elfking

This is for a 89 GTU.

Ok, I know there's 1000000000 threads on "HELP MY TACH DOES NOT WORK!!!!" and 99% of them were related to the trailing coil being bad.

Things ive tested:

1. Swapping trailing coils with my 88 Turbo II.
2. Cleaning up all the grounds under the coils and running a new ground to the coil from the (-) on the battery.
3. Tested the coil with a timing light, it shows up every time. No issues with it not blinking.
4. Took a spare spark plug, removed T2 and hooked it to the plug wire, watched the arch'ing fun for a second to make sure it was 'lively'.
5. Measured OHM's resistances on both trailing and leading. Seems good to me. (Same as my Turbo II.)

I have just finished droping a mazda reman in the car. When I first fired it up the tach didn't work, wiggling around one of the wires with that resistor on the end made it come back to life... However I think it maybe just have been a luck shot.

I know there's that test wire for servicing under the coil, but is there an actual wire which runs from the tach in the dash through the eletrical system to the trailing coil? One of those wires in the white plugs for connection of the coils should be a signal wire, unless those couple of one wire plugs with a resistor at the end are pickups?

Or anyone have any hints on where to look next?

Icemark

do you get an AC signal on the Yellow/Blue wire at the test connector on the trailing coild while the engine is running???

(digital multi meter set to AC voltage, ground the neg (black) wire of the meter, red (Positive) wire of the meter to the test connector yellow/blue).

elfking

I didn't try that, I thought about it but wanted to hear it from someone else first, as not wanting to short something out and cause more problems...

I will try it when I get home from work tonight...So if that works, then what does that tell us, the wire from the coil to the tach is bad??? but the service spot is still good?

Icemark

That will tell us if the coil is sending out the tach signal.

If it is not, then the ignitor on the coil is bad. Simple as that.

If it does have AC on that wire while the engine is running (and probably around 3-6 volts AC- but possible as high as 12 volts AC) then the problem will be in the harness (which then we will do the same test at the power steering computer or cruise control computer yel/blu wire) or at the gauges (in which case we will check at the gauge the same test).

elfking

Alright thanks for that extra info, I will definately report back with the findings or more questions.

elfking

Well I had time to take a look into the problem this morning. Tested with two volt meters:

Both my DMM's only have two settings on the V AC which are 200 and 750, these were taken at 200 setting.

89 GTU: 1.3
then I swapped the coil with a spare and it put out: 1.2

88 TII (Reference, since that tach is working.): .9-1.0

So it looks like the problem is somewhere in the harness to me... since they HAVE voltage running through them... What do you think? I was going to pull out the cluster tonight and take a peek behind it for some grounds/connections begging to be re-soldered or cleaned up connections...

Thoughts???

Thanks!!!

elfking

Ok, so I back probed the wire to the cluster and this morning (car cold) I got 1.8 (again with the setting on 200 ACV) to the yellow/ with blue striped wire.

Tested against the test wire for service (same color at the trailing coil) and I got the exact same readings...

So to me that screams bad ground on the cluster or a faulty tach. Since it seems to work some of the times and the connectors from the harness TO the cluster look clean im going to re-solder the solder joints on the back of the cluster.

I will report back if this fixes the problem.

By the way, if anyone has a non tilt wheel make sure to take it off before pulling the cluster. I didn't realized how spoiled I was with the TII.

If anyone has any input or other thing to try lets hear it!

gonzz

I had the same problem and when i swapped the cluster out my tach works.. Just swap it and see..

Icemark

Yep, sounds like a bad tach in the cluster

elfking

Thanks for the help Mark, the problem was the solder joints on the back of the cluster. I de-soldered every connection on the back and ran new solder. (I figure why not while im back there for the tach. Only took 10 min or less anyhow.)

After that its been working every time now. Unfortunately I just started smelling raw fuel smell so time for ripping the upper intake manifold.

