Did you find out why you were having a FP drop? I too was tuning my car on the dyno, and all of a sudden my FP dropped. My car was running with a new supra pump, and filter. I would love to hear what happened to your car as I have not figured mine out yet.

I was running a Marren replaceable/washable stainless steel filter. I changed that out for a much larger Aeromotive filter and datalogged the pressure differences. There is less than 1psi drop across the Aeromotive. The Marren was higher even after cleaning it. I'm currently running the Aeromotive.

The tank was in excellent condition. I cleaned it by hand as well. The contamination wasn't in that tank.

I did, it turned out to be the wiring afterall. What was happening was the wiring was getting hot on the dyno after all the abuse it was taking. 57psi run after run after run after run and eventually the wiring would get warm, causing resistance, causing the a drop in voltage causing the pressure to fall like a rock. It was an unfortuneate set of events that basically started @ DGRR '09. Anyone with me witnessed me testing the first filter by pouring acetone and fuel into the filter and having the filter hold it like a cup of water. After that and popping an engine on the dyno from a clogged filter I was convinced that was the problem even after it was solved which is why I kept on chasing contamination and bad fuel pumps. In the end though, after I replaced a known clogged filter and a known bad pump, the problem persisted (although it was taking MUCH longer to show up) and we finally found it to be the wiring. Basically Dave and I were running the car and as soon as the problem showed up we tested the wiring - WHEN IT WAS WARM - found the voltage drop, jumped it from the battery and the problem was gone. So we jury rigged some wiring till I got home and could properly strip everything out and run some marine 10ga wire. Haven't had a problem since.

Lesson being, if you're chasing your tail, theres a good chance that there is no problem to be found were you're looking.

Interesting.... I should have given a bit more info. My engine was rebuilt and running fine. I had brought it in to have new BNRs put in. While there I had them do the fuel pump mod. After it was completed it went on the dyno for a tune. The car was running fine did 4 or 5 runs then all of a sudden it went lean like you mentioned above. They stopped tuning made some adjustments to the car and hooked up a fuel pressure gauge. Tried again and you could see the pressure drop right off at transition. They stopped and we went over the list of parts on the car.

4000km ago the engine was rebuilt, a new supra pump, and fuel filter was put in. They figured it must be the stock FP regulator since every thing else was new.

We put it back on the dyno and things were going well. We picked up right where we left off and did another 4-5 runs then bam it went lean again. This time the car sounded different, and it had lost vacuum. So it was torn apart and rebuilt. It looks like my seals had slightly warped.

There are only a few things I can think of that is causing my FP to drop. My pump, stock FP regulator, fuel filter, wiring, or the fuel temperature sensor - not even sure what that thing does.

Is it possible that I got a bad pump, yea. Is it possible the FP wiring job is not good, yea. Is it possible my fuel filter is plugged, not sure. The shop gave it back to me and I drove it home 500km without incident. Of course I was not pushing the car as I am now breaking it in again. Some people say do disconnect the FP temperature sensor since they do not know what it does and they do not use it.

Do you have any suggestions or how would you go a bout attacking this?

next time the thing goes lean on the dyno measure the voltage at the pump with warm wires. Or, completely rewire it with new 10ga wires and ground the pump directly to the battery and see if it happens again