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'86 B2 2.9 miss at ~3200 RPM


G8orFord

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I've got a miss at or about 3200 rpm. Doesn't matter if it's sitting in neutral revving or going down the road. It runs good up to that point with maybe a little miss just every once in a while. If you run it on past the miss to say 4000 rpm, it clears up and smooths out. Compression checked good, fuel pressure checks good. It's got new wires, plugs, cap and rotor button, new TFI module, new injectors and new MAP sensor. None of it has made a difference.

It was this way when I bought it, though I thought the miss was nearer to 2500 rpm at that time. I'm guessing it's probably the ECM, but according to the paperwork I got with it, that was changed previous to my purchase. Possibly the wrong one???

Any ideas from the group?
 


rusty ol ranger

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I've got a miss at or about 3200 rpm. Doesn't matter if it's sitting in neutral revving or going down the road. It runs good up to that point with maybe a little miss just every once in a while. If you run it on past the miss to say 4000 rpm, it clears up and smooths out. Compression checked good, fuel pressure checks good. It's got new wires, plugs, cap and rotor button, new TFI module, new injectors and new MAP sensor. None of it has made a difference.

It was this way when I bought it, though I thought the miss was nearer to 2500 rpm at that time. I'm guessing it's probably the ECM, but according to the paperwork I got with it, that was changed previous to my purchase. Possibly the wrong one???

Any ideas from the group?
It runs good above and below that?

Have you tried pulling the codes?

It almost sounds like a distributor issue.
 

G8orFord

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4WD
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Just the right size to touch the ground.
It's not showing any trouble lights. I don't even remember how to pull the codes on an EEC-IV it's been so long. I used to have a reader, but the was 15-20 tears ago.
The P.O. is going to warranty the Autozone ECM he had put in it to verify that's not the problem. Assuming that doesn't fix it, the distributor is next. I checked for slop in it before and it seemed fine by feel, but it could be the internal electronics are screwing up. It's just odd that it always seems to happen at the same RPM. Load or no load.
 

rusty ol ranger

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It's not showing any trouble lights. I don't even remember how to pull the codes on an EEC-IV it's been so long. I used to have a reader, but the was 15-20 tears ago.
The P.O. is going to warranty the Autozone ECM he had put in it to verify that's not the problem. Assuming that doesn't fix it, the distributor is next. I checked for slop in it before and it seemed fine by feel, but it could be the internal electronics are screwing up. It's just odd that it always seems to happen at the same RPM. Load or no load.
Thats why it makes me think its something in the dist. I would think anything else it would be load dependent or flutter around other places.

Wondering if its the pickup coil or PIP or something.

It could be the ECM to i suppose.

I bought an EEC IV reader for 30 bucks from amazon...its an innova...makes reading the codes on these blinky old bastards real easy
 

G8orFord

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New distributor and coil. The only change is the miss is now back to about 2200-2500 RPM instead of the 3200 RPM spot it was at.

I did notice when setting the timing that the timing light would lose light when it was revved up to the point it started missing so it must be something to do with spark.

@RonD any thoughts?
 

RonD

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If the timing light's strobe stopped pulsing then yes that wire/plug was losing spark
Check it on a couple of other wires/plugs to see if it was specific to #1 only
i.e. see if the strobe starts to cut out on 2-6, at least 2
of them
If its all cylinders I would GUESS coil first, new or not, coils are very hard to make well, lots of things can go wrong with them

At 2,500rpm that requires 3,750 sparks per minute

Swap old coil back in and see if it moves back to missing at 3,200 again
 

G8orFord

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Just the right size to touch the ground.
The change from ~3200 to ~2200 happened on the distributor change. I changed the coil after that since that and the TPS are about all that were left to change. The coil I replaced was fairly new, likely changed along with plugs, wires and cap, before I bought it. I'm thinking that I'm chasing the same problem they were chasing before I bought it. The seller did tell me about the miss, but down-played it won't it just needed to be driven. I knew better than that, but I didn't expect this much trouble with it.
 

G8orFord

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The RPM range for the miss today was 1500-2000.
 

RonD

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Did distributor come with new grey TFI Module?
 

G8orFord

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I'm pretty sure it was black.

Yep, just checked. It's black. Is that the problem now? The one on the old distributor was gray and new.
 

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G8orFord

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Just the right size to touch the ground.
Now that you've jogged my memory, I remember reading about that before. I just wish I'd have remembered it before I put the distributor in. Not a big deal though, I've got the special little tool to do it. I hope that finally solves my problem. If not, I'm not sure what else to test/replace.

Thanks for your insight.
 

rusty ol ranger

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Now that you've jogged my memory, I remember reading about that before. I just wish I'd have remembered it before I put the distributor in. Not a big deal though, I've got the special little tool to do it. I hope that finally solves my problem. If not, I'm not sure what else to test/replace.

Thanks for your insight.
Ill bet on that being it.

All 2.9's had grey modules.

Ive heard that the wrong module will work...but itll cause goofy issues
 

G8orFord

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4WD
Total Lift
0
Total Drop
0
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Just the right size to touch the ground.

RonD

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:(

So idles smooth and no issues under 2,400rpm?
Does it stumble when REVed and only start missing above 2,400?

I assume cold or warm has no effect on the 2,500rpm?
 

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