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Poor Idle while in Park, decent while in Drive

RonD

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Yes, you can unplug the 3 wire connector on alternator and run the engine, but only run it for 10-15min if you have a good battery, you are running the whole vehicle off the battery so lights OFF and fan OFF or low

If stumble happened before engine was warmed up then its not the TFI, their biggest issue was running hot and failing

See if its related to gas pedal position, i.e. TPS position, if stumble felt like "you took your foot off gas pedal" then maybe that is what the computer "thought you did"
TPS gets 5volt
Sends back 1v to 4.5v
1v being foot off the gas pedal
4.5v being foot to the floor
IF(big if) a dead spot in TPS caused volts to drop suddenly...............foot off the pedal as far as computer is concerned
 


RustyDusty

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Yes, you can unplug the 3 wire connector on alternator and run the engine, but only run it for 10-15min if you have a good battery, you are running the whole vehicle off the battery so lights OFF and fan OFF or low

If stumble happened before engine was warmed up then its not the TFI, their biggest issue was running hot and failing

See if its related to gas pedal position, i.e. TPS position, if stumble felt like "you took your foot off gas pedal" then maybe that is what the computer "thought you did"
TPS gets 5volt
Sends back 1v to 4.5v
1v being foot off the gas pedal
4.5v being foot to the floor
IF(big if) a dead spot in TPS caused volts to drop suddenly...............foot off the pedal as far as computer is concerned
Well I might be onto something with the alternator being the new suspect. I disconnected both harnesses from the alternator (one plugged directly into the back/top of the alternator (is this the voltage regulator?) and the one that comes from the bottom of the alternator that goes across the engine bay with 3 wires an connects to a harness on the drivers side above the wheel well. I started the truck and I couldn't recreate the surging idle. I didnt run it for long so I wouldn't kill the battery but I did a little loop around the property, revved it up, did the things that would normally cause it to stall out and it was running great. I plugged the alternator harnesses back in and the issue returned, surging and dropping idle and it stalled when the idle went low enough. I started it again with everything connected and the issue was there, I tried unconnecting the alternator with it running just as a test and the issue persisted even with the alternator disconnected. I wonder if maybe thats just because the system is already out of wack from the bad alternator being present when starting the truck? I shut it off again and started it with the alternator disconnected again and the problem was gone. Reconnected the alternator and the issue returned. Seems fairly damning to me but I wonder if there are more tests to do? First off I should find out from one of you what the two different harnesses are and maybe test specifically if one causes the issue over the other. I did fiddle around with them at different times and I believe the harness that plugs directly into the top/rear of the alternator made the biggest difference. Im guessing thats the voltage regulator? Is that a part I would replace separate from the alternator or is it all the same part on this truck?

Thanks!
 

RonD

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Use a volt meter set to AC Volts
Test battery, no AC Volts
Start engine
Test battery again, should be under 0.08v AC if higher alternator is leaking AC Volts

Switch volt meter to DC Volts, engine running
Should see 13.5v to 14.8v
Lower or higher means alternator is failing

Vehicles use DC Volts, 12 to 15volts
Generators produce DC Volts, but not as efficient
Alternators produce AC volts, more efficient than generators

Alternators use diodes to change AC to DC, but these can leak AC Volts, if more than 0.5vAC then it can effect electronics

The 3 wire plug on an alternator is the Voltage regulator, you only need to unhook this plug to turn off alternator, before start up
If you unplug it after alternator is on/working the it will NOT shut off alternator

The B+ wires,larger wires, are just hooked to the battery via fuse/fusible links, sends power OUT but only if alternator is working, so no need to unhook these if regulator was unplugged first
 
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RustyDusty

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Use a volt meter set to AC Volts
Test battery, no AC Volts
Start engine
Test battery again, should be under 0.08v AC if higher alternator is leaking AC Volts

Switch volt meter to DC Volts, engine running
Should see 13.5v to 14.8v
Lower or higher means alternator is failing

Vehicles use DC Volts, 12 to 15volts
Generators produce DC Volts, but not as efficient
Alternators produce AC volts, more efficient than generators

Alternators use diodes to change AC to DC, but these can leak AC Volts, if more than 0.5vAC then it can effect electronics

The 3 wire plug on an alternator is the Voltage regulator, you only need to unhook this plug to turn off alternator, before start up
If you unplug it after alternator is on/working the it will NOT shut off alternator

The B+ wires,larger wires, are just hooked to the battery via fuse/fusible links, sends power OUT but only if alternator is working, so no need to unhook these if regulator was unplugged first
I haven't gotten around to testing the battery/alternator for AC current yet because the symptoms ended up reappearing even with both harnesses from the alternator unplugged so now I don't think that is the issue anymore. When I took the truck back from the shop the guy who did all of the testing on it was stumped and said the only thing he could think of would be a bad ECU or faulty wiring to it. The owner of the shop didnt do any of the testing and said he was pretty certain it was the IAC. I told him I had tried 3 junkyard IACs and a brand new motorcraft one and he said he gets bad IAC's out of the box all the time. I've kind of exhausted all of my ideas now so I'm reconsidering their ideas now. Maybe its a bad computer? Theres an '89 ranger with the same engine and transmission as mine in the local junkyard, would the computer work for mine or would that one have two solenoids in the transmission? Theres also an '86 with the same transmission and engine. Will either of these work in my '87?
 

RonD

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1986 only had 1 solenoid, so would work
1989 had 2, for sure, so no
 

RustyDusty

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Well turns out the computer was already snagged from the '86 ranger so before I buy a new one I decided to borrow the one from my friend's '89 ranger to see if the idle issue persisted. I've driven it around town (not in overdrive since I assume thats where I'll run into issues with this computer) and while its not a very impressive idle (still swings a bit here and there) it hasn't died on me once yet. Usually if I'd driven it around and parked it when I started the truck up again it would die several times before I even put it in gear and then when I put it in gear it would die again. With this '89 computer I cant get it to die. I opened the original computer up again just to check for anything fishy again but it looks pristine in there, can't find a single questionable solder, theres only one capacitor and it looks perfect, no bulge, no leaks etc.. but I guess I'm coming to terms with the fact the computer might actually be causing my issue. Does anyone have a recommendation on which kind I should buy? Rock Auto has some made by BSE and some by Cardone. Seems like the Ford ones pulled from old trucks are even more expensive.
 

RustyDusty

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Does anyone have a ECU recommendation?
 

RustyDusty

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I bought a new ECU and while it seemed to solve my problems at first I'm starting to notice the same symptoms showing up but now with the new ECU it finally provided me with a trouble code that seems like it might relate to the issue at hand. The new code I'm getting is 14, a problem with the PIP sensor. From what I've read online it seems I should replace my distributor with a new one rather than just trying to replace the PIP sensor as it's easy to mess something up dissembling the distributor like that. Sounds fine to me as the distributor is likely original with almost 200,000 miles on it. What I'm unsure of is how to get the actual distributor out from behind/under the air intake and the A/C lines. It seems impossible tight to pull it out. Does anyone know for a fact theres enough clearance to remove it on a 2.9 without removing the air intake? Im trying to prepare the tools necessary for the job and if the air intake and A/C line needs to come off that makes it a whole other sized job. Also curious if anyone has any recommendations on purchasing a new distributor. I hear the remanufactured ones often have bad PIP sensors already in them?
 

RustyDusty

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Here's a photo of the PIP sensor in there and the space I'm working with to pull this thing out
 

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2 bronco 11s

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There is a bolt on the rear side of the plenium holding the AC hoses. Remove it and you can raise the hoses . Remove wires and cap . The distributor will come out.
 

fixessaxes

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Try replacing the starter solenoid. I had similar idle issues that went away when I did that. 🤷‍♂️
 

RustyDusty

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Try replacing the starter solenoid. I had similar idle issues that went away when I did that. 🤷‍♂️
Did it ever give you a code 14 for the PIP sensor? What issues did the new solenoid resolve?
 

fixessaxes

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No codes I know of. I was replacing it because I could tell the solenoid was going bad (sticky, unreliable start), did not expect the idle improvement.

Resolved sticky start, also nearly all of my idle issues.
 
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