1992 4WD trans problem?

[mtglick]

Hi, all, newbie to the Explorer, just to establish my FMC bona-fides I do have a '96 4-banger Ranger XLT 5-speed since new, 225K on the odo, still ticking along just fine on the original clutch!

I'm looking at a '92 Explorer tomorrow for the wife and kids, 4WD, has an intermittent trans problem that I can't explain, would love some insight from the auto trans community.

Apparently, the truck stalls out under braking...sometimes. The behavior is intermittent, and only affects the truck when slowing to a stop. Under all other conditions (driving forward, reverse, etc.) the truck supposedly does fine, including downshifts (so I'm told) when changing gear at driving speeds. Once it stalls, the owner says he just starts it up and drives away, until the next stoplight when it stalls again. He says it will do this for a day or so, then go away for a few days, then it comes back.

He strongly believes this is an electrical fault, but do you folks have any ideas? I cannot for the life of me think of a point of failure that would cause this behavior on the electrical side, if it's a transmission issue I would think it would be consistent--help!

I'm looking for diagnostic tips as well (apparently the CEL does not illuminate under the fault condition), I will attempt to coast it down in neutral to see if it's a transmission issue at all, any other tips are very, very welcome.

TIA,

Matt in TO

 

[FIND]

sounds more like a vacuum problem

 

[mtglick]

sounds more like a vacuum problem

I'll check the lines where I can, but why would it only stall some of the time, and under braking? Vacuum reservoir should be full coming off of the throttle, and stall under throttle away from the line, before vac pressure builds, shouldn't it?

 

[Curmudgeon]

I saw something like that a number of years ago, but it was permamnent.
Torque Converter locked.
Cannot imagine a TC doing that intermittently, unless the lockup electrical is an issue (solenoid, if I recall).
Codes may help tell if the TC Lockup is continuing to hold a signal.

Like I said, been a lot of years, but stoplights seemed to be involved in the circuit........disengaged the TC Lockup when you applied brakes.

Been away from this stuff for about as long as the year of the Explorer you're looking at.

 

[mtglick]

I saw something like that a number of years ago, but it was permamnent.
Torque Converter locked.
Cannot imagine a TC doing that intermittently, unless the lockup electrical is an issue (solenoid, if I recall).
Codes may help tell if the TC Lockup is continuing to hold a signal.

Like I said, been a lot of years, but stoplights seemed to be involved in the circuit........disengaged the TC Lockup when you applied brakes.

Been away from this stuff for about as long as the year of the Explorer you're looking at.

Thanks, that makes more sense than anything else I've heard so far. I just don't fully understand why it's so regular, always under braking, and then that the restart clears the issue, if it's holding current it should hold current after the restart, unless the PCM resets at ignition? Something to think about, anyway.

 

[nismotunedgtr]

Thought about the IAC at all? I was having this same intermittent problem with a '93 5 speed. Push in the clutch and come to a stop and DEAD. Turned out to be the IAC.

 

[DeRocha]

I saw something like that a number of years ago, but it was permamnent.
Torque Converter locked.
Cannot imagine a TC doing that intermittently, unless the lockup electrical is an issue (solenoid, if I recall).
Codes may help tell if the TC Lockup is continuing to hold a signal.

Like I said, been a lot of years, but stoplights seemed to be involved in the circuit........disengaged the TC Lockup when you applied brakes.

Been away from this stuff for about as long as the year of the Explorer you're looking at.

Thanks, that makes more sense than anything else I've heard so far. I just don't fully understand why it's so regular, always under braking, and then that the restart clears the issue, if it's holding current it should hold current after the restart, unless the PCM resets at ignition? Something to think about, anyway.

There is a vacuum modulator on-top of the transmission that when it's diaphragm is cracked will start allowing Transmission fluid to get sucked into the Intake manifold... It any of the vacuum lines on the rear of the vacuum tree are loose or oily then the modulator needs to be replaced.

 

[mtglick]

Thought about the IAC at all? I was having this same intermittent problem with a '93 5 speed. Push in the clutch and come to a stop and DEAD. Turned out to be the IAC.

Certainly something to look at, but what's being described to me is a shaking, shuddering, stall-out, not a sudden dead engine. I'll be sure to listen for that whine, though. Thanks!

 

[mtglick]

There is a vacuum modulator on-top of the transmission that when it's diaphragm is cracked will start allowing Transmission fluid to get sucked into the Intake manifold... It any of the vacuum lines on the rear of the vacuum tree are loose or oily then the modulator needs to be replaced.

Thanks, that's one of the first things I thought of as well, but apparently the current owner has taken it to a couple of shadetree guys, who I presume thought of that too. Thanks for the pic, very helpful. Seems weird but I'm really hoping that the truck is behaving badly when I drive it tomorrow, just to get a better sense of the problem.

The TC lockup issue would seem to describe the symptoms closest, with an intermittent vacuum leak being the cause, but I'm stumped as to why an instant restart fixes the issue, at minimum until the next braking point, and sometimes for days at a time. That's just throwing me for a loop--is the ATF aft (ha!) of the diaphragm? Maybe under hard braking the ATF sloshes forward?

 

[mtglick]

OK, report from the field. Truck is in, um, interesting condition, cosmetically (it's baby pink!), but everything else looked ok. Alternator is bad, battery gauge was flicking around like a seismograph, rest of the gauges were steady. One of the nipples on the vacuum body (the round object with vacuum lines on it) was disconnected, no apparent hose missing--is that normal? No clamps on the lines. Previous owner replaced a lot of the emissions equipment as well--might have screwed something up?

ATF was OK, used but not trashed.

Test drive was fine. According to the owner, throwing it into neutral will save a stall, so absolutely trans related, but everything was smooth on the road, so it's something that's controlling the torque converter, instead of a straight failure.

Any ideas?

 

[FIND]

I have never seen a torque converter that stays locked intermittently. These transmissions just aren't set up in a way that it would keep the torque converter locked when downshifting, besides, it only really locks up in 4th. Fix the vacuum problems. The vacuum modulator on the transmission works on.... vacuum, this is why shifting into neutral may save you from the stall.

Don't assume other mechanics would have thought of checking the modulator either, especially if you are talking about someone's shadetree buddy.

 

[mtglick]

I have never seen a torque converter that stays locked intermittently. These transmissions just aren't set up in a way that it would keep the torque converter locked when downshifting, besides, it only really locks up in 4th. Fix the vacuum problems. The vacuum modulator on the transmission works on.... vacuum, this is why shifting into neutral may save you from the stall.

Don't assume other mechanics would have thought of checking the modulator either, especially if you are talking about someone's shadetree buddy.

Thanks for the info, absent the possibility of something truly weird the consensus seems to be vacuum, vacuum, vacuum. So that's where I'll begin, along with a new alternator and battery, just because I don't trust the ones on there now.

Will update as more data becomes available!