Truck has been idleing rough for about a month. I seafoamed it thru the brake booster line 3 days ago. it progressively got worse. This morning I started it up and when i came out to leave the cel was on. I pulled the codes( cosco reader $29 no having to go to AZ ) and it threw a p0303, misfire on cyl 3. I went to AZ and bought a large techron and put it in 3/4 of a tank. I then headed over to the junkyard. I was going to see if I could get some coil packs. the junkyard had no 4 cyl. I pulled a maf and and iacv off a 12 year old ranger. I went to check out and the guy wanted $55 I said forget and left. seemed like a crazy praice for 2 things that might not work. So as I was driving the misfire seems to have cleared up. I erased the codes and am waiting to see. I was planning on swapping the coils to see if the misfire came up on a different cyl. I think I will wait and see what happens. Any how please give me any feedback you have. could the techron have cleared some carbon off a plug or and injector. Do you think I could have an injector going bad? Plugs and wires were replaced 5k miles ago with bosch DP( I recomend the motorcraft DP) and I think duralast wires( I recomend the motorcraft wires with the pulls on them)Could the sefoam have thrown some carbon onto an injecter or a plug and made it worse?. any feedback would be appreciated.

 

I see you have an air box mod, so is it such that you've moved or eliminated the IAT sensor, or that the mod sucks in heated engine compartment air & are you also using an oiled foam, or cotton gauze type air filter too???

If so, this arrangement could have messed up the laminar air flow through the MAF sensor, or contaminated it such that it's PID to the computer is corrupt & or messed with the air temp entering the engine, or it's accurate sensing by the IAT sensor & any or all of that could mess with the computers control of the air/fuel ratio, all a vicious circle!!!!

The cyl 3 misfire could be caused by a number of things from plugs, wires, fuel injectors, to compression or sticking valves.

Yup better to use the specified Motorcraft wires & fine wire platinum plugs, as they're designed for the double work load our waste spark ignition system puts on them.

Why not consider waiting until you use up the Techron treated tank of fuel & see how it goes, before going off on another change tangent.

 

pawpaw thx for the response. I always had the oem airfilter,box and intake on. I just did a litle mod that STL had on another site. This morning I put the 2 piecs back onto the airbox. I am going to wait and see what happens. I did pull the #3 plug on the passengers side. the plug was fine. Does anyone know what side of the engine does the main combustion? I think it is the drivers side but I am not sure. The truck appears to be running the way it was before this all started. it always had a little tweak in the idle occasionaly. I had alway thought that the coilpacks on this engine had different wire placements and that if you swapped them they would be firing on a diffent cyl. I looked at them closely today and I think if you swap them they still fire on the same cyl. so by swapping them it would not help DX if a coilpack is bad. Does this sound correct?

 

the cel has stayed off the the truck still has a little hesitation that has been there for a while. this morning I changed the fuel filter. it was pretty dirty. The truck immedialy ran much better. I then went down to AZ and borrowed a fuel pressure tester. It took 8 cylces of the key to get the koeo pressure to 62. I then started it koer pressure 64. I turned it off pressure went back to 62. I let it sit 6 minutes pressure went down to 54( I had the gauge on finger tight with no teflon). So what do you think how long do I have on the pump?