Tachometer Fault Tracking - 89 Master Ace Diesel

[89MasterAce]

Hello all,

I have a mostly non-working, sometimes intermittent tachometer. I want to check if the tachometer is getting the signal it should from the pickup sensor. (From what I understand the pickup sensor for the Master Ace diesel is on the fuel pump, and I'd like to check the tachometer side before I attempt to exhume the fuel pump.)

Does anyone have information on the pin outs on the combination meter on an 89 Master Ace 2C-T? (Looking specifically of course for the tachometer signal.) The US combination meter has an 8 pin connector and two 10 pin connectors, while the Master Ace has an 8 pin connector and two 12 pin connectors.

I have the US van repair manual, US van electrical wiring manual, and 2C-T repair manual; but they don't cover these JDM differences.

I've attached a pic of the back of the Master Ace combination meter and the US pin outs.

Thanks!

[Jan-Willem]

How good is your russian? ;)
I found this picture online, the one the user points to google translates to 'tachometer'


https://a.d-cd.net/9ec1f96s-960.jpg
https://a.d-cd.net/48c1f96s-960.jpg

[89MasterAce]

Thanks Jan!

I tested that port, but got nothing out of it. My tach was working at the time, so I don't think that port on my van is signal or power for the tach.

However, I did find a tach signal on pin 4 of the vertical connector.

Now I'll wait until my tach doesn't work again, and then test for tach signal. If the signal is still there, I'll open up the tach and see if the capacitors are starting to go.

[originalkwyjibo]

How do you like your oscilloscope? I used to have an old FMC Engine Analyzer with o-scope that was the size of a small car but didn't use it enough to justify the floor space. I've been thinking about getting a handheld one for diagnostic use for awhile. Do you mind sharing brand and model and any good or bad thoughts on it's performance?

[89MasterAce]

This one is one of the cheapest on Amazon. I've only used it once for this really. It appears to be ok, but it certainly feels cheap and the leads are short.

It only comes with an AC adapter, no battery, but it is 9V in, so you could buy or build a 9V battery cable for it.

Time will tell how long it will last.

https://www.amazon.com/dp/B081Q2KDJT?psc=1&ref=ppx_yo2ov_dt_b_product_details

[originalkwyjibo]

Thanks for the info and the quick reply:thmbup:

[89MasterAce]

I believe I have tracked the problem to the Emission Control Computer which is behind the passenger seatbelt in the pillar next to the passenger's left shoulder. The tach signal goes from the pickup at the fuel pump where it is a 2v sin wave, to the computer, then out to the instrument cluster where it is a 6v square wave.

There is no tach signal at the intrument cluster when the tach isn't working. There is no tach signal from the computer when the tachometer isn't working. There IS signal from the pickup at the fuel pump at the connector on the computer when the tachometer isn't working.

The tachometer will work for 3-10 minutes, then it will go dead. If I unplug the Emission Control Computer for 1 minute, then plug it back in, the tachometer will start working again for an other 3-10 minutes. Turning the car off and back on again doesn't always make the tachometer come back on.

I opened up the computer and everything inside it looks good. No leaking capacitors or anything. I HOPE it's one of the capacitors or resistors that I can actually get a replacement for, but I'm not entirely sure how to figure out which thing is bad.

Anyone have any thoughts?

[89MasterAce]

.

[thepuzzlemaster]

I've got a similar-ish problem in my '92 TownAce. I've never tracked down the cause in my case, but I do notice that it is affected by driving over bumps - so I assumed it to be a mechanical issue, rather than an electrical/computer issue. Striking the top of my dash will snap the tach into working/not-working depending on its current state. Not sure if that info could be helpful, but might be worth some small troubleshooting steps to see if it might be some sort of mechanical/connective issue on your end?

[89MasterAce]

I was hoping it was a connection issue, but I've wiggled just about everything involved, and it seems to not be.

[89MasterAce]

Solved!! (I think)

So I did a test drive with the tachometer unplugged and with the ociliscope plugged into the emmisions computer. The tach signal was steady the whole time.
I took an other look at the tachometer itself (I had already replaced the capacitors, even though I found out they weren't bad), and one of the thermistors on a different board was pushed over onto some resistors. After straightening the thermistor, the tachometer seems to be working perfectly so far. I THINK the thermistor was causing a problem that then caused the emissions computer to freak out, which is why the tach signal was disappearing from the emissions computer. We'll see if it stays fixed!