New IAT, temp goes above 293, watch it drop on the code reader

[Tim Waldo]

So the last code I had to deal with was one for the IAT... ordered a replacement and put it in...   The old one looked "melted" https://photos.app.goo.gl/T5s5ek2kwEQnGqBE6 and I discounted because I haven't touched it since 2008....  WHAT would make the temps in the IAT chamber go up so fast?  Burnt valve? I don't have an exhaust brake... 

ECM??? would the ECM somehow confuse the interpreted signal? I mean I did watch the temp slowly drop when I turned vehicle off.

Vehicle did get new injectors, it is possible valve clearances got "changed", guy doing the work stated the rockers appeared "loose" but I don't know on which valves.  I don't think this is a new thing, no codes were being thrown BEFORE I had the VP44 issue.

 

[Mopar1973Man]

Bad ground signal wire? The ECM senses and supplies +5V on the same wire. The ground gives bias. If the ground leg is bad it will go to max voltage and most likely trip high volt codes.

 

When the 5V line is shorted to ground it will show lo volt codes.

 

So I would ohm from IAT plug to the ECM plug. Of course both endsneed to be I plugged to do this test.

 

Highest even only truck with a exhaust brake I see about 140°F. I would say bad IAT sensor or bad wiring.

[Tim Waldo]

would that then allow the "temp" to slowly drop back down?  that was the part that confused me... its like it honestly was cooling off.

 

 

[Tractorman]

1 hour ago, Tim Waldo said:

would that then allow the "temp" to slowly drop back down? 

 

Anytime poor wiring connections are a possibility, the symptoms may or may not be predictable as the resistance value can change at any time for no apparent reason.  The only time an electrical connection will have resistance stability is when the connection is good electrically - which means virtually no electrical resistance. 

 

- John

Edited April 1, 2023 by Tractorman

[Tim Waldo]

John,

did you look at the photo of my old IAT?? it was MELTED.... I don't think this is a matter of a grounding issue.

[Doubletrouble]

 After I looked at the pic I understand your concern. The sensing end within the intake melted. I assumed the plug end melted. 

 Somehow there is an excessive amount of heat getting into the intake track.

 Do you have boost gauges? Was it building that same amount of boost? I would think a valve hanging open would affect that reading?

 Maybe with the engine cold, pull the valve cover and check valve lash?

 Also, inspect the turbo for shaft play? I don't know if it's possible for heat to transfer to the pressure side due to a failure within the turbo?

 I'm spitballing here, I'm sure so.one else may have better ideas.

 I'll be watching, I'm curious of the cause now as well 

[Mopar1973Man]

Valve hanging up or open would cause misfire and engine shake. Compression is what makes it run so intake vale would make it miss. The only thing I can think of is a compression test which is way better than blow by test.

 

As for the IAT it's plastic on the cage. Now it's possible to have it start and run backwards. I've seen a few report this but very rare. I've seen 2.5 ton military truck do this and melted the air filter.

[Tim Waldo]

2 hours ago, Doubletrouble said:

 After I looked at the pic I understand your concern. The sensing end within the intake melted. I assumed the plug end melted. 

 Somehow there is an excessive amount of heat getting into the intake track.

 Do you have boost gauges? Was it building that same amount of boost? I would think a valve hanging open would affect that reading?

 Maybe with the engine cold, pull the valve cover and check valve lash?

 Also, inspect the turbo for shaft play? I don't know if it's possible for heat to transfer to the pressure side due to a failure within the turbo?

 I'm spitballing here, I'm sure so.one else may have better ideas.

 I'll be watching, I'm curious of the cause now as well 

 

50 minutes ago, Mopar1973Man said:

Valve hanging up or open would cause misfire and engine shake. Compression is what makes it run so intake vale would make it miss. The only thing I can think of is a compression test which is way better than blow by test.

 

As for the IAT it's plastic on the cage. Now it's possible to have it start and run backwards. I've seen a few report this but very rare. I've seen 2.5 ton military truck do this and melted the air filter.

 

DT, so it builds boost... not as much as before but I'm also babying it right now so I wouldn't expect boost past 10psi the plug end was gummy, not "melted" but yes it got warm.

 

MM it does shake a little on starting but immediately goes away, but I THINK it always did this... I mean I havent' really driven my truck since the end of January and those things don't stick with me. I don't think it is running backwards, seems like that would be VERY obvious. What about loose valve train? the mobile mechanic said my lifters/valve assemblies seemed loose and he felt should be replaced.... is this really a thing? 

 

I'm not running it now except for short runs for test, definitely not driving it... should I have it towed to a shop because I am done with mobile mechanics.....   

 

[IBMobile]

Check the intercooler for some type of restriction performance problem.  It may not be sheading heat. 

[Tim Waldo]

I will check that...maybe a cloth got stuck in the intake.... tomorrow though, I'm busted for today

 

[Tractorman]

6 hours ago, Tim Waldo said:

John,

did you look at the photo of my old IAT?? it was MELTED.... I don't think this is a matter of a grounding issue.

 

I have looked at the photo.  It looks as you described. 

 

If I am understanding correctly, the sensor in the photo had been in operation since 2008.  According to the title of this thread, you installed a new sensor and observed a very high temperature reading (above 293°).  You also noted that the temperature dropped off slowly after turning off the vehicle.  My previous response was based on this information regarding the new sensor - not the old damaged one.

 

So, I am thinking that there are two possible problem areas:

 

*  One - the temperature reading (over 293°) is real and the previous IAT sensor was overheated by excessive of heat of an unknown source.  This source of heat, if not found, will damage the new sensor.

