davidh99

So this weekend I did not have an issue starting it and running it. Turned it off 6 or 7 times always restarted. It started yesterday at lunch time. But this morning I get nothing. Again seems the problem is no cam signal. I was having a problem starting it on Friday but after re gaping the crank sensor and having it hooked to a battery charger I got it started. So I though it may of been a weak CCA on my battery. I have a smaller battery then stock. And every time I have an issue with it starting it seems the air temp and coolant temp are at there lowest. I dont know if it is a setting that may not let it see crank because of temperature? So this morning I tried switching the battery with another Miata battery i have and it still did not work. Then I tried jumping the car with another car and still no start. Do you have any idea where I should look next for diag?

Braineack

iTrader: (62)

the 99 is notorious for bad cam sensors. you keep losing your cam sensor signal. put two and two together.

davidh99

Yea that is why I swapped it for the other cam sensor on my other 99 Miata and still the same issue. Can the sensor be bad and still run the car on factory computer?

Braineack

iTrader: (62)

if your composite log looks like this:



your MS is not reading a cam signal and the car will never start.

you need to figure out why the MS is not receiving the cam signal.

davidh99

Yea but it does start on megasquirt. Just not in the morning where the temp outside is less then 80. Last night I started it first try. Signal was there and everything ran fine.

davidh99

And last night turned the car off and on over 10 times started every time first try.

Braineack

iTrader: (62)

When it doesn't start, are you still syncing? are do you just have horribly tuned startup settings that prevent the car from firing?

davidh99

When it does not start I don't have sync. If it syncs it starts up no problem. I do have a smaller then factory battery in there and maybe the voltage is dropping too low during cranking to power the cam sensor?

davidh99

That is the tune I had on it that did not start in the morning and worked at night.

Braineack

iTrader: (62)

pretty sure the crank and cam sensors are powered off the same 12v feed...


what exact MS2 variant is this?

davidh99

And I know it works with the OEM computer because when I can not get it started I unplug the MS and plug in my MAF IAT and O2s and it starts no issue.

davidh99

It is a DIYPNP followed the diyautotune site to set it up. I have a alternator off of a NA Miata to get rid of the voltage regulation

Braineack

iTrader: (62)

I've never seen a DIYPNP with this issue, only thing i can think of is the pullup was incorrect on it.

davidh99

How could I test that it is the correct one? And would that be effected by the physical temperature outside?

Braineack

iTrader: (62)

with your voltage issues, you may want to move the VR2 pullup from 5v to 12v.

davidh99

What does the VR2 pull up do exactly?

Braineack

iTrader: (62)

provides the 5v pull-up on your cam signal.


when the cam passing along the sensor it grounds the signal, and the MS can read that, but it has to drop to ground from voltage. if no voltage is provided on the cam signal, there's no difference between grounded and not grounded. so we apply a little voltage to the signal, so the MS can see it floating at 5v and then drop to 0v when it's grounded. whenever it sees that, it knows the cam made a rotation.

the crank sensor has a 12v pullup, but with your battery issue, the voltage may be dropping too low from 5v for the MS to pickup a signal from it...

davidh99

Well without having to change the pull up. If I just put a much bigger battery in the car temporarily to test that should show if that is the issue? Or would I also need to change the pull up to 12v?

davidh99

I read this on the DIYPNP site

Cam Adjust: This lets you change the trigger voltage on the VR2 input. R20 increases the threshold trigger voltage, R21 decreases the threshold trigger voltage, and R39 can be adjusted to move it either way. If you already have information on what works for your sensors, solder a fixed resistor to either R21 or R20 as documentation recommends. For example, most Nippondenso ignitions work best with a 51K resistor in the R21 slot and R20 empty. If you’re having triggering problems and want to be able to adjust this yourself, leave R20 and R21 empty. Install R39 and adjust as needed to get a clean signal.

Do you think I could put a resistor in the R21 or would that make too much noise?

Braineack

iTrader: (62)

no.