Hello,

Car is near stock with just a cat-back and ~67k miles. It was sitting for a while (less than a year) and ran fine the last time I took it out. I charged the battery, primed the fuel system, and gave it a go..

It was a nice day out. Started on the first try (took a few seconds and seemed a little slow to turn over), but it sounded like absolute crap.. No 3k jump, just a lumpy idle and sounded "different than usual". Sounded like it was really struggling. No smoke that I could see. I kept it running, pumped the accelerator a few times and after a minute or two the idle smoothed out, just over 1000rpm and it sounded "normal" again. I was thinking maybe it was bad gas or was struggling to get through whatever water or gunk had built up. I let it fully warm up until it was idling pretty steady at 750rpm and shut it down. Didn't feel super comfortable driving it yet, so I took the family truckster to the gas station and bought 5 gallons of "100% gas" (90 oct ethanol free) and a bottle of techron.

Came home and dumped the 5 gallons into the tank, decided to hold off on the techron, and started it back up. This time it was quite normal. Quick start, sounded fine, idle settled back to ~750rpm. Oil pressure, coolant temp and voltmeter all looked good. I let it run this time for probably 30 minutes total. During that time I noticed some strange things..

Before I started it, I had the key ON and was paying attention to the idiot lights. I know they are all supposed to be on with the key ON/engine OFF. That happened, but not all at once. I want to say I got like 3-4 lights at first, then another, a second or two later, then another, then another, until they were all finally on (I sort of remember my old 88's lights all coming on instantly at once). When I finally did crank it, I had the ebrake engaged and the door open. As expected, all the lights had gone off except for the Door light and the Brake light. There was no beeping. I got out and left the car running while I walked around checking things. After a few minutes I started hearing some beeping. Not the buzzer, but the beeping you typically hear when the door is ajar. I can't remember if it's supposed to do this while the engine is running or not, but it wasn't doing it earlier..

I also noticed that the idiot lights had gone from solid, bright Brake and Door lights to a very faint Brake light and Charge light. When I got in and closed the door, the Charge light went off, leaving just the faint Brake light. I open and closed the door a few times and was able to toggle between these two displays. The beeping continued while the door was open. I started messing with the little pressure sensor in the lower door jamb manually to see if anything interesting would happen. Nothing at first, other than simulating the door being open/closed, but after more jiggling, the lights now showed a faint Door and Charge light? The ebrake was still engaged. Closing the door in this scenario resulted in all lights going off (no ebrake even though it was still engaged).

After all of this, I decided to play around with some of the other accessories to see what would happen. Headlights worked. Wipers worked. Stereo worked. Climate control.. I had it set to the front facing vents, full cold, A/C off. The motor came on as I slowly pushed the fan control slider to MAX. The motor would be blowing at MAX but would then slow a little. Adjusting the control back and forth, I could get it to stay at full power. I reluctantly pressed the A/C button. It made a horrible sound and the engine almost died, BUT this was the first time in the 7-8 years I've owned this vehicle that the compressor actually kicked on! Why now?? The idle finally smoothed back out while the noisy compressor carried on.. the air from the vents remained warm and after about 30 seconds I disengaged the A/C. Everything sounded normal again. It was at this point, that I noticed the voltmeter reading 12V. The fan control was still set to MAX (with the A/C off) and the car was idling fine. I moved the slider to OFF and watched the voltmeter slowly climb back to ~14V. Seemed like enough for today.

So, any idea what could be going on with my electrical? I changed out the CPU and the warning light cluster a few years ago due to different issues. CPU was NOS from Mazdatrix. Cluster from eBay.

 

Sounds like it could be a ground issue. I would start at the battery, then the ground cable to the vehicle.

 

Thanks for the reply. I added an 8 gauge grounding strap from the battery to the strut tower and it didn’t seem to make a difference.. any other locations to check? I know there’s supposed to be a smaller wire behind the engine that goes to the firewall. Is there a better way to “redo” this one?

 

Did you have the battery checked too?

 

Just to be safe, I would measure the alternator output directly at the alternator. Should be 14V directly at the alternator at idle. A weak alternator can cause funny electrical issues and it only takes a minute to verify that its good.

 

Yep, I think the next step is to test the battery and the famously weak s4 alternator. I did read something about "exciting" the alternator by revving past 3k.. perhaps this is supposed to happen when you first start the engine, b/c of the AWS, but that's not currently happening on mine.. I assume that should occur before testing for 14V