'94 4.0 Ranger - Misses Under Load and at WOT

[pxbacher]

1994 Ranger 4.0 idles fine but has been running real rough since this past summer when it started suddenly missing while driving. For a while the rough running would come and go. Now it runs rough all the time, though sometimes lots worse than other times. It starts and idles fine.

Yesterday when I first started it, it ran so badly I couldn't get it over 15mph. When I gave it gas, it backfired (which it often does when it's acting up like this and I give it more gas). After it "warmed up" it drove, but real rough. It runs worst the more I press on the pedal. It runs best when I really baby it and keep the RPMs as low as possible.

Stuff I've done so far:
1. Replaced the MAF sensor (with a used one, after cleaning it with electronic cleaner spray (not brake cleaner)) - no change
2. Replace the fuel filter - no change
3. Replaced the FPR - no change (fuel rail pressure is 29psi or better, and goes up to maybe 35 psi when driving at higher RPMs)
4. Replaced the coil pack with a used one - no change
5. Tested TPS - .95v - 4.6v nice and smooth from close to full open

Any thoughts on this? I'm thinking it's just running way too rough for it to be an ignition wire or plug problem (i.e. too many cylinders missing - can't be a single plug or wire, and there's no "central" distributor wire given that it has a coil pack). The fact that it runs fine at idle was leading me to think it was a fuel pressure problem, but after testing, the pressure seems fine. Could I have a sensor problem? What sensors would come heavily into play with higher RPMs?

Aside from sensors, I'm starting to run out of things to check/swap out, and hoping the evidence isn't pointing toward a bad ECU.

-Pete

 

[Big Jim M]

I'd sure be looking at the spark plugs... What brand are you using? Plugs cause a LOT of chuggung problems..
Big JIm

 

[pxbacher]

...I would change the ICM and see if that fixes your problem.

I will look into that. Looks like I also need to check grounding and wiring to/from the ICM (based on other ICM posts I've since read here and elsewhere)

Do you remember where the ICM was located?

Thanks-

-Pete

 

[pxbacher]

I'd sure be looking at the spark plugs...

Yeah, I'll check them too but pretty sure they're not the issue. Plugs are only about 6 mos old. Motorcraft plat IIRC...

-Pete

 

[Nhaz]

You will also want to go over the vacuum systems lines. Backfiring can blow a line off the vacuum tree. Or blow the cap off a spare capped line on the vacuum tree.

 

[dennis461]

to be an ignition wire or plug problem

Guess again or should I say test again.
Tonight in the dark, open the hood and look for sparking along the wires while someone revs up the engine.

DON'T GET HURT

My Fords wires only last a couple of years.

As for the coil pack, that could easily be the problem, swap with one from a bud's truck or junk yard. Were did the used one come from?

 

[pxbacher]

As for the coil pack, that could easily be the problem, swap with one from a bud's truck or junk yard. Were did the used one come from?

Used coil pack came from a junk yard. While unpacking it, I dropped it and cracked one of the six plastic (bakelite?) connector surrounds so I could no longer install it as a replacement, but could put it in for a day-long test on a sunny day. Exact same behavior as with the original coil pack

I'll check the wires for arcing. Note that no change in behavior on wet vs dry days - another reason to not suspect bad wires, but worth a look-see.

Thanks for everyone's help so far...

-Pete

 

[Z3CHYD]

My 93 explorer is having the same exact problem, starts backfiring and popping under load and WOT, and just like you it came and went at first, but now its there as soon as my engine warms up. I was thinking maybe it could be o2 sensors?

 

[pxbacher]

I was thinking maybe it could be o2 sensors?

My understanding is that under near WOT conditions, the O2 sensors (my Ranger has 2 - one on the downpipe end of each exhaust manifold - hope I got this terminology right) are ignored by the ECU. Here's a thread that talks about this:

http://www.therangerstation.com/tech_library/O2Sensors.htm

So I hadn't considered the O2 sensors, but may end up taking a look at them as I run out of other things to check

Oh yeah - and the CEL has not come on once on mine - how about on yours?

-Pete

 

[Z3CHYD]

My understanding is that under near WOT conditions, the O2 sensors (my Ranger has 2 - one on the downpipe end of each exhaust manifold - hope I got this terminology right) are ignored by the ECU. Here's a thread that talks about this:

http://www.therangerstation.com/tech_library/O2Sensors.htm

So I hadn't considered the O2 sensors, but may end up taking a look at them as I run out of other things to check

Oh yeah - and the CEL has not come on once on mine - how about on yours?

-Pete

yea my 93 explorer has 2 o2 sensors on each side of the y-pipe also. And if I hold the pedal down for awhile while its popping an backfiring the check engine light does come on sometimes, but it goes away when i "baby the throttle" and it doesn't act up. The only reason I suspected the o2 sensors was because I had an 86 ranger that ran similar once i bought it, and once I replaced the 02 sensor on it it ran perfectly the rest of the time I owned it.

 

[pxbacher]

...but it goes away when i "baby the throttle" and it doesn't act up. The only reason I suspected the o2 sensors was because I had an 86 ranger that ran similar once i bought it, and once I replaced the 02 sensor on it it ran perfectly the rest of the time I owned it.

Sounds exactly like mine. Thinking I'll buy one sensor and swap it out one at a time to see if it makes a difference... Wonder what the likelihood of both gone bad is? Gotta see if I can find a test procedure for O2 sensors...

And Quarryville? Seriously? I'm in Kennett!

-Pete

 

[Z3CHYD]

Sounds exactly like mine. Thinking I'll buy one sensor and swap it out one at a time to see if it makes a difference... Wonder what the likelihood of both gone bad is? Gotta see if I can find a test procedure for O2 sensors...

And Quarryville? Seriously? I'm in Kennett!

-Pete

Yea I was thinking just one sensor might of gone bad, since it'll still run fine if im not on the gas. But also my dad was suggesting that I might have water in the gas tank, from condensation, which I'm not really sure about but I'll humor him and dump in some stuff he has called "dry gas". if that doesnt work I'm replacing my o2 sensors.

and yea, I'm about 5 miles outside of Quarryville, off of Valley road

 

[pxbacher]

I was reading about "Dry Gas" and supposedly it's just Isopropyl alcohol. Some say you shouldn't need to use Dry Gas given that 10% or more of our gas these days is alcohol, so water shouldn't be a problem... At this point I'd piss on a spark plug if I though it would help, so I guess I should try some Dry Gas (Isopropyl) too...

-Pete

 

[Z3CHYD]

I was reading about "Dry Gas" and supposedly it's just Isopropyl alcohol. Some say you shouldn't need to use Dry Gas given that 10% or more of our gas these days is alcohol, so water shouldn't be a problem... At this point I'd piss on a spark plug if I though it would help, so I guess I should try some Dry Gas (Isopropyl) too...

-Pete

Yea I was trying to explain that to him, but my dad likes to reminisce about the "olden" days were everything was carbed, gas was up to 118 octane, and still had lead in it, He doesn't really understand Fuel Injection works completly different than carb'd lol. So yea, "dry gas" tomorrow, if that doesnt work o2 sensors. If that doesnt work....umm I might have to have someone look at it...

 

[Z3CHYD]

I was reading on the 4.0 page about cleaning the MAF sensor, and I was unaware you had to take apart the little plastic black piece to clean it properly, I always just took out the whole unit and sprayed cleaner in the housing itself, I guess I'll try what the page says also, just have to buy some maf cleaner
http://www.therangerstation.com/tech_library/CleanMAF.html