87 rx7 FC w/ S5Turbo II swap with LT9C ECU tuned by Kilo Racing in Orlando
I recently had an alternator start squealing on me so I had to disconnect the battery to get the alternator replaced. When I finished it I plugged the battery back in and the car refuses to idle and the Tach wont read anything. Car will start, and if you hold the pedal down it will run, but if you let off it dies. Whats interesting though is that the tachometer wont read above around 1200 rpm, so if i let off enough to get it below that point the tachometer will read, but past that it will go back to 0 and wont read the idle. I've had the problem with the tachometer last time i unplugged the battery and it went back to normal, and it definitely did not give me an idle problem. so whats the deal? Did the ECU reset or what? Just thinking about every possibility.
I put this in the Microtech forums, but im not sure how active that forum is and I could really use some answers, It also may very well not be about the ECU itself, but i digress.

 

how does the tach work with that ECU? if its stock ignition no tach = ignition not firing. if the tach is running from the ecu directly, then idk, but it seems like the map is scrambled

 

Thanks for the reply.
Correct me if i'm wrong, but the FC has two wiring harnesses, one for the driver side and one for the passenger, both connected to the ecu and Im fairly certain the one on the driver side is the one connected to the tach. if im correct, then it would be the stock setup since we just changed the connector to fit the new ECU.

 

so the stock tach works from the coil, just like any old car, and if you're still using all that stock stuff and the tach doesn't work, then the ignition isn't firing.

 

yea, im running the stock coil setup. Whats odd is I can rev it past the point where the tach stops reading, so im getting a spark form somewhere. I think the leading plugs are the one's that give the tachometer the reading, correct me if i'm wrong, so if what your saying is right, my leading coils aren't firing above 1200 rpm or so, but wouldn't that mean the engine wouldn't run at all? or can the trailing spark plugs alone keep the car running?

 

tach wire is on the trailing coil

 

oh my bad. So could my trailing coil be bad then?

 

unlikely.

 

so then what are the possible culprits? im also going to look into the ECU relay because the first time we had the problem with the tachometer not working (not the idle problem though) the relay was bad. Heres a picture of the wiring diagram if you want to have a look


And this is the relay I am referring too.

 

Have you checked all of your fuses? Particularly the 15A engine fuse.

Edit: I have no idea how you're wired up so it's hard to say really.

 

checked every single fuse, nothing wrong with any of them. the passenger side wiring harness is set up as that diagram i posted above, the driver side harness is the same as stock just modified to plug into the new ecu.
here's microtech's wiring diagram if you want to have a look: http://microtechefi.com/download/LTX10_13B.pdf

 

Im not a microtech guy but it does sound like your settings have changed... sounds like the tach is no longer set for a 13b, I'm just guessing. I would check all settings.

 

Gonna check just in case, but I dont this this is the answer, as this issn't the first time I've unplugged the battery with the new ecu and i never had this problem.
EDIT: so a little update! Out of sheer curiosity I unplugged the battery and waited 60 seconds to plug it back in. That seemed to fix the tachometer issue and semi-fixed the idle problem, as in it will idle with a bit of coaxing after start.

 

These things aren't optimized like the stock oem ecu as far as noise and grounding circuits….reloading a saved tune eliminates that...not sure how easy that is in a proprietory microtech...that's one of the reasons most want to kick those into space.

 

lmao, if it helps my washing machine is doing the same thing...

i wonder if the battery connections aren't great or there is a not very good ground or something?

 

Yup and I thought I was done too, now I have a new problem..... went to turn it over again to be sure, now the Fuel pump wont turn on....... Eliminate one problem, and another appears....... I think it may have something to do with the main relay. The fuel pump issn't turning on, the car will crank but it wont start and im not getting any spark either.