Tune 'n' 'charge 'n' tune

[twistedwankel]

I used to send my injectors away to get them tested/cleaned and new o rings every 10 years or so. You could have two never shutting off or just plain not putting out but a drip.
So you being cheap and this being really cheap therapy you should simply swap the good injectors with the dead ones for a free test.

Play it some music and sing: "I'm gonna make you into a Ford baby soon."

[Native]

I'll dig into the injector thing. Seems to make the most sense at this point.
It just seems strange - it ran fine, then after sitting for two hours, it didn't.

[twistedwankel]

Only takes a little blob of dirt or crappy gas/goo.
I ran fine and then my heel swelled up and stopped me cold an hour later.

[Native]

^^^ shoulda changed the ankle bearings / fluid...

[AScoda]

I have 2 sets of mazda lavender fuel injectors, if you need/want. stock mazdaspeed stuff.
Cannot vouch for the condition of seals or level of inner gunktitude.
Do you plan on upgrading injectors? If so, do that now. They come with new seals, you know.

[Native]

Thank you Drew.
I wasn't planning to change the injectors. The low bewst pressures I'll be running shouldn't overwork the stockers.
That said, if in fact the injectors are shot, and I have to spend money...well, that's upgrade time, right???

Really, first I gotta find out if it is in fact the injectors/seals. Signs do seem to be pointing that way...

[twistedwankel]

Once upon a time:
I drove a virgin car to a Kokomo event Tour a long time ago. Drove 300 miles to event no issues. Filled up car with premium upon arrival. Within 10 minutes car ran for shit with little power. Assumed bad gas. Others who use the same station had no issues but shit pants knowing my cars are "tits".

There were 500 racers there with at least 250 brilliant mechanics. Many stepped up to evaluate the issue. After many drives and looks and tests the consensus was "fuel". A friend took me to a parts store. Replaced the fuel filter, plugs and for the hell of it distributor cap. Car ran super for 10 minutes and started to crap out again.

Only one guy "Hoosier Tom" figured it was ignition and started to dive into the distributor until I told him the sideways screws of the 2.6 Mitsu fall out. So he stopped. Story short but he was on the right track. Crazy guy offered to haul the car home if I rented a Uhaul. I did that and missed the two day event.

The "crazy guy -who saw me coming" I hired dropped the car off at a local dealer, I paid him in cash and waited for a couple days. The dealer replaced the new plugs and it ran great for 10 minutes then quit again. The final result which was 100's of dollars later was a cracked (not old) rotor and a weak original distributor pickup. Damn.

All hail Hoosier Tom. Who was the ONLY guy to ask me at the next event what the problem was.

So the "Crazy guy" made me (at wife's insistence) buy a pickup and a trailer. From that time on my cars were 'Trailer Queens". All because I stopped Hoosier Tom from completing his mission. Life sucks and then you die.

Go Steve.

[Loren]

What's a "rotor"?

[CaptainSquirts]

What's a "rotor"?

I heard that the Rx-8 has a couple a those.

[twistedwankel]

What's a "rotor"?

Yep. So 80's. What's a distributor for that matter?

[Loren]

My '97 S10 has both.

[Native]

So I got me a can of starter fluid. Got the engine idling and sprayed it at the injectors.
Made no difference.

So, if per advice the fuel pump/pressure is ruled out, I guess my next move is pull the fuel rail, swap some injector positions, and see if the dead cylinders change. If they move with the injectors then I have bad injectors. If the dead cylinders don't move, then I've got bigger grief.

Am I on track, or is there a better play at this point?

[Loren]

Check supply voltage to each injector. Should have 12v going to one side of each injector at all times. You didn't change any wiring in the factory engine harness, so that SHOULD be there unless something is broken.

From there, if an injector isn't firing, it's either because it's not getting the ground signal from the ECU to fire, or it's a bad injector.

It is possible to have an injector driver transistor in your MS fail. I don't remember if you're wired for sequential or batch or semi-sequential fuel. I think the 94's were still semi-sequential, which means if you have a bad output... it would affect two cylinders. Pairs, just like the ignition.

Testing for proper signal at the injector is a little harder to do. Proper way to do it would be with an oscilloscope! (I actually do have one if you want to learn how to use it) But, they do make "noid lights" that plug into the injector harness. Plug it in, and it will flicker if it's getting signal. They're not too expensive, but I think Andy LaChance has a set.

https://www.amazon.com/dp/B004FEHZZU/re ... B0071JJYLO

Before you go pulling the fuel rail, I'd try to make sure it's not electrical. Could very possibly be either a bad MS output (possible, but not extremely likely)... or it could be the connector where the injector harness plugs into the engine harness (at the back of the head). There's probably one wire on that connector that connects ground from the ECU to two injectors. See where I'm going with that, right?

