EFI Issues (again) - I think I found the problem!

[BroncoMarc]

After having EFI issues for well over a year, I think I finally found the problem.

Previous posts:
http://classicbroncos.com/forums/showthread.php?t=122956
http://classicbroncos.com/forums/showthread.php?t=129691

Getting ready for a trail ride on Friday it was running rough, so I replaced the HP fuel pump AGAIN. Pressure was still low, so I ran an extended line on my fuel pressure gauge so I could see it while driving. I noticed that just before cranking I had 40 PSI, but it immediately dropped to 30.

I started playing with things and found that when I unplugged the vacuum line from the regulator that the pressure went up to 40! I ended up leaving it disconnected and I had the best 3 days of wheeling I've had in a long time! No EFI issues!

The pressure did gradually rise during the day. When it got up to 55 I put the vacuum line back on for a second and reset it back down to 40.


So... Since I replaced the regulator 6 months ago, I'm guessing I've got it plugged in the wrong place. Where should I plug this into a 97 Explorer upper manifold?

This is where I had it plugged in. I had the C4 T-ed in to it:

 

[Socal Tom]

The way the pressure regulator works is that pressure - vacuum =40, if you have a lot of vacuum ( like an idleing engine) then the pressure would be lower ( like 30) pressure is only 40 at low vacuum ( heavy throttle). I don't think that was it. I think you have the vacuum line plugged in the right place, but I would run it direct without the c4 hooked up to it.
Tom

Reread your prior posts. This seems more like an electrical problem keeping the injectors from firing. When I fired mine up for the first time the injectors were plugged. I manually fired the injectors until I had 5 of them clicking. It started with just the 5 injectors. The point being, that this is an all or nothing issue. Some where in the ground system the injectors aren't getting what they need to fire. They ground through the ECU, so you could have an intermitant problem with the ground between ECU and ground, or between the salt and pepper connectors and the injectors, or a bad ecu. Do you have a spare you could try?

Alternatively, it could be a dizzy problem. Next time it won't fire, put a timing light on one of the plug wires while cranking and see if you get flashes. A loose tach wire could ground the ignition and keep you from getting spark when you need it.
Tom