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Discussion Starter #1
ok guys, really need some help here. Sorry if its long, but i really want to fix this. i have searched all over the DF and others, with no luck. i cannot, for the life of me, figure out why my temp gauge going crazy! i have found a few other threads with people having the same issues, but not one solution for it(many guesses).

heres the issue-

the temp gauge will fluctuate from side to side, 160 - 260, very erratic and random. and DIC will say "coolant hot"/"engine overheated"

it doesn't matter if the truck is warm or i just started it first thing in the morning.

seems to do it mostly at idle or when i let off the throttle, but it is random and will do it cruising on the highway as well.

when it is happening the idle seems to jump around (~100-200rpm's) and the truck sounds rough.

here is what i have done to try to fix it-

changed the thermostats, full coolant flush, new overflow cap, new temp sensor, new temp sensor plug and leads, i've bled it many times, checked and cleaned grounds(read a thread that suggested this), and next step i have a MA water pump i was gonna throw in this weekend.

each time i do something it seems to make it go away for a few weeks, but then comes back.

i have checked the FCM harness to see if maybe it was that with no luck. no codes come up and i don't know what to do next, really desperate here!

i have some videos that may or may not help, anyone who has had this or seen this, please let me know how you fixed it!


(if someone could help with how to post the videos i will they are .MOV files)

thanks for any input!
 

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Honestly I would probably buy a cheap water temp gauge from an auto parts store, install a slip in sensor in one of your hoses and compare that to your cluster/ dic to rule that out. That way you can see if it is actually a temperature issue or if it could just be some electronics messing with you. Just an idea. Maybe some others can shed some more light for ya


Definitely NOT sent from my iPhone while jumping on a trampoline wearing a banana hammock..
 

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Discussion Starter #3
no, i had not thought of that, but i really dont think the water temp is the issue. i'm leaning towards it being electrical, i went and unplugged the temp sensor to see what it would do and it seemed to do it much worse and truck ran horrible, i didnt drive it like that, just started it for a minute.

i wonder if the ECM could be going bad and this is a result??? i'm reaching for anything right now...
 

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Mine did this before I installed the mp and Efi tuning. Not so much any more.


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Discussion Starter #5
i am 99% sure now that it is electrical, i hooked up the laptop and drove around while it was doing it. and the temp would be at ~180 then spike to 300 and back down in a split second, the cluster gauge just couldn't react that fast so it moves slower.
i checked my codes and i had a soft code for a bad fuel temp sensor, i read that this is linked with the ECT sensor, so i swapped it out and it seemed fine. it did spike once on the first test drive, but hasn't since.
hopefully all my hair pulling might help someone out in the future!
 

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i am 99% sure now that it is electrical, i hooked up the laptop and drove around while it was doing it. and the temp would be at ~180 then spike to 300 and back down in a split second, the cluster gauge just couldn't react that fast so it moves slower.
i checked my codes and i had a soft code for a bad fuel temp sensor, i read that this is linked with the ECT sensor, so i swapped it out and it seemed fine. it did spike once on the first test drive, but hasn't since.
hopefully all my hair pulling might help someone out in the future!
That's good to know. Glad u got it figured out



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Nice to be able to see the spikes on EFI.

Did the new sensor fix the issue for good?
 

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Discussion Starter #8
so far so good(knock on wood), after replacing the sensor it spiked twice, but been a few weeks now with no issues, i am being very observative of it because if it comes back i will go crazy!

but to answer your question, yes i think(hope) that was the fix.
 

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I have seen lots of vehicles have issues as this from a bad ground. My brother had bad ground on his truck and when he would come to a quick stop all the gauges would stoP working along with lights and such. All from a ground issue. Doesn't sound fixed but better. Good luck.
 

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have u checked for other signs of headgasket failure?
 

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Discussion Starter #11
Yes, I have checked for head gasket issues and everything checks out fine.

A bad ground does sound like it could be a possibility, do you remember which ground your brother had issues with? I just don't get how nothing else would be affected by it, only the ECT gauge, but I will take a look.
 

