Timing errors with AEM EMS-4 (crank sensor)
 

Car: 1994 w/ VVT Swap
ECU: AEM EMS-4 Series 2

I'm getting timing errors all over the place and the logs point to the crank sensor picking up teeth that aren't there, this causes a nice jolt as the car misses and has been a pain in my ass. AEM techs have advised me to put a pull-down resistor on the signal wire, and then an RC circuit in an attempt to filter it; however, still getting timing errors and the RC values are getting ridiculous (lol .5 milliseconds).

I am curious if I should just do Abe's NB Crank circuit (Schmitt trigger) and then just fuck with the AEM to make it either rising or falling edge. I have a track day that I'm trying to make in 2 weeks, but I've been fucking around with this timing error shit for almost a month.

Fun aside: the IAC also seems to be wrecking havoc (with the IAC plugged in, I get way more timing errors), so I've just unscrewed the idle screw and I'll just let it idle high.

I'll try to post with any requested information.

You shouldn't have to jump through hoops to fix your problem.
Sounds like a grounding problem. How is the sensor ground pin connected to the sensor ground in the car's harness?

Spliced the 94 CAS wiring into the individual crank and cam sensors. The power and ground are shared between the two sensors.

The signal wires from the crank and cam need to be shielded, ground the the shield to the engine block near the sensor.

I can move the drain to the valve cover real quick; it's currently grounded to the chassis. BRB.

EMS-4 is really sensitive about the crank and cam signals.

Just moved it over to the valve cover, still getting a shitload of timing errors with the IAC plugged in. I do get timing errors with the IAC unplugged; however, it seems like it isn't as violent; I just cranked the idle speed up to 1200rpm on the TB in the mean time.

Right now I'm running 16awg shielded to both the cam and crank from the factory 94 wiring and the shield drain is connected to the valve cover (like I've said about 5 times in this post) currently.

I have some 18awg, 3 twisted pair shielded cable I can use. Tie the +12V and GND on one pair, and then put the signal and a spliced GND to another twisted pair; tie the shield drain back to the valve cover.

Can you drive with the IAC unplugged to see if the timing errors are really gone, your IAC may bad or wired incorrectly.

The timing errors still increment with the IAC unplugged, but it's a lot less frequent.

I want to see what the twisted pair will do, and go from there. (fuckin' 5th time creating this harness shittttt)

Is the cable running near the coil pack or spark plug wires?

Nope. This is a bit outdated, but it's completely over the intake. The route is pretty similar (blue)

https://www.miataturbo.net/attachmen...ine=1364246990

Well, moving to twisted pairs didn't work. Still getting timing errors.

Isnt one of the sensors that came on VVT engines known to have problems (cam/crank) or was that the 99-00? You have me worring because I just wired mine in, and used the stock NA cas wiring. The NA cas wiring is not shielded and the wire I used to extend the crank sensor wiring isnt either. I didn't think shielding was really required with hall effect sensors.

I'm doing that Schmitt trigger circuit. If that doesn't fix it, I'm out of ideas.

Now to pay 5 dollar shipping on a 48 cent part.

I'm battling the exact same issue as you right now! I've been battling the timing issues for a few weeks now. We should compare notes...

I have a 95 car with 99 head and I've spliced in the wires exactly like you did. I used to have a shit ton of timing errors. I flashed my firmware to v24 and it actually got a lot better but I still have timing errors every few seconds. According to my logs the ems seems to be picking up extra crank teeth where there arent any (sharp drops in crank tooth period time). I thhought that might be due to noise so I've been all up and down the chassis searching for faulty grounds or ground loops and I can't find any obvious error. I'm in the process of running shielded wire all the way back to the ecu for cam and crank, but somehow I doubt that will fix it. So far the ems4 seems extremely finicky with these inputs.

What is this Schmidt circuit mod? I may have to try it as well...

I just fixed this (i think). Do the Abe NB circuit.

I don't have the trigger in yet, but the passive filtering (RC circuit tied to ground with the +12V pull-up) got rid of all of my shit. Now to bitch out Sav..

Can you tell me exactly what you did? Quick diagram would be cool if possible. I tried a. Rc before but I might have used all the wrong values. Or just wired it wrong.

Which crank sensor and trigger wheel are you gays using?
99+, or 94+?

I'm using the oem 36-1 wheel.

OEM by Ford?

Which crank sensor?