A while ago I got a '99 Ranger, 3.0 auto, flex fuel compatible, now the check engine light is on & the codes show a #5 misfire. It was time for an oil change so I also I did plugs, wires, & air filter hoping one of them might be the problem but no-go.

Before I take it in & get it checked out for more info than what autozone's little code checker can tell me, what is the better bet, coil pack vs a fuel injector? Or is there something else it's more likely to be? Thanks.

 

Do I Look Like I Can Detect From Here? heh. Actually, if you don't notice the misfire at idle, I'd be looking at the injector more than the valves. A bad valve will show up on each power stroke (that isn't) as a missfire detectable by the engine shaking or the exhaust sound changing. An injector, on the other hand, can misfire intermittently due to several causes.
A coil would cause misfire in both of the cylinders that it operates. Doesn't your 3 have a six-pack coil that is actually 3 coils wired to fire 2 cylinders each? If it does, then the other cylinder would be misfiring also.
tom

 

Thanks for the reply tomo.

Some more info: The misfire/engine shake is worse at idle & low, low rpm. If you stomp it getting on the highway, (or cruising at speed) the misfire seems to clean up & it pulls good.

At times the misfire goes away for a while, (about a week) then comes back. And other times it stays around a good while. It seems some times that running the A/C kinda helps clear it up after a while (maybe the higher rpm's with the A/C on??).

The coil pack looks to me like a solid block with 6 plug wires, & an upright connector, (didn't look like 3 coil packs as a block, with 2 wires each pack).

It does't smoke, doesn't run hot (a little lower than half the temp guage), has good oil pressure, has about 80,000 miles, & at times smells like it's running a little rich even after it's warmed up.

 

Memo to self: tomw, not tomo (Jeez, looong day)

 

Well, FWIW, I once 'added' a misfire to my car, a 3.0 Vulcan, by replacing a perfectly good coil with aftermarket. The original had arcing marks around the core, so I thought it was on its way out. Added an intermittent miss.
In your case, a bad valve will not come and go. It is bad or it is not. It could be the coil, being weak, but I thought the coils operated in pairs, and would affect the other cylinder also.
Two things I'd try. 1) put an inductive timing light on the #5 plug wire and watch to see if the coil fires all the time at idle. 2) open the hood in a dark place and see if your new plug wires are arcing anywhere. Even new can be defective.
I have heard elsewhere on thhis site that some styles of spark plugs are not very good in FoMoCo prods. If you went with any 'dual' or 'multi-electrode' styles, I'd be thinking about taking them back for Motorcrafts or Autolites.
You can get the injectors cleaned with a fuel system cleaner that disables the fuel pump and runs on the injector cleaner fluid. Motorvac(?) costs about $75 depending on where you live.
Go back to basics. fuel air spark. Check your fuel pressure at the schrader. You've done the air filter, and replaced spark components.(some) A coil is not cheap enough to just throw one on there without checking. Make sure that the ground is good on ALL of the coil(s) as if it is not grounded all around it may not work well. Have you cleaned out the intake manifold, cleaned the EGR pintle valve, and cleaned out the IAC passage? Does your PCV valve work right. Just basic stuff that you eliminate to narrow down the problem.
tom

 

It has either Motorcraft or Autolite plugs (don't remember which) & whatever brand wires Autozone sells, so I will check for glowing/arcing wires.

I did read elsewhere on this site about cleaning the MAF sensor with throttle body cleaner, and will try that, (if I can find my torx bits) and also will check the coil ground(s) this weekend. How hard is cleaning/finding the other stuff you mentioned, (EGR pintle valve, IAC passage)?

 

Similar problem here except number 4 cylinder. I forget the code number but 3 mechanics who ran the disagnostic all say #4 cylinder misfiring. Plug wires have been replaced as have the plugs. Injector has been cleaned. Misfire still there, especially 40-50 MPH. Pressure good in cylinder, no oil lost.

Engine is 3.0 V6 with an automatic transmission.

Any other ideas as to what may be the cause? The mechanics here are mystified.

 

The misfire continued to get worse over time until the point where the truck was undrivable because it was so far down on power. Many cylinders had terrible compression numbers that kept getting worse over time. I had hoped it was just blown head gaskets, but no such luck.....

A friend with a busy repair shop finally had an opening to look at it. Turns out almost all (5 of 6) of the exhaust valves/seats had receded into the heads. He was amazed it was even able to still start and try to run as bad as it was. In the past I have seen older (leaded fuel) 302 & 460 exhaust seats recede a given amount, but these V6 heads were much worse. How did these unleaded fuel V6 heads sink the exhaust valves so bad?

Two junkyard heads with fresh valve jobs & a gasket set later & it's up and running again with power like it used to have. I still need to replace the cat converter because it was so sludged/clogged up. The cat was so bad that now there was a ton of back pressure choking the engine above idle because the motor was once again making power. Since the cat was junk we decided to knock a hole in the honeycomb to let the exhaust flow better just so I could drive the truck back home without the engine fighting all the back pressure.

 

Dave, I had the exact same problem about 6 months ago. I installed two replacement heads and now everything is prefect. Mine also threw the #5 cylinder misfire code. I am glad to here you have it fixed.