1989 Ranger 2.3L random idle missfire?


winmag4582001

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New here and I tried to search year specific but came up emty.
I was given this old Ranger and the water pump was leaking bad so I replaced that and did all 8 plugs and all the basic tuneup stuff.

Strange issue is, when it warms up and is idling, it missfires out the tailpipe once every 10 seconds. Comes off idle and drives fine. Just at idle it does this. It'll run 85mph down the interstate just fine.
Should I check timing or ICM? I'm kinda thinking it may have jumped a tooth or two on timing but some of my searches say that the ICM is a known issue in these. Appreciate any advice.

TIA
 


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RonD

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Welcome to TRS :)

1989 to 1994 Ranger 2.3l will be the same as yours, dual spark plugs with external ICM
1995 got new computer with ICM built in

Slipped timing belt would cause a big lack of power at higher speed so 85mph wouldn't be possible, 50mph would be tough, lol

Backfire from tail pipe means a cylinder misfired and the unused air/fuel mix was dumped into exhaust manifold and ignited by next firing cylinders hot exhaust gas, pop

Have you tried running a can of Seafoam, or similar injector cleaner in the gas tank?
A fuel injector with a dirty tip will drip fuel at low RPM/low flow instead of spraying it, this can cause a bad mix and misfire
At higher RPM the faster flowing air and longer open time for injector gets a better mix
 

winmag4582001

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I'll try that. It had been sitting for about 5 months because of the water pump being bad, it was taken out by the fan clutch loosing the bearing and shaking the water pump to failure. Fuel injector could definitely be it. Off idle it runs just fine. Just when you stop at a light it will sit there and pop every 10 seconds. The plugs I pulled out looked horrible!
I unplugged the driver's side wires at the coil pack and it still did the same thing. Seemed to idle exactly the same with those plugs undone.

Thank you!
 

RonD

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Yes, both spark plugs fire at the same time so a misfire from spark in this engine means both spark plugs didn't fire

Just a heads up on the 1989-1994 2.3l, only the exhaust side(passenger side) spark plugs work when starter motor is active, after engine RPMs are above 400 the intake side plugs start to work

Its also a waste spark system, this means each cylinder gets spark at both its TDCs, compression and exhaust stroke, so one spark is wasted, this is done because its distributorless and its just easier to time spark that way.

So only 2 coils are needed inside each coil pack because engine is balanced by have #1 and #4 at TDC at the same time, and then 180deg later 2 and 3 are at TDC
So 1 and 4 spark plugs fire at the same time using 1 coil in the pack, then 2 and 3 fire using the other coil in the pack
 

winmag4582001

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I changed the fuel filter, didn't seem to have much fuel pressure left in the lines for only being off for 30min.
I'll run some seafoam or BG44 in the tank.
I'll also disconnect the vacuum line to the FPR at idle to see if that helps the little misfire. I'll have to borrow a fuel pressure tester from Autozone if the fuel injector cleaner doesn't work.
The number on the coils are referring to the cylinder location correct? #1 cylinder being closest to the radiator, then 2, 3, 4?

I've had vehicles in the past that would lean pop between shifts and on decel or have a flat lobe on the cam and constantly bang, or rough idle and hard starts due to low fuel pressure. This is the first time I've had a vehicle run and start just fine but miss randomly at an idle.

Appreciate the help!
 
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tomw

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Have you looked at the engine running at idle after dark? You could be getting some spark leakage if the wires are aged or damaged. Normal wires are made of a fiber impressed with carbon. They will have some Ohms/ft, but not infinite or OL reading when checked with a VOM. If they are 'open', the spark has to jump multiple gaps, and sometimes takes a shortcut. You also have the spark going across two spark plugs & wires...
It is not unusual to have an intermittent misfire now and again. The injectors on Fords don't seem to get gucked up as often as some other brands, so that is sort of unlikely. It wouldn't hurt to check fuel normal pressure, and un-regulated pressure, to insure pump and regulator operation. You might also check fuel flow at the same time to give a general reading on pump and filter flow capability.
Anyway, run it after dark, and open the hood. If you get a light show, you know what to do.
tom
 

toby'87xlt

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New here and I tried to search year specific but came up emty.
I was given this old Ranger and the water pump was leaking bad so I replaced that and did all 8 plugs and all the basic tuneup stuff.

Strange issue is, when it warms up and is idling, it missfires out the tailpipe once every 10 seconds. Comes off idle and drives fine. Just at idle it does this. It'll run 85mph down the interstate just fine.
Should I check timing or ICM? I'm kinda thinking it may have jumped a tooth or two on timing but some of my searches say that the ICM is a known issue in these. Appreciate any advice.

