2003 missfire problems

[Acecom]

Ok guys working with a 2003 ford ranger 3.0L v6 auto 2wd with 119.xxx miles I am having a missfire in cylinder # 5 the engine idles hard, acceleration is shit sometimes i'll be driving and then it will start to run like crap and shake really bad then clear up and run fine then do it again. if i step on it while it does it, it seems to work fine until i get back to a normal running speed. loss of power when this happens as well. check engine light flashing at me under power and idle.

Truck is not smoking, or burning oil, or has any loss of coolant. Took it to someone that hooked it up to a machine they confirmed that my o2 sensors are working fine. Truck is a flexfuel (which has never had any of that in it) and the truck does NOT have an egr vavle.

i have read through the forums and have found some great info and based on what i have read here in the past week this is what i have done.

Replaced:
Coil Pack
Plugs(104 autolites)
Plug Wires (duralast)
Alternator (NEW no refab)
Serpentine Belt
Air Filter
Fuel Filter
injector # 5 (new)

(All of this was done within the last 2 weeks) inc. Compression Test
_________________________________________________________________
Compression Test:
cylinder # 1= 140psi
cylinder # 2= 139.5psi
cylinder # 3= 139.5psi
cylinder # 4= 121.5psi
cylinder # 5= 120-119.5psi
cylinder # 6= 140psi

I attached photo of plugs from cylinder # 1&5 they do not smell like gas or oil.

what do you guys think?

 

[uksparky]

Could be other injectors....but first add some oil in cylinders 4 and 5....if the compression does not come up you have exhaust valve leakage...check engine light...what code do you get

 

[Acecom]

code is always p0305 misfire in #5 cylinder.

 

[Rearanger]

The symptoms just don't look compression related and plug #5 appears not to be firing. I'd pursue electrical at this point.

When you had your O2s checked did you get some fuel trim numbers?

Does it idle OK?

 

[Acecom]

after being warmed up it idles at below 1k maybe 500? and most of the time is rough. like "loping" ? is the correct word? and yes i did get fuel trim numbers but i dont remember what they were exactly the guy said that the injectors where over compensating for something as he said they were dumping about 25% more fuel than normal. he thought it was due to injector 5 not working at all or very little, thats what the guy said anyway. which is why i just replaced it all together. but to no avail, the truck still runs like horse shit on a hot day.

 

[Rearanger]

he said they were dumping about 25% more fuel than normal.

That usually means a vacuum leak, especially with "loping", but could be low fuel pressure. The O2s are telling the computer that there's a lean condition so the computer attempts to fix with holding the injectors open longer. 25% is quite significant as 10% is upper reaches of acceptable.

If you had a scanner showing fuel trims then you could use propane or carb cleaner in the intake to see if that corrected the trims - that would show excess air. As well vac leaks are more significant at idle and less in higher rpms - this would also show with scanner trims.

If you can do a fuel pressure test that would help check that off the list.

#5 could be injector wiring. If you had a noid light or other sensor you could see if that injector was firing. Even a stethoscope or long screwdriver to your ear will indicate clicking of the valve to confirm open/close.

 

[JP02XLT]

you can use an un-lit propane torch to poke around the intake, throttle body, air intake tube and any vacuum lines, pcv etc, any leak and it will suck in the propane, increase the rpm of the engine to tell you where the leak is. Check anywhere that engine vacuum is present.

You can also pull the connector off the injectors with the engine running and feel if they cycle, of course engine rpm is going to drop each time you remove the connector, or atleast it should.

JP02XLT

 

[Acecom]

OK guys thank you for the info and suggestions. I'll start looking for a vacuum leak. At this point i would be thrilled to find one, also i can't unhook the electrical plug to injector 5 without taking the top housing off which exposes the Manifold? maybe? I'm not sure, but wouldn't that just suck a ton of air? or am i wrong? I'm probably totally wrong lol

 

[Rearanger]

i can't unhook the electrical plug to injector 5 without taking the top housing off which exposes the Manifold?

Yes, you're right. The intake covers the injectors on that side. Just try the vacuum leak for now, if you find something the intake may have to come off.