I got a 92 F150 and it ran rough at idol. Sense getting the truck I have put in a new engine with all new ford motor sports injectors. The truck idols exactly the same and it runs good but feels slightly slugish running it around 80 and over the passes. I took it to a shop and they said the the # 6 injector was 30% below the rest. I am not sure what he ment, but I think he was measuring the voltage. He never had the injector out. SO he told me to replace the injector and see what happens, but why would the truck run exactly the same with a 200k mile engine with old injectors vs the new engine and injectors? Is there any thing else that could be causing the injector to draw 30% less? Is there any possibility that it could be the wiring for the injector?
Thanks for any input

 

Are they the same size as stock injectors? Have you checked the computer for codes? I would also replace the fuel and air filters if it has been a while since they were last replaced. If the injector is has a low voltage, that is a problem with the wiring I would think. Also check all the obvious stuff - cap, rotor, plugs, plug gap, wires, etc. I would also check the timing to make sure it is set at spec, and maybe try advancing it a degree or two.

 

I had a rough idle problem it turned out to be fuel pressure regulator.It was on recall a while back but i had alredy replaced it. 93 F150 5.8 4x4

 

new air and fuel filters, new pressure regulator, cap rotor, wires etc, egr valve/sensor, o2 sensor. All injectors are 19 #. THe guy at the shop said that the low volatage indicated a bad or pluged/dirtty injector, but I did not think that made sense becasue every thing is new!! THe idol problem is exactly the same as with the old engine. Again I am not sure exactly how he determined the 30% drop, but it sounded like a voltage measurment of some kind. I know he did not take out the injector to test it. I would just buy a new injector, but I kind of wanted to keep all the injectors the same ( cannot buy single motor sports injectors). But I still am not sure why it would idol the same and the chances of getting a bad injector that exactly duplicated the problems the old engine are slim. Also no codes.
Thanks, keep the feedback coming

 

What's the timing set at? Are the plugs gapped correctly? Is the idle rough all around, or can you tell that one cylinder is not firing (i.e. the miss or roughness is cyclic and occurs at a specific interval)? Did you run both KOEO and KOER tests? Sometimes codes will not show up in one, but will in the other. I would check the wiring on the injector that he says is bad and see if there is a fault in the wiring between it and the computer. I wouldn't think that a brand new injector would not function correctly. Have you tried running any fuel injector cleaner in a tank of gas? I'm running out of ideas for you, hope you can find something out about it.

 

timing is at 10BTC and all the plugs should be gaped correct. No codes in either key on or off. It is deffently running rough in a pattern, it feels like it is missing, RPMS drop then raise, a real PITA. Remember this is the same problem I had with a completly different engine and different plugs etc. If the wiring is the problem, how could I even go about checking it? Should I just look for a wire that has the inslation torn, etc? Sense it is still firing the injector it cannot be a broke circut? I would like to fix this my self becasue it seems like shops always charge an arm and a leg for any thing that cannot be easly checked through the computer, or give you a bunch of BS which is kind of what I felt like this shop did in regards to the rough idol, They said it was almost 100% sure it was the injector, even though I told him the cercumstances. I brought up the wiring but he said doubtful. I have run a can of BG 44K through it and it did not do a thing.
Thanks

 

Swap the "bad injector" with another one. See what it does. If it still runs bad, which with all you've said it probably will, take it back to the shop and have him do the same check on the injectors. Then you'll know if the problem follows the injector or stays with the cyclinder. Maybe the injetor got damaged when being installed. If the problem stays with the cyclinder, then your injectors are fine. Then I would start tracking down possible wiring shorts or a computer problem that doesn't throw a code. Start eliminating things that are common between the old and new engine.

 

So the idle speed cycles up and down? I would double check to see that the TPS is sending the computer the correct voltage at idle, and make sure that it is a linear change in voltage as the throttle opens (Do this with key on, engine off). Does it matter if the engine is warm or cold? It sounds like a problem in engine control somewhere since it did this with the old engine too. Check the computer and battery grounds too - bad grounds can cause lots of problems. Maybe take a look at the TFI module to be sure it is working properly.

 

thanks for the replies, i will try the TPS first and then start messing wiht the injectors.
Let you know how it goes, when I get to it.
Thanks

 

you may have checked this before, but did you test to see that the fuel rail is clear? I have heard that it can have rust on the inside and plug/restrict. If that happened right at the bend/joint before the bad injector it might be restricting the volume that can get to it...

 

I got a 1989 ford f150 built 351 I would like to put, atrim blower on it for pulling power it is speed density and has stock injectors an fuel pump,would I have to change the fuel pump or will it even work because of the speed density,maybe put a fmu an.......?