Fuel System Pressure

One would expect to see between 35 and 45 PSI....

Some disclaimers. IF engine vacuum is low (as in engine off or wide open throttle), you would expect closer to 45 PSI. When the engine vacuum is high (as in idling or close throttle coast down), fuel pressure would be closer to 35 PSI. The critical number here being the pressure drop across the nozzle.

When testing the fuel pressure, it is vitally important that the test be carried out when demands on the fuel system are high.

HTH

Thanks for the reply Jim.

I have 40 lbs. KOEO (key on engine off) I have 30 lbs. running. I have 35 lbs. running w/ regulator vac line off. I have good volume also.

Checking against a 91 TC w/ the 4.6 which runs great, I get the same readings.

The 94 acts like its fuel starved & doesn't want to take gas above an idle. (idles fine)! JK

I would recheck the fuel pressure while driving before ruling it out. This is the kind of "gotcha" that I've seen bite far too many techs. It is vitally important to test fuel pressure when system demands are high.

What your are describing sounds more like the MAF sensor needs cleaning. It can also result in ping because of the lean mixture it causes. They sometimes (almost always given enough time and miles) become contaminated or encrusted with crankcase vapors and/or bits of debris that escapes the air cleaner. The solution is to remove it and clean with a residue free electronic or electrical cleaner. You can use a cotton swab to gently assist the process. Dry and remove any residual fibers with compressed air. You will need an anti tamper torx bit to remove. You can buy an inexpensive set at most of the Auto****** whatever stores for less than $10. Be careful with the cleaner as it is fairly potent and can damage paint and some plastics pretty quickly. You may be able to unplug the sensor and clean it away from the vehicle.

While you are cleaning, you may want to clean the throttle body. Be sure to clean the EGR ports under the throttle body. The ports are more like slots in the lower gasket surface on the intak manifold port. You will need a TB gasket which is usually available where you get your torx bits. The Ford TB cleaner is one of the better ones if you can find it. A stiff tooth brush or similar brush will aid cleaning the TB. You may nee to do a bit of manual scrapping to clean the EGR slots. Be careful not to damage the gasket surface.

Also, be sure to check the tubing for the PCV installed in the right cam cover. The bend to cross the back of the engine and that stretch of tubing tend to clog and/or crack over time - another characteristic of aging.

All of this is cheap taking mostly a little time and patience. It can yield more reward that you expect on these engines. You will need some basic metric hand tools to remove the TB for cleaning. Using a google search, you can find nu,erous instructions and pics of cleaning these items.

Good luck

Lugnut

I own a '93 Mark VIII with the 4.6 DOHC. Jim and Lugnut have some good advice, especially about the EGR and MAF. In my case, the MAF failed and would not respond to the cleaning. Thanks to the me drastically needing it on a Sunday afternoon, my replacement was from a chain store with a "lifetime guarantee". (Well, in this case, exactly one year) The part I bought worked, but it looked like it was taken directly from a salvage yard. It was filthy. It worked for exactly 11 months and two weeks. I managed to exchange it with a couple of days to spare. The new one looked good and has worked fine since. While this probably isn't causing your idle/rpm problems, my car had to have the EGR cleaned also.

Thanks again guys,

EGR checks out fine as do all hoses etc.

Swapped out MAF sensor w/ a known good unit (exact same part #) ,Same problem !

Swapped out DIS Module too, thinking maybe the coils were losing fire. No dice, same problem.

Triple checked fuel pressure again. Holds steady at 35 lbs. while its dying !

Fuel volume is almost 2 pints in under 30 seconds.

I'm thinking I may have a PCM problem thats shuting down the injectors.

Will check out all sensors etc later today.

JK