This may be a long post but I'll try to cover the relevant info so the community might help me track down the source of this maddening problem...

The car is a '89 T-II with a mild street-ported rebuild from Pineapple Racing with around 15k miles on the motor (approx 150k on chassis). The car was running excellent (and has/had been for all of its rebuilt life) when I returned one day from a leisurely drive and parked it outside the garage to let the turbo timer do its thing for ten minutes. I come back later to pull it in once it's cooled down and it will crank and crank and crank but will not fire up. A buddy and I push it into the garage where I figure I'll mess with it later when I have more time.

Fast forward several months (not my daily driver obviously) and I decide to finally start to get to the bottom of this issue. Mind you, I know a bit about cars in general and these cars in particular as they've held a certain fascination for me since I bought an early production '79 model as my first car at the age of 17 almost 30 years ago...but I digress.

A couple of years earlier I had experienced a very similar intermittent firing problem on occasion and was able to pull a DTC from the computer pointing to the crank angle sensor ground. Upon inspection I did notice a small crack in the insulation of one of the four small wires leading out of the sensor to its harness plug. It didn't appear that the wire was completely severed but it was hard to tell as I could see the miniscule copper strands but didn't want to aggravate that tiny, old, brittle wire any further, especially with it being at such a difficult location to affect a proper electrical repair easily. It turns out that in the gentle maneuvering of the wires/harness around the area I was able to get the car to fire up just fine and the DTC was gone...for the moment.

So I dealt with it in this "fingers-crossed" condition for quite some time since it was only a very rare occurrence and a slight wiggle in the area would allow it to start up and run perfectly afterward. No such luck on the day(s) after pushing it back into the garage in frustration. After it was out of the driveway I immediately noticed a considerable rust-colored wet spot on the concrete leading up to where the battery had apparently boiled over. Upon inspection I found that the voltage regulator on the back of the alternator had been/was failing as there was minor melting around its output connections and it tested bad at the parts store. The "lucky" wiring rustling around the crank angle sensor was no longer having any effect so I began to check other things including the large EGI (fuel pump) fuse in the engine compartment. Bingo!!! Fuse was blown and I felt silly that it could be such a simple fix that I hadn't caught immediately. I changed the fuse and replaced the battery with a fresh charge, and after some cranking was able to get it to fire up and run normally, knowing that an alternator replacement was now needed.

So, being out of free time, patience and having to move and not at all confident that a simple alternator swap was going to get to the root cause of the no-start condition I decide to get the car towed to a highly reputable mechanic. When the tow arrives and I go to push the car out of the garage it of course fires right up and runs perfectly to operating temperature. I turn it off and get ready to load it on the flatbed... but again no start from it now in the driveway.

The shop put an alternator and fresh spark plugs in it and test drove it, unable to get it to replicate the no-start condition for weeks. I was beginning to think that I was either crazy or lucky that it might be fixed, until they were finally able to witness it not firing in person. They've now had the car for quite some time; putting a crank angle sensor and new coils in it as it appears they aren't igniting when it's not wanting to start. Apparently, sometimes it starts right up on the first crank and other times they can't get it to fire for weeks. I'm running out of time, patience and ideas to suggest and I'm sure they want to get this car out of their shop and get paid.

All that being said, I'm here to ask the enlightened community for some insight into all the conditions for various sensors and wiring circuits that must be met for the computer to allow the plugs to fire. I obviously know of the crank angle sensor (which I'm assured is functioning normally) and the clutch pedal lockout (which never seemed to be an issue before as I could always start it in neutral without the clutch being depressed.) Where is this electrical gremlin? Possibly ignition switch itself (although the starter is spinning up just fine)? Could it be related to a security/ alarm system on the car even though the first signs of trouble predate that? What is a potential workaround to ensure this thing will start reliably and consistently? Any ideas or a diagnostic procedure/list to try would be very appreciated! Thank you and sorry for the long post!

 

Chasing intermittent problems can be the worst.



Step one is figure out what is missing when it won't start. Presumably it's got compression. Is the tach bouncing while it cranks? Are the injectors firing and is there fuel pressure?

Are the spark plugs making spark?


This is where to start, and you might not be able to make any progress on the diagnosis until it does it to you again and you can troubleshoot those things when it happens.

Good Luck.

 

You should search this forum, there are a lot of threads detailing how the ecu, coils get power and fire.

It’s been a long time since I forgot the details but they exist on this forum.

Here are all the manuals and wiring diagrams. https://foxed.ca/indexmobile.php?page=rx7manual

yes there is a factory security system which does not allow the car to start, I forget if it does not allow the starter to turn though. Think tied to the door lock…?

I had that issue as my car is a 88 and I wired it up to 90. There is a thread I made or at least commented on years ago how to disable it due to safety reasons in case I stalled and had to restart it. Otherwise I had to disconnect and reconnect the battery and I think that reset it. But the lights would flash (as most alarm systems do), so guessing that’s not your problem.

sounds like the wiring harness is frail so that doesn’t help, it’s not getting any younger. I’ve had intermittent shorts when going up hills, weird huh. Ended up replacing with a low mileage harness.might be a good idea, but I’m all for you not throwing parts at the problem, but rather identifying what’s the problem.

Could investigate how the electrical system works and probe for voltage & continuity. Also check the engine fuse under the dash. And check the related relays.

 

1993 gen 3, but similar symtoms. Random times would not start. I had to put in a switch for a hot-wire start, so I would not get stranded again. Stopped happening when I pulled the electronics board behind the speedometer and replaced a bunch of leaking liquid capacitors and cleaned the gunk off the board. The speedometer now works, but the odometer resets at every on/off. But there has not been any more random no-starts for a couple years now. Suspicion is that the bad electronics was messing with the anti-theft function.

There are a bunch of posts here on fixing the electronics boards. good luck.