TIA
From my personal experience I had this happen on my 1987 ranger xlt with the 2.9l in it. It was misfiring horribly and seemingly out of nowhere. After a long trouble shooting fiasco and lots of time under the hood I found that my grounds were crap. So I ran a 6 gauge cable from my coil to the alternator bracket and from my alternator bracket to the engine block and from my block to frame and then to battery negative. I threw in some smaller gauge grounds here and there under the hood (overkill I know) but after that the truck stopped misfiring! It also made all the lights brighter and the truck had alot more low end power coming off a stop and just all around felt great improvements. I would just check the grounds first!
 

winmag4582001

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OK. So here's where I'm at.
Dumped some seafoam and chevron in a 1/4 tank of fuel and ran it 25 miles to work on the interstate. Ran great.
Got to work and it still misfires at idle.
Opened the hood and checked for spark leakage. None seen.
Took the vacuum off the FPR so the injectors had full pressure at idle. Still misfire.

I think Toby may be onto something...... My 1980 GS1000 had a misfire at high rpm after I repainted the frame. The coils grounded to the frame and the new paint interfered with the grounding giving me a weak spark at high rpm.
I'm going to check grounds in the morning.

Also. Idle seems to be on the low side. Is there any adjustment to idle on these?
It fires up instantly when cold and high idles probably around 1200rpm for a minute then drops. No tach so I can't say for sure where it's settling at but it seems probably around 600rpm.

Thank you all very much!
 

winmag4582001

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From my personal experience I had this happen on my 1987 ranger xlt with the 2.9l in it. It was misfiring horribly and seemingly out of nowhere. After a long trouble shooting fiasco and lots of time under the hood I found that my grounds were crap. So I ran a 6 gauge cable from my coil to the alternator bracket and from my alternator bracket to the engine block and from my block to frame and then to battery negative. I threw in some smaller gauge grounds here and there under the hood (overkill I know) but after that the truck stopped misfiring! It also made all the lights brighter and the truck had alot more low end power coming off a stop and just all around felt great improvements. I would just check the grounds first!

Are the coils grounded to the bracket by the bolts or is there a specified ground wire from the coil to the frame/motor?
Thanks
 

RonD

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Coils are grounded by their wires, thats how they are powered up and then ungrounded to spark

The ICM does have a ground that a known issue, one of the bolts holding it to the lower intake
 

scotts90ranger

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I don't remember paying too much attention, my '90 does crazy stuff just from it's random assortment of stuff on it so it isn't the best to judge by right now...

There's no MAF on an '89 (that's a mid '90 change) so not an issue there like could be with newer ones, but there is an IAC and the spark stabilizer circuit in the DIS... being that old the spark stabilizer is probably rough (just being early in implementation) and might reset itself every now and then but that's just a semi educated guess...

Trying to dig deep into the memory banks (I think I went turbo 11 years ago) but I think it could be normalish...
 

winmag4582001

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I think I may have found it.................
So, i was listening under the hood, I could hear the pop at the tailpipe but wasn't feeling anything at the motor.
I got under the truck and heard the pop in the muffler.
I hit the muffler hard and the popping stopped for about 30 seconds and then started rattling and popped again.
The truck sat for about a year and the exhaust looks to be old, but not rusted through.
Going to change the muffler and see what that gets me.
I did add a ground strap from the motor to the neg. side of the battery for good measure.
I'll report back if the muffler internals are collapsed.

Thank you all for the input and advice. Really appreciate it!
 

toby'87xlt

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Coils are grounded by their wires, thats how they are powered up and then ungrounded to spark

The ICM does have a ground that a known issue, one of the bolts holding it to the lower intake
If you look at the coil there is a ground wire screwed into the right side of it just above the fender. If you cut up the wire harness and separate all the wires (I did this to search for bad spots on all wiring u der the hood) you will find that it grounds out on the driver side of the intake plenum. It's at the top right behind the EGR senspr and is held down with a 8MM bolt. That is the one I did away with and uprgraded
 

scotts90ranger

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On the DIS system the coil packs have a 3 pin connector, one power in the center and two signal wires that are the ground, the ignition module is mounted to the front of the intake manifold and grounds through the 3 mounting bolts.
 

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On the DIS system the coil packs have a 3 pin connector, one power in the center and two signal wires that are the ground, the ignition module is mounted to the front of the intake manifold and grounds through the 3 mounting bolts.
Yup, and if you snap one of the little tiny bolts, You cant get away with not fixing it. I just got my 89 2.3l running after ten years of sitting. Went to the junk yard and got some new wires and a starter relay. Started up first try. but now its missfiring cause all the shit its spitting out. I suppose I would too if someone woke me up after ten years. Oh yeah and I got an Icm that the counter guy sold me as a relay. Good guy.
 


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