 

*  The other - the high temperature is false and the false reading is caused by a wiring issue or an improper signal.  The temperature slowly dropping off after turning the vehicle off could naturally happen because the signal voltage to the sensor would have been switched off at the same time.  The cause of the previous melted IAT sensor would be difficult to determine because it had been in the truck for years without observation of condition (assuming it had never been removed and inspected).

 

It may be worth pulling the IAT sensor for inspection to see if it is being exposed to excessive heat.

 

I think you have a unique and a difficult problem to solve here, but the folks here will help you through the process.

 

If I have misunderstood anything you have said, please disregard the above.

 

- John

 

 

[Tim Waldo]

John,

key on, engine off immediately after running and throwing the code... it took a few minutes to throw the code and then ran a few minutes more.  I left key on so I could watch the reported temp... at first it didn't drop any (thinking it was so high out of range) and then slowly started dropping 2 degrees at a time and then finally it ramped up to 5 degree drops (I watched for 5 minutes if not more).  The sensor I replaced would swap between 142 and 293... typical response to a thermistor that has gone bad... that or hanging on one resistance.

But AGAIN... this was not an issue before the VP44 failed... so it is something that happened while I've been swapping VP44's

 

Based on what I've read so far the plan of action tomorrow is to replace the air filter and examine the full path of the intake air (have an S&B cold air system) I bought a dry filter to replace the oiled filter but wasn't going to do it till the truck is running...  Here is the kicker... none of this was a problem until the VP44 went down and I basically parked the truck..  I am THINKING that there is a blockage at the air filter OR in the air intake system...  we have rodents (not sure they are squirrels) of some sort and now I'm wondering if they did something (they built nests in my sons jeep, but not in the engine compartment.... this could account for the air starvation I have been keying on thinking there was a split in the intercooler boots causing the whiteish grey smoke... it is sucking as much air as it can get , but it isn't enough to pull down the air temp at the IAT sensor (no I wasn't paying attention to my EGT's)... I'll watch both boost and EGT's next time I start the engine up.... boost was slow to spin up but it did spin up.... anyway I may go as far as pulling the intercooler out if something doesn't jump out as DUH on first inspection.

 

Thanks for reviewing, your response just justified where I am going to start.... any other ideas would be much appreciated because honestly I studied up on this engine quite a bit when I first got the truck and then never had a problem with it... I think I dropped 5th gear pretty early on... and had a ton of issues with the brakes until I realized the shops were using non-synthetic brake flue and I was baking it off .. I've changed a couple of alternators... but NOTHING else... so now I'm struggling to recall all the possible things that could cause the issues.

[Tim Waldo]

SO I went out this morning, started at the air filter and examined everything but the intercooler... all seem to have good air flow... so I resigned myself to removing the IAT again.. (I know, it isn't that hard, just greasy)  I also started and checked the IAT temp and again watched it ramp up and then start falling when engine was turned off.... removed the IAT and THIS is what I found...    I'm going to buy a retractor (push button jaws extend, release button jaws close) this afternoon and see if a mechanics towel got sucked in...  SO how hard is it to pull the entire air chamber?

did some more googling.... found this...

 

https://www.cumminsforum.com/threads/ait-sensor-melted.978842/

 

What would you guys suggest I do?

 

[Tractorman]

Tim, I reviewed that same post yesterday.  I am glad you decided to inspect the IAT sensor.  I certainly think you now have proven the source for the damaged IAT sensor is from a source of high heat.  And, since it appears to happen right away with no load on the engine, the only thing I can think of that could generate that much heat in a such  short period of time would be a nearby cylinder with an intake valve that is leaking - not a large leak, but enough of a leak to allow combustion gases (a flame) to enter the intake manifold.  The leak would have to be small, otherwise there would not be enough compression to ignite the fuel.

 

Possible causes:

*  an intake valve adjusted too tight

*  foreign material passed through an intake valve and is still lodged there or has damaged the intake valve or valve seat. 

 

Is it correct in assuming that the intake manifold was opened for replacement of the VP44?

 

Not sure how hard it is to remove the intake manifold.

 

You might try barring the engine over to see if you can feel a cylinder with less resistance on the compression stroke.  It would help determine which cylinder is the problem. 

 

- John

[Mopar1973Man]

Personally, I think you going to be pulling the head off.

 

If you roll the engine over using the alternator you can check the valve lash of each cylinder as it comes up on TDC for each cylinder both intake and exhaust rockers will be loose and have clearance. Still, the easiest to find would be to pull all the injectors out and then use a compression tester injector blank and put compressed air into the cylinders. Then you would hear it in the intake. Still you'll have to pull the head to have the valves serviced.

 

[LorenS]

Is it possible for the grid heater to cause this through some fluke?

[Tractorman]

I wondered the same, but I can't imagine that even if both grid heaters were activated how the air temperature could rise from ambient to 300°F with the engine idling.  However, it would certainly be easy enough to remove them from the equation.

 

- John

[Mopar1973Man]

Grid heaters can be unhooked at the driver side battery positive post. Just the two smaller black wires. It will not throw a code. This will disable the grid heaters.

[Tim Waldo]

Guys thanks a TON...  shipping it to a reputable diesel shop today or tomorrow should have done this when I had the first VP issue but tried to save $$$ by having a mechanic come to me... this will end up costing me (already has actually) than if I had just sent it to them in January....  Just hope I haven't done irreparable damage by running it as much as I already have.

This all started after he replaced the VP the first time and dropped something into the air intake.... is when I started throwing IAT codes.

[Tractorman]

I know it will be awhile before your truck is fixed, but don't forget to let us know the exact cause.  We are all interested in knowing.

 

- John