Misfire on 2.5 4cyl - 4 Cylinder Gasoline - Ranger Engine Tech

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sheltonfilms
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For the past few weeks I've experienced a miss at idle. No solid or flashing check engine light so the misfire monitor isn't above the threshold for catalytic converter damage. Did have pending P0301 and every once in a while P0302.

It's been 100k miles since spark plugs and wires so I went ahead and swapped those out. Motorcraft plugs as always and the older plugs looked great (good color no deposits). Cleaned the throttle body butterfly while I was at it.

Did a compression test immediately after a drive to get temps up to normal. Throttle body held open:

cyl 1: 185
cyl 2: 180
cyl 3: 180
cyl 4: 170

Before removing wires I used a grounded test light to test all coil pack towers. All had good color spark and bright and was able to spark to about an inch away from the towers.

ST and LT fuel trims look great at closed loop. LT stays right at 0 and short term may be a max of postiive 4% to min of negative 3%. So I'm not thinking bad injector.

So I removed the IAC leaving the connector connected, fired up Forscan and started changing the IAC duty cycle. I can't see any changes. Do hear a little noise but no movement. IAC is closer to cylinders 4 and 3 so I could see this valve not being opened enough and starving cylinder 1 and sometimes 2. Ohmed out at 10 ohms.

With nothing connected the plunger it does allow some light though.
Anybody looked at the movement of the IAC before?

Last edited on Mon Jan 15th, 2018 06:24 pm by sheltonfilms

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Posted: Mon Jan 15th, 2018 07:02 pm

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sheltonfilms
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Vacuum Gauge and Compression Testing:

Last edited on Mon Jan 15th, 2018 07:02 pm by sheltonfilms

Posted: Mon Jan 15th, 2018 09:40 pm

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JAMMAN

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I hear it is like a slow stepper motor, have never held one in my hand and watched it move. If you can make it move take a video!

I have one but have no idea if it is good or not, they only cost 30 bucks. If you want mine I'll dig it out and send it to you I still have most of the top end of my 2.5

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Posted: Mon Jan 15th, 2018 10:13 pm

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sheltonfilms
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I messed around with it some more and if the engine is running it does have an effect of idle speed changing the duty cycle.

I’m scratching my head big time on this misfire. I can find a point of attack on it.

Last edited on Mon Jan 15th, 2018 10:13 pm by sheltonfilms

Posted: Mon Jan 15th, 2018 10:24 pm

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JAMMAN

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Injector possibly?

We have an injector tester at work (why I'm not sure since we are a diesel shop) and I have seen ones not start pulsing till a higher rpm all the way to stuck open, seems to be no logic. If you can tell which cylinder you could swap injectors to see. Else there might be some weird carbon tracks on your coils. Can't be spark plugs or wires since it acted the same after changing them. Well it could but it would be a huge coincidence.

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Posted: Tue Jan 16th, 2018 12:04 am

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Just a wild guess, did you try cleaning the IAC?. On our last 99 Explorer Sport we had a idle problem & one of the techs at the Ford dealership I was working at told me to remove it & spray it with carb cleaner because they get gummed up & stick. Fixed our problem.

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Posted: Tue Jan 16th, 2018 12:24 am

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sheltonfilms
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Cleaned it when I cleaned the throttle body.

Posted: Tue Jan 16th, 2018 12:35 am

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It's fairly easy to test IAC operation, and i can't remember more than that right now! :( Sorry.

I looked up IAC cleaning videos and they included testing procedures too, mainly involving unplugging them if/when looking for open/close.

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Posted: Tue Jan 16th, 2018 01:11 am

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sheltonfilms
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Well I think I found a way to test it. I set forscan to read IAC duty cycle and RPM and then setup controls to change the duty cycle.

RPM follows IAC duty cycle changes except for anything below 20%. 20% and below stays the same RPM.
I took it for a drive and before I did that I cleared PCM adaptations. No misfires list in forscan and also no misfires counted in Mode $06. Idle is still kinda garbage at some points. Give it a slight bit of gas (like 1500 rpms) and I can fill it mis.

Last edited on Tue Jan 16th, 2018 01:13 am by sheltonfilms

Posted: Tue Jan 16th, 2018 01:52 am

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JAMMAN

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I never did think it was IAC. High,low, pulsing idle.. IAC. Have never personally seen it cause a "miss".

If it is an injector I get a dollar. LOL

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Posted: Tue Jan 16th, 2018 02:24 am

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sheltonfilms
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JAMMAN wrote: I never did think it was IAC. High,low, pulsing idle.. IAC. Have never personally seen it cause a "miss".

If it is an injector I get a dollar. LOL

But why the hell are my fuel trims showing good? I can pull a tiny vacuum line and keep my finger over most of it so it's the tiniest of holes and my fuel trim will shoot right up to 35%.

What else should I be looking at? MPG seem alright (23 mpg combined) so I wouldn't think an O2 sensor is going out. Switching seems ok.

I know you can feel the bad idle when it is still in open loop at first startup.

Last edited on Tue Jan 16th, 2018 02:25 am by sheltonfilms

Posted: Tue Jan 16th, 2018 03:52 am

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Fuel trims are what the engine *wants* - it tells the injectors, doesn't mean the injectors listen properly ;)

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Posted: Tue Jan 16th, 2018 10:22 am

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JAMMAN

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The only thing that doesn't point at fuel injector is the miss in 1 and 2.

Swapping injectors 1 and 4 would disprove the injector theory if you were still getting P0301 and P0302 afterwards and it is only labor.