[Native]

So, 5 weeks later, I finally got back to this. Feels like 6 months.

Check supply voltage to each injector. Should have 12v going to one side of each injector at all times.

I did. Each injector is getting about 13v actually. Same amount as the spare power source under the hood. So that's good.

or it could be the connector where the injector harness plugs into the engine harness (at the back of the head

Sooo...if all 4 injectors have proper voltage, then it could be that connector not sending on signal from the computer... and I'd have no idea how to check that?

OR am I at noid vs oscilloscope? This is a bit beyond me at this point... Anybody know a good mechanic?

[Loren]

Noid is easy to use. The signal that's firing your fuel injector, as you know is a pulse. It's not constant on or off. But, it's "on" enough that it's going to light up the noid light so that you can see it. If you know you have 12V source power, and you DON'T get a light with the noid plugged in (when the injector should be firing), then you know that either the ECU isn't switching the ground as it should, or there's a signal (ground) wire problem to that injector.

Don't give up your troubleshooting just yet. You're half way there!

You could also use a meter to check the resistance of the wire from the injector to the injector harness connector near the back of the intake manifold. If you have continuity from the injector to there, then check from there to the ECU connector. If you have continuity there... then it's starting to look a lot like an ECU problem.

My bet is still on a dirty connector, probably the one in the engine compartment at the back of the intake manifold. The fact that it was intermittent before it failed makes me think it might be something like that. And ECU failure is usually a hard fail. (a transistor blows up)

So, either try a set of noid lights, or just get your trusty ohm meter out and start poking around. It ain't rocket science. Just wiring.

[Native]

So let's say I do the noid thing. I get lights. That means injector. No lights means I keep looking.
Yes?

Or I go section by section looking for a break in continuity, or is it resistance? Electricity is my weakness...

[Loren]

Yeah, if the noid light works and the injector ain't workin'... that would indicate a failed injector.

Resistance 101 as it relates to basic troubleshooting of wiring:

0 Ohms (or very near zero) = continuity, a circuit completed by an uninterupted piece of wire.

>10 Ohms or so, or some kind of variable reading, especially when you disturb the wire or a connection = a weak connection.

Infinite Ohms = no continuity, an open circuit. No connection.

You can do these checks with a "continuity test light", or with a multimeter set to measure ohms.

You really don't have to get deep into electronics theory to do this kind of troubleshooting. I think you'll ultimately be glad you did.

[Native]

My bet is still on a dirty connector, probably the one in the engine compartment at the back of the intake manifold. The fact that it was intermittent before it failed makes me think it might be something like that. And ECU failure is usually a hard fail. (a transistor blows up)

I'm only guessing it was intermittent before it broke, cuz the AFR at idle had become wonky. But, it was idling just fine in the driveway doing autotune on the warmup enrichment. It finished and I shut off the engine. When I restarted it a few hours later, it was dead.

TLDR:
The dead injectors aren't getting signal, and it's either the computer or the wiring from the computer to the plug at the back of the motor (which was clean and bright yellow inside, with shiny copper contacts).

Today I started by rechecking the resistance of each injector which was 13.6 on 3 of them and 13.7 on the other. So that's good. Then I rechecked that they were all getting 12v at the injector plug, and they are. So that's good. Then I unplugged the harness at the back of the motor, and checked continuity on the wires for the 4 injectors. There's 8 slots on the main plug: 1 is the constant 12v. 1 each is the ground for each injector. And the other 3 do nothing. Makes sense. So the injector harness on the motor is good.

Then I went to Auto Zone and borrowed a set of noid lights (refundable $25 deposit). The noids lit up for the two good cylinders, and not for the 2 bad ones. Rats.

So somebody check me on this: at this point, I can get the diagram for the main computer plug, find the wires for the injector grounds, and look at that continuity. Or I can pull the MS module, open it up, and see if I can tell if anything exploded. Or what should I look for?

[Loren]

Wouldn't be unreasonable to do a smoke check inside the MS. Smell for burnededness. Look for anything that looks burnt.

There are still more connections (and lots of wire) between the engine harness and the MS, though.

So, if you pull the MS to inspect... Also check the rest of the wiring while you're at it.

[twistedwankel]

Geeze Louise. Leave the car with me for a couple years and I'll eventually tell you it's "perfect". It's a frickin' old Miata not a Vette or some exotic stuff from Italy.
I'll figure it out eventually. I'll let you know when the tires smoke. Ok? No charge if you bring all your parts.

**Actually you reminded me of something from when I was very very young. My buddy and I went drinking on Front St in Toledo and met a sailor in a tough bar. The sailor gave me/us some advice when the beer girlies came around. Son, if you mess with that you might as well toss your dick over your shoulder for all the good it will do you for the rest of your life. Said the sailor with his dick over his shoulder. I have always heeded that advice. You should too.