Hey Guys,

Maybe a simple question. If anyone can help I would appreciate it!

Is it possible to have a P0128 code low engine temperature and have a CHT sensor reporting 298 degrees. Can I make the assumption the CHT is incorrect?

Also, if it's reporting 297 degrees could it be shutting down 4 cylinders and causing an intermittent lean code P0174 and engine bucking like crazy? I pulled the data with an elm code reader and extended Ford PIDs. They just seem in opposition of each other. I can upload the data spreadsheet if you want to see it.

Thanks again for the help!

 

Can you set up your code reader to simultaneously display, or better yet, graph, the CHT_V PID and the CHT/ECT temperature PID from a cold start?

Do you have the PCED for your truck? If so, see the introduction to Section 5, Pinpoint Test DL for an explanation of how the CHT sensor circuit is interfaced to the PCM.

Go ahead and upload your existing spreadsheet data, don't know if it would help or not since we don't know what it contains.

I just assume that if you fix the obvious issue, the rest can wait and see if those other issues are by-products of the primary failure. The obvious issue is the CHT circuit malfunction.

Edit: I assisted another F150 owner earlier on another forum with a similar (but not identical) issue. You may find important insights (as well as links to the above mentioned PCED documents) at https://www.fordf150.net/forums/view...5303&hilit=cht Be sure to read all of the posts.

 

Hey wow thank you! That's super nice of you! The attached is all the PIDs I have the ability to collect. It was captured during a PO128 MIL if I look at the CHT it seems crazy high. It seems like it won't let the car go over 50 and it bucks violently. Like I'm leosing four cylinders. Also, it seems to not let me shift into OD. I will jump on the freeway today and and capture data during the worst bucking.

In the attached you can see coolant temp went up to 176 which is low. However, CHT temp went to almost 300. Voltage dropped though on the CHT as it got hotter which I would expect. So that's not the problem. The IAT was reading like 128 degrees earlier. I cleaned the MAF and it we need to down to 100 degrees which still seems high.

Since it logs to a csv I can bring it into Excel and graph any of the PIDs in the attached.

Thanks again I really appreciate you looking at it. I will be log much more data tonight and upload it. Let me know what you would like to see graphed.

I get the P0174 Lean Bank 2 an P0505 Misfires intermittently be as well. Front 02 sensors,plugs, cops, fuel filter PCV elbow and cam position sensors new within 1000 miles. About to change VCT solenoids today.

 

Oh forgot I have an All Data subscription with access to all pinpoints. Been poring over CHT operation documents for 36 hours. Lol I know it should be 5v and go down as it warms.

 

Oh sorry one last thing. No coolant loss. It's full.

 

From what I can see, that data capture is from a cold start with the engine in the mid to upper 70s (F)

Look at the data in columns AZ and BA. The CHT voltage says the temp should be in the 70s. The PCM is reporting it as 158F which is an illogical value, it doesn't match either the "cold end" or the "hot end" V/T chart.

I think your PCM's input for the CHT sensor is hosed, just like the guy in the thread from the other forum.

I'd fix this issue before even thinking about anything else. If the PCM thinks the engine is overheating, it puts the PCM into FMEM mode which will alternately shut off injectors to limit the effects of overheating. You have a false overheating condition but the PCM is going into failure protection mode based on faulty data.

 

Thank you so much!!! I have pored through 1k line spreadsheets looking for the issue then last night I spotted the inconsitentcy out of nowhere. It was in the the 70s when this test was run.

You can feel when it shuts down the cylinders on the freeway. It jerks so bad you could get whiplash.

It's so crazy how it randomly went after all that work was done. Literally for a week after it was like I had a new truck then bam.

Thank you so much for taking the time to review all that data! Can I PayPal you a tip? If not I just bought the first round.

 

I'd give someone like www.circuitboardmedics.com (a forum sponsor) a call and run it past them before condemning the PCM. They work on that sort of stuff and may be able to offer insight into what the problem might be and can give additional guidance. Or, maybe you can send them a PM and ask them to look at this thread and comment.

 

Thanks for the suggestion. I'll give it a try. Just out of curiosity could a faulty air filter that was leaking cause something like this? I made the mistake of buying one at AutoZone, just before all this started, and the filter media became unglued from the felt on top causing a possible vacuum leak and non-filtered air to enter the intake. I was camping and driving in dusty conditions gravel etc. with possibly no air filtering. Pic of the filter below:

 

I don't see any way the air filter issue would cause the primary symptom(s).

 

Cool, I figured it probably wouldn't have, but the timing was just really coincidental.

 

Well, I guess you don't see many updates after folks help with troubleshooting, but I figured I'd provide one in case another poor soul runs into the same problem.

​​​​​​I've been traveling a bunch for work and the truck has been mothballed since. Definitely several issues since I put 5k miles on it after purchasing.

The Cylinder Head Temp sensor went bad and is reporting a false overheat. Along with that the thermostat is sticking open. The CHT is a little bit of a pain to get to. Remove the intake manifold. Also, noticed a little seep from the valve cover gasket on the driver side so I guess while the intake is off, I'll be replacing that gasket. One of downstream O2 sensors was getting lazy. Replaced both at at the same time found a small exhaust leak under a heat shield.

So I think I'll try my hand at fixing it all this week if weather holds out. I put about $1500 into it since buying it. Once it's all fixed maybe I'll look for something different and put it up for sale. Too bad loved that truck.

​​​​​​Anyway, thanks to all that helped! 🍻 Hopefully it will be a fairly smooth repair. Fingers crossed!