No codes, but misses occasionally at idl - 6 Cylinder Gasoline - Ranger Engine Tech

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jbbenni
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My 2000 4L OHV has only 65k miles. It runs fine except: after it warms up, it idles a little rough at around 700. It misses occasionally - sometimes it runs perfect, sometimes 3-5 misses in 10 seconds, once or twice over the last month it even stalled.

It starts fine, has decent power and gas mileage. I think it does slightly better when the AC is on - but that could be my imagination.

Problem started soon after I changed the spark plugs and wires.
I've checked for vacuum leaks, and not found any - I may have overlooked something.
I'm not getting any engine codes, and it recently passed inspection with no problems.
I did check the Mass Air Sensor by disconnecting - it stalled when disconnected, as expected.

Where should I look? Thanks!

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Posted: Wed Mar 27th, 2019 05:48 pm

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black06xlt
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Had a similar problem. Find out my fuel pump was going bad. It had plenty of pressure just not enough volume. I seen you just changed plugs. Dud you gap them?

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Posted: Wed Mar 27th, 2019 08:10 pm

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JAMMAN

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Welcome!
I have one of those. I would re check where it plugs in to the coil, and check the wires where they connect to the plugs to see if they are seated.

If it started right after you changed plugs and wires it probably has something to do with that.

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410customs

Posted: Thu Mar 28th, 2019 08:29 am

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Mike69

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Back when I was working in a Ford dealership in the late 90's I had a 1996 Ranger with a 4.0 OHV with a stalling problem, one of the techs told me to pull the IAC & spray it with carb cleaner because it can get gummed up & reinstall it& see if it fixes the problem. Sure enough it fixed it. It never did set any codes or a CEL.

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jbbenni

Posted: Thu Mar 28th, 2019 09:43 am

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check your firing order first since you just did plugs and wires

What type of plugs did you install?
What brand of wires?

Cheap wires are no good for these engines
You likely have a miss that is there 100% of the time, it is just more noticeable when under a load, like the AC is on

If it was running perfectly before the tune up and has a miss afterwards, check your work
You MUST use OEM plugs or better, Motorcraft or Autolite double platinum. You do NOT gap platinum tipped plugs, you can chip off the platinum material.
Also cheap parts store wires cause more problems then they fix. I suggest a good set of OEM wires or better, you can save alot of $$$ ordering these online. The same wires that are $120+ at the parts store are $45 on Rockauto

Last edited on Thu Mar 28th, 2019 09:45 am by 410customs

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jbbenni

Posted: Thu Mar 28th, 2019 11:13 am

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JAMMAN

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+1 on the no cheap wires, been there.

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jbbenni

Posted: Thu Mar 28th, 2019 12:06 pm

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Idahome

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a good tip is to watch your engine running at a warm idle in the dark...you are looking for blue arcing from the wires/boots to the block
If you see blue arcing in the ignition, sparking from boots to the block, you need better wires and you found your misfire

FYI the computer cannot detect a misfire in the ignition so easily, so usually if you have a miss and no CEL/codes it is in the plugs/wires on these trucks. If it was in the injection or a lean condition (weak pump, intake air leaks) you would likely have a CEL

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jbbenni

Posted: Fri Mar 29th, 2019 06:34 pm

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jbbenni
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Lots of good advice, thanks.

I like the wires and plugs theories; the problem really did start after I replaced them.

I used Motorcraft SP500 plugs and WR5791 wires. I swapped one wire at a time, so I don't think I messed up the firing order - besides it runs fine above idle.

I had already re-seated the wires onto the plug tops and into the coil, figuring that was a likely culprit. No joy.

Now I'll check for blue arc in dark - I've seen that on other cars back in the day, and would recognize it.
I'll also double check the plug gap. (I remember that the plugs in the box were gapped wider than spec and I reduced the gap.)

I'll pull a plug or two and check that the gap is correct - in case I read my gauge wrong on the day I installed.

Cleaning the IAC can't hurt - but I'll try the wires and gap checks first.

Great advice all. Will post follow-up.

Thanks!

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JAMMAN

Posted: Sat Mar 30th, 2019 10:11 am

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Idahome

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You can also try cleaning the mass air flow sensor

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Posted: Sat Apr 6th, 2019 09:58 am

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jbbenni
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The experts of the forum (thank you!) seemed to focus on plugs and wires - which I had recently changed. Turns out they were right. I had gapped the new plugs wrong - too narrow. Doh!

The advice to check for arcing from the wires was smart, but not the problem this time. The suggestion that the fuel pump was weak or the firing order was wrong seemed like those problems should show symptoms at other times (my problem only showed at idle, after warming up). The IAC and MAS were the next likely candidates. Happily I didn't have to look any further than the plug gap.

Thanks all, problem solved!

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410customs

Posted: Sat Apr 6th, 2019 10:47 am

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Well done! A big thank for coming back and reporting the fix!!
Always check your work, 99% of the time if the problem is new with the work you performed, then its time to check your work!
Be careful when adjusting the gap on platinum tipped plugs, you can knock the platinum plating off the electrode if you are not very careful.

Last edited on Sat Apr 6th, 2019 10:47 am by 410customs

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jbbenni