Now I'm thinking coil. Coils don't always follow normal failure protocol

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Posted: Tue Jan 16th, 2018 02:21 pm

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sheltonfilms
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I'm wondering if these engines can even have an ignition based misfire since it has the dual spark setup. Even with one coil going bad the other one should take up the slack. One spark or wire goes bad the other side should keep it going.

I probably should have swapped injectors when I took the top intake plenum off for the spark plugs.

I guess next step is to mess with PCV valve. Also, need to do an IAC unplug test.

Last edited on Tue Jan 16th, 2018 02:21 pm by sheltonfilms

Posted: Tue Jan 16th, 2018 06:07 pm

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Well got a P0300 code in memory and I pulled up Mode $06 and see that it's still biased towards cylinder 1 and a little on cylinder 2.

Started thinking about about the IAC unplug but figured you don't have to do that if you set IAC duty cycle to 0%. Runs fine after warmed up.

Posted: Tue Jan 16th, 2018 08:41 pm

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sheltonfilms wrote: I'm wondering if these engines can even have an ignition based misfire since it has the dual spark setup. Even with one coil going bad the other one should take up the slack. One spark or wire goes bad the other side should keep it going.

I probably should have swapped injectors when I took the top intake plenum off for the spark plugs.

I guess next step is to mess with PCV valve. Also, need to do an IAC unplug test. I know that when I had duel fire ignition on my 96 Harley it was always stumbling at idle. When I changed the ignition to single fire the bike smoothed out and ran much better.
I am on ignition number four. The replacement of #2 was because it was a cheap chinese knockoff that lasted just under 6 months. I do know the single fire causes premature spark plug failure and my truck has never had a very smooth idle.

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Posted: Tue Jan 16th, 2018 11:56 pm

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Tsquare wrote: sheltonfilms wrote: I'm wondering if these engines can even have an ignition based misfire since it has the dual spark setup. Even with one coil going bad the other one should take up the slack. One spark or wire goes bad the other side should keep it going.

I probably should have swapped injectors when I took the top intake plenum off for the spark plugs.

I guess next step is to mess with PCV valve. Also, need to do an IAC unplug test. I know that when I had duel fire ignition on my 96 Harley it was always stumbling at idle. When I changed the ignition to single fire the bike smoothed out and ran much better.
I am on ignition number four. The replacement of #2 was because it was a cheap chinese knockoff that lasted just under 6 months. I do know the single fire causes premature spark plug failure and my truck has never had a very smooth idle.
Did it have two spark plugs per cylinder or are you referring to waste spark (firing on combustion and exhaust stroke)?

Last edited on Tue Jan 16th, 2018 11:56 pm by sheltonfilms

Posted: Wed Jan 17th, 2018 02:43 am

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Waist spark is the same a duel fire. There are sometimes leftover explosive gases on the exhaust stroke that will ignite - this is where the rough idle comes from. It is very prevalent in V twins but I have had a rough idle in my Ranger since I got it.

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Posted: Wed Jan 17th, 2018 02:52 am

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It's ironic this is the case when the V6 is the smoothest engine configuration made :whatever:

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Posted: Wed Jan 17th, 2018 04:03 am

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What I was getting at is this Ranger has both waste and dual spark plugs firing. Contrary to popular belief both spark plugs in a cylinder fire at the same time (1 from each coil pack) as well as the cylinders complement cylinder (1 and 4, 2 and 3) as waste spark.

So at any given time there are four sparks happening (2 sparks in cylinder 1 during compression, and 2 in cylinder 4 during exhaust as waste).

Remove any coil pack and you still have a waste spark system, just spark plugs are firing on one side.

The only time this doesn't happen is during startup, where only the exhaust side fires until normal engine speed is met.

So if a wire is bad, a spark plug is bad, or even a coil, these engines should in theory still run fine.

Posted: Wed Jan 17th, 2018 05:08 am

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Both? really?

There is only one per cylinder, i don't think i'm truly getting what you're saying.

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Posted: Wed Jan 17th, 2018 10:46 am

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Yes the 2.5 has 2 spark plugs per cylinder, 4 on the left, 4 on the right. I have seen them listed in craigslist before as an 8 cylinder :whatever:

It is commonly thought that the right side (passenger side in the US) only fire during the exhaust stroke which is what I was told but have never found solid evidence to prove it, that's why I didn't put it in this thread.

If Anthony says both are firing at the same time just double I would tend to believe it since he has been deeper into the systems than most people I have chatted with and has probably tracked the spark patterns on some sort of graph generated from some sort of gizmo he programmed using a laptop he found under a seat at a junk yard.

Now this is scary, my Dodge 4.7 had even compression throughout all the cylinders, nothing bogus in the oil,but a test revealed exhaust gasses in the coolant. Would miss at idle. Had a blown head gasket between 2 and 4 (same bank on a 4.7) but ran great beyond idle. :eek:

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Posted: Wed Jan 17th, 2018 02:29 pm

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sheltonfilms
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Well I knew that each coil pack has shared coils (1 and 4 and 2 and 3) so each coil pack already had a waste spark setup. So the addition of the 2nd coil pack had nothing to do with it firing on the exhaust stroke or not. So it was kind of a hypothesis. Then pulling each coil pack connector confirmed it.

And also the part that the service manual says it works this way.
May have to rent a cooling system pressure tester.

Last edited on Wed Jan 17th, 2018 02:29 pm by sheltonfilms

Posted: Wed Jan 17th, 2018 04:00 pm

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Ahh ok, i didn't realise we were talking about the 4 cylinder.

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Posted: Wed Jan 17th, 2018 04:15 pm

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Since I'm pulling away from the IAC now, probably need to move this to the 4 cylinder section. Can the mods do this and also change title to Misfire on 2.5L?