Erratic idle and wont rev up very well at all

[Snoranger]

I guess I didn't read the part about it running perfect with the alternator disconnected . Well, at least that narrows it down to an electrical problem. Have you checked the connectors that are on the drivers side inner wheel well. The insulation on the wires there have a tendency to shrink and have been known to cause problems.
Have you tested the voltage output of the alternator as you're attempting to rev it (at least 1800 rpm)? Also, when you check the voltage, check for AC voltage. If you have any AC voltage it's the alternator. I just read that a shorted diode in the alternator will introduce AC voltage. Real bad for your electronics, and not necessarily detectable when testing the alternator at your local auto parts store. It's too bad you don't have an old spare alternator to try a swap.

I ran into a Chevy cavalier about 15-16 years ago that was “leaking” AC voltage from the alternator... it would run 100% perfect with the alternator disconnected, but you hook it back up and all hell broke loose. Every light on the dash lit up, random misfires, wouldn’t accelerate, etc. AC voltage can cause havoc.

 

[rusty ol ranger]

Okay....went ahead and replaced HP fuel pump. Cleaned all grounds again. Took the alternator wire harness completely off and inspected and wrapped with new electrical tape reinstalled. STILL having the same problem. It will mot Rev past 2k without throwing a huge fit, cutting out and almost sounding like I'm losing all electrical power. Tried using a brand new battery, no change. It will idle just fine, and it runs perfect with the alternator unplugged. It has a brand new alternator with new regulator. I had it tested at autozone and tested good. And I've tested it, it is putting out 14.4 volts at idle.

How does that little tiny wire look that is grounded to the core support off the negative terminal...thats an ECM ground

 

[Nez'sRanger]

...Have you checked the connectors that are on the drivers side inner wheel well. The insulation on the wires there have a tendency to shrink and have been known to cause problems...

I just found that on a junkyard harness I picked up, only this one had bare wires on the relay connectors (all three of them) and on one of the main plugs on the engine (the one that plugs into the tfi module). That one was actually hidden by the factory electrical tape.
With the problems flatbedder81 has, bare wires may not be affecting it, but I say it never hurts to check. These old trucks are only getting older. I guess we're bound to run into weirdo problems that most cars never live to get.

 

[Flatbedder81]

All the grounds checked out good, and they have all been cleaned and inspected. This is a brand new alternator, I replaced the last one because when I unplugged it, it ran perfect. So I thought, huh...must be a bad alternator. Now, that being said, it seemed it run perfect for a few minutes after new alternator was installed, but quickly started acting up again. Just a side note, this has a red top Optima battery that is dated from 2016. I did buy and install a new battery, and it had the same issue, but it was after it started acting up with the new alternator. Is there any way a battery could screw up the voltage regulator on an alternator? I am going to see if it's throwing and AC voltage if my DVOM is capable of reading AC.

 

[Flatbedder81]

Can I check for AC at the battery?

 

[Flatbedder81]

Okay....went out and checked voltage at coil. With key on, all checks out. When it cuts out, it will spike up about a ¼ to a ½ volt right before it cuts out and drops about the same during and after the cutout. Another interesting thing is I took the voltage at the voltage regulator connector (harness side), I get full volts at the yellow/white wire with key off, which is correct according to my manual. But I also get voltage from the middle wire (yellow/black?), when I wiggle my probe it jumps from 5 to down to a ½ a volt?? Could this be my short or is this normal?

 

[Snoranger]

Can I check for AC at the battery?

I would think so, but I’ve never tried it. Test it at the alternator.

 

[Chad302]

Hello all. I have a 1988 ford ranger xlt 4x4 with auto trans and 2.9 v6. It has devoloped a condition that has me stumped. It starts up pretty easily, but will quickly start idling very erratic. And is very hard to Rev up as the idle cuts out the whole way up the rpm band. Here is a list of everything I have done to the truck so far

-new o2 sensor
-new iac valve
-new intake air charge temp sensor
-new coolant temp sensor
-I rebuilt the distributor with new hall effect sensor, rotor and cap and retimed to 10 btdc
-new plugs and wires
-new ignition module
-new coil pack
-refurbished injectors
-new Delphi in tank fuel pump and sender
-new fpr
-new fuel filter
-new ecm

I have a new Delphi high pressure in line fuel pump on the way. This problem is driving me crazy and I am tired of throwing parts at it. Could this be a fuel problem? Any help is appreciated

I’m having the same problem did you ever find the fix for this?

 

[Ranger 1988]

I’m also having the same problem. Idle is not bad but breaks up as rpm increases. Won’t go over 2000 rpm. Has no power so can’t be driven. Problem occurred suddenly while driving a few weeks ago. I’ve replaced all parts the original poster replaced.

 

[Cees Klumper]

Sounds electrical to me. Having a different, but equally elusive and perplexing problem that has to be electrical. Truck runs like a champ for say 120 miles, then suddenly dies 3 times in a row on the highway, or at a traffic light. But starts right up again each time. Thinking it has to do with interference on wires in the ignition circuit. Getting code 18.