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Discussion Starter · #1 ·
Forgive me if I just couldn't figure out the search function, but I tried to no avail. The title pretty much explains it. Although the AC works quite well, as long as it's running I get a constant feeling of misfire from the engine, regardless of speed. Curiously, it will idle just fine, the hesitation only happens in motion. I just swapped out the spark plugs with the motorcraft platinum, made no difference. I'm hoping for some diagnostic advice because I'd like to fix this, but my old strategy of throwing parts at the problem until it's solved, though effective, tends to be costly.

It's a 97 stick shift with 184k miles.
 

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I hope those were double platinum plugs!
How about the spark plug wires?
Did you check for vacuum leaks?
I don't know about the 1997 model year, but for the 1991-1996 the vacuum hoses that go to the charcoal canister rot away, and you really can't see them unless you remove the air cleaner box.
I also wonder if you might be having AC clutch issues that aren't affecting it's ability to cool.
 

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I dont think there is any interaction between the a.c. system and the engine, other than the engine driving the belt that spins the a.c. compressor. So: As you drive along, does the engine run smoothly if you dont have the a.c. on.
If so I could suspect what you feel as a misfire is caused by some slight irregularity of what drives the a.c. compressor. This could be some problem internal to the compressor, or the big bearing on the clutch at the end of the compressor, or the clutch itself skidding, or evwen a bad bearing on one of the other pulleys that the belt goes over. The idler pulley and the tensioner pulley, plus the power steering pump each have bearings in them that can go bad and be momentarily handing up. The spring inside the tensioner could be weak and letting the belt skid sometimes.
One of my Escorts has had a very minor misfire when fully warmed up, and happened from speeds of 35 or higher. Above 65 it became less noticeable though. I never found the cause; its been running the same for 80,000 miles. I only know its not the a.c. on that car, since the a.c long since quit working.
With three of my Escorts, I didnt like the idea of a the 25 year old bearing for the clutch pulley on the a.c. compressor - which cant be lubricated- , so got the "compressor bypass pulley", that replaces the entire a.c. compressor - just to get rid of that original old bearing.
 

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Discussion Starter · #5 ·
Yes, they were double platinums :)

Being there are really no other problems, I'm going to throw a few parts at it and see if they work. I was already considering doing the motor mounts as idle vibration seems a bit excessive to me. So I'll do the mounts, a new belt, and an AC cycling switch. If none of that works, I've got a few other ideas lined up. I'll let ya'll know what works when I find out :)
 

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cycling switch wont make any difference, don't waste your money. belt wont cause this issue either. thre is a bulletin out on these cars for excessive vibration at idle. not sure where the thread is tho.
 

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Discussion Starter · #8 ·
D'oh... I figured it was worth a shot. I really don't want to go without AC and I really don't like the hesitation feeling. Argh.
 

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its possible that your compressor could be failing internally putting more than usual drag on the engine, but thats not very common. does your car have a tach on the dash?
 

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Discussion Starter · #11 ·
I do have a tachometer, and it doesn't seem to misbehave with the AC on, but I noticed recently that AC east more has than I would expect, like an extra 5 mpg it seems. Spark plug wires should probably be replaced, I'm going to grab a set of motorcraft wires soon and see if that helps. I know the previous owner did the plugs, wires and distributor just a few years ago.
 

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Discussion Starter · #12 ·
$53 for motorcraft wires ar the only store near me that has them?! Guess I'll try advance auto "premium" and see how they do.

If my AC blows cold, would it be a waste to refresh the refrigerant in hopes that new lubricants might prolong the compressor life? I can do it for about $50-100, but if it's pointless, I won't bother. I need my AC, so I'd rather save that for a new parts kit if necessary.
 

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Discussion Starter · #13 ·
New "premium" wireset definitely made a difference (didn't realize how much smoother she could run!), but still feeling the AC hesitation, any gear, most pronounced over 2500 rpm. No hesitation at idle or cruising through town at lower speeds. Argh. On another note, I'm surprised at how cheap an AC repair kit is for this car!
 

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On another note, I'm surprised at how cheap an AC repair kit is for this car!
I have noticed that as well. I might actually try fixing mine now.

Anyway, Motorcraft spark plug wires are cheap enough off eBay.

I am wondering if your real problem is the compressor clutch.
 

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Discussion Starter · #15 ·
I looked at replacing the clutch, but if that was the issue, I shouldn't be getting cold air. I'm trying the fuel filter next, as the old plugs looked like she could be running lean. I'll report back after I get it swapped out.
 

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Discussion Starter · #17 ·
If the clutch is cutting in and out you can still get cold air. As to exactly how much is unknown.
Duly noted. I intend to swap out the fuel filter today. I'll get someone to give her some gas while I watch the compressor to see if that's what is happening.
 

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Discussion Starter · #18 ·
Fuel filyer made zero impact. Didn't see any stumbling from the compressor while running. I did however notice some leakage on the low pressure line. I wonder if it's just a little low on refrigerant or something.

At this point, I'm just going to use AC sparingly and drive her until she breaks beyond my willingness to keep her running. Aside from the imperfect but cold AC, everything works well enough I'm just going to deal with it.
 

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If the compressor is still okay, the sure sign of low refrigerant charge is the cycling of the compressor clutch; being on for a couple of seconds, then off for a few seconds, back on again for a few seconds, etc. And with the couple of Escorts I had that had working a.c. systems when I first got them, both of them had some oil showing up on the ends of the hose, near one of the crimped ferrules. It didnt show up on the high pressure hoses though.
 
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