LongDuck

In terms of;
1) What the driver sees / feels?
2) Dash Idiot Lights on / off?
3) 20A Main Engine Fuse in the fuse block?

For context, backing out of the driveway this morning (*just like yesterday and all last week...), engine shuts off with a 'click' under the dash, no Idiot Lights, cranks but won't start.

Just 2 weeks back, I fixed a 20A Main Engine Fuse issue by replacing the Alternator with a used, known-good unit with untold # of miles on it, and the car started right up and ran well for 500 miles,... until today.

For further context, that original issue of the 20A Main Engine Fuse frustrated the hell out of me - as researched here with all of you guys back in April of this year - and had the car down and out for over 3 months while I trouble-shot everything.

Ironically, just yesterday I received the Atkins Rotary 1986 model year 70A Alternator (Bosch) that I ordered on recommendation from you guys so I'd have a new Alternator instead of the unknown miles one which I think blew out this morning. Instead of just throwing the NEW Alternator in there and hoping it doesn't blow out, I thought I'd check in with you guys first and see if there are other suggestions I should be looking at, first.

TIA, and at least the car didn't leave me stranded somewhere like last time... it was easy enough to push it back in the garage this time.

GSLSEforme

Key on,all dash lights illuminated. Engine running all lights off if charging. Engine running,lights on=no charge. Another alternator failure could be a coincidence. Is the fuse blown,again,was that the click? What happens if you replace it and turn key on? If all lights on,start car. Put voltmeter on battery,what's reading?

If fuse blew immediately on replacing it...leave key on and put your test light rig in place of blown fuse. Is test lamp illuminated? If yes,leave key on,go under the hood and disconnect plug from back of alternator,lamp still lit,yes? Disconnect alternator output wire from back of alternator,place couple wraps of tape around lug on cable and pull boot up tight-so it doesn't touch ground anywhere. Your alternator is now out of circuit,if it was the component with the fault,the test lamp will be out. Test lamp still lit,short remains. I think this may be the scenario.

Alternator failure in this manner is not common,2nd failure in 2 weeks,even less likely. Suspect same gremlin that gave you fits before,can't explain why problem was dormant,have seen intermittent shorts do this. Pinched wire,insulation near rubbed thru...a very likely scenario is when you had things apart previously and moving things around,the short"disappeared",only to resurface as it has been there all along.

Post back what you find.

LongDuck

It was 114F today and too hot to work out in the garage, but I'll get to your sequential steps one of these mornings. I really appreciate you keeping on this with me, and am open to any other suggestions, as well. Thanks!

Also,... what circuits / relays power the Alternator? I'm wondering if my short is in one of the main engine relays that power up the Alternator, the Field, or the Charging circuit...?

GSLSEforme

No relays power alternator. Three wires: 1) output wire that goes back to battery.2) two wires,black/white and white/black,i forget which is which without either looking at car or a diagram but easy to figure out. The wire that goes to R terminal(cast in back of case),this is the upper terminal in connector is 12 volts from ignition switch to excite the regulator. The L terminal is from the stator which is grounded til alternator begins to turn at which point regulator energizes it and ground goes away. This is the ground that supplies all the dash warning lights to illuminate key on. Alternator begins charging and ground turns into voltage,no ground to warning lights-they turn off.

Unless the ignition feed to regulator has a short in it somewhere between inside the car to the alternator,that circuit can be ruled out. I recall directing you to look at this circuit in your original thread..

Holdfast

It looks very dark.

GSLSEforme

Lol.

Holdfast

I agree with gslseforme that this kind of alt. Failure is very rare. If you are blowing a main fuse then you have a power wire grounding out some place. If your just lost power no fuse blown. Look at your grounds. The biggest current draw is your starter and the fact that you had this problem right after starting the car up. I would look there. If it was me i would replace the whole ground and power wires going to the starter. U can pick them up at your local auto parts store usually pretty cheap.

LongDuck

Temps here are still 109F, and my garage isn't air conditioned, so when I get home and park the LandCruiser in the garage, the engine heat dissipates into the air in the garage, making it unbearable out there. I truly appreciate the advice of this group, and will get to this shortly (pun!),

AAAOA

An old mechanic showed me a trick when my 84 was giving me hell. Same sorta thing, car would just die and wouldn't really want to start. Thought it was the battery, thing got me there with a jump and gave up right out front lol. New battery didn't fix it and the guy rolled up and asked if I had jumper cables. Connected one end to my negative side and one end to my alternator. Started right up, I had a bad ground. Ran a wire from the negative side to the engine block. Haven't had an issue since. Check your grounds, those stupid things had me chasing my own tail for weeks.

