Hello.

I have problems with my 89 350TPI Firebird. Runs not too smooth at idle and at around 1500rpm it backfires badly out of the exhaust and splutters. Have checked most things and timing is okay so have done my first datalog.

Is there anything obvious?? Really appreciate any help.

I have done a screen grab of the data at idle and at 1575RPM.

Thanks!!

 

Your target AFR is about 1/2 point leaner than stoich. Did you modify that value in the code?

You're also not in closed loop even though you're at operating temp. Your o2 sensor could be bad and causing you to run lean.

 

I haven't made any changes to the codes, have only read the existing conditions. I recently had the engine out and since putting back in and replacing various components had this problem. At 1500rpm the engine shakes badly and backfires. I seem to be getting intermittent spark.

Have replaced the O2 sