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Sporadic hard miss


tmcalavy

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Little green, my 93 Ranger XLT with 3.0, has developed a hard miss that comes and goes. It shows up most after the truck has been run an hour or two, not hard but put down the road at speed, especially when the AC is on. Shows up most noticeably at stoplights, when you can feel it occasionally miss. Also stumbles slightly sometimes, but never enough to rob you of power. More annoying than anything else, and it doesn't seen linked to weather or temperature. Doesn't affect performance, speed or mpg that I can tell...just finished a day trip and it was missing at lights on the way back, but after being shut off at home for almost 30 minutes it started right up with no stumble, even with the AC on Max. Starts good and idles smooth. I checked the wires tonight after dark, no obvious shorts and didn't get a jolt from any when I checked them. Cleaned the dist. cap contacts and rotor not long ago...looks worn and the contacts were oxidized, but not now. I'm thinking age-related, maybe heat related pickup coil failure...my early 80's F150 suffered from that, but they had a different name for it back then. Any ideas or suggestions are welcome. Gonna check, clean and regap the plugs tomorrow. Running stock autolite/motorcraft plugs...ends of center electrode should be tapered, right?
 


Mark_88

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Sounds heat related but not familiar with the 3.0 stuff...haven't seen any single plugs lately but every one that I've ever seen the electrode has always been flat...other than some platinum tipped ones that I tried...the electrode on those were needle thin compared to regular plugs.

Maybe you have a humidity difference from where you moved recently and that could cause corrosion faster than a drier climate.
 

tmcalavy

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Maybe the plugs will give me some clue when I check them later today. I replaced the dist. cap and rotor and plugs, along with all the basic fluids, when I got Little Green about 3 years ago. The fact that the miss pops up after its been working for awhile on the road makes me think of the pickup coil failure I experienced years ago with my old F150...as that problem progressed, it would occasionally fail and wouldn't start until you fiddled with the pickup coil a bit. I don't want to do the cap and rotor thing again unless I find a crack or something else after I check them again...when I looked last time there was some oxidation on the cap contacts and rotor tip, but that came right off with a little bit of pocket knife scraping. Oh well, it's a 20+ year old Ford so little problems are expected...to a degree. Supposed to rain here today and tomorrow, so maybe I'll get to check the weather-related theory more...we moved 500 miles West, but are basically in the same latitude here in East Tejas as we were in NE Mississippi...course it is not nearly as humid here as there, cause we get our weather from the Plains and a completely different part of the Gulf of Mexico. Will probably see lots more winter, too. Hello snow shovel!
 

Andy D

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Plugs will tell you things. I have distributors on th 528s and the Rat's ignition is an unknown. On the wife's 528e, the cam seal weeped just a bit into the distributor cap. Itwould get whipped by the rotor to the sides of the cap. There it mixed with bits of brass and carbon to rob voltage.from the spark. Once I figured it out, I could do the fix in a half hour. I replaced the cam seal and the trouble hasn't been back.
 

tmcalavy

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Cleaned and reinstalled the plugs...they look good. Checked the cap and rotor again. Got a jolt out of the plug boot from two wires after I fired it up and checked boots by hand. I'll try a wire set and see how it goes.
 

Andy D

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Pick up a few packets off boot grease too It will save the wires come the next plug change. The Rat came with Belden wires. No clue where the PO got them but they're new and the truck runs great. :D
 

tmcalavy

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Well, it's a fix...but not. I dropped a new set of wires on it this morning and it ran great...smooth as a baby's ear...all the way to Wallworld and back. Thought I had it licked, so spent the rest of Memorial Day hanging out, doing stuff, etc., etc. Went outside a few minutes ago to put some plywood in the garage so it won't get wet in tonight's rain (truck bed) and starte it up just for grins. Ran good, then started missing...switched the AC on and the miss is back big time...even from a cold start. So my theory about the pickup coil seems to be out the window. What a pisser.
 

Mark_88

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When you checked the wires at night, did you spray water around the engine bay before watching for the light show?

Moisture in the air (humidity also) could be the culprit...but if you changed the wires it should be less pronounced...anyway...hypothetically...

Something came to mind when I first read this...I remember someone else having a very similar problem and that turned out to be something to do with a modification to the light wiring...can't remember what it was but it sounds familiar.
 

tmcalavy

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No modifications done to this truck in any way...entirely bone stock. It was humid today, but the way it comes and goes, sometimes in the same day, doesn't fit with weather-related woes. It's supposed to rain off and on the next four days, so we'll see. Oh well, it's an old Ford...bound to have problems. Noticed this afternoon that it didn't do the high-idle on the cold start, even though I set the accelerator pedal before I started it. It did that this morning after I put the new wires on, then ran great.
 

Mark_88

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How about the ground on the ECU? While pulling my 96 apart I found a few of the ground wires were corroded pretty bad. The ground wire where the ECU (computer or whatever) goes was looking pretty bad...

Also, the heater control box has many vacuum lines and I was playing around with mine before taking it apart and then a while later I started the engine to warm up the truck and it started running really rough...stumbling badly also...and at first I checked a few things under the hood (didn't know what I was looking for because it's all new to me this FI stuff)...then I remembered that I had pulled the vac lines from the back of the heater controls...sure enough...I didn't quite connect it properly...

Maybe your A/C control vac line has a pinhole in it or is not quite connected properly...or something to that effect...you can try capping the line that comes through the firewall and see if it makes any difference without the vacuum lines connected.

there are also a few lines like the ones on the driver side for the evap canister, the brake booster...worth looking at.

And wasn't it you that found the breather hose had a hole in the bottom causing a similar stumble? Maybe your patch came off or opened up...
 

tmcalavy

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Yep, vac is always a possibility. I made sure I didn't get too rough boisterous when I replaced the plug wires and I made sure I got all the connections on the vac tree up by the distributor back on correctly. I replaced the air intake hose with an intact used one that one of our forum members sold me for a cool price, so that is not the problem. Guess it's down to pulling codes...which I hate on these EEC-IV vehicles, counting flashes over and over again is not my thing. Much easier to just plug in a code reader, but that's what I get for buying an older vehicle I guess. Haven't started it up this morning and it did rain a little last night, so it'll get the humidity test when I leave for work. Gotta get goin.
 

tmcalavy

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Well, it ran poorly on the wet drive in to work. At lunch I rechecked the plug boot connections and the front boot on the driver's side was loose. Reseated it and it ran better, but was still missing...so I walked across the street to the auto parts store and bought a dist. cap and rotor. Put those on this afternoon after work and it's running smooth...on a warmed up test drive anyway. I'll check again after it has a chance to get cold. May need and coolant temp sensor...didn't do the high idle/cold start thing when I started it up at lunch.
 

tmcalavy

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Well, it runs smoother above 1K rpm but acts weak at idle rpm so I guess I'll have to pull the codes to root this problem out. Still not doing the high idle warm up from a cold start.
 

tmcalavy

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It's running better now, smooth at rpms above idle but still won't do the cold start warm up routine. Reset the computer. Will drive it a day or two and pull the codes then.
 

Mark_88

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Maybe it's too warm for a cold start routine...or ECT is wonky?
 

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