shmitty

I recently aquired an 89 f150, but the truck didnt run when i got it. its not getting any fuel out of the injectors i checked and the fuel pumps are working correctly there is pressure to the rail but im not so sure there is power to the injectors. I pulled the intake manifold and lifted the rail and injectors out of the block turned the truck over and the injectors are still dry as a bone. is there any type of relay that could be preventing power to the injectors?

BigIrish

If you have checked for proper fuel pressure at the rail using a pressure gauge and the injectors don't fire, then a few things could have happened:

1) Simultaneous failure of all injectors in the closed position. Unlikely but possible if the truck sat for a while. Take the injectors off the rail and check for varnishing, gumming or other debris that are clogging things. I'd just replace them if they look original.

2) Faulty ground somewhere in the system. Get a good service manual and check condition of all grounds on the truck. Pay special attention to the grounds for the PCM. Replace any damaged or frayed ground straps. Unbolt and clean corrosion from all ground points. Do a quick visual on all interior and engine bay wiring harnesses for chafing or other damage.

3) Failed Injector driver in the PCM. Check and see if it will properly flash the check engine light in diagnostic mode. On my 89 Chevy that involved jumping two pins on the OBD1 port. Again, a good manual is valuable here.

Good old Bill

PCM relay, but there would be no spark also. Then again, how about the timing gears, this is a 4.9L? Does the engine fire when starting fluid is sprayed into the intake?

shmitty

This truck has sat for a while and i did pull the injectors off the rail and there is buildup of junk all over them so it is very possible they are clogged. I installed a new sending unit and pickup pump in the front tank as well as the master pump on the frame rail along with a new filter so i do belive the proper pressure is comming to the rail, but to answer your question the truck will fire off of starting fluid, i know thats not good for it so ive tried to do it as little as possible. and yes this is a 4.9 but i dont belive the timing gears are a problem, but then again im not real familiar with this truck so i could be wrong.

Good old Bill

If the engine is fireing when starting fluid is used, your ignition and timing should be good, you are on the right track, am not sure if a secondary sensor is used for the 4.9L to fire the injectors. ie the cam position sensor used on the 96 5.0L engines.

shmitty

yea i checked around on it with my volt meter and there is no power comming to the injectors at all. I dont know if the fuel pump relay would have somethin to do with this, i cant hardly belive that because the fuel pumps work, so could it be a bad eec power relay or a computer?

BigIrish

As the computer drives the injectors with a PWM signal, you won't necessarily be able to check voltage with a volt meter. You usually need an oscilloscope to read the signal to the injectors. A test light might give you some indication if it flashes, but I don't know the injector pulse voltage off hand, it might not be high enough to drive through a test light or the test light might not react fast enough.

krayjones

have you check the injector its self? my 89 5.8 sat before i bought it due to bad fuel pump. my injectors had power to them yet they were not letting fuel in. took one out and the injector would not open when i grounded it. i was told i could soak them in a cleaner but i opt to just by some refurbished.

Dmpaul89

I know thios is an old thread, but did you figure out your problem? my truck is doing the same thing. I have spark, compression, Good fuel pressure and a pulse going to the injectors but it wont run. I have the 4.9 1988 the truck did sit for a while

Gary Dolph

Had this happen 3am and 400 miles from home. Coasted up the ramp and to an open station. Checked spark at the coil. Listen to fuel pump. Checked for fuel at fuel rail. All ok. Next grabbed a jug of Heet for each tank. Waited 15 mins. Spray a little starting fluid in the TB. Turned key and it has been good ever since.