1990 95' Swap misifre issues

[swindian1991]

OK so ii just finished my 1.8 rebuild and swap into my 90'. i used all of the 95 1.8 harnesses. When i first started it ran bad but i went through and fixxed all the Vcaccum leaks and now after adjusting the idle runs good but it is missing on cyl 2. i pulled the injector plug and it doesnt change anything, ive used a noide light to make sure im getting injector signal and i am, i then swapped cyl 1 and 2 injectors and drove it around and it sputtered until 2.5-3k rpm and then it felt like it opened up and ran fine. Got it in the garage and pulled cyl 2 and it was firing, pulled cyl 1 and it was not firing, so i was done for the night since i had an idea what it was. Next day i fired it up and again cyl 2 was not firing and cyl 1 was firing... so ive swapped out the entire set of injectors and still getting the same results. I broke out the stethoscope to listen to the injectors and cyl 2 is not firing if it is, its not firing strong i can hear a very very slight tick but when i plug up a spare injector it ticks loud.. im lost and dont know what else to do. ive done a compression test with a shitty tester and cyl 2 was a little lower than than the rest and it did bump up with a wet test. Ive only put about 8miles on the rebuild. Anyone have any ideas?

[kung fu jesus]

Just a few questions, for clarity...

"i used all of the 95 1.8 harnesses."


Does this mean the engine harness and ECU, or are you using the 1.6 ECU and '95 engine harness?

If you used the 1.6 ECU, I would check the ignitor, re-check your wiring connectors, and check the resistance on your coils.

If it is the injector, I would unwrap the injector harness to look for nicks, breaks or shorts in there. Look for corrosion, make sure your grounds are correct.

[swindian1991]

I used the body/engine, engine sub harness, dash harness. Every bit of wiring in my 1990 is from a 95. I had a donor car that was totaled in the driver rear quarter so i stripped down my 1990 and swapped everything over from the 95. The only thing that is orignally from 1990 is the dash and body panels.

But im getting injector signal constnaly with no issues, I have used a a noid light, a spark tester, multimeter, compression gauge, to do all my tests. Im a automotive tech but new to Miatas and theyre common problems and if this has been an issue for anyone.

[kung fu jesus]

I had a link that detailed this, including signal waves, let me see if I can find it.

[kung fu jesus]

Injector 2 and inj 1 misfire at low RPMs, swapping injectors doesn't help, you get a signal, you hear the ticking (cycling) of the injectors. Because it is #1 and #2, is it fuel pressure related? Weak FPR (or weak FPR vacuum signal), clogged filter, weak pump? I mention this because of the fuel rail. I am not sure I understand it is the injection system, but the ignition system instead. The '95 is sequential injection.

I am not sure if this will help your cause, but I am going to post it for you anyways. It is ignition based info.

http://www.sergionicolau.com/viatura%20-%20mazda%20mx-5%20-%20base%20-%20motor%20-%20ignicao%20-%20cas.php

[swindian1991]

Thank you Kung Fu Jesus. Im gonna run some of the tests, Ill use the Oscope from the shop and see what i come out with.

[kung fu jesus]

Good luck! I hope to hear what the diagnosis is, very interesting problem. I am wondering if maybe your CAS is failing.

[swindian1991]

OK so i out the oscope on and i was getting the correct signals and voltages still confused i pick up an injector and put it on two. Well wouldnt you know the miata runs like a champ now. Apperntally i had a 1.8 set of injectors with one bad one and a set of 1.6 injectors with one bad one and i just happened to put the only bad ones on cyl 2. Just my luck but regardless i have it up and running 100% at the moment. Im gonna go home tonight after work and fire her up and see if it acts up like it did last time or continues to run fine. Thanx for all the info and help Kung Fu Jesus.

[kung fu jesus]

WOW! What are the odds? I chuckled. I felt bad for doing that, but still...that is pretty crazy!

Good on getting it solved!