1994 4.0 PCM Pin #7 voltage reads 9.4V. Too high? - JeepForum.com
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Unread 05-13-2013, 08:16 AM   #1
Alheim
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1995 YJ Wrangler 
 
Join Date: Apr 2002
Location: nyc
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1994 4.0 PCM Pin #7 voltage reads 9.4V. Too high?

Hi folks,

So as per the title of this thread, the PCM on my '94 YJ (4.0, manual trans) is reading approximately 9.4V at Pin #7.

The PCM appears to be working correctly, but I am in the midst of 4.0 swap and don't want to fry all of my new sensors or subtly throw off the operation of my new motor.

The FSM refers to this pin as the "Vehicle Speed Sensor - Mag (+)" or the "Sensor Mag (+)" but does not specify a voltage as far as I can tell.

I have read elsewhere that this pin is to supply +8v.

This pin provides power to the Crankshaft Position Sensor (CPS), the Camshaft Position Sensor (distributor pickup), and the Vehicle Speed Sensor (VSS), as per the wiring diagram below.

Anybody have any input? Is this too high?





__________________
'95 YJ 123bhp 4-banger powerhouse.
UPDATE: 2.5L ENGINE RETIRED; she was still running strong at 212,000mi.
4.0 swap in progress.

Last edited by Alheim; 05-13-2013 at 09:24 AM.. Reason: typo
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Unread 05-13-2013, 08:18 AM   #2
Alheim
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Join Date: Apr 2002
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Now that I've thought about it some more, this probably isn't a crucial voltage, as the CPS, the Cam Sensor, and the VSS do not really provide a variable output - they either work, or they don't.

On the other hand, a +5v sensor such the TPS or MAP provides a varying voltage output depending on conditions. And others, a varying resistance (i.e. Coolant Temperature Sensor).

Thoughts?
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'95 YJ 123bhp 4-banger powerhouse.
UPDATE: 2.5L ENGINE RETIRED; she was still running strong at 212,000mi.
4.0 swap in progress.
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Unread 05-13-2013, 08:58 AM   #3
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 14,549
You arent going to blow anything up. The 5 volt is a totally different regulated supply then the 8vdc supply. The ecu should be fine.
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Unread 05-13-2013, 09:10 AM   #4
Alheim
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Thanks Que.


I have a much more interesting (and tricky) wiring situation that I'm going to post about in a few days. I feel that you might be able to help. I'll PM you when I put up the thread, if you don't mind. Here's a quick summary anyway:

I'm installing a '94 4.0, '94 4.0 PCM, & '94 wiring harness (all from same donor) into my '95 2.5 YJ. Everything's going great, but the wiring layout at the 16-Way 'Engine Wiring Connectors' (ENG-1 and ENG-2) do not seem to match between my 2.5L body harness, and the 4.0 engine harness. I haven't been able to really get into it and determine which wires match the '94-'96 FSM Wiring Diagrams (as below).

I got the motor to run, but I had to run a jumper to the ground of the Cam Position Sensor (Distributor Pickup). The Sensor Ground from PCM Pin #4 (K4) does not travel through ENG-1 and/or ENG-2 as it should. In the engine wiring harness, the K4 ground connects to the VSS, the Cam Position Sensor, and then runs to ENG-1, but at ENG-1 it does not mate to a ground in the body harness. Ever seen that? If not, no problem, I'll post with more details & photos when I can. Thanks.

Edit: Also, the donor had ABS, but my Jeep does not. It probably had AC as well but I can't check right.

__________________
'95 YJ 123bhp 4-banger powerhouse.
UPDATE: 2.5L ENGINE RETIRED; she was still running strong at 212,000mi.
4.0 swap in progress.

Last edited by Alheim; 05-13-2013 at 09:26 AM.. Reason: typo, added details.
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Unread 05-13-2013, 11:18 AM   #5
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 14,549
You could have added a couple injector wires and extended out the temp and alternator wiring instead of doing the entire harness swap. I cant see pics at work but the engine harness should be the same for 94/95. Post when you get to it. No, I havent see it before but you might conside going back to the 2.5L harness and doing the mods I mentioned. Either way we can get it going. I am going to be hit and miss on the forum because I have been dealing with medical stuff. Pm me when you are ready and I will try and make the time.
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Unread 05-13-2013, 11:45 AM   #6
Alheim
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Thanks Que. And hey look at this, my 500th post. I joined this board in April 2002 so it only took 11 years! Hope all is well by you. I will be in touch when I have photos, and don't feel obligated to help out if you're busy with other things.
-Alex
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'95 YJ 123bhp 4-banger powerhouse.
UPDATE: 2.5L ENGINE RETIRED; she was still running strong at 212,000mi.
4.0 swap in progress.
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Unread 05-13-2013, 11:58 AM   #7
idaholtby
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I agree that using the original 2.5L harness is the easiest way to go. I did exactly that. Besides melding in the two additional injector wires, all else you would need do is to elongate some sensor wires here and there along the front of the block to account for the longer engine. This completely eliminates any differences that would be seen through the firewall which can be a major headache to sort out. If you decide to go this route, I can walk you through it.
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Unread 05-13-2013, 12:03 PM   #8
Alheim
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Part of me wishes I had gone that route.

But on the other hand, my 2.5L harness is an oil-covered disaster. I don't even want to touch it. I suppose I could still do it, but being that I already got this to motor to run, I'll diagnose the firewall wiring a bit further first.
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'95 YJ 123bhp 4-banger powerhouse.
UPDATE: 2.5L ENGINE RETIRED; she was still running strong at 212,000mi.
4.0 swap in progress.
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Unread 05-13-2013, 12:10 PM   #9
Que89YJ
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1989 YJ Wrangler 
 
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I just like seeing people get em running. It sounds like you have a handle on it but I will be around. If the harness was trashed then you did the right thing.
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