93 ZJ Long Crank

this is after the engine has been idling for 20 minutes now. I'm going to start spraying and see if it starts acting up

 

fuel pressure is going down faster than a cheerleader on prom night.

Either the injectors are leaking- there would be trace fuel in engine oil OR the tank check valve located on the fuel pump.

Engine Vacuum is just like the gauge colors tell us MARGINAL right on the break.
A warmed up engine timing is computer controlled. We have done a compression test and no leakage or low readings?

FUEL drop is place (shinny object) to work on.

 

Where do I start and how do I go about it?

 

We did a compression test back in August but not a current one

 

OK now I see 18inHg - that is better.

The fuel pressure drop is your long crank in AM or after a long sit time.
As mentioned - injectors leaking we may see a puff of black at restart, evidence of fuel in engine oil, maybe wet black fouled plugs, a knock at restart (hydrolock), a code for inj circuit, a RICH code*, BUT I do not think any of those 'tells' are apparent here.
Next suspect is Fuel pressure regulator**, remove vacuum line- look is there any fuel in the vac line?
We can clamp off fuel return and do the test again - hopefully with return clamped the pressure stays up there.

NOW i WILL TRY TO DETERMINE WHICH IS PRESSURE LiNE AND WHICH ONE IS RETURN line.
And post back later. Coffee awaits,

PS "I don't like Mondays , Tell me why"

*IIRC you had a LEAN code.
** we were just F'in around here

 

I read you loud and clear and I was actually suspecting the fuel pressure regulator myself because it leaked. I'll go ahead and check out that vacuum line and clamp down return hose when I get off of work today around 5:30 p.m. Central Time.

 

We did a compression test back in June. Here are the results... https://www.jeeps.net/threads/93-zj-5-2l-compression-test.3602/