At idle 2005 4 litre mustang shows 50 psi at 75 degrees, when at normal temp pressure drops to 15,20 at idle. At 2,000 rpm shows 40 psi. This sounds low to me, is this normal?

Check the coolant temperature sending unit it sounds like it's starting on a lean mixture or warm engine even when it's cold.

15 seems low. Ford gives a spec of 40-70 psi with the engine speed @ 2500 rpm engine hot. Most cars I see are around the 25 psi @ idle. If your idle is lower than it should be it will make your pressure lower. This should be a direct reading on a good mechnical engine oil pressure gauge.

Check wiring harness around and including plug to the coil pack. Also check fuel pressure with vehicle running. I'm not sure of the specs but, Iit should be around 35 to 40 psi. at idle, and 50 to 75 at higher RPM's. I've seen Fords run with a bad fuel pump and demonstrate these exact symptoms

you probably have your finger on the problem. have oil pressure test .when engine hot minimum 12psi.and change the thermostat.Don't cost much

It all depends on the outside (ambient) air temperature. Your A/C low pressure switch is designed to turn the compressor off at 24 Psi. and turn it back on at 45 Psi. Most systems will normally run at between 25 and 40 Psi when the system is running on HIGH blower and "MAX" or "RECIRCULATE". A system that is fully charged may run at 25 Psi when the ambient temperature is 75 Deg. (F) and may run at 40 Psi when the ambient temperature is at 90 Deg. (F). (it can be even higher if ambient temperatures are higher than 90 Degrees.)

To properly diagnose a malfunctioning A/C system, the HIGH side pressure must also be checked. Restrictions in the system can make the low side pressure look normal while the high side pressure is high enough to blow hoses apart. (400+ Psi.)

Oil pressure drop after reaching operating temp is normally caused by worn main bearings (depending on mileage).Worn bearings will allow pressure drop at idle and increase when accelerated above idle.

at what? depending on engine temp and rpm, normal oil psi should read 30-40 psi at idle and at cruising speed of 1500 to 2000 rpm should read 60-70 psi. most bonnevilles from 1992 to the last year run of 2005 have the 3.8 liter V6 which was updated over the years.

the tracer is the same as the ESCORT, right?? TRY THIS--I WORK ON PLENTY OF ESCORTS--LOOK UNDER THE AIR CLEANER/CONE ASSEMBLY--THERE WILL BE A BLACK METAL BOX(FULL OF RELAYS) ONE OF WHICH IS THE A/C RELAY--TRY TAPPING ON IT WITH A LONG SCREWDRIVER OR SOMETHING SIMILAR WHILE U HAVE THE A/C ON. IF THE A/C SUDDENLY STARTS WORKING U NEED TO GET A NEW RELAY BOX(I THINK ITS CALLED A GEM MODULE) i do have a question- does the blower motor work?? how do u know the compressor is good??do you have 12 volts going to it??? this relay box is pretty common to go bad--u have to remove the air cleaner in order to get to it.get back to me.

bout the oil pressure gauge its normal to go up but not to high coz u might overheat, try checking the cylinderhead gasket if there is pressure coming out, replace the gasket if needed

At operating temp 171 - 181 F, with SAE 10w-30: idle @ 700 rpm 11 psi min, 1200 rpm 28 psi, 2000 rpm 43 psi, and 4000 rpm 57 psi.