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I agree, if it's not the sensor itself it it probably an electrical issue (chaffed wires, bad ground, etc)
 

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I know these trucks have had a history of guage failure. My father in laws '05 has a dead volts guage, a fuel guage that has a mind of its own and a speedometer that likes to float around 120. We need to pull the cluster and have the guage motors replaced, just dont have the time or money to do it.
 

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Discussion Starter #14
yes i know what you're talking about with the gauges, my speedo was bad and i replaced the stepper motor, but this is different, the ect gauge works, its the signal that it is receiving is messed up, weather by bad ground, sensor or who knows. i just need to keep digging to find it. Thanks for the input though.
 

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I know these trucks have had a history of guage failure. My father in laws '05 has a dead volts guage, a fuel guage that has a mind of its own and a speedometer that likes to float around 120. We need to pull the cluster and have the guage motors replaced, just dont have the time or money to do it.

He logged the signal on EFI so that rules out the gauges right there.
 

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Discussion Starter #16
I'm bringing this thread back up because the problem is back and i am still at a loss. so today i was changing the power steering fluid, afterwards i hosed the engine down. after that the gauge was going nuts, and it kinda chugs also RPMs jump slightly. also noticed when it rains it happens more.

i went through and opened up the FICM harness and inspected all the wires, found nothing chaffed or cut. i changed the ground strap on the back of the motor, that did nothing. did the icepick trick, nothing. i know it is something electrical, i have searched for hours, on ALL forums and found many threads with these exact symptoms but know one ever has a solid answer.

:help PLEASE!!!
 

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I'm bringing this thread back up because the problem is back and i am still at a loss. so today i was changing the power steering fluid, afterwards i hosed the engine down. after that the gauge was going nuts, and it kinda chugs also RPMs jump slightly. also noticed when it rains it happens more.

i went through and opened up the FICM harness and inspected all the wires, found nothing chaffed or cut. i changed the ground strap on the back of the motor, that did nothing. did the icepick trick, nothing. i know it is something electrical, i have searched for hours, on ALL forums and found many threads with these exact symptoms but know one ever has a solid answer.

:help PLEASE!!!

Since you've already looked at the most common LLY issues (FICM harness at Alt bracket and ice picking injectors) it sounds like you may have an electrical issue that requires a bit of sleuthing to figure out. At least you've narrowed it down to being an electrical issue in the engine bay. Now you'll need to be very methodical about wetting just certain sections of the engine at a time (use a water pitcher rather than a hose) to locate where the issue lies. Try to pick a drier day so you know it's not a humidity issue. Once you find an area that's repeatable (ie when it gets wet, things go crazy), then post up and we can help you with where to look.
 

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Discussion Starter #18
Since you've already looked at the most common LLY issues (FICM harness at Alt bracket and ice picking injectors) it sounds like you may have an electrical issue that requires a bit of sleuthing to figure out. At least you've narrowed it down to being an electrical issue in the engine bay. Now you'll need to be very methodical about wetting just certain sections of the engine at a time (use a water pitcher rather than a hose) to locate where the issue lies. Try to pick a drier day so you know it's not a humidity issue. Once you find an area that's repeatable (ie when it gets wet, things go crazy), then post up and we can help you with where to look.
yes your right, i need to really sit down and go at it, i just get so frustrated with it. and i know if i took it to the dealership here they would just blame it on my mods and dismiss it instantly.

i'm wondering if the FICM could possibly have a short or be bad??? because i know it says not to spray with water pressure on it. IDK, just a thought, its amazing how yesterday it was going crazy, now today no issues! but i know it will be back.
 

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Not to get you on a wild goose chase, but a bad ignition switch will cause all sorts of bs with these trucks especially with the trans and the nsbu switch which runs the trans and or maybe the ficm. Just a thought anyway a new ign switch is 20 bucks and the install is super easy.
 

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I have been through the electrical crap before, it took me saying screw it, pulling the truck in the garage and sayin i dont care if the tires rot to the floor, its not moving till its fixed.

i would check ignition switch, and also just for the hell of it swap clusters and check it.
 
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