Misfire in cylinders 3 and 4 ??????
 

I bought gas at a station that now looking back may not have been the best place to buy gas, and ever since have had a miss in cylinders 3 and 4 and the truck runs really crappy. I've since added gas from another station after running all the gas from other crappy station and the problem persists. I've checked the plugs, wires and everything i could think of to be the culprit and no such luck. I'm at a loss ??????? :-X09

How did you determine which cylinders are misfiring? Also it would be helpful if you would tell us what kind of truck you have and what engine is in it?

Sorry about that :-lamesign I know, It's a 1995 F150 4.9L I6. I used the tried and true method of removing a plug wire at a time. Whatever cylinders are not firing will have no effect when the plug wire is removed. I determined that 3 and 4 are not firing due to the engine sound of running on four cylinders instead of six and that the removal of the plug wires from the 3rd and fourth cylinders had no effect on the runability.

You already checked wires & plugs , you can switch them to a different clylinder to make sure , check your compression next ....Lew

I switched wires around and it's still missing on 3 and 4. I'm thinking it's a fuel issue:-banghead and that's what i'm dreading. I'm gonna run a compression test next and see if anythings wrong there.

Well better a fuel problem than a comp problem , let us know the results of the comp check ...

Yea a compression test is a good idea but first I'd swap injectors around, swap injectors from known working cylinders over to the cylinders you know are not contributing.

If it the miss follows the injector/s I'd buy it a fresh set, if not I'd give the harness a good going over verifying the injectors do in fact all pulse. And of course the compression test, exact order done depending on how ambitious I was at the time!

That and I'd rather believe it was a fuel/injector/spark or harness issue of some kind rather then one or two suddenly toasted cylinders......

Well, I talked to some other people and they said that the gas station has sold them bad gas, so that's where i'm at now. the truck has 223,000 miles and I've changed the oil and done the other maintenance at the recomended intervals and I've had the truck since new give or take a few years. I didn't think it was a sudden drop of two cylinders either so I haven't run the comp. test yet, I I ran a KOER test on it and came up with the following codes

173 EGO Not switching
213 Spout circuit open
411 RPM Otu of specification, Normal Curb Idle

That was with a Snap-on scanner.

The spout is plugged in so I don't understand why it's saying it's open, I even ran a jumper in it's place (which is all the spout is) and it still said open circuit. I'm thinking one or more of the following:

Bad injectors
Bad EEC module
Bad O2 sensor

Any, some or all could be bad.

Sorry it's so long, just trying to give you all as much info as possible.

P.S. tested the injectors with a noid probe and the cylinders in question have a pulse. Doesn't necessarily mean they are getting proper fuel mix tho.

Well you can switch the injectors around like danr said , & check compression , that will elimanate a few things , with 223.000 miles it could be anything , but when you have a dead miss on cylinders next to one another im thinking head gasket for starters....Lew

Thanks lew, I'm gonna run the comp. test as well as check some other things tomorrow. I was kinda thinking that as well, it's not burning coolant or running hot, but if it is the head gasket it could just be leaking into each other, right?

truck has 223,000 miles

Yea I think I'd start with a compression test knowing that, even with a life time of proper maintenance that's kinda high.

Eliminate that as a possible problem and move on from there.

Yea if all other cylinders are at a normal range but two adjacent cylinders share the same low reading its a pretty safe bet its the gasket between the two.

Okay, cool. I'm hoping it's not a head gasket only cuz I don't have the time to fix it.:-banghead I know the compression should be around 180psi (a little lower due to mileage) if I'm not mistaken.

I started smelling anti-freeze in the exhaust two weeks back, and did the compression test and cylinders 3 and 4 were at 25 and the rest were at 150 so head gasket is bad.

Bought everything to do head gasket.

While doing the repair, took off the valve cover and found the intake pushrods for cylinders 3 and 4 were bent!!! :eek::'(:-banghead WTF!!!!!!!

So now I'm worried as to what has caused this and what kind of damage has been done.:-X13:(

When you pull the heads off you will find out , have a good look at the valves