87 2.8 MFI

Backfires between 1-2 shift from about 4500 RPM.

What I know is good:
Plugs, Wires, Cap/Rotor, Ignition Control Module, Timing, Vac lines.

What has been suggested:
02 Sensor, MAP sensor, Take it to a shop.


According to my Autoxray scanner... the car stays in open loop... until it's running down the freeway then it's in closed.... once I let off the gas coming to a stop it's in open for the whole city drive.

The idle doesn't come down very fast at all.


Any ideas?

 

Definately replace o2 sensor, because a bad one can keep you in open loop. Do that first, its cheap and easy, and then tell us what happens.

 

If it still backfires after the 02 sensor has been replaced , I think you can test your MAP with a multimeter . I know you can test a MAF with a multimeter . I don't know how , but Tom knows .

 

how much/easy is it to change the o2 sensor? and what exactly does it do?

 

If I remember correctly they are around $20.

Tip for removal-- run the car and get the exhaust warm to hot. Use gloves and be careful- this will expand the bung that the o2 sensor screws into and will make removal easy. They are next to impossible to get out when the exhaust is cold.

 

Mine is in the in the area of the pipe right before where the catalytic converter would be, after both left and right side pipes come together.

I think it just unscrews.

If your o2 sensor is bad, it can give false readings about how much air is going through your pipes and keep you in closed or open loop mode.

 

O2 is totally easy...but like AF said, hard as **** to get off without warming the pipes. Trust me..I tried....and succeeded....*** that was painful. And yeah it just unscrews..it's in the Y-pipe...sticks out horizontally. Just unplug the connection..it's way up top, just follow the thin line. With the pipe nice and warm, screw the old one out. Take the cap off the new one, and CAREFULLY insert it and tighten it down with a deep well socket. Be EXTREMELY careful with your new O2 sensor..they're very sensitive and can be damaged easily. Removing my old one completely broke it. Friend tried to use it and it didnt work at all. After tightening it, reconnect the pigtail and reset your ECM. Bam, done. Shouldnt cost any more than $20 for one..I got a Bosch replacement.

 

By the way.. Computer needs several things to check out to go to Closed Loop operation. One of which is that it has to receive a signal from the O2 sensor. If it doesn't, it can't switch to closed loop because it doesn't have enough data to run the car properly in closed loop..could cause a stall..therefore, the computer being as smart as it is, runs only in open loop.