1986 Ford Ranger runs rough sometimes


Old 05-26-02, 10:09 PM
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Unhappy 1986 Ford Ranger runs rough sometimes

I own a 1986 Ford ranger with a rebuilt 2.9 liter EFI engine. Auto Trans, air, power steering. about 50K on the rebuild.
City: When weather is warm engine keeps trying to die, as it almost does it kicks in idles fast then slows down to normal idle quickly. will do this 1,2,3...6 times then runs OK until I turn off and restart(in and out of store) then does it again. If I attempt to accellerate while engine is slugging it aggravates the condition and extends the problem. When weather is cold does this once or not at all and then runs ok most of the time.
Highway: When weather is warm truck will not "cruise". (I have no cruise control) As I accelerate no problem but once I get to my chosen speed (anything from 45 to 75) the tranny hits overdrive and I get 2 seconds nice drive then the engine starts to slug down. I will lose up to 15MPH and then it jolts in and I climb back to chosen speed. As soon as I get there it starts again. Engine will not run right on highway in warm weather. In cool weather it usually does not do this even after 45 minutes at 75mph. It will do the cold weather thing as I leave the city and then run fine.
I have taken to my mechanic twice and tried to fix myself twice. First time mechanic fixed they replaced the coolant temp sensor (not guage sensor other one). Next time I replaced coolant temp sensor did not fix. took to mechanic again he replaced my new coolant temp sensor and told me Idle motor (on side of plenum - not sure of name) was carboned up and causing problem He had cleaned it and problem was mostly gone. I replaced this motor. OK for a while or at least not a real hassle(cold weather) Now it is warm again and problem is BAAACK

This time I have replaced coolant temp sensor, and even put on a new TPS at butterfly and no help. Idle motor on plenum is shinny new inside, not carboned as old was.
I cannot take to garage again - no $$$$$ to spend on labor.
Please help
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Old 05-26-02, 10:17 PM
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Check engine light on? Go to Knuckles website at www.batauto.com and learn how to pull your trouble codes. Tell us if you fnd any.

Does the truck have a Mass Air Flow Sensor (I believe it might). If so, look here. Make sure the wires inside are clean. If not, take a Q-tip and gently clean the wires of any carbon.

Try that as well.
Old 05-27-02, 11:37 AM
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have you tried the idle air control valve or the accelerator pump
Old 05-27-02, 01:19 PM
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Joe_F: No check engine light. I don't think I have a MAF but a MAP ( I get this by looking at engine and reading, I have no idea what one really looks like) and I haven't tried that yet. It costs $80. Is there any way to check it before I change it?

Raggy: I think the Idle air control valve is the dooly on the side of the plenum that I have replaced. The old one was very sooty and the new(8 months ago) is sparkly pretty on the inside. Where and what is the accelerator pump. Forgive my ignorance.

Addendum: My son had same problem on his 85 Topaz with 4-cyl. His problem was not as severe and is gone now since he drives an 87 Town Car. This problem existed on the 2.9 that died at 175K and I took out to put in the new rebuilt. I did this and did not put in all new wires and hoses and sensors. Rebuilt did not have problem at first.

Thanks to you guys for answering and please be patient with me. I am cheap by necessity as well as inclination.
Old 05-27-02, 03:33 PM
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Old, Ford and cheap don't go together as they start to soak you when they get old .

Any parts store can check a MAP sensor before you buy it to tell you if it's bad or not. The emission diagram under the hood will tell you if it has a MAF or MAP sensor and where it is.

That being said, what's the fuel pressure? Has it been checked with a reliable gauge.

Should get a factory service manual or alldata.com subscription to start to track it down, but in lieu of that, you might check some of the links I have below.
Old 05-30-02, 02:03 PM
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Just an update, I changed the MAP and it didn't cure the problem. It seems better but not cured. Then again maybe I am just hoping it's better. Joe_F, I don't have a fuel pressure gauge, I'm checking with friends to see if they do.

When I was checking the MAP (NAPA couldn't) I pulled the vacuum line going to it and blocked the port to conserve vacuum for the other systems. The engine ran rough but did not drop and surge as it has been doing. As soon as I reconnected the vacuum line for the MAP the engine immediatly slogged down and surged doing that 7 times before it again leveled out and ran fine.

I'm looking for an instruction on how to pull codes with an analog meter. The diagram at batauto.com doesn't help me.
Old 05-30-02, 06:19 PM
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have you tried disconnecting the idle air control valve and setting the idle speed somwhere between 600 and 700 rpm and shut off vehicle and reconnect idle air control valve and then disconnecting the battery for atleast 10 minutes and then reconnect im sure it will not help with your cruise problem but it could very well help with your idle surge.
Old 05-31-02, 06:33 AM
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You can head to any Autozone and they should be able to scan your vehicle or rent you the code reader to do so.

Typically, you check the MAP output with a vacuum pump and a scanner. I know on GM you watch for a voltage drop when you pull 10" of vacuum. I know this is how I tested the MAP in my grandparent's Cavalier.
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