Cylinder 4 & 5 misfire

[Fordmikeyranger87]

Hey there, looking for some help to track down the cause of a misfire on cylinder 4&5 on 87 Ranger 2.9 v6

Pulled the truck out of the garage today noticed it had less power starting off, little less noticeable at higher speeds. When I got back home and popped the hood the engine had a a lil shake to it while idling, Pulled the plug wires one at a time and sure enough cylinder 4&5 had no effect on idle. There was still spark so I know that’s good and wires and plugs are new as well. tested connections for those injectors with noid light and I’m getting pulse on both so as far as I know the injectors are good as they were replaced about a month ago.

Im fairly certain there are no fuel issues, inline pump and filter are new and pressure test was 40psi key on and 35psi running holding steady.

Compression checked out good
#1 - 160 dry 170 wet
#2 - 155 dry 170 wet
#3 - 155 dry 165 wet
#4 - 160 dry 165 wet
#5 - 160 dry 170 wet
#6 - 160 dry 170 wet

No codes are showing up either and I know I don’t have any vacuum leaks as all lines have been changed with In The last month along with the map sensor, tps, FPR, air filter, EGR, O2 sensor and cat has been hollowed out so I know that’s not clogged either. Timing is good, triple checked to make sure.

So that where it stands right now. Last thing I can think of is that pick up coil may be going bad but I’m just not sure if that would cause only 2 cylinders to misfire.

 

[SenorNoob]

Bad gap on the plugs?

 

[Fordmikeyranger87]

Bad gap on the plugs?

Plug gaps are at recommend specs

 

[SenorNoob]

It would seem you've covered literally everything.
I would think if the pickup coil is bad you'd either have no spark or maybe random misfires.
It has to be plug, wires, or fuel injectors to effect only certain cylinders. I suppose maybe the distributor cap could have problems only affecting 2 cylinders. Maybe slightly out of alignment with the distributor if it isn't a very tight fit?


There has been a rash of bad new injectors lately. Something to consider...

 

[Fordmikeyranger87]

It would seem you've covered literally everything.
I would think if the pickup coil is bad you'd either have no spark or maybe random misfires.
It has to be plug, wires, or fuel injectors to effect only certain cylinders. I suppose maybe the distributor cap could have problems only affecting 2 cylinders. Maybe slightly out of alignment with the distributor if it isn't a very tight fit?


There has been a rash of bad new injectors lately. Something to consider...

Thanks, Cap is new but I’ll take a look and make sure it’s seated properly and tight yeah, thought the same about pick up coil truck starts up great and spark seems strong and trying to avoid pulling the dizzy if possible. Might go ahead and just swap injectors with one of the working cylinders to see if it makes a difference.

 

[Rick W]

Your first problem is you fixed too much stuff at the same time. If you move like molasses like me, and you just change one thing every other month, then if it doesn’t run right, it’s easy to look at the last thing you did!

OK, that aside, I agree with @SenorNoob on plugs, wires and injectors. My 97 4.0 has about 320,000 miles, and I ended up with a rough idle and a little loss of power. Like you, everything checks out correctly.

I’m trying a hot soak with Sea Foam like I do on my diesel. I ran the tank down to about a quarter tank or less, poured in a full can of the Sea Foam, and then I drove it 30 or 40 miles to make sure that it was all down through the fuel system while the engine was stinking hot. Then I let it sit for a a few days.. The heat and the time help the Sea Foam work better removing varnish and gunk.

I’m still evaluating if that has made a difference. I used premium in the first tank of gas, and I’m just about to put the second tank of 87 gas in. I mentioned it because it’s a relatively inexpensive effortless way to clean things up a bit. The injectors may be new, but who knows what they might’ve sucked up in an old system.

How many miles on your truck? I’m not sure of the answer, but I know an old trick on older engines was to get a hotter spark plug, and maybe adjust the gap a little bit. I’m sure some of the better mechanics on the site can guide you how to try that. When fiddling with using different plugs, you just have to be very careful of the penetration so they don’t contact a piston or valve.

Another thing you can do is to swap the plug wires around. Do you still have the old ones? If you’ve got a shaky wire, the problem should move wherever you put that wire.

Another possibility is to use an engine stethoscope, and touch it near each one of the cylinders, and see if there’s any extra knocks or clicks or taps or whatever. If some of the valve guides are sticky, it could affect a smooth, even ignition.

That’s the best I’ve got, my two cents, I hope it helps

 

[Fordmikeyranger87]

Thanks for the tips Rick! yea, kept the old wires but i did swap 4&1 cylinder wires and same with 3&5 wires to see if I got the same results and I did, so I assume the wires are good. I’ll have to try the stethoscope suggestion, first time hearing of that. Truck has 109k, original owner I bought it from said it was at 100k and I’m taking his word for it only cause the interior seats, floorboards and gas Pedal were in great condition and showed very little wear.

 

[Rick W]

Thanks for the tips Rick! yea, kept the old wires but i did swap 4&1 cylinder wires and same with 3&5 wires to see if I got the same results and I did, so I assume the wires are good. I’ll have to try the stethoscope suggestion, first time hearing of that. Truck has 109k, original owner I bought it from said it was at 100k and I’m taking his word for it only cause the interior seats, floorboards and gas Pedal were in great condition and showed very little wear.

If it’s only got 109, I wouldn’t think it’s going to be anything mechanical in the engine. If it’s got 209, that’s a different story, depends on how it was maintained. The sea foam trick is cheap. If it makes any difference at all, then I’d try moving around the injectors and see what happens.

Keep reaching out, there are really much better qualified mechanics than me in TRS. I’m an old shade tree, a lot of these guys do this stuff for a living.

Good luck