I might have some questions later on the air pump. The air pump is blowing alot of air, and all the solenoids work, but I don't think my VDI or 5th/6th are operating... I tested them with 12v and they will operate if I rev the engine while having the solenoids live. Its just when im driving the car it rev's slower past 4k. As a friends N/A pulls like no other above 4.. and his is a 87... so I figure mine should at least rev/pull just as quick if not quicker.

I am getting no air to the CAT either from the small metal tube, I disconnected the hose coming out of the back of the block for the air, going to that filter/one way valve. There is NO air coming out of the back of what I think is the dynamic chambers for the VDI? (Im not 100% on the terms) but basically coming off the back of the manifold int he back and no air.... so im a bit stuck on that right now...

If you have any ideas I am thinking about pulling the 5th and 6th port manifold and checking that small little filter in there and make sure its clean. However im not quite sure that would do much good, I think there's something else going on...

Thanks so much for everyones help.

Icemark

Cool, sounds like an easy fix then for the next person who reads this.

, probably a PD. I have seen the S5 ones leak more than the S4 ones. Could also be bad injector O rings... but I would put my money first on the PD...

There is a small vac hose sized output hose on the ACV for the VDI and Aux port air pressue. Check that first. It should always have air coming out of it, if the engine is running.

elfking

Haha, I spoke too soon went out this morning to look at the ACV and no tach. Looks like I will be hunting for a replacement. Can I just swap it or do I need to swap the whole cluster? Anyone selling a S5 cluster?

Damn, for some reason I was under the impression S5's didn't suffer from the PD problem becuase they were different... My mistake... That shouldn't be bad to fix it though.

I checked it out this morning, there is plenty of air coming out of that little hose and the big hose coming out the side. What I found was one vac line I forgot to hook up and couldn't see under all that crap in the way. I hooked it up and now I get a little air out the split air pipe for the cat. How much should be flowing out that pipe? I revved up the car and more air started pouring out, but not a whole lot of pressure behind it...

Icemark

you can just swap the tach as long as it is also a S5 tach


again, I have seen more S5 and S6 versions leaking than S4 versions. The bummer part is that the whole rail needs to be replaced (for added cost) on the S5 and S6 PDs.



Should be pretty low until 5th gear

elfking

That seems easy enough.....Just need to track down a spare S5 tach then.

Hmm, well I guess that answers that.. I really only heard of the S4 PD's having problems. That was long ago when I first got my TII though and was only really paying attention to the S4 stuff.... I will report back with the findings.. Hopefully I will get time to take a look into it this on the weekend. Hopefully its just one of the old mazda clamps not holding well enough and not the whole rail needing to be replaced....(I can dream can't I ??)


Ahh ok, I was not sure what an acceptable amount would be. I know you don't wan't too much as it would throw off the good ol smog sniffer.

Thanks again for the responses, I think I am getting somewhere.

elfking

Since I can't seem to make a new thread at the moment. (Those errors we're all getting.) I wanted to see if someone might see this new question in hopes for an answer.... My tach problem is indeed a problem with the tach from what I have figured out... Tested soo many things its the only thing left... Anyways, new question!
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Im almost done with the GTU but I think I may have one or two of the vac lines mixed up on the ACV side/ intake manifold area on the passanger side.

I read OVER AND OVER the FSM but the one or two decent vac diagrams have a poor angle of that side of the vacuum setup. So if anyone has some pictures or a better diagram I can take a peek at. I just want to make sure I have things hooked up right.

I passed CA smog so I must be in the general area... but Im not 100% on things on that side... I have one line capped off becuase I cant see anything unhooked... I would rather find the proper way... I think the ACV is not working correctly and there is most of the time zero air getting into the cat from the split air pipe... so i think maybe I have a hose mixed up for tha ACV....

So if anyone has any good pictures or diagrams again of a stock vacuum setup. I need ALL emissions equipment and vdi/5th and 6th actuators in tact. I like stock setups....

Thanks!
-Brian.