BelowRadar

Hi Folks - I've been posting my saga in my local forum here:

https://www.s2ki.com/forums/index.php?showtopic=776334

To boil it down - I've been fighting a P300, P301, P302, P303, P304, P410(occasional) misfire codes situation with no apparent cause for weeks. Finally, I seem to have narrowed the cause to the following scenario:

ECU pin A28 sends 5.7V down the control line to the Air Pump Relay, instead of the required 12V (Or battery Voltage). This causes the Air Pump to never turn on, but the ECU is thinking that it is operating. This causes the engine to run rich, occasionally causing a misfire due to too much fuel in the mixture, and soot-covered plugs. Also, it causes poor gas mileage and slightly less power output.

My questions to the community are these:

Given: new Honda ECU: $720 + $80x2 (keys) + Programming of Keys ~= $900
new AEM or other aftermarket ECU with lots more capability: $1400
I am an EE - not scared of programming the ECU, etc - in fact I would love that control.
Engine is currently stock - future FI or at least I/H/E plans.


1. Is there anything else I should check or do? It seems pretty clear to me that the ECU is bad, but I might be missing something. I followed the P0410 troubleshooting flowchart in the S2000 Service manual.

2. My logic is that I want a fancy ECU I can program, use better keys/fobs/maps/VTEC points/etc on anyway - is this a good excuse to upgrade?

3. If I did buy a new aftermarket ECU which should I choose? (it seems AEM is popular with the shops down here)

Thanks! I am very new to ECU swaps and mapping engines etc - I am teaching myself a crash course right now!

S2kRally

can you actually confirm the air pump never turns on via sound?

are you going about this using a honda manual?

s2k16803

If the ecu is your problem and you decide to go aftermarket.... get hondata. Capability wise its about the same as the aem but if need be, the kpro can pass emissions testing which is a good feature to have considering you won't have a working factory ecu....

S2k_MoZo

You can buy a used ECU for $150 to $250 easily.
If you really want to save money, just look up on that used parts website or craigslist, there are tons of ECUs out there for cheap!
All you'd have to do is get your key programmed from Honda and you'll be set.
Just my .02 cents.

BelowRadar

Yeah, I suppose swapping with a factory one is the cheapest. I just figure all the pain in doing that (key changeout etc) I might as well go aftermarket and gain some cool features?

So are there only two? Hondata vs. AEM?

BelowRadar

...Shameless bump... need some advice, please!

spectacle

I have a 01 ECU you can have for free. If it fixes your problem, have at it. But again, I doubt the air pump is your issue. Trust me on this.

BelowRadar

And the mystery deepens!

I was able to successfully swap Spectacle's 2001 OEM ECU with my own by doing the blank key trick specified in the service manual. Guess what? 5 minutes into running, cylinder 2 misfire code appears (302) along with P1399. After the drive back here to the office, we have the old friends P300, P301, P302, P1399. Still poor gas mileage with Spectacle's ECU, and the air pump is not running!

I need to now check that pin for voltage (A28) to see if Spec's ECU is driving the relay or not. But for right now - it seems that the ECU swap does nothing.

Dum dah dum dum dummmm.................

BelowRadar

Update:

Spectacle's ECU is indeed turning on the Air Pump properly. I was wrong, above. This means that at least that system is broken on my ECU.

Still getting these misfires. They seem to happen at low rpm, under load, or right after starting the car. Still all 4 cylinders and P300. I seem to get one at a a time, e.g. 302, then 300, then 10 minutes later 303, etc.

I am worried that it's the valves, but that doesn't make sense. Seems a bent valve would only affect its cylinder.

BelowRadar

Update: Dyno performed - 210hp/145tq! Obviously my valves and rings are ok. Also, O2 was at 12.83 at the end of the pulls, and the fuel/air setup confirmed that the mix was right.