I would think Crank sensor, but...do you have a new car battery that you could swap in? Sometimes a failed cell inside a car battery can do trippy things to your electrics when the alternator is at low output (e.g. when idling).

And for free, I'd suggest pulling your Idle Air Control valve and spraying the hound out of it with cleaner.



Since you aren't getting any SES codes your problem would seem to need to be mechanical/vacuum or crank sensor.

 

That sounds more like a battery/alternator issue.

 

Well I checked the battery terminals, they were tight, but a little high on the post. I disconnected them and set them lower on the post. I also verified the ground connection to the alternator bracket it was tight.

When I started it back up I noticed the UG voltage above 14 so I thought I did something good. Then I took it around the block and turned the A/C back on and it dropped down to 13.6 so that looks normal.

Unless anyone has any other ideas I'll just continue to drive and monitor.

 

I think your problem is solved. Cheers!

 

There are a whole bunch of chassis grounds all over the truck.
I go around once in awhile and crack them loose and retighten them to make sure they have good contact.
There's a diaphragm showing were they are floating around somewhere.
Fenders, core support, firewall, under the kick panels, etc.

 

Well not out of the woods yet. I drove my son to school this morning and the UltraGauge stopped reading temp at a stop sign. I think it also tried to stumble but it happened as I was accelerating away which kept it going.

Anyway when I got back instead of stopping/restarting the truck I just unplugged/replugged the UG and it was able to read everything. So the ECU was good and online my UG just needed to be reset. Voltage on the UG remained good the entire time; over 14v with the AC and radio off.

I really don't think it would be a loose ground, it has been fairly predictable when it occurs. It's usually on the first crank of the day and only appears to happen at idle.

Is there anything I can test besides just replacing the ECU?

 

Have you removed connectors from your ECU, checked for contamination/corrosion, cleaned with contact cleaner and reinstall them? Often just a connector reset will fix intermittent and/or hard electrical faults.
......

 

I'll just throw it out here. All my trucks run well and I see that happens all the time with the temperature disappearing. Unplug and plug will do the tick and often, I dont unplug it and it shows back up again. 3 out of 3 trucks have same issues. Not saying but I am guessing its the UG firmware that might need some updating or something. It sometimes shows (err) on the temp gauge. I also use iCarsoft and Innova which checks fine.

 

Yea I seem to remember temp dropping out before all my engine work on rare occasions. If it weren't for the engine stumble occurring at the same time I wouldn't mind the reading disappearing. It's the stumble that really concerns me, since I believe it actually stalled from the stumble yesterday morning.

I will pull the ECU and check the connectors today.

 

Well it happened to me again, but stalled out at a red light. Thankfully after about 30 seconds I was able to get it cranked again. It didn't happen at the first few stop signs while the truck was still warming up on first crank of the day. I had gotten up to temp and came to stop at a redlight when I felt it stall and die. I would normally think its the CkPS, but I'm not sure if that would cause loss of communication to the ECU? I was also able to get it running after a few seconds trying to crank it.

So I've noticed based on past experience and today, that it is usually a type of stall that is overcome if I'm on the accelerator. Yesterday it happened while accelerating along a straight away and I felt it jerk and the UG stopped reporting temp. I only keep mentioning that because I'm using it as a sign of loss of connectivity to the ECU.