Topic: OBD-I Question After Header Install

[Kurlee Daddee]

So I installed my new exhaust system (Downey headers, high-flow cat, Magnaflow bazooka muffler) this weekend (Pics soon to come). I went to an exhaust shop yesterday to have the tailpipe section bent up over the axle. Runs good but its LOUD.

Anyways, my question is on OBD-I equipped vehicles, is there a learning curve for the ECU like on OBD-II vehicles? What I mean by that is in a OBD-II vehicle, when you take the negative battery terminal off and reset the ECU, it has a learning curve that it uses after the ECU reset. Is it the same for a OBD-I vehicle. I feel the low end torque this exhaust system gives me, but I think the ECU is holding back some of the power. What do you think? Do you think its necessary to adjust the mass air sensor after this install? I want the maximum performance from this modification.

[Blingn]

Is there a check engine light on? It might be in fail safe mode? 

Might give this a shot?

CANCELLING OUT DIAGNOSTIC CODE


After repair of the trouble area, the diagnostic code retained in memory by the ECU must be cancelled out by removing the fuse EFI (15A) for 30 seconds or more, depending on ambient temperature (the lower the temperature, the longer the fuse must be left out) with the ignition switch off. NOTE:
Cancellation can also be done by removing the battery negative (-) terminal, but in this case other memory systems (radio ETR, etc.) will also be cancelled out.
If the diagnostic code is not cancelled out, it will be retained by the ECU and appear along with a new code in event of future trouble.
If it is necessary to work on engine components requiring removal of the battery terminal, a check must first be made to see if a diagnostic code has been recorded.
After cancellation, road test the vehicle, if necessary, confirm that a "normal" code (No. 1) is now read on the "CHECK ENGINE" warning light. If the same diagnostic code is still indicated, it indicates that the trouble area has not been repaired thoroughly.

[Blingn]

I went off your 85 toyota efi in your sig line

[Kurlee Daddee [OP]]

I only get a CEL when I am on the freeway doing around 70mph. Once I decelerate the CEL goes off. Not sure why that happens. Maybe the header is scavenging more exhaust and allowing the engine to breath better? We used to pull the O2 sensor out of the exhaust stream a little bit with a spacer on turbo cars. Not sure if that would work in this truck. And yes its an 85'.

[emsvitil]

With the headers, you probably need to change the 1-wire O2 sensor to a 3-wire so it stays hot enough to function properly.

[Kurlee Daddee [OP]]

With the headers, you probably need to change the 1-wire O2 sensor to a 3-wire so it stays hot enough to function properly.

The exhaust system I bought came with what looked like a 4 wire O2 sensor. How do I wire that to the 1 wire coming off the harness.

[emsvitil]

You have to figure out which wire is which............

2 wires are for the heater (most likely same color)

The other 2 are the O2 sensor signal wire and the sensor ground.

The sensor ground is probably connected to the shell...........

Connect sensor signal to existing 1 wire.    Sensor ground to good ground.

For the heater wires, connect 1 to ground (not in same place as sensor ground) and other to 12v ignition source.

[Kurlee Daddee [OP]]

You have to figure out which wire is which............

2 wires are for the heater (most likely same color)

The other 2 are the O2 sensor signal wire and the sensor ground.

The sensor ground is probably connected to the shell...........

Connect sensor signal to existing 1 wire.    Sensor ground to good ground.

For the heater wires, connect 1 to ground (not in same place as sensor ground) and other to 12v ignition source.

Awesome. I will try that.

Am I correct that the harness coming off the 1985 SR5 pickup is indeed 1 wire? The previous owner  clipped off the original connector on the harness side and installed a female electrical connection to the O2 sensor side that still has the connector. When I stripped it back to extend the harness for the new position of the O2 sensor, it looked like it was 1 wire. But I couldn't tell if the insulation was part of the wiring or not.

[emsvitil]

86 was still 1 wire, so the 85 is too............

[Kurlee Daddee [OP]]

86 was still 1 wire, so the 85 is too............

Thanks Ed. I appreciate the help.