Ok fellas need some help here this problem seems to be far more advanced than me and my cronies can handle. I have a 89 HF with a B20VTEC in it completely stock except for the ECU which has a Hondata on it. Ok my problem is this, for some reason when i out it in reverse my CEL light comes on and the engine idles up to about 1700 rpm. Now Im not a pro but Im pretty sure that putting a car in reverse should not affect the engine rpm. The only CeL code I get is (6). Replaced that and still get a code and same problem when shifting into reverse. WTF?? Anyone have any ideas? Thnx.

 

Code 6 is the ECT, right?
If for some reason the engine shifts enough in it's mountings when in reverse, you could conceivably have a wire between the ECU and the ECT that is damaged and breaks contact. With an open circuit, the ECU will sense the engine is cold. That would explain the high idle and the CEL.

Why this wouldn't happen while you're bouncing down the road, I can't explain.

That's my theory anyway. Post back if you find the culprit because I'd like to know the cause.

 

You sure that you didn't accidently rewire the ECT to the reverse light switch?? When you shift into reverse the RLSW is closed completing a circuit with very low resistance... The only thing i see wrong with that is it is working in the complete opposite if something was wired wrong... As the ECT heats up resistance across the sensor drops.. So if the two were wired incorrectly and you put the car into reverse it should think that it is warm, NOT COLD... Perfectionist is probably right but i'm just thinking of other reasons to cause this... Just as he said it's just my theory, but let us know when you get it figured out... Latez