Honda S2000 won't start at hot | AEM
2 posts / 0 new
Last post
Last seen: 1 year 4 days ago
Joined: 01/10/2015 - 18:37
Honda S2000 won't start at hot

Hi Aem, i'm a italian tuner and i work a lot with Honda Car / Engine :-)

I have a Honda S2000 AP1 with a rebuild engine (piston and rods combo) and also a Toda A2 Camshaft !

I use a AEM EMS 2 30-6052 in this car.

The car start at cold fast and every time i start the crank, but if i shutdown the engine when hot (Coolant over 80 °C) and i try to restart nothing happen.

I take a look at the log, and the Stat Synch'd is OFF so no fire to coil and no injector opening.

In the first i have work to the electrical wiring, with new ground cable from battery to engine, a new positive cable from the battery to starter motor and a new fresh battery Optima YellowTop 38 Ah. Now in the cranking the battery voltage stay around 11.8 Volts so it's fine.

After a few test i take a look at the log parameters for try to figure out where is the problem. I see, when at hot the car don't start , i have no Synch and i don't see the cam count in the cranking or if i see the cam count change the synch is off and the engine don't start.

I done a few test with a new cam sensor (The Ap1 have the VR sensor) , i made a new cam sensor harness directly from the ecu to sensor, change the distance from the sensor to the wheel tooth but nothing happen with the hot startup.

I use my scope to cam sensor and i see the wave when i crank at hot and not start..The wave have a peak at +0.3 to -0.3  Volts so after this check i change the cam H sens level to 0.08 and don't help

I try to change the crank H sens level to 0.08 and nothing, change the crank h sens below to 225 rpm ( my rpm cranking is about 200-220 rpm) but the car won't start at hot

All this test was done with 11.8 v in the crank session

If i use a extra battery to my car battery, it seem to help a little and the car start 4 time to 10 test at Hot engine.

I have measured the pin C20-C21 with the cam sensor disconnect and i have NO voltage so this is fine, the ground is present in one sensor wire, and the sensore Ohm is 2.55-2.6 Kohm

i have try to reinstall the firmware, downgrade the firmware but nothing change.


If i connect the stock ecu, the car start and run fine at Hot condition


I attach a few document, the scope cam signal at crank


Cam signal in cranking but don't synch and don't start

Cam signal with engine running at 80°C water temp


Last seen: 10 months 1 week ago
Joined: 08/31/2019 - 16:48
I am having a similar issue. 

I am having a similar issue.  Have you been able to figure it out?  My tuner is leaning towards an issue in the actual cam sensors.  Just very strange it is only when HOT.