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It will give you time to clear your mind and come up with a good diagnostic approach. Possible issues to keep in mind: intermittent fuel supply blockage, especially suction side of lift pump large amount of air in fuel system (not likely) intermittent power to lift pump faulty lift pump (pressure regulator issue) When things get difficult to diagnose for me, I change tactics and try to prove what is working CORRECTLY, not what is working INCORRECTLY - a process of elimination. This method will sometimes get the issue resolved sooner than focusing on things that one might think is wrong. John

Are you referring to the wiring connector to the blend door actuator that shows a three-wire connection? It looks like others have had the problem you are having. Have you confirmed that you really have a blend door motor actuator problem, or is it possible that the interposer (plastic shaft) is cracked and slipping on the old one? In that case, you can just replace with Heater Treater's steel interposer. You will have to reset the gears though. Heater Treater has a video how to get the gears timed. John

100 GPH. Spellcheck got me

Give details of your bucket test. Have you ran the engine while drawing fuel from the bucket with a separate power source to the lift pump? I'm having a hard time with believing it to be a VP44 overflow valve problem. Did the FASS representative explain with detail on exactly how an VP44 overflow valve problem would adversely affect lift pump pressure? Also, if there is a restriction in the fuel supply anywhere in the lift pump circuit (especially the suction side), then unpredictable fuel pressure could be expected. What it the GPH rating on your lift pump? John

I have a bad blend door actuator on my father's truck (2002 3500 stock) ordered a replacement and all I can find is 4 pin units when plugged it it only rotates 1 way and makes a full 360 turn ( when installed it goes hard agains the blend door in the cool position. no matter the temperature setting. The old unit was a 3 pin but every part numbers listed is for a 4 pin. Am I missing something?

I bought a tow tune from him but it didn’t work. I’m still waiting for him to make the correction so it will work for me. Looking forward to it. Thanks Thank you sir glad to hear from the man himself. I’m not big on power, just like having better mpg and “ unloaded” power while towing my camper. Thanks

It seemed like I might have had another bad relay , so I jumped it, pressures were all over the place, from 20 to 12psi varying rpm’s. I did another bucket test had a constant 15-16 psi for an hour. Hooked the pump back to the truck, keyed it on psi went to 20 briefly while the truck warmed up then psi was all over the place 20 to 12…. FASS is leaning heavily towards OFV in VP 44. IDK

Hello everybody, I used to have a Quadzilla Xzt and had the 3000 tune on it and I just got another Xzt and I was wondering how or if I I can put the 3000 tune on my new one. Thanks

That’s right, same symptoms after 100 miles or so and it seems I’m starting to get the not answer the phone/ not call back run around game on the lifetime warranty from FASS as it now seems to be an electrical issue in pump, best I can tell. Just ordered one. Unfortunately, I have to go back to work and I won’t be able to get back on this with the code reader until February.

Then 2 things. Quadzilla only programs a running truck. There is the ability to see live data that's about it. OBDII code reader like OBDLink MX would be a good option.

Can you recommend one? I’ve been meaning to get a quadzilla . Does that have code reading? Or maybe just a basic code reader for now?

I had a scan gauge on a power stroke. It worked well. Can you suggest one for this pickup.

Just a flag or marker there is another error. Use a actual OBDII code reader.

I’ll definitely take a look as soon as I can get back on it. I just realized I have a P1693 code. I also have not yet done the W-T ground wire mod. I’m starting to wonder if this is what’s giving me relay problems

So the pop off fuel from all 6 injectors will bleed off inside the rail in the head that exits the head at the rear of the engine. Then the second line is the return of the VP44 which is the second line to return to the tank. This is what the square cuts o-ring will seal at the rear of the head. I'm talking the return of either of a FASS or AirDog fuel systems use a check ball and spring to control fuel pressure and flow back to the tank for seperating the air bubbles and fuel excess return is on this line. The fitting in the pump will have a black plastic check ball and a spring.

I have a service manual but , have not opened it up for this yet. Why is there a return tee and not just a single discharge to tank? I’m pulling and returning from a new fleece sending unit. I’m not sure there is a check valve there . I did a bucket test the other day and confirmed the relay was cycling on and off. Replaced relay and it seemed to have fixed the problem…. Not

Dang! If it wasn't for bad luck I wouldn't have any luck at all. Front speakers got installed and hooked up properly for polarity but now my driver side speaker must of come apart in the wiring. Arrrghh! I'm ordering more door panel retainers. 😖

Actually, you can open this up. The return line to the filler neck to the tank is the fitting you remove, and behind that is a spring and check ball. Just be aware the check ball is plastic and could wedge it way down in the coils of the spring. This is why the sudden change in fuel pressure and then later it pops back up when the vibration shakes it loose again. Here is my new spring for Thor. Yes, you are correct, those square cut o-rings are for the return tee in the rear of the engine on the driver side.

I assume you’re talking about an internal check valve in the pump? I can’t open up pump without voiding warranty. While I got ya , the square cut o rings you mentioned, are they for the return on back of head?

Is the check ball getting shoved back into the spring? I typically bend the tail of the coil over so there is a tail tip in the middle of the coil. This will prevent the check ball from wedging into the coil.

Seems to have fixed it for 100 miles or so. Odd, going to run another bucket test and see what’s going on…… PIA!

So, it sounds like the lift pump relay was not the issue? Symptoms remain the same? John

Lost pressure again today on a short trip. Psi dropped to 15 at cruise, 12 at WOT. Got it home , tuned it off, re keyed it went to 18, started , it dropped to zero , but still ran. Shut it off quickly. Going to get on it again tomorrow

You could just disconnect the fuel pump relay to test a warm start condition. Rig up a jumper wire to hold in your hand while you start the truck - that way you can control when the lift pump runs (or doesn't run) for your test. At least, it would let you know if too high lift pump pressure is causing your long crank on a warm start. John

Starts right up when cold. Slow start is only when warm. Relay is wired to battery and fuse block. There are no psi adjustments on this pump. If I was to attempt by opening up, thus breaking the seal, it would void warranty. Are these square cut o rings the ones for the return on back of head? What type of thread comes out of back of head? Any way to maybe convert this to a jic type fitting? Something without o rings