89C2500

I've been using an external Aeromotive FPR with a Holley 670 TBI and Walbro 255HP fuel pump running 53psi. I left the TBI regulator in place, but with the adjustment screw backed way off. With this arrangement, I tuned the VE tables.

This weekend, I removed the "internal" TBI regulator diaphram as I was concerned it might not hold up to the higher pressure. At first, I made a block off plate to replace to old regulator housing, but then I decided to just seal up the housing instead. Pressure gauge still shows 53psi under all load conditions, but with the internal TBI regulator gone, my BLMs have shot through the roof! Before removing the internal FPR BLM's were 126-132 range, now they're 140-150. (150 is the max BLM allowed in my bin).

This makes no sense to me at all. Any ideas?

Brent

dimented24x7

iTrader: (2)

How is the regulator mounted? Is it basically a 3-way with the return at the tbi blocked off?

What your seeing may just be a fluke. Weather changes and such can do this.

89C2500

I removed the internal tbi regulator diaphram and routed the tbi return to the external regulator. So the Aeromotive regulator is between the tbi return outlet and the return line to the fuel tank.If I understand correctly, wouldn't this type of install leave the injectors with a dead-headed supply? I thought the regulator should be positioned after the injectors in the return line? Yes, but not in this case (baro reading in "normal" range). BLM correction was driven past it's ability to compensate. I had to up the BPC(F28/cell 0) from .042 to .047 and increase VE tables values by 15-20% just to get close! I should have just used BPC changes but I tried adjusting VE values first. It was a HUGE change....that's what has me confused.

dimented24x7

iTrader: (2)

That way works better and is how I would do it. I was just curious as to how you where doing it . The 3-way will dead head the tbi, which will mean the fuel will be hot and possible vapor lock or overheating issues with the injectors. So long as the present regulator is designed to maintain the inlet pressure at the desired pressure with the outlet freely exhausing you should be ok. If the gauge is hooked up to the supply side of the tbi and it says 53 psi, then WYSIWYG.

With a SD system, none of the parameters are expicitly known, so the BLMs will be effected by: coolant temp, intake charge temp, humidity, baro pressure, minor changes in engine VE, temperature of the oxygen sensor, phases of the moon, the tide, the alignment of varous celestial objects, etc... IOW, take the blms with a grain of salt. If the BLMs remain consistantly high, which I take it they are, then its definatly an indicator of a problem, but if the pressure at the tbi on the supply side is what its supposed to be, then that shouldnt be a problem. If you where measuring the pressure on the return, then all bets would be off. The stock type regulator is a hit or miss sort of thing with the high flow pumps so it could have been much higher at the injectors with it in place.

89C2500

Thanks...I figured I had the ext. reg. installed properly, but when you mentioned "3-way" I thought I might be missing something!

The gauge is on the supply side so I guess the injectors should have been seeing 53# with or without the internal regulator in place. I doesn't make sense.

One possibility could be a problem with the Walbro. Athough I can set the regulator at 53psi, at different times/days the gauge can read 50-55psi. I'm not sure if this is normal...due to baro, tide and moon phase changes?

I hit another snag yesterday as my block-off is leaking now. It might be tough to get it to seal at 50+ psi. At least I didn't set anything on fire!