classicgranola

Hey everyone, I just acquired an 88 MJ with just over 200k, auto and the infamous Renix 4.0. When we got the truck it wasn't running but it was cheap...🙃

The problem seems to be no fuel is getting past the regulator....fast forward to new pump, filter, some new fuel line, and regulator but fuel still won't get past the regulator.

Someone told me to pinch the return line shut and try to start it, amazingly the truck fires right up when we did that but when I remove the line locks from the return line it does 30 seconds later.....

Any ideas to try next would be greatly appreciated....thanks!!!

cruiser54

Test your fuel pressure with a gauge to verify you have 31 at idle and 39 with the vacuum hose pulled from the regulator

classicgranola

It's zero pressure unless I'm crimping the return line. I haven't felt the need to test pressure while the line is crimped and it runs so poor..... there's something I need to find/fix before I get into fuel pressures being correct you know.

cruiser54

Well then, perhaps the fuel pressure regulator isn't holding pressure in the fuel rail or the fuel pump is weak.

With a fuel pressure gauge on the fitting, the fuel pressure should shoot up to about 100 PSI when the return line is crimped if the fuel pump is good.

That should help narrow it down.

classicgranola

I've replaced the regulator 3 times and the pump twice.....i mean it could be possible I've got bunk one's over and over but I feel it's highly unlikely

cruiser54

Well, one of them makes pressure and the other one controls pressure.

One of them isn't working.

If you got an Airtex pump, it's possible you got a few bad ones.

How much voltage do you have at the pump while cranking?

classicgranola

I'll have to check the voltage, what should it be?

cruiser54

About 12 volts DC.

classicgranola

Awesome, I didn't try that yet but I'll give it a shot, thanks!!!