A little background: 2 days ago, i got a p1281-engine taking too long to warm up. Under the assumption that the stat was stuck open, i went ahead and replaced it.

Heres the fun part- after replacing the stat and waiting for the rtv to dry, I started it, and BAM cel comes on within 3 seconds. Drive for another 5 or so seconds and my check gauges light pops up. Look down at temp, and its sittin at 260, another 5 seconds and it whips back to all the way cold.

Parked the truck and checked the code by cycling the key 3 times (love being able to do that). Po118-ECT voltage too high. I'm wondering if my ECT just fried itself, or if the problem is simply because i didnt top off the rad after completing the stat job (didnt have any coolant, and only had to drive a block to my house). Wont be able to update until afternoon tomorrow

any advice or opinion is appreciated
Mad_Sci

 

Air (way too much of it) in the system will cause the symptom you saw on the temp gauge.

The code is usually a bad temp sensor or a wiring fault.

 

^^^^thinkin its the second option, thanks for the reply.

New and interesting development: topped off the coolant and reset pcm before i went to help my brother out. Truck started and ran fine on the way there, temp gauge acted normal.

As i went to leave, it hiccoped once like it wanted to die when i switched from reverse to drive, then popped back up to normal idle. About 2 blocks later, it died when i slowed down to take a turn. Had to pump the gas a bunch to get it to start back up.

I parked at a gas station and popped the hood to see if it was something obvious, but nothing was out of the ordinary. Started fine when i left the gas station, after 2-3 more blocks, it gave me the same problem stated in op (temp gauge went nuts, CEL came on-po118).

Pulled in to advance to try and pick up an ECT, and it died when i put it in park. Had to pump the gas to start it, drove fine all the way home (2-3 miles), temp gauge read fine. Tested to see if changing gears was the problem: put it in park, stayed at good idle no hiccup or anything.

At this point Im thinking its a short in the wiring to the ECT: while driving the wires bounce up and down and short, giving false info to the PCM making it think the engine is hotter than it actually is and it meters A/F ratio as if it was at operating temp, while it should actually still be in open loop

Anyone else have ideas? C'mon guys I need some more opinions. Thanks in advance
Mad_Sci

 

I would check the connector at the sensor. I don't know if resistance goes up as temp goes down, or vice versa, but, if the PCM suddenly saw the temp going to -40..... it would dramatically alter the amount of fuel it was dumping, and you would have all sorts of interesting issues. (like you are seeing.....)

 

Thanks for the quick reply HeyYou, thats exactly what i was thinking. Waiting for it to cool down a bit, then i get to whip out the old volt meter and see whats up.

Probably disturbed the wiring when i took off the alt (stat housing still had that damn tab on it, so i couldnt just pull it up) for the stat replacement.

 

Bring it up here, its colder than a witches tit in a brass bra..... My truck goes from fully warmed to stone cold in less than 20 minutes.....

 

LOL Thats why im glad i live in the south, id rather sweat my ***** off in 105 deg 99% humidity heat than to be cold. Must be pretty cold up there if it cools that quickly (to think i was bitchin this morning when it was 32 out... its 60 now, feels great [icon_mrgreen])

 

Got her fixed: before diving in with the voltmeter, i took the pigtail to the sensor and wiggled it and the wires to it around a bit. Pushed it back down onto the ECT, and went for a short drive. lo and behold: CEL went bye-bye. This is just a temp fix, Ill pick up and install a new pigtail for good measure next time im near a pick-a-part.

Wish every problem was this easy lol

thanks
Mad_Sci

 

Good find! Glad you got it figured out.