Does anyone know if there is a way to check the injectors on a 1993 F150 w/a 5.0. I am still having a problem with spark knock and was wondering if my injectors are going bad. It has 172,000 miles on her and I have tried the sea foam, lucas products, changed several parts and still spark knocking.

The other problem that I am having is when you start it after it has set for awhile there is a slight vibration that comes and goes until it comes down off the fast idle. Any thoughts? Thanks

 

Have you checked ignition timing?
Pull the Spout plug and set it hot, then see what you have.

Has the cap/rotor and wires and plugs been ruled out as problems?

 

I have checking the timing. As a matter of fact I have set the timing to 6* and still the samething as well as a loss of power.

I have change the cap/rotor, wires and the plugs as well as the o2 sensor, map sensor, checked the egr valve to make sure that it is working, changed the egr position sensor, tps, knock sensor, cleaned out the carbon behind the throttle plate, fuel pressure reg., checked the fuel pressure. I'm thinking now that maybe the injectors are getting week causing a lean mixture? Oh, I have also changed all vacuum lines on the engine. Any help would be greatly appreciated. Thanks

 

Weak injectors is wrong thinking in my opinion.
If they are metering less fuel the Ox sensor will detect it and richen up the fuel to compensate.
If the computer tables go to their end and cannot adjust any more then you get a MIL lamp and a code telling you this.
I suspect at 172 k miles you have carbon build up in the chambers and on the heads of the intake valves that may be causing some problems.
If you retarded the ignition timing and still have a problem then it's not a lean condition as per normal.
The fuel pressure should be close to 39 psi +/-. If this is low then you will get a lean metering condition at times under load.
The knock sensor should under normal condition retard the timing as much as 8* when detected.
Are you sure your not hearing something else like the heat shield on the cat that has come loose and rattles.
The MAP sensor controls fuel vs load vacuum. Unless you get an outright failure it won't set a code.
The timing chain should be well worn by now and have the cam timing retarded some amount from chain wear and strech.
Good luck. I went thru all the major areas I can think of for you.

 

Thanks for your help. I have checked the timing chain and it is within specs for wear.

 

u can try an injector flush. take it to a car shop or a ford dealer and get the injectors flushed. if that is what u want to do. but that high of miles probably wouldnt hurt to replace em. i got a full set for my truck off ebay for about 48 bucks. had less then 15,000 miles on em. the ones for yours are 19lb's same as mine. hell i have my stock set if u want them just pay the shipping. they all work have about 120K on em. i just got a new generation injector thats more efficient. so i gained a whole 1mpg maybee out of em.

 

I did the injector flush twice. Still didn't help as well as did about 3 cans of sea foam. Still nothing. I was just wondering if injectors go bad and if there is a way to check them. I will look on ebay. Thanks

 

injectors either work or dont work... but if u want mine they all function fine... they are just taking up space just pay shipping for em. shouldnt be but 10 bucks.

 

About the only thing to do is listen to them with a long handled scredriver when the truck is running and see if they click. You can also purchase a 'noid' light from AA or AZ to see if they are getting the firing pulse. You could have a broken wire or the PCM could be malfunctioning... Good luck.

 

Your vibration at start up may also be due to your main bearings going south. With that many miles it is very possible that your main and rod bearings will need replaced.

 

how about the plug wire routing on the 7 & 8 cylinders.they have to be routed right or they induce a spark premature and predetinate. Have had holes in pistons from people who ignored it. There is a tech service bulliten on it. covered mote of those 5.0's. easy and cheap thing to check for the most part the wires should only cross at 90 degrees and not run side by side close togather 7 & 8 wire next to each other in the fireing order of the moters it covers. I have the bulliten in my toolbox at work and refer to pictures on it as needed

 

That's a very good suggestion.



There is a handy dandy tool for testing injectors. The one I have is made by OTC (p/n 3398), and is called an Electronic Fuel Injection Tester. You attach it to each injector, one at a time, and it sends one of three specific signals to the injector. Monitor the fuel pressure before and after the signal is sent, and compare the pressure drop among all of the injectors. They should be the same. Very handy tool to have.