you are seeing. So if you are seeing that kind of error for IAT on the scan gauge I would replace the MAP sensor first.

[wakerc]

Thanks AH. I am going to try that first before messing with anything else. also if it is something with the fuel pressure, couldn't it also be the fuel pump not creating enough pressure? if so how could I distinguish between the pump and the injectors? cp3 builds the rail pressure correct?

[AH64ID]

Thanks AH. I am going to try that first before messing with anything else. also if it is something with the fuel pressure, couldn't it also be the fuel pump not creating enough pressure? if so how could I distinguish between the pump and the injectors? cp3 builds the rail pressure correct?

If it starts fine when warm then it's probably not the lift pump. There are lots of options, once you get the MAP sensor replaced and if you are still having issues I would give my business to Todd at T&C Diesel. He knows the CP3 and injectors as good as anyone.

[wakerc]

viewing the live data from autoscanner shows that M.A.P sensor reading is at 29 with engine off. doesn't sound right to me....

[AH64ID]

viewing the live data from autoscanner shows that M.A.P sensor reading is at 29 with engine off. doesn't sound right to me....

No, it should be reading about 14.7 ± for elevation and weather.