need help with missfire

[DarkDragon]

Need help here guys/gals…

 

My 95 PF is acting up again. I just changed the plugs, wires, cap, & rotor not even 2 months ago. I cleaned the MAF and changed the fuel filter about 2 weeks ago. Yesterday, started acting like its misfiring. This is only happening when it warmed up, (want to say closed loop) and mostly under load. Once in a while in park or neutral. You can hear the backfire while trying to drive. Yet when the engine is cold, (open loop) and get the lubes up a few minutes…, it runs smoothly.

 

This happens under load as well. In park it free revs. I unplug the MAF and it free revs up to a certain point (rev limit, then the check engine light come on). So I want to rule the MAF out because the ECU sees it connected / unconnected.

I have no check engine light with this misfire.

 

could it be the o2 sensor? And the MIL pick it up. Will be checking for codes here in a minute.

 

Please help.

Thanks

Tony

[DarkDragon]

Ok here is the deal. The ECU had no codes.

So I did the following:

Checked battery voltage, 12.89v off and 14.39v car on.

Connected my AEM wide band o2 kit to the exhaust, and started the car.

WB- 16.2 AFR open loop / idle

WB- 16.6 AFR closed loop / idle

1200 RPM cold, down to 1000 RPM warmed up on all 6 plug wires (multi meter)

PF starts to stumble in park.

Using my digital multi meter at the ecu:

MAF Signal 1.103v / idle

MAF Signal 1.7v / light rev

O2 heater (-0.514v) (pin 106)

O2 signal (-0.262v) (pin 19)

O2 signal 0.214v heavy revving (pin 19)

 

Driving in my drive way, which is long enough to test a few things, the car was now smooth. My WB read 13.0 AFR in closed loop at WOT up to 30mph as I had to hit the brakes to slow down.

 

I did notice this odd thing, my WB was a steady 15.8AFR which equal to (-0.333v) at idle, 990-1000 rpm. What is this? Is my o2 going bad?

 

The ECU I have looks to be new. In any case the numbers on it are: H9 MECM-V260 A1 4831, if that means anything:

 

Also one last thing, I did notice a loose plug. It’s a blue with white plug, with female pins on it.

Colors are:

Orange White / Pink

Black / empty

Any ideal?

 

Thanks a bunch.

Tony

[DarkDragon]

it ended up being a bad o2 sensor....