I have a 1994 4.9 f150 that runs rough

ive checked and adjusted the ignition timing and still ran rough.i noticed plug 2 was sooty and others were worn out so replaced plugs rotor cap and leads. cylinder 2 is not firing but has a spark. the plug is sooty but not wet so now starting to wonder if its the injector. i dont own a compression tester but she sounds ok on a polish test.

is injectors a common problem with these trucks?

thanks for your help

 

Bad injectors could be the problem, but so could bad plug wires, distributor cap, etc. Just because it has spark doesn't mean it will fire properly. I would lean more to electrical rather than fuel. How old are the plug wires, dist cap, rotor, etc.

 

i replaced the cap,rotor and plugs. i swapped the leads around and the fault stays with cylinder 2. judging buy the old plug its been like it for a while.(just bought truck).

I have got a signal going to the injector. but thats as far as ive got.

if the rings were gone the engine would smoke wouldnt it?

 

Not necessarily. The only way to tell is a compression test. I had a 90 F150 with the 5.8 liter. A lot of hard miles. No smoke, but a lot of blow by causing it to use oil.

 

ill give the compression test a go first then. thanks for your help

 

Also in relation to the injectors, it could be not a bad injector, but a dirty one. Where the fuel doesn't spray, but drips. Have you ever had the injectors cleaned? By that I mean the type where a can of cleaner is hooked to the fuel rail and the engine is run off that can for about 10 mins. Not the type you put in the tank.

 

i swapped the injectors 2 and 3. still cylinder 2 not firing. ill see if i can find this can that goes on the rail.

compression test (dry) came up with

1 - 105
2 - 105
3 - 120
4 - 125
5 - 120
6 - 140psi

makes me think head gasket but when you disconnect plug wire 1 it make the engine run rough and disconnecting wire 2 makes no difference at all. the piston is very carboned up and plug is sooty and dry every time i remove it.

got me stumped.

thanks for your help

 

check oxygen sensor and i don't know much about those trucks but on my '97 i had similar problem that was coilpacks. don't know it your's has those but thought i'd mention it.

 

well i took rocker cover off and made sure push rods and springs looked good. used remote starter and span her over and all looks good. i swapped the injector again just incase and still the same. sprayed intake cleaner down inlet manifold aswell.

got some errors on the scan tool tho. im pretty sure they are all there because of the misfire and not causing it but i could be wrong.

CODE 10 - snap throttle

173 - ego not switching bank 1 rich

213 - spout ckt open

411 - rpm out of spec - normal crb idle

538 - cylinder ballance test - fail restart

45 lbs of fuel pressure at idle

so now im lost any ideas?

 

going by the codes i'd say egr sensor or o2 sensor. but check you air filter. if it is full of oil then you have a blow by. which will cause the compression to be the way it is. what brand wires did you get? if you got autozone then thats probably your problem. they fail when there sitting on the shelves.

 

i can see what you mean about the o2 sensor but its only cylinder 2 thats not firing all the others are burning fine. if you disconnect the number 2 plug lead it makes no difference at all but has a spark when you check with plug attached.

i think the o2 error is because its reading rich constantly because of the missfire.

its as if the cylinder is being starved of something but as far as i know theres nothing i havnt checked.

air filter and breather is nice and clean.

 

Have you verified that the injector is getting power to fire? It may not be the injector itself, but the power leads to it.

 

if you got spark from the plug then the cylinder is firing but if the injector is sticking open then it will run rich and weak on that cylinder. its most likely something electrical if it didnt make any difference when you swapped injectors around. clean the spark plug then unplug that injector and start the engine. then after a couple of seconds of running shut it off and check the plug, if its still sooty then its something with the injector. if its good then its something in the electrical end of it.

 

i disconnected the injector plug and put a injector led tester into it and it was flashing.

bloody thing is getting to me.

 

Cars and trucks are like precision watches. They need to be properly tuned at all times to get best performance. Cars and trucks today do not need tune-ups as often as was necessary 20 or 30 years ago. The recommended frequency for a tune-up is once every 25,000 miles, or as specified in your owner's manual. In some cases, it may be necessary to get a tune-up more frequently depending on the type of driving that you do. It is time for a tune-up whenever your engine is "knocking" or not firing on all cylinders
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