idcard

My 86 seems to run fine while I am driving it. The problem is at idle is wants to surge 400 - 700 rpm. The fuel pressure is 38-39 psi at the valve, but it drops about 8 lb in 1 min. and about another 4 after 2 min. with the engine off. I have read other threads that say check the injectors if this happens, but all have been cleaned and tested a Cruzin Performance and were all fine - he even cleaned the 9th injector. I can't fine in the FSM anything about the vacuum connection on the regulator. how do you test it? With the engine off, it won't hold any pressure using a hand vacuum pump. I have tested the EGR system and it seems OK and no vacuum leaks. Is the regulator vacuum causing the problem.

MK 82

Could be. Diaphragm may be broken. Do you smell gas when you remove the vac hose?

SAY WHEN

If you're using a known good vacuum pump and have a tight connection on the pump and regulator nipple--the diaphragm in the regulator is bad--replace regulator--you would usually have raw fuel on the vacuum side either around the nipple or in the vacuum hose--will usually cause a multitude of driveability problems--such as difficult HOT starting.

idcard

Thanks for your help. I will change the regulator. Does anyone know what the vacuum does to the fuel pressure regulator - increase vacuum will increase fuel available to the rail?

rodj

"it drops about 8 lb in 1 min. and about another 4 after 2 min. with the engine off."

Or the non-return valve on the pump is worn allowing pressure to bleed off on supply side.
When you have the idle surge , does indicated fuel presure change also?

High vac (idle) closes reg reducing fuel ; low vac (accel ) opens reg increasing fuel.

MK 82

It's the other way around. Low vacuum under acceleration raises fuel press app 5 psi.

Attach your press gauge with the vac tube attached and the eng at idle. Remove the tube. The press should rise.