Good morning!
I've been beating my head against the wall the past two days.... After a 20 yr sit accompanied by a recent emissions delete, we've been able to start the car and run it intermittently over the past week or so. Went to start it again yesterday afternoon and nothing. It cranks over just fine (until the battery dies down) but doesn't want to fire over. I had it idling the day before for 10-15 minutes then I'd shut it down and start it again. I figure running it for short periods of time after 20 years would help loosen thigs up.

Below lists what I've done thus far:
new fuel pump/strainer
new coil packs (leading/trailing)
new ECU (I fried the original by accidently hooking the battery up backwards, I thought Black was (-)...)
flushed and bled coolant
new thermostat

I've learned about the flooding issues and fixes (both pulling the EGI fuse and removing the plugs/ATF trick) this is how we initially got it started, quite the smoke show.... Like I've mentioned, we been running it the past week or so, literally nothing was done to the after the last run and now it won't fire over. It almost sounds like it wants to go immediately after a deflooding but then back into a lifeless cranking.
I checked for spark using testers and there's spark going through all four wires (I haven't checked the actual plugs for spark). Seems to be getting fuel and the MAF flapper's flapping away. I also was using a temp gun when it was running to keep track of the idling temps (the dash/gauges are not working) I would temp each upper housing around the plugs (~180-195*) and the coolant temp sensor by the filler neck (~160*). The fuses in the cab by the kick plate all seem fine, I can hear the main relay click when the key is in the on position.

I did notice an odd ground that I can't identify that goes from the firewall to the to the intake manifold. At one point over this process it seemed to get really hot but then it didn't seem to be an issue anymore, although I disconnected this at one point with the car idling and it almost died so I reconnected it and left it. Yesterday I noticed the wire covering was melted (I've included an image of that) I cut part of the covering away to inspect the wire. It seems like it might be damaged so I'll replace it, but still not sure exactly what it's for.
I haven't checked compression yet, I just assumed that it's fine because we were able to get the car started previously.
Maybe something melted or blew the last time I had it running? I don't know, kinda lost and all I can think of doing is to keep trying the unflood methods until the starter goes out....

Any help would be greatly appreciated,
Thank you!

 

The hot ground wire tells me that your main engine ground is probably weak or not hooked up at all. That smaller gauge wire should not have to bear the brunt of all that current, and therefor was hot and burning down. There should be a large ground lug on the drivers side of the engine that hooks up near the fuse block. Is this present, hooked up and not damaged? If in doubt, you can add an additional large gauge wire to ground to ensure proper electrical.

It wouldn't be a bad idea to change your plugs too. There's a chance they might have fouled, and i've chased non-running issues for far too long overlooking the simple thing like throwing in new plugs to verify.

 

I will look for that ground today; you're not talking about the ground going to the fuse box itself are you, the 80-amp fuse?

One more thing I forgot to add which leads me to think it might be the plugs. Earlier this morning I tried starting it again and had the same luck, but this time I shot starting fluid into the intake (where the intercooler hose connects to the intake) expecting to get some kind of excitement - nothing. If there was spark, I would assume it would've at least popped.

Your suggestion on the ground might lead me to the issue I'm having with my gauge cluster.....

Thank you!

 

When I hooked up the battery backwards, could I have blown the CPU as well as the ECU? Would a bad CPU keep my gauge cluster / cabin blower from powering up? There are a lot of people confusing the CPU from the Cruise Control Unit... I had to look a few times, being that it was black it didn't stand out. I actually bought a cruise control unit thinking it was the CPU...I know.....

 

That is some good advice @GtiKyle. I just wanted to add, in the N/A at least.... the chassis ground is near the fuse block on the drive side shock tower, lower engine side. Clean the lug, remove some paint on the wheel well, chase the threads and replace the screw. You can get by just cleaning the lug but I don't recommend it. Do at leas the shock tower and the lug. Treat with dielectric grease, too.

On the shock tower too. toward the windshield after removing the coil pack, you will see a bunch of black wires converging to a single spot. Clean all connections as above. That might get the dash stuff working. there are multiple chassis grounds in the car, most of which, I have no clue where they are. There is one behind the drive cluster that might help, too.

