I recently replaced the fuel pump (Autotrust - Christmas present from the kids, can't really complain, I guess) and the truck ran fine for about six blasted days before acting up again .

Then I replaced the ECT sensor (thought I had it licked at that point) before the problem returned yet again. Before the ECT replacment, I discovered that I could disconnect the battery and unplug the sensor to get it going. Now I can use a squirt of carb cleaner in the TB and it will start and continue to run and start (which it did not prior to ECT replacement) until it cools. This problem only occurs when the ambient temperature is below 40 degrees (F) . One thing I noticed after the ECT sensor replacement is that the temperature guage seems to "spring" to its position at times, especially when you turn the key off then quickly back on - something that I have never seen it do before. In other words, I am used to the guage slowly creeping up toward the current temperature instead of behaving in this fashion. I checked the sensor with an ohmmeter before installation, and got a reading of 3.94 on 20K scale at around 35 degrees, which I assume indicates a resistance of 3,940 ohms. I heated the sensor slightly in my hand and the reading went down as expected.

I haven't had the chance to perform FP dead-head pressure test yet (raining like crazy right now), but I did get a reading from the pressure test connection. It read 52 psi (spec. 57-66) KOEO which was disappointing, with a 10 minute bleed down of <4psi, which was encouraging. The fellow that let me borrow the fuel pressure tester said that it seems like it may be a weak spring in the regulator allowing a "blowby" of sorts into the return line, but I won't be able to confirm that until I do the dead-head. I expect to see >75psi beyond the filter, using a hose that I can clamp from the QD side of the filter to the tester. If that reading is low, I'll go ahead and use another adapter that I can attach to the QD hose that connects the pump to the steel line along the frame rail to rule out the filter itself, which is also new, so an unlikely but not impossible cause.

No SES, and no codes from OBDII were stored, even prior to FP replacement. I did get a "high voltage ECT circuit" code (SES ON) one time right after ECT replacement, but not one since. I dropped the sensor into the coolant catch pan while trying to install it, and I guess I didn't dry it out well enough before connecting (oops!!), so I sprayed the connections with contact cleaner and allowed them to dry before reconnecting. The coolant temperature on SCAN was around 170, with an increase to 180 after raising idle slightly...seems to coincide with the temp guage, but I can't figure out the increments on the scale - they don't make any sense, and I don't know what temp thermostat is in the truck. Also, reference voltage on connectors for ECT, MAF, and IAT sensors are all at 4.95 VDC KOEO, and voltage to all injector connectors are equal at 11.54 VDC. The battery voltage was 13.26 VDC.

Any input would be appreciated on this issue, as I am at my wit's end . Also, if I find that it is the FPR, do I need a gasket for the plenum? Any other special considerations, tips, tricks?

 

I wouldn't look any further into other things until you get the pump dead-head pressure. Aftermarket fuel pumps have a notorious reputation for failure ranging from days to months, rarely years...

 

I figured as much . Last one I had was an Airtex...Thing lasted 6 years, to my surprise!! Must've lucked out, lol.
I'll post back with dead-head tomorrow. Thanks for your prompt response - I was surprised to hear from someone so soon! I really appreciate that

BTW, LOVE that '74 K!! I sure do miss that body style; they were so cool!

 

At filter outlet earlier today: 55 psi

At pump outlet to frame rail a little later on: 52 psi (it's a bit colder now than it was before)

10 minute bleed-down: 11 psi right off the tank outlet. NOT GOOD!! Although I admit that the bleed-down may be due to the way I attached the pressure tester to the outlet hose, it may also mean that now the pump isn't holding pressure as well as it did when tested at the pressure test port.

I think that, because I have to drop the tank again, I'll get rid of the butt connectors that came with the harness kit and solder the connections so that it's one less thing to worry about.

At any rate, clearly, this pump has screwed the pooch already! Jeez - a whole six days of proper operation...What's worse is that I don't have the money to buy a "good" Delphi pump, either, so I might be going through this crap again if the replacement comes from the same lot .