I've been having this issue for while now. Pick up idles around 400-500 rpm at all times and Temps. Sometimes it stalls when starting up. Shakes bad when at a stop but drives fine. Has brand new IAC, Spark plugs, wires, and coils. Can't find any obvious vacuum or exhaust leaks. Constantly has a po305 cylinder 5 misfire code. Anyone have any ideas before I go and buy a compression tester?

1999 Ranger 4.0 v6, XLT, auto tranny, 4x4 Misfire & Rough idle, po305, 180,000 miles

 

Welcome to the forum

Do the compression test first
Cold engine
Pull all 6 spark plugs out
Press gas pedal down to the floor when cranking engine over, this turns OFF fuel injectors
Listen for 5 "hits", more is fine, less is not, you will know
Then write it down

What did the old #5 spark plug tell you about conditions in that cylinder?

Change the ECT sensor, that's what tells computer the coolant temp so computer will run high idle and Choke on cold start
There is also a temp sender, for the dash temp gauge, its 12volt, the sensor is 5volt so not interchangeable
Sender will have red/white wire, sensor grey/red wire

IAC Valve needs to be Motorcraft or Hitachi brand, they are the only ones that work well with Ford computers

Coil pack wiring is odd
3 4
2 6
1 5
front

The 5 6 4 side often gets mis-wired, either at the coil or at the cylinder

 

Alright ill run a comp test this weekend when I have time. The spark plug was pretty scared up but not super bad. Was just old. Every where else online and in my Chilton book says the coils are

3 6
2 5 Driver side
1 4
Engine Front

Thats the wrong order?

 

Yes, thats is wrong

Ford's cylinder numbering is
Engine
3 6
2 5
1 4
front

But that's not the Firing order, coil pack is Firing order
Coil pack
3 4
2 6
1 5
front

Drawing here: https://www.explorerforum.com/forums...f-jpeg.160382/

3 4 is a matched pair
2 6 is a matched pair
1 5 is a matched pair

Match pairs are how V6 engines are balanced, each matched pair is at top dead center at the same time, matched pairs and Cam are what decide Firing Order for an engine

 

Ok thank you for the info. I'll run a compression test and swap out sensors this weekend. Do you recommend any brands for the sensors?

 

Only sensors that wear out are O2 sensors, and its unlikely to be a sensor issue

If you have coil pack wired wrong it should have made a BIG difference when it was corrected, so not sure whats up with that??????

 

I had the wires right in the first place. I was hoping maybe I got them wrong. The IAC is a napa brand so ill probably swap it out with a Motorcraft as the idle is worse now. Still gonna run a comp test this weekend. I'm still stumped on the misfire though. Hope this doesn't get major as its my only vehicle till I graduate college.

 

Ran the comp test today. With all spark plugs out and engine cold. All cylinders sat around 120 psi while cylinder 5 stayed at 60 on the dot.

 

Piston 5 at TDC of compression stroke....fit air hose to spark plug hole....listen at tail pipe and at throttle body for air leakage.

 

Yes, most likely you have a burnt exhaust valve on #5
You can put a teaspoon of oil into #5 and then re-test compression, it will probably just go up a bit, may be 70-80, that would confirm Rings are OK and its a valve issue, or possibly, a head gasket issue, but I would expect other issue with a bad head gasket, not that it matters, head has to come off either way
4.0l OHV heads are known to crack so need to be tested for that BEFORE any valve work is done

 

Ok thanks for the information! I'll post an update if/when I figure more out.

 

The 4.0l SOHC was used in 1997-2000 Explorers as an "upgrade", Explorers also had the 4.0l OHV in those years, a 1997 explorer 4.0l SOHC PCM wouldn't have PATS and would work with your 1999 automatic as is

1998-2000 would have PATS but would still work with 1999 Trans
In those years you need to get the PATS module, above glove box, with the 4.0l SOHC PCM, PATS module and PCM come in "matched pairs" in each vehicle

2001-2003 had PATS in computer but also need the 2001 and up transmission