There will be a ground wire on your starter as well. Check that one as is should handle most of the load while starting.

I have seen some really bad grounding threads on here. One that states, "I had a ground melt so, I just made it bigger" Like to above post mentioned, someone installed band aids on the electrical system instead of fixing it correctly. What exactly correct is... is up for debate. I will say the Mazda engineers design isn't perfect but has been quite adequate and has served these cars well, until it doesn't.

There is one ground from the bell housing that is a smaller gauge that goes to the firewall. Mine was disconnected and had the 3,800 hesitation but ran ok otherwise.

There is a small possibility that someone modified the engine to ECU ground as well. When these get spliced to chassis ground in the passenger foot-well and the other grounds in the starting system are crap, when starting the car, these added ground straps will overheat, melt and possibly take out your ECU. I have seen it happen here a few times.

Just as a finisher, the lug at the battery ground can go bad, too. Kind of rare but it can happen.

I forgot to mention Aaron's OEM grounding tutorial. This scheme has worked for decades for people. If you take the time to do it correctly it will last another 30+ years.

https://www.aaroncake.net/RX-7/grounding.htm

 

This is all great info, thank you!
I ordered new NGK Platinum plugs and a new CPU (assuming I cooked mine). I'll start digging into the grounds today.
With the car suddenly not starting, is there a chance the CAS is went bad?

 

Crazy things can end up happening when the negative and positive terminals get swapped. Not to add salt on the wound lol.

I would definitely start with the grounds, since the car ran even after the mixup. I don't believe it's the ECU, but it would be good to rule it out.

 

Thanks for the extra input. I did the -/+ swap on my S4. Fortunately, it only took out the fuel pump and main fuse. Many aren't so lucky, depends on how long it was connected that way. Usually when sparks fly, the full connection isn't made, at least when it happens to me.

Everyone be carefull out there.

 

BAM!!!
It was either the new plugs or replacing the intake manifold ground, or both.... But she running again, and the smell of premix exhaust never smelled so good!
Still have the no power to the gauge cluster, but I'll keep looking into that. My 16-yr old is now happy again😁
Thanks for the pointers and advice!

 

Check the ground that Jeff mentioned above, near the driver side shock tower.

And congrats on getting it running again!

 

Evening Fellas,

Still searching for the gauge issue, grounds seem to be good and tight, while under the car replacing the fuel filter I did notice a ground of 4 or 5 disconnected wires on top of the tranny...

I am having a bit of an issue at idle... Lots of stuff on here about low idle issues, so I've been digging deep.
We did the emissions delete and found that our Intake Temp Sensor had a broken prong. I soldered a male connector onto the broken prong for now while I wait for the Bosch replacement part, seeing how the sensor is no longer available. Aside from that, I cleaned the BACV and tested the, AWS, and the ASV solenoid. All the valve/solenoids check out except the Air Supply Solenoid Valve - I get the resistance but no clicking when I jumper it... Are All of these necessary following the emissions delete?

Aside from the above, I have cleaning the injectors and replacing the coolant temp sensor. Am I missing anything else? Cold start (relatively cold, I'm in South Florida) idle seems ok until it warms up then she idles out..

 

I am not trying to be difficult. Lately when people show up here with idle issues some have recommended to add the emissions back in. It makes it harder to diagnose with it out. Getting the car running correctly and selectively removing parts slowly, one at a time to see what happens and correct one thing at a time.

Vacuum leaks and TPS adjustment is the best place to start though. Don't forget about plugs and wires. Get a timing light to verify all coils are firing, too.

I had major stalling issues, once the TPS procedure was completed correctly, I no longer needed to bump the pedal to keep it from stalling, I would start there....

I forgot to mention that if you take out the primary injectors, pull the EGR and add a block off plate. There is little chance that it doesn't leak. Also. Those wires on the transmission could have been from an auto swap, if this wasn't originally a manual. Note the wire colors and look it up in the FSM wiring section.