Cranks funny and won't start. 94 Miata
 

So I bought a non running 94 Miata with a turbo a few weeks ago and when I bought it the car cranked over fine. but wouldn't start but after cranking the car a lot, when it cranks it slows down and then cranks normally for a bit and repeats while I have the key turned.
My guess is that the starter is bad but I don't know too much about Miatas so maybe there is something I am missing. I have not checked compression but I the previous owner said that it was good, it has spark and fuel.

If you have any ideas of things that could be wrong I would love to hear it because I don't really want to remove the starter if I don't have to.

Thank you. -Karl

First things first: What ECU? Correct diagnosis by anyone on here will likely require a copy of your tune file and a catalog of the car during cranking as well.

The diagnostic process on a turbo Miata is different and generally a little more intensive than with a regular fuel injected vehicle running a factory ECU.

If you’re running a standalone ECU (and your car likely is) there’s a ton of items in the tune that can cause a crank no start concern. I’m personally not the most qualified to give insight on this, but if you provide a tune and datalog of the engine cranking, some of the smart guys on here may be able to help.

So currently I am running the stock ECU that I was told starts the car and I was having even less luck with the standalone. I have a speedy EFI ECU that I have tried but it feels like the issue is more of a hardware issue than software but I might see if I can get that datalog today but I don't know much about tuning. Also it cranked fine before I cranked it a bunch

I would love to know if anyone has faced a similar issue or can point me in the direction of a forum of someone who has.

Thank you for the help.
FYI I am probably not going to look at this forum for a week or two due to the holidays.

Turbo
stock ECU


Pick one.


Specific amounts of compression, spark, and fuel are required for the engine to run. Beyond that I don't know how to advise you because it sounds like the PO screwed up the car and partially reinstalled the stock ECU system but not enough to make it crank. You've got a lot of unfucking to do. Good luck.

Yeah, what Six said. Photos of the ECU and its wiring harness, as well as the engine bay might help. I’d be interested to see if it’s just a completely stock ecu or if it’s got powercards, a MAF signal modifier, etc etc BS tied into it.

This project is probably more than what was bargained for.

The fm voodoo box retards timing and adds fuel in boost, otherwise stock ecu. Runs quite well, albeit rich, for a very daily-able 200ish horsepower. Come on guys, you don’t ALWAYS need a standalone.

the speedy ecu is not considered a good ecu around here, however it can give you a lot of data you otherwise couldn’t get to help you diagnosis your crank-no start condition. If it powers on and primes the pump, Take a datalog with it hooked up, if you see rpm, your CAS is working, if it syncs the cam portion is also working, and cold, the coolant and air temp sensors should read ambient. 94-97 can also go from close to full throttle to verify the tps reads 0-100%. MAP sensor should read atmospheric (100kpa at sea level) with engine off. All these except the map sensor verify your power/ground/wiring for the stock ecu as well, and is difficult to do with a stock ecu without numerous diagnostic tools and a skill mechanic with a decent multimeter.

im not sure if speedy can do this, but there is usually also a test mode to check injectors and coils too.

after this is all confirmed, verify fuel pressure, timing, and compression, install new spark plugs, and it should start. That last piece is very important, because with all this cranking you’ve most likely flooded the current ones.

Thank you. I will check everything in a week when I get back.

So the biggest question that I had was about the starter, because it worked fine until all of that cranking and now it doesn't crank right. So aside from what you mentioned I cannot figure out any of the other issues because the car can't crank properly. So for all I know the fuel relay was the only issue and this starter thing happened after.

So if anyone knows of anything other than a bad starter that would be great to hear

Curly wins again. Yeah, checking the basics is the best place to start.

Can you expand on what you mean by cranking weird? I was assuming you meant the concern was a crank/no start. However, rereading the previous post, it sounds like I might have interpreted that wrong.

Two things, any time you have a crank no start issues, the battery NEEDS to be on a charger 24/7. A
little trickle over night, something 5-10+ amps while you’re working on it. Do not skip this step.

secondly, if it’s injecting fuel while you crank, you’re also washing out the piston rings. This can cause a weird sound if you lose compression on a bad cylinder. Likewise if it’s a timing issue like a slipped belt/etc, it’ll sound weird.

Or the cylinder is full of liquid and unable to be compressed.

I am currently letting the cylinders dry out due to an excess of fuel. when they are dry I will try to crank the engine and see if that was the problem. I will also check the ECU data for information tomorrow.
Also thank you to anyone who has commented I really appreciate the effort, and hopefully this will help me get the car running.
One more thing. I think I misspoke when I said that it cranked funny what I meant was that when you turn the key to run the engine turns and stops and turns and stops. It does not crank smoothly it is not that it sounds off

Edit. So I tried cranking the car with the spark plugs out and it spun freely. So I'm pretty sure that the car was just hydro-locked. I'm letting it dry out right now will update tomorrow when I try to run it with everything dry

Change your crank advance in tunerstudios, try 0 or even -5.

Thank you. this was the issue. now it cranks over just fine and all I have to do is go back to the normal crank no start diagnosis

Most of these looked good aside from the tps going to 200% and map reading 97 when it should be 103kpa. Also I wasn't sure how to check the coils or injectors so I haven't done that yet.

One other thing is that the fuel pump won't prime unless I jump the connector to the fuel pump relay. when I use a new relay it doesn't work do you have any idea about what the problem could be?

Take a datalog and post it here, along with your current tune. We're all guessing without this.

Update. I have been really busy recently, so this project sat on the back burner. But I have good news I got the stock ecu to work and I learned that the aftermarket was not getting fuel. So I installed an oem maf where the air filter would go and plugged in the connector and it runs albeit a little rough. For the speedy ecu, I talked to the speedy efi customer support and they were amazing and helped me figure out that the fuel pump pin was set to default and not a9 as it should have been, so now the car will crank and squirt fuel, but I think I have the tune set up wrong.
I finally figured out how to setup a datalog so I will post it here incase anyone has advice. Thank you to everyone who has responded I am a bit to much of a novice to have made proper use of it but nonetheless, thank you!

This is the tune that I originally had tried to use, but I think it's just a base tune so it's not setup right