How to use datalogging to diagnose no start after head gasket replacement
 

Hey guys.

As the title says, my turbo Miata doesn't want to start after I changed its head gasket. It's a 99, non-vvti head. The car didn't overheat, and started fine before the replacement.

Trying to diagnose what's going wrong, and was hoping to use datalogging from my Hydra nemesis 2.7 to help me.

Does anyone have any tips/pointers on what to look for in the logs, or what values to log? Any advice is appreciated.

I've already double checked timing, and have a compression tester and ignition tester on the way.

Thanks.

If you simply changed the headgasket datalogging won’t help. Something isn’t connected or you have broken a wire moving things around during the work. I would follow FM’s Hydra and turbo installation guides to verify everything is hooked up correctly. If it ran before and won’t start now, it is 100% something you touched removing and installing the head. There are trigger tests, which I know nothing about, but as I said the Hydra settings should be fine. A head gasket change has zero effect on the ECU. Also, what prompted the head gasket change?

Not likely to be the problem, but if you pulled the head, you had to move a lot of things around. Make sure the Hall effect crank sensor is within range. It has to be very close to the pulley to fire.

Paul

Give us some more description of this "no start".

1. Does it crank when you try?
2. Are you able to check spark and how is it? (you don't need a fancy tester just another person to crank while you hold spark plug ground against any ground)
3. Are you able to check fuel (hint pull spark plug is it wet?)
4. Any connectors in engine bay not connected to anything.

Replaced the head gasket because coolant was being blown out of the front of the motor during full boost. I replaced my FM ARP head studs with the 949 racing head studs rated to 35psi as well.

Compression test is good, 140 across the board.

I checked the spacing on the crankshaft position sensor, was about .025in.

I was hoping a trigger test would help confirm that it's correct. I've sent one of my logs to flyin' miata tuning help to see what they think, awaiting a response now.

I've confirmed with Flyin Miata that my trigger test is working as well. I had them compare a trigger test from 12 months ago when the car started to one now when it's not starting.

They said 'the cam sync is occurring a little earlier in the cranking trigger pattern (on the no start test). However the igniter output is still solid so i don't think it's a problem.'


Which puts me back to square one. Kinda unsure how to proceed now honestly.

Take crank pulley off and flip the crank wheel. Or verify it's not flipped with a good picture diagnosis. There was a pic I once had because I had installed it flipped and it was not apparent except my car would never start. I must have checked the gap like 50 times.