That was weird.

I left Blue Mesa Reservoir, headed home, roughly a 20 mile drive.

As I accelerated onto HWY 50, I felt 2 very minor misses. Then a mile or two later felt like the truck died for a couple seconds. It continued to happen all the way home. I'd pump the throttle & it would snap back to life. Seemed to happen more at partial throttle. I could put the clutch in and spin the motor up at WOT.

Progressively worsened the whole trip home, wasn't sure I'd make it. By the time I was pulling up to the garage, the truck was dead at all throttle positions. Had to restart and pump the throttle to pull up completely, barely made it. I was sort of sure I had a TPS problem.

I ran inside, grabbed a multimeter & started testing the TPS. I expected to see an erratic TPS signal, but did not.

I have 5.01V feeding the TPS, a good ground to the PCM, and the TPS sends .87-4.7V from closed to WOT. I can't get it over .87v at closed throttle.

Right after testing, roughly 5 minutes after it barely crawled into its parking place, the truck fired up and seemed to run fine. I haven't put it in gear and driven it yet.

I admit, I have screwed with "the idle screw you never screw with". I did this out of desperation immediatly after installing EFI about 3 years ago. I was trying to fix a hanging idle. Gary/EFI Guy briefly explained how to readjust this screw, I've asked him to post it up here so I can fix this. He has had one of my ECUs for a while now, and made a valiant attempt to diagnose & repair the faulty board. He has come to the conclusion, my boards (both rebuilt Cardone) were incorrectly rebuilt and have problems that are contributing to my hanging idle. I doubt this screw has caused this problem, but may be causing the low .87v reading at my TPS.

So....my thoughts, in my order of probablity

vapor lock/failed fuel pump- just replaced the LP pump with new Carter just before Moab, running 3 year old, new Airtex HP pump- crosses to late 80's EFI truck pump.

MAF?- running junkyard/ebay'd 70mm 4.6L MAF, have my old 55MM MAF to swap back in

TFI?- 3 year old new TFI, forget the brand but it wasn't a cheapo

???

First real problems with my EFI in 3 years.

Ignition switch?

Fuel pump relay?- Original RJM relay

I know nothing about EFI, but do you have fuel filters?

The accumulator between the LP & HP pump is a large fuel filter, and there is carb style filter at the tank.

http://www.summitracing.com/parts/rus-r45020

Maybe I need to check it.

I had some similar type hesitations when I would try to go full throttle. It would eventually choke completely out. If it sat awhile I could drive it normal for a mile or so before it's repeat. My assumption is the gunk in the filter would settle after a bit and I could start it up. After being at full throttle, it would throw all the gunk into the line. Once I removed the filter, the problem was gone. It'd be nice if that's all it was.

Sounds like a fuel pressure problem.

Cool, I'll check the fuel filter tomorrow and get the fuel pressure gauge on my fuel rail.

I agree that it sounds like a fuel delivery problem. Pull out the pressure gauge and see if you can catch it in the act.

As for setting the throttle stop, at warm stable idle with no adders in effect, the IAC should be running at 35% duty cycle. Leave the IAC plugged in and back probe the wires with your meter. Slowly adjust the screw until you achieve 35%. It might take a minute or two between each little tweak of the screw before the reading stabilizes.

I wouldn't rule out the TFI. When mine went out, it seemed to have similar issues. It would slightly miss a little here and there. Then it died all together, or so I thought. I was snow bashing with a group of Jeeps. My bronco died as we were headed out on a uphill. Popped the hood, scratched my head, let things cool down and waited for someone to notice I was no longer behind the group. Got towed to near the top of the hill (took four jeeps), where the darn thing started. So I drove up the trail, but only made it a mile before it died again. This time, no refire, not even when trying to get it on the trailer. Went to the junkyard and pulled three or four more modules, popped one into the bronco and she fired right up. Took all the others to Autozone to have them tested and they all checked good except the one that failed on me.

There is no one in Gunnison with a proper adapter to fit my gauge to the fuel rails. I found one for about $7.00 on Amazon, I'll get it in a few days.

I pulled my filter and found a fair amount metal slag & metal shavings from the new Aero tank I installed in November. I wonder if this would clog the filter enough to cause problems. I'm glad I cleaned it. I installed the spare element I ordered with the filters. I'll soak the dirty one and cycle it into my on-board parts bin.

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Not related to this problem, but I got to thinking about the stuff that was in my filter. That filter was installed when I upgraded to a Carter LP pump a week or so before Moab, in April.

I happen to still have the pump & filter I removed. This was the pump & filter that was on the new tank from October until April.

I cut it open

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*****WARNING THE FOLLOWING IMAGE MAY BE STARTLING******

I'm more than a little surpised by what I found. It was packed full of metal shavings & welding slag. I had to pick it out with a small screwdriver, the debris were packed between the metal housing wall & element.

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I'm surprised I didn't have trouble with that filter. Needless to say, this is a dramatic illustration of the crap left behind in a new fuel tank.

So have you tested it with just the new filters? Or are you waiting to install the pressure gauge?

I drove it to work today & around town, before cleaning the filter. Didn't have any problems. But didn't drive more than a mile.

Recently it seams there are a couple of folks having fuel filter / delivery problems after installing new 23 gal tanks. I think Rox was fighting junk in his tank also.

I'm really starting to think it was just a clogged fuel filter. I haven't taken it on any long runs, but around town, and, to and from work, it hasn't stumbled.

Also, my Carter LP pump is much quieter than before. I can barely hear it run to prime the EFI when the key is turned on.

Fingers crossed.