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Discussion Starter #1
Ive seen it before somewhere. Theres a wiring diagram that shows you how to wire around the PSOM so the speed sensor output gets sent to the ABS controller.

If anyone has it, please post it up or a link.

Thanks.
 

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There's the bypass thread that's a sticky, and there's a diagram @Mikey350 has. Im sure one if those is what you're asking for.
 

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Discussion Starter #3
So I rounded up some of the appropriate wiring diagrams.

The signal path is.....
VSS ------> ABS Computer ------> PSOM ------> EEC

So I will try the ABS computer bypass and see what happens. I doubt its that since I have no speedo sweeping problems. Im thinking its an intermittent component on the PSOM. Im ordering one from ebay tonight. If it works, I know that was the problem and can send it off to be fixed. Either way I have a good spare.

The main signal line from the PSOM to the EEC is 679 (GY/BK) and VSS Ground 676(PK/O). I have an ocilliscope at work, I suppose I could rig the leads into the cab from those 2 pins and monitor it. Sounds like alot of trouble though.









 

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If it is not a Bronco, it's just not worth driving.....
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Just out of curiosity, why are you trying to bypass the psom?
 

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Here's the simplified VSS wiring for a '94 (the '96 is the same EXCEPT the PCM pins are different). The diagram has connector pin numbers that the other schematics don't have, useful for actual tracing the circuitry.
The jumper denoted was installed as I was having a very intermittent loss of VSS signal (and a code 452 - loss of VSS signal). By intermittent, I would lose the VSS signal once or twice A YEAR, after tearing apart the wiring harness and splices, I put in the jumper and replaced the PSOM on the same weekend, that was in 2014 and the problem has not recurred.
When you scope the signal, you'll find the VSS signal from the mag pickup to the PSOM is an analogue sine-wave signal, after the PSOM, the signal going to the PCM from the PSOM is a digital (square wave looking) signal. When the engine is running, there is a lot of RF noise, use the shortest ground lead you can find on the scope probe, and put the scope ground on pin 2 when scoping pin 7 of the PSOM and use pin 5 for the ground when scoping the analogue VSS signal on pin 4 of the PSOM.


1996 Ford Bronco '94 EVTM picture | SuperMotors.net
 

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Discussion Starter #8
Thanks mikey. I contacted module mechanics up in Jacksonville and talked to them about the situation. They do psom repair. They are pretty sure it's the psom as am I. So I'm pulling it tonight and sending it in tomorrow for repair.
 

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Discussion Starter #9
So what are the symptoms that you think bypassing the PSOM will fix it? Not trying to be a dick, just trying to understand whats going on that you think you need to bypass it.
After reading mikey's post, i see the psom transforms the signal, so bypassing the psom will not work.
 

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Thanks mikey. I contacted module mechanics up in Jacksonville and talked to them about the situation. They do psom repair. They are pretty sure it's the psom as am I. So I'm pulling it tonight and sending it in tomorrow for repair.
Remember that if you get a different PSOM (not your original back), you may have to reprogram it for your tire size. And record your odometer reading in case you get a different PSOM with a different odometer reading. My replacement PSOM had over 72K miles less that my actual odometer reading.
The speedometer on my old PSOM worked fine even though I was getting the full line pressure shifts in the trans, the odometer was registering correctly too. I guess if I wanted to torture myself, I could cut the jumper and see if the problem would recur, it might take another year before I would know for sure, same as reinstalling the original PSOM.

Good Luck
 

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I have extra PSOM units in my stash with varying mileage, all tested and working. If you want me to check for a certain mileage, etc. send me a message and I'll pull them all out and have a look for you,
 
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