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Neutral switch on Manual Trans


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14 replies to this topic

#1 yourmom

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Posted 26 May 2005 - 01:06 AM

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Hi folks - first post. The board has definitely been a resource however, I've used the search function for several months now to keep my car up and running. Thanks for all the shared knowledge.


I'm getting a code 51 on my 88 GL 5spd. I've fixed the other codes and this is all that's left. I don't have a good manual that tells me the location of this switch though. Has anyone made the replacement that can give me some advice? Is it the same as the reverse switch or are they two separate pieces? Approximate location on the tranny? What sort of work is required to remove and replace this piece?

Thanks!

-Hamish
88 GL - "Pedro" 248K

#2 [HTi]Johnson

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Posted 26 May 2005 - 01:20 AM

Very nice wagon. Just wanted to say that, sorry I don't know where the switch is.

#3 Hank Roberts

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Posted 26 May 2005 - 02:23 PM

I see the "Similar Threads" feature has supplied five links below this one -- maybe the artificial intelligence here has found the info for you. I didn't follow them, but they look likely.

I've had problems finding info with searches here-- something about the "Similar Threads" feature is smarter than I am about picking keywords.

#4 yourmom

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Posted 26 May 2005 - 09:07 PM

Thanks for the compliment - I have to credit the first two owners who were meticulous about maintenance. I really lucked out there.

A little backstory here:

When I bought the car the check engine would intermittently flash several codes - primarily one which indicated a broken throttle position sensor. After replacing it several times over with junkyard units, I began to think the problem was something else. Indeed, there were some splices in the wiring harness I had never quite figured out, since the wiring was otherwise completely stock. Appears that the harness was determined bad at some stage, and someone had tried to bridge the bad section. Maybe it worked for awhile but it wasn't working now.

I found a junkyard engine harness and the codes went away, save one - code 51 for neutral switch.

Making some adjustments to the throttle sensor position, I found that when properly adjusted, there was a noticable flat spot when the throttle was shut. It's clear that when the throttle is shut, the fuel delivery is significantly reduced. Enough to be really annoying in traffic because it causes a sudden clunk of decelleration.

My theory is that a properly functioning neutral switch will avoid that - if not in neutral then no sudden fuel cutoff. Other than that I have not noticed any loss to drivability, save running a bit hot/lean at fast hwy speeds. It's possible that the neutral switch is reducing the fuel at these speeds too, which would explain the lean condition - however I haven't ruled out the fuel pump yet either.

Both the search function and the related links have been of limited help to my specific question - they are generally focused on the newer cars or the automatic transmission neutral switch.

My fallback plan if nobody knows is to hit the junkyard this weekend and pull one apart. I'll update the post for the next poor sap if I find the answer.

-Hamish

#5 yourmom

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Posted 26 May 2005 - 09:11 PM

, I found that when properly adjusted, there was a noticable flat spot when the throttle was shut. It's clear that when the throttle is shut, the fuel delivery is significantly reduced.


Reading this again I realize this sounds a bit silly - of course the fuel delivery is reduced with a closed throttle but this is a noticable switch - as if the car had died. It's enough to throw you forward when you hit the threshold. This is the point at which there is continuity between the top two pins of the sensor so the ECU is obviously interpreting this as time to conserve fuel.

-H

#6 hooziewhatsit

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Posted 26 May 2005 - 09:42 PM

are you sure you have both the TPS and throttle plate (?) adjusted correctly? Within this thread is a pdf that tells how to properly adjust both.

My initial thought is that the throttle plate is misadjusted to close too much, causing the engine to not be able to get enough air = eating dashboard with a closed throttle.

of course, I could be completely wrong though :drunk:

#7 subynut

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Posted 26 May 2005 - 09:52 PM

I wonder if that's my problem. I got that sudden decel when I get off the throttle. I can accually feel when the idle switch kicks in and out. It's really bad when she's cold. I got another throttle body that I'm gonna swap and see if that makes a difference.

anyways, back on topic......
Beutifull wagon, yourmom!

#8 yourmom

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Posted 26 May 2005 - 10:46 PM

What makes me pretty sure that this is the problem is that when I adjust the throttle sensor so that pins A and B are never connected, the problem goes away. This is presumably because it never gets the cutoff signal.

It idles smooth but a little high adjusted this way, whereas it idles about 200 rpm lower with what I'll call the "cutoff" circuit adjusted to kick in.

Subynut, I don't know the total context of your issue but before you take the drastic step of replacing the throttle body, you might just try adjusting the TPS so that the top two pins (A and B) are not connected, even with the throttle fully closed.

According to the Chilton manual, the proper adjustment is for them to be in contact at full close, but not at full open. Subynut, if you're getting the same code as me (51), this might be your problem too.

