3cyl high idle Electrical bug! Bad ECM

[Mopar1973Man]

Then the ECM is good. If that resistor is clearing the codes. Then you back to the sensor being bad.

 

Dumb question, does the truck have a high idle kit on it? Is the switch left on high idle by chance?

Edited December 9, 2017 by Mopar1973Man

[dripley]

11 hours ago, Chris O. said:

I bet they are not even ECMs but PCMs.

You are definitely correct. Almost all the big box stores list them as ECM's while they are actually PCM's.

[JP907ATB]

22 minutes ago, Mopar1973Man said:

Then the ECM is good. If that resistor is clearing the codes. Then you back to the sensor being bad.

 

Dumb question, does the truck have a high idle kit on it? Is the switch left on high idle by chance?

No such thing as a dumb question. Truck dose have high idle kit on it, the switch is off... it’s the actuator type. Flip switch and tap foot feed because actuator isn’t strong enough to open throttle by itself. I can engage and disengage high idle just fine. While high idle is engaged truck runs/sounds good at 1200 rpm. This kit dose not give me 3 cyl option. If i ever get this beast figured out i think I’m going to order one of the moparman kits. Of the resistor con IAT plug allows me to clear code, but truck is still doing high idle and 3cyl high idle by itself in 40 degree weather. I’ve put two new IAT sensors in already, i suppose i could get two bad ones in a row from oreillys.. I’m going to have a look at the oil pressure sensor and the cps this morning I’m hoping i find a problem with one of those.

Dose edge juice w/ additude mess with IAT, cts readings? I know there’s a map fooler.. i have the edge main harness disconnected and the map fooler unplugged.. so edge shouldn’t be doing anything now 

Edited December 9, 2017 by JP907ATB

[Mopar1973Man]

I need to know what values your live data tools shows for both ECT and IAT on a cold engine. Thet should match exactly. Both ECT and IAT are the same thermistor and typically are exactly the same on a cold start. +/- 1*F is nothing to worry about but if it greatly different then I would have to say the sensor is bad.  

 

6 cylinder high idle requires <32*F IAT with gird heater firing. 3 cylinder high idle required <15*F with gird heaters firing. This is why I need to see the IAT and ECT values at first key on. This will validate the sensor and it value. 

 

Another dumb question. The sensor is it stock location at the rear of the head correct? I've seen some people move then to the intake horn this will create all kind of weird problems because the IAT temp table is based on it location so if it has be relocated then it will make things behave wierd. 

[JP907ATB]

Yes the sensor is still in the original location on the back of head, drivers side. Right now the truck has the starter out and ecm plug out, after i test the wiring to the other two sensors i will put it back together and look at live data and get back to you. But normally the ECT read outside temp +\- a few degrees but IAT always reads -40, it read -40 as soon as i put new sensor in.. could something in my wiring or computer be shorting out the sensor? 

So it’s not cold enough here now for truck to be going into highidle or 3cyl high idle by itself 

The other weird thing is if i plug in my edge monitor and bring up IAT and CTS on there they almost match identical

[Mopar1973Man]

I wonder if you getting the right sensor? 

 

The ECM only supplies a 5V signal. Now on the 5V signal line is also the sense for the value. So with the IAT plug empty it should throw a high volt code. Now if the plug is short to the signal ground (NOT body ground) it should report a low volt code. Because now the sense should see 0 volts now. So your resistor is creating a value that is usable and not tripping a code but it is starting the high idle.

 

So if it was me I would look into another source for IAT sensor. 

[JP907ATB]

I have a lifetime warranty Borg Warner IAT now, and the resistor is making the ecm see around 114 on iat. Why would high idle still engage if iat is reading 100 plus degrees?

Sorry I'm new to diesel world, i have owed this truck for a year now. This is my first major issue besides rebuilding the rear end... that just took $$$$  lol

[JP907ATB]

What is normal Oil pressure @ start up and @ operating temp??

[Me78569]

at idle ~70 when cold and 30 when hot however not all trucks have a true oil pressure sensor, some have a switch.  

[JP907ATB]

13 hours ago, Me78569 said:

that was me.  the oil pressure sensor shorted internally and caused the entire 5v system to go wacko.

So i just checked wiring to the oil pressure sensor and it ohm test good, I’m wondering if there is a way to test the sensor itself, or of i should just replace it now while it’s easy to get at before i put starter back in

[JP907ATB]

Do the wires in this diagram for crankshaft position sensor go to ecm or pcm? I thought that the crankshaft sensor was on the same circuit as; Oil pleasure, coolant temp, map and iat sensors. Am i wrong?

[Mopar1973Man]

Crank senor all goes to the ECM.

[JP907ATB]

Okay, I have ohm checked all wires to all sensors on the IAT circuit.( CTS, IAT, CPS,MAP, and oil pressure sensor) they all ohm check good through sensor connectors back through ecm plug. I have new CTS, MAP, and IAT. Going to put new oil pressure sensor in before i reinstall starter, thinking about putting in a new crankshaft sensor to. Is there a way to test these two sensors?(OPS and CPS) just trying to eliminate last few ideas before going after new ecm...

[JP907ATB]

well after triple checking all my wiring to all sensor connectors back through ecm plug, testing alternator, replacing batteries, cleaning grounds, and various other electrical tests. I have pulled the trigger on a used know good ecm, same year truck, and part numbers match, hoping for the best. Will let you guys know of it cures my headaches. Also is anyone taking faulty ecms and repairing them?  

[dripley]

There are a lot of places attempting to rebuild them. Most are not very good at it. We have heard of 2 or 3 that seem to be having success. That is another reason, along with cost, why it is difficult to advise someone to replace theirs. When mine went back in 09 it was mostly unheard of. I had a hell of time getting advice. No one really new what to look for. I went the rebuild route and spent a lot more money than just buying one from Dodge. Hope all goes well for you. 

[GSP7]

I just bought a completely re-manufactured ECM, with updated software, and programed to my vin # for my truck, from a reputable known quality company

 

How much $$ did you pay for that used ecm of another truck?

 

 

Edited December 31, 2017 by GSP7

[JP907ATB]

The one I’m getting isn’t rebuilt, it came off a cracked 53 block, i was just wondering if i could get the one i have repaired if it turn out to be the culprit

[dripley]

A small list is in this article. The third one is the one that @GSP7 used I believe. What did the rebuild cost you?

[JP907ATB]

3 hours ago, GSP7 said:

I just bought a completely re-manufactured ECM, with updated software, and programed to my vin # for my truck, from a reputable known quality company

 

How much $$ did you pay for that used ecm of another truck?

 

 

400 shipped, how much was your remanded one?

Edited December 31, 2017 by JP907ATB

[JP907ATB]

Alright so you guys are gonna shake your heads... I put in my new  ECM, and no change in my high volt code to IAT... so i decided to cut plug off IAT connector and wire in a new one.... that cured my po113 code... now i have taken new ecm out and put my old one back in, and the check engine light stays on however something fishy going on... truck was sitting in my shop at 45 degrees and when i fires off and backed it out the door, it sat at idle for moment before kicking into 3cyl high idle, with both ECT and IAT in the 40s. It stayed in high idle welll above 120 degrees on Coolant temp... i don’t think that it should be going into 3cyl mode being this warm.... the outside temp was zero, but everything was warm from being inside shop. I am thinking the bad IAT connector shorted out and damaged the ecm some how, but Its not throwing any codes. When i had the new ecm in, it did not go into high idle at all even with the Po113 code... what do you guys think? I am also wondering at what temp 3cyl high idle will engage and at what temp will it disengage when working properly?

Edited January 7, 2018 by JP907ATB