LongDuck

I'll be pulling the Starter out to have a look at all of the wiring and connectors on the back of it, as I've already rebuilt the (-), (+) and extra ground cables (*extra ground goes to the alternator mounting bracket to Negative, and scraped and filed the body ground at the DS Strut Tower a few weeks back, which didn't change anything. At the time, the only thing that changed the intensity of my Test Light rig was u plugging the connector from the Alternator, which signaled to me it was a bad Alternator.

Replaced the Alt with a used, known good, and it bought me 500mi and about 2 weeks of driving it daily - and then back where I started, Again.

It's got to be the wiring from Alt to Starter, Ignition to Starter, or Battery to Alt - and I'm looking for a short.

Incidentally, why did Mazda use a plastic block for a Positive Alt terminal on the EGI Dynamic Chamber on the DS? Seems like an odd place to insulate / isolate a Positive connection. There isn't anything in there, right (*Diode, ground, or resistor)?

GSLSEforme

No,just a mounting block.

LongDuck

Alright - here's what I found, and it turned out NOT to be a bad alternator, but back to that original short - which I finally located at the BACV solenoid. Here's the pic (*look for the spark and wisp of smoke):

<img>http://oi66.tinypic.com/2u9s4s3.jpg</img> http://oi66.tinypic.com/2u9s4s3.jpg

What had happened is that the insulation from the wiring was worn away from vibration, along with the rubber grommet used to isolate the wires from the metal solenoid can deteriorating enough to that it crumbled away, making a path to ground. Under any motion of the engine - or just the wrong combination of movement - the wiring harness would pull the wiring tight in this area, which caused the Idle Compensator solenoid to dead short, popping the 20A Main Engine fuse in the interior fuse block. This is the very issue I'd been fighting since the beginning of this year, and while I've been driving the car for less than a week, I'm ready to declare victory over electrical system shorts and move on, knock on wood. My confirmation test was to put a new 20A fuse in the Main Engine slot, turn the key to 'Run' (*not Start), and then pull on the wiring to create the short and it popped the 20A fuse immediately, which is exactly the failure mode I'd been chasing for months and months...

Here's the engine bay showing the replacement BACV which I pulled from the spare parts bin, and which has been thoroughly cleaned up, tested, and the rubber grommet and wiring isolated by pinning the wire leads to the Idle Compensator adjustment port housing with the yellow zip tie. This entirely prevents any chafing of the wiring due to vibration;

<img>http://oi66.tinypic.com/2zia8aq.jpg</img> http://oi66.tinypic.com/2zia8aq.jpg

I'm also linking the prior posts I made dealing with the same 20A Main Engine fuse blowing, along with all the troubleshooting threads you guys helped me with. Once again, thank you to everyone who took their time to offer suggestions and sequential steps to find the root cause. I still have the 86 model year Alternator (70Amp) sitting on my workbench, and I'll give it another few weeks before I install that just to be sure everything is settled.

https://www.rx7club.com/1st-generati...block-1133620/
https://www.rx7club.com/1st-generati...-84se-1137288/

GSLSEforme

That’s exactly the scenario i envisioned. No doubt you had manipulated that section of harness in search for the “original” short and at same time moved it just enough to keep from touching and after driving for a time,the harness returned to it’s natural position and blew the fuse.

These cars,especially SE are very reliable and can achieve miles you have on your car and many more.
I have seen 330k miles on original engine in an 84SE.
When something like this short happens in a mature car,almost always rubbed thru/pinched wire(s).
Good find/fix!

Safe to install new alternator-or original one,lol.

LongDuck

Thanks to you, GSLSEforme for all of your patience and troubleshooting help along the way. I've managed to clean up the Ground at the Starter, the DS Strut Tower, rebuild both (+) and (-) Battery Posts, and cleaned up a bunch of parts looking for the short, so I've learned quite a bit from the effort. Take care, and thanks for all you guys do to help each other out on this forum. You're amazing,

GSLSEforme

All good my friend. Am sure there’s some collateral good that came from going thru all those connections.
Though they didn’t solve your original issue,you got to know your car better,pick up some knowledge you can apply down the road.
I would be surprised if you didn’t see .5 volt increase or better with electrical system operating voltage,even with original alternator in place. Might be able to see that on dash voltmeter,but should be a tick faster power window up/down,and brighter headlights,running lights,brake lights. I know you don’t use wipers much where you live but they would be a bit faster. Also maybnotice the blower motor runs a bit faster on all speeds.

Your electrical system will now be able to use 100% of the higher output alternator you have.
With it installed,you will see yet a further improvement in all those accessories, particularly when operating them all at same time.