Course this may be a case of the blind leading the blind :D

#9 subynut

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Posted 27 May 2005 - 12:07 AM

Yeah, I did adjust the TPS according to the FSM cause she wouldn't drop below 1500 RPM. Now she idles at the proper RPM, but I have that dead spot and she runs rather rough too. Vaccum is wandering around 10-12 in/Hg @ ~800 RPM.
Drastic? Nah........since I've converted from carburated, swapping throttlebodies is a snap: depresurize fuel lines, drain coolant a little, pull fuel, 2 vac lines, and a couple of connectors and it's out. Slice of cheese.:grin: But, you are right, if I can get that dead spot gone without swappage that would be ideal.

#10 Skip

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Posted 27 May 2005 - 06:40 AM

the neutral switch is indeed on the transmission

the ECU needs it's input to discern when to use
the "idling in nuetral" map

By chance was the wiring harness you used from
an automatic trans. car?

#11 yourmom

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Posted 27 May 2005 - 09:04 PM

the neutral switch is indeed on the transmission

the ECU needs it's input to discern when to use
the "idling in nuetral" map

By chance was the wiring harness you used from
an automatic trans. car?


The harness was from a California Manual. Mine is a 49 State manual. The difference is some sort of EGR control, so my harness now has an extra unused connection for that EGR valve. I had to modify the harness (pull a couple pins) to make it similar to a 49-State harness. The ECU was giving me a "bad EGR" code until I did that.

I was getting the code 51 even before the harness swap, so that makes me suspect the problem is unrelated to my harness swap, which solved the other problems.

Any chance you know more specifically where the neutral sensor is located on the transmission?

#12 yourmom

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Posted 28 May 2005 - 10:39 PM

Well I spent the better part of the day in the junkyard, but it looks like this one is solved. We'll see if the CEL comes back on but tentatively, looks good!

I was fortunate to find that the neutral switch is actually located for reasonably convenient access from below the car. The hardest part is getting the wires/harness accessible as it is held down by a metal bracket that must be bent up so the wires may be removed.

The neutral switch is near the back of the transmission on the driver's side. It is best identified by looking for where the shifter rod enters the transmission. The neutral switch is about an inch from the end, directly in line with its stroke. There must be some detent which is triggered in neutral. It can be removed with a 19mm wrench.

The switch lever itself is made of plastic which may explain the reason it failed. Over time, the plastic nub wears down and does not fully engage. If you pick up a junkyard one, make sure it is not too worn. I took my multimeter to the JY and made sure it had good continuity when car was in gear.

Kragen and other parts houses don't have this on the books, so if you want one new it is probably a dealer part. I found one on an 86 GL and two others on a 91 and 93 loyale, so they are not uncommon. The quality of the contacts was pretty varied, which is why I picked up 3. If the problem is simply the worn nubbin, you could maybe build yours up with JB weld or epoxy.

Nice to be finally free of error codes. Hope this helps the next lucky sap in my position. :grin:

-Hamish
88GL "Pedro" 248K

#13 PopsicleMud

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Posted 01 November 2005 - 12:10 PM

I'm getting a code 51 on my '92 Loyale. That means that there's always continuity at the switch, right?
The reason I'm asking is to be sure that I couldn't have caused the code to show up when I swapped the clutch. If it means that the switch always has continuity, I couldn't have caused it by damaging a wire or leaving a connector disconnected. I suppose I could have made the switch stick on by smashing it under the tranny...

Anybody know the fuel economy ramifications of a neutral switch that's always on?

#14 yourmom

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Posted 01 November 2005 - 12:19 PM

I'm getting a code 51 on my '92 Loyale. That means that there's always continuity at the switch, right?
The reason I'm asking is to be sure that I couldn't have caused the code to show up when I swapped the clutch. If it means that the switch always has continuity, I couldn't have caused it by damaging a wire or leaving a connector disconnected. I suppose I could have made the switch stick on by smashing it under the tranny...

Anybody know the fuel economy ramifications of a neutral switch that's always on?


Actually the 51 means there's never continuity - the switch is broken or the wire disconnected. What I found is that the plastic nub which triggers the switch can actually wear down. I think the internal contacts may get corroded too. I pulled a few in the junkyard and picked the best one - they are all kind of flaky.

I believe my fuel economy actually went down with the fix - makes sense as you would think an idling car would back off the fuel curve. The nice thing is that it also loses that surge I referred to in an earlier post.

#15 PopsicleMud

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Posted 01 November 2005 - 12:24 PM

OK. That gives me hope that I can fix it by finding a connector that I missed while reconnecting everything. :banana:
Of course that would mean that I made a dumb mistake while reconnecting everything (or not quite everything). :banghead:

Thanks for the quick answer. I love this board. :D




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