I am running between 79 - 80 psi at the fuel filter return.
At the back of the heads I am running 76psi no load and 69 psi under full load.

Why is the pressure so high?

Might try dropping it back down to 60.

We installed a different fuel pressure spring in the return. This was done over 2 years ago, to smooth out the idle, and cold weather starts. It also brought the fuel economy up just a touch. It is still with in Specs from International and ford.

We have taken all mods off, returned the truck back to stock. The truck will run great until we install the FU Chip, then everything goes back to the bad running motor.

Just like this post:

Here is what I have done since last post.
Did the buzz test, everything sounds good on all 8 cylinders. Contribution test is good on all 8 also.
I am lost as to what is going on here.
Now the truck doesn't have the miss, but also has very low power even with the FU chip on 100 hp setting. It feels like the chip isn't even in the truck. my boost used to go to 26-28 psi now it only goes to 15 psi max, blows black smoke really bad. Even smokes on the idle, it is also black, sitting in garage for 3 to 5 minutes, when warm and idling, will burn your eyes really bad.
Oh MPG is down to average of 8.

I took the new injectors out of 7 and 8, put old ones back in, truck still has no miss, but the rest is still the same- no power, smokes on idle when warm, smokes driving it, with the FU chip in.

Take chip out and everything runs perfectly. No smoke, no miss, nothing, and has power, contribution test good, buzz test good, boost up to 26psi, 16 mpg average. I am LOST

Any ideas now? Ready to trade truck off, but can't with it running like this.

Could there be thick oil trapped in a injector boss that causes the solenoid to buzz correctly but injector not work right??????

Guess I missed that post......

Would have to be a calibration issue then.

Well, IT is FIXED finally. :happy-dancing:
There was a bad calibration in the chip. I think it was from when we updated the chip burning program for the FU Chip. I wiped all programing off the computer, reinstalled and re-burnt the chip. Now everything is back to normal. Who would have figured that it was a cheap fix.
Thank you everyone for all your help in this matter, it has been a long drawn out test.

Not sure but someone may want to put this in a sticky somewhere on this forum. There is a lot of good testing info from everyone in this thread.

WOW!!!:doh:

Glad its working for ya!

Moved from emergency....
A thread this old will be closed otherwise....