Hello everyone! My first post, and I require some assistance on a project my shop has been working for the past few weeks.

Basically, we acquired a 95' Civic project, that already had a D15B7 block, Z6 head, Z6 manual harness, P28, and the remaining parts necessarily for a mini-me build. Well we completed it successfully, and it starts and runs nice and smooth.

Unfortunately, it appears that the computer is stuck in closed-loop. The computer does not respond when the coolant sensor is unplugged, nor if the O2 is unplugged. Also, with a A/F gauge. If the O2 is unplugged from the computer, the A/F reads both full Lean and full Rich, indicating that it is osculating back and forth very rapidly. With the O2 plugged in, there is no reading.

Any ideas?

 

Does the engine warm up to normal temperature? Check that thermostat is the correct stock one, I think it should be 85 C.

When you unplug the ECT sensor (which is under the distributor with two wires, the one on the thermostat housing controls the fan not the ECU), the CEL should come on. Make sure the CEL passes the bulb test, should come on when you turn the key on and don't start. It's possible for the ECT to be out of calibration but not bad enough to throw a code. Test it with an ohmmeter. Resistance is in the service manual or compare to a new one that is at the same temperature.

Also it's possible to swap the plugs on the IAT and the purge valve, this causes a mixture problem due to faulty IAT readings. I don't have a lot of faith in those fuel air meters. If it runs OK, no CEL, passes smog test if required, and good gas mileage, leave alone.

 

The engine does indeed reach operating temp, the thermostat opens, and the fan kicks on when needed.

With the ECT unplugged, the CEL does indeed come on, as it does with the O2 unplugged. I'll check the ECT though.

I'll check the IAT and Purge plugs. The reason I initially hooked up the A/F gauge is because it doesn't run right. It's VERY sluggish below , say, 3K, and even then it's slow. You can't even chirp the damn tires, so I know something quite wrong. The A/F gauge is known to be in good working condition, and it has even been connected to a healthy D15, and it swept back and forth normally.

 

Ok, tried a few things tonight.

Unplugging the ECT does cause the idle to jump up.

Unplugging the O2 does nothing. With the O2 plugged in, the A/F gauge shows nothing. With it unplugged from the harness, it reads full rich.

Purge and IAT are correct.

Engine is warming up and thermostat is opening. Fan kicks on.

It runs the EXACT same with 4 different computers. 3 P28's, and a P06. All run the same.


ALSO, unhooking the FPR line, and plugging the intake nipple cause the engine to idle around 400 RPM. Is that normal?