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If you can turn the engine with the starter and the tach moves, and you have an early 1995 or older (4 pins on the coil), then the coil is working (and >=90% working CAS). In an OBDI car its easy to know if you have spark and a good CAS if the tach moves when cranking because those two pieces work together.Quote:
Originally Posted by Jiggerachi
^Have not had a chance to try this. Do you mean the half sec of cranking before the engine fires up?
So rethinking this logically. If the CAS and ECU provides the tach signal, SPark, and fuel signal, but replacing it didn't fix the problem. The coil pack provides only spark. The car had spark after it died the time I checked. If it was losing fual pressure the car would sputter before dying, this seems like an ignition cut.
This makes me think ECU. Could the ECU crap out while hot, can the ECU even get hot, behind the seat? I would guess it could be some resistor or something overheating unrelating to engine temp. Would it cut ignition and tach signal? Is my line of logic retarded here? I keep thinking out loud here on this since searches on the issue aren't returning anything new.
Does anyone else have a 94(or compatible) ECU I could borrow for testing?
I'm pretty sure we do.Quote:
Originally Posted by Jiggerachi
There is a guy on miataturbo.net selling a 94 ECU for $30 shipped
^Ooh, thanks for the heads up. I'll email him now.
Yall think it's worth $30 gamble? Kindof shooting in the dark buying one. I guess I could sell it later worse case.
I still think it is the coil pack, but $30 shipped sounded cheap. BTW I still haven't located the coil pack I thought I had.
I tried this Saturday. For the 1/2sec before the car fires the tach sat at zero, although I'm not sure I understood the procedure since I dont think the starter can move the engine fast enough to register on the tach. Can you elaborate? The tach works normal with the engine running, for about an hour or so, then goes haywire.Quote:
Originally Posted by mr brg
Flyin96m, you might be right. Either way I emailed him, cheap enough that I can hawk it on ebay later if it's not the problem. Whenever I can get my hands on a coilpack for testing and an ECU i'll test them one at a time to rule them out. Then I guess start hunting electrical shorts. If it ends up being the latter the poor car will sit at least until this semester is over... Probably longer. Time is precoius these days.
[QUOTE=Jiggerachi;261333So rethinking this logically. If the CAS and ECU provides the tach signal, SPark, and fuel signal, but replacing it didn't fix the problem. The coil pack provides only spark. The car had spark after it died the time I checked. If it was losing fual pressure the car would sputter before dying, this seems like an ignition cut.[/QUOTE]
Wrong. The CAS tells the coil when to fire through the computer. Then, the blk/wht wire goes from the coil to the cluster and drives your tach. The factory computer uses the signal from the CKP and CMP in the CAS to fire injectors and count RPM but the tach is controled by the coil, not the computer. I know this becuase I recenly cut the blk/wht wires on my coil to allow the tach-out header on MS2 to control the tach. :)
Your logic is retarded. Well, maybe not but highly unliekly. The factory comptuer is not set-up to "cut spark" in any condition. It will retard spark in some conditions, but will always fire spark. The long story made short, if you want to check for spark, just crank the car. If the tach moves, you have spark. If it doesn't move, the CAS is bad, the spark-plugs are bad, the coil is bad, or the computer is fried. So if that tach is moving when you crank, but the car is not starting, you can be 90% certain you don't have a spark problem. I say 90% because you don't know if the CAS is acting naughty and various unknown unknowns.Quote:
Originally Posted by Jiggerachi
The starter turns the engine about 300 RPM, if the coil is firing you can typically see the tach moving on an NA Miata. If the tach were going haywire (like my turbo car has before) then the problem is either the CAS, the coil, or the cluster. If the car is running fine when this haywire tach thing occurs, it's the cluster and you should clean the contacts or look for a chaffed wire.Quote:
Originally Posted by Jiggerachi
If you want my 1994 computer, come by and get it since I have MS2 in the car now. I live in Lewisville.Quote:
Originally Posted by Flyin96M
I still think its the fuel pump relay.
When my CAS died, I had spark while cranking the engine. I had not figured out a way to verify the timing of that spark without the engine running. I did not even check if the tach registered while cranking.
Your symptoms are roughly consistent with my experience. Intermittent problems that get progressively more consistent.
Remind me the source of your replacement CAS.
Edit: Fuel pump and associated relay can be tested without spending money. Does your fuel rail have one of those bungs for a manual tester gauge (looks like a tire valve but a different size)?
Quote:
Originally Posted by mr brg
Thanks :DQuote:
Originally Posted by mr brg
Seriously this is good info. At least I have enough to fill an afternoon of testing. I had abandoned the idea of the fuel pump relay since the tach is going haywire.
So here's the deal with the tach. When the engine runs fine the tach is fine. The tach will start to dip & flutter, then drops to zero approx 1 second before the engine dies. It does this every time. The tach is 100% normal any other time. The two are related, no question, I would be shocked if it was just the cluster acting up.
When I get a second this week i'll rule out the FPR. When I get a coil pack i'll rule that out as well.
I suppose you could lose the CKP or the CMP signal and that could affect fuel too since the fuel is triggered off the CMP and tach/coil is on the CKP; I didn't consider that earlier. He could always pull the CAS, open it up, have a look, and possibly clean the dirty teeth. I made a single-tooth CAS last year (cut out 3 teeth for sequential fuel on my 1.6 chassis, now I have to build the harness) and was surprised by how nasty it was inside.Quote:
Originally Posted by boisking
I have a spare CAS too, btw.
I got a replacement CAS from 90 turbo here on the forums. It's a 1.6 CAS so it's mechanically different but I confirmed they produce the same signal(well I read it on Miata.net). I believe the 1.6 is optical whereas the 1.8 is magnetic, so my thinking was that having a completely different design would make it more unlikely to have the same failure.Quote:
Originally Posted by boisking
I guess it would be prudent to try another CAS from the correct year if I got desparate. mr brg, i'll take you up on the offer if all other avenues fail.
Yeah, the 1.6 CAS won't work on a 1994 because the 1.6 is batch-fire fuel and the 1.8 cars are sequential; instead of each injector firing once per cam cycle/alternating crank cycles, it's firing twice per cam cycle/every crank cycle. I believe the factory computer reads a leading-edge square wave signal on the 1994 and I think the optical might run the car, but you've have to cut two teeth off the CMP side for it to work.Quote:
Originally Posted by Jiggerachi
If you want them, come get them now so you can take them with you and swap them the next time the car fails.
^Really. I drove back & fourth to work for 3 days and some fun back roads with the 1.6 CAS installed. Engine ran smooth and strong, wouldn't even know anythng was changed. Only when I got stuck in traffic on the way to class is when it cut out on me.
A guy on Miata.net has(supposedly) been running unmodified 1.6 CASs for years on this 1.8s. Reading the thread they apparently output the same signal. (I don't have the tools or the know how to confirm this, so take it for what it is)
I do wonder though, if the 1.6 CAS might have long term issues? I only used the 1.6 CAS because it was what was available at the time, i've swapped my 94 CAS back in for now.
then there's something going on that I don't understand because my 1.6 chassis car requires trigger adjustments for MS.Quote:
Originally Posted by Jiggerachi
Ok, maybe I should just shut up and let the pros handle this because I have no clue what's going on, lol.