7.3 IDI Tachometer Woes

[scooterrr]

That capacitor next to it also doesnt look too happy....

Good eye, I totally missed that. I'll try to replace these at some point here soon and see what kind of results I get. I'm still a little suspect of that blue square component. It's got a part number P33M63 on it, but I'm not finding anything related to that.

Generally on old auto boards, just replace every cap on the board and reflow the solder on everything else and they are like new. Electrolytic caps are polarity dependent so keep track of that when you replace them. They generally have a 12-20 year lifespan so definitely due and it’s a fairly easy job. In some cases the boards are lacquer coated and need a soak in lacquer thinner before you work on them. I redid the cruise control, climate control and temperature sensor interface board on my 300D Mercedes and it went pretty smooth and if you shop around you can find better NOS caps on eBay, like Phillips etc instead of ****** junk

That's very helpful, thanks. I was wondering how to go about dealing with this coat. I'll write again once I've gotten some results from this.

 

[Nero]

If you dont feel like getting to nutty about repairing the module, O'Reillys sells refurbished units with warranties

 

[scooterrr]

If you dont feel like getting to nutty about repairing the module, O'Reillys sells refurbished units with warranties

I'm keen for that if this goes poorly, but I could use saving some money so I'll give it a go. If it doesn't work out a core is a core haha

 

[Nero]

Well, let me just put this bug in your ear...

You must be registered for see images attach

I have used their module before with good results.

 

[scooterrr]

Well, let me just put this bug in your ear...

You must be registered for see images attach

I have used their module before with good results.

Oh, that's not as bad as I was thinking it would be. About the same as scratch and dent specials on eBay... Thank you for that

I've got a buddy that specializes in micro soldering and he said he'd be keen to take a look at it. He'll do a much better job than I would, but if that doesn't work out I'll be swinging by O'Reilly's

 

[scooterrr]

I just wanted to follow up with where I ended up on this. I ended up replacing that swollen capacitor and re-flowed a few things. When I plugged it back in it worked 1 time, then went kaput again... Well I just decided to order an eBay unit, and got a F4TF-12B565-AA (had a F2TF-12B565-CA in it) for only $50. That seemed too good to be true considering all the other units were >$120, but it has since arrived and is working like a charm so far (knock on wood). It seems like I got a pretty nicely done reman unit when I took a look inside, so should do well by me I hope. Now I just gotta wait on this fuel injector return like kit to come in so I can fix my pretty decent fuel leak and she'll be good to go.

For anyone else that may end up reading this through with these symptoms, a new computer might be the answer. I think what was going on is I had an intermittently working PCM from the get go, and I just so happened to correlate my wiring repair attempts with it's sporadically working nature. Who knows, maybe one day I'll dig into the old unit some more and try to get a good working backup and actually find the answer.

 

[NaiveRancher]

Good morning all, I have a 1991 7.3IDI, however mine doesn’t have any OE wire harness on the engine. I have had to reassemble if you will a new one. Tach sensor is a 2-wire AC, correct? Because that’s what I’ve read and how I understand it. Guages I have are a single wire pickup for tach signal. Would I be better off just wiring to alternator? Or should I try to sort it out? Truck had an E4OD, I swapped in a ZF5.

*** truck had excessive wire modifications over the years, so much so, it started a small fire and I removed everything and starting back tracing wires and have almost completed my harness, but tach has me at a standstill. NOT 911, just some insight would help. Thanks ***

 

[scooterrr]

Good morning all, I have a 1991 7.3IDI, however mine doesn’t have any OE wire harness on the engine. I have had to reassemble if you will a new one. Tach sensor is a 2-wire AC, correct? Because that’s what I’ve read and how I understand it. Guages I have are a single wire pickup for tach signal. Would I be better off just wiring to alternator? Or should I try to sort it out? Truck had an E4OD, I swapped in a ZF5.

*** truck had excessive wire modifications over the years, so much so, it started a small fire and I removed everything and starting back tracing wires and have almost completed my harness, but tach has me at a standstill. NOT 911, just some insight would help. Thanks ***

That's correct, it's a 2 wire magnetic deal that sends an AC signal directly to the PCM through pin 4 and 44. You need this signal for proper function of the E40D. The two wires from the tach should just be a straight shot to the pins on the PCM harness plug, I'm pretty sure the dark green wire is pin 44. Then your PCM takes that signal from pin 4 and does some magic sending that signal back through pin 36. Pin 36's wire is what goes to the tach giving it signal.

This is all to say, use some wiring diagrams to figure out the wire colors and figure out where the wire for pin 36 is. Then jump pin 4 (striped wire from tach sensor) to pin 36 (tach signal to instrument cluster). This will give you tach signal to the tachometer. If you still have issues then it may be the tachometer itself. It's a pretty easy fix other folks have talked about, and I tried doing earlier in this thread.

 

[NaiveRancher]

That's correct, it's a 2 wire magnetic deal that sends an AC signal directly to the PCM through pin 4 and 44. You need this signal for proper function of the E40D. The two wires from the tach should just be a straight shot to the pins on the PCM harness plug, I'm pretty sure the dark green wire is pin 44. Then your PCM takes that signal from pin 4 and does some magic sending that signal back through pin 36. Pin 36's wire is what goes to the tach giving it signal.

This is all to say, use some wiring diagrams to figure out the wire colors and figure out where the wire for pin 36 is. Then jump pin 4 (striped wire from tach sensor) to pin 36 (tach signal to instrument cluster). This will give you tach signal to the tachometer. If you still have issues then it may be the tachometer itself. It's a pretty easy fix other folks have talked about, and I tried doing earlier in this thread.

Yes, I was trying to read all of it but got distracted and threw in my question. I appreciate the insight. I screenshot and will review when I get home tonight. I should’ve mentioned I made a new fuse panel too, so I need to confirm I wired in a very similar fashion to OE harness. But again, thank you!