Check the headpipe between the exhaust manifold and cat.

 

Mine has only high pressure pumps in each tank - no pump on the frame rails.
Pressure is the same - running or not. I don't even see a discernable drop in pressure in relation to injector pulse.

I thought the pump should shut off after bringing the pressure up to operating pressure; tain't doing so. A new pressure regulator was installed before I got the truck - although with todays quality control standards, it might be bad as well. Prolly come on a slow boat from china along with the poison meat and lead painted toys.

Alas . . . can't seem to locate my timing light. The truck cranked and idled okay yesterday - wouldn't crank without starting fluid this morning.

Left the batt disconnected last night - before attempting to crank it I hooked up my new handy dandy scanner - no self test - no nothing.

Any way to test the PCM?

I feel like that little ant who exclaimed "I'M LOST!!".

 

The fuel pressure should stay constant, any dips in pressure during the injector pulsing would affect the flow and be a real byte to calculate. I remember reading somewhere that something like 90% or so of the fuel is recirculated back to tank. This return flow value probably has to be relatively high so to minimize any pressure dips during injection.

Wonder if the fuel pump relay isn't stuck on? If power is supplied to one side of the contacts when the ignition switch goes to ON, and the contacts are stuck closed, it won't matter what the computer does with the relay coil. Just a thought. It's also my understanding that the initial fuel charge is done on a timed basis, not on whether a pressure is achieved?

I would think the PCM is working if the truck starts at all - it controls the ignition. Don't know anything about the testing of the PCM. Do you get the 'check engine' self-test light when you try to start?

 

Well,I would first pull the plugs and check compression.That will tell you whether the engine in fact can be tuned.The 4.9 does have gear to gear timing gears.They are a form of kevlar from the factory and can wear out.The new gears will be steel on the crank and aluminum on the camshaft.The next step will be to remove the O2 sensor and check exhaust back pressure.I am not sure if you have two front exhaust pipes or not.You will need to make sure that you have no back pressure.I think the spec is less than 2 or 4 psi.I cannot remember.Usually if they are stopped up they will peg my 15 psi gauge.The next step will be to check actual fuel pressure.The fuel pressure will be from 38 - 45 with the vacuum hose disconnected from the fuel pressure regulator.around 35 with it connected.If it were mine,I would also check for trouble codes.If you have any questions,feel free to ask.I have seen several of those shear the distributor roll pin.They will do all sorts of crazy things when that happens.Just rule that out.Hope this helps.

 

Yuck, I had that 'plastic' timing gear setup on my 1974 2.8L Mercury Capri. When they failed, the motor just sounded off even while turning over. Very uneven sounding, almost like a dead battery.

Sheared distributor pin could be why it's running so badly - it maybe spun and caught somewhere else due to varnish binding on the dist. shaft.

Thanks, svt_tech - I love these forums for what I learn from others!

 

No problem.Just hope it helps.

 

I really appreciate all your tips and suggestions. I'll start on this thing again tomorrow. First thing is to purchase a compression tester I suppose. I think I read somewhere that compression in all cylinders should be within 10 pounds of each other - is this correct - and what is the minimum I'll be looking for?

The guy I got this truck from said it went something like this: The truck was running great - stopped at a store & wouldn't crank; ran the battery down trying - called a buddy & waited about a half hour - as soon as they put the cables on it it fired right up. Ran as good as ever the rest of the day - next morning wouldn't crank. Been sitting now for 5 or 6 months. Same with me now, have to use starting fluid to crank it the 1st time each day, then cranks okay, but not great - not like it should, being MFI.

So far:

plugs, wires, cap, rotor, fuel prussure regulator, fuel filter, ignition module

Tried to set base timing Sat morning - either starter or starter relay gave up the ghost while I was bumping it over searching for the timing mark on the balancer.

Thanks again, Guys! Ya can't get better knowledge than that from those who own 'em & drive 'em. . .

 

I suppose there are several rules-of-thumb for compression testing.

I like the more liberal guideline of the lowest cylinder should be no less than 80% of the highest, with no cylinder below 100psi.

Be sure the throttle butterflies are wide open for maximum airflow during the test.

Are your battery, cables, connections, and starter in good shape? Wondering if maybe the cold start problem may be related to the speed the motor is turned over?

 

yea im gonna agree with the other guys check your plugs ive got one and it fouled one plug after another till it wouldnt even start

 

im new here and im having prblems with my 1992 f 150 fuel pump runs constantly with key on changed plugs wires cap and rotor changed regulator valve for the fuel changed the relays as well truck ihas a straight six in it wont start on its own but will with starting fluild will run then but with a low idle will speed upbut you have to be easy on the pedal once its floored it acts like its outta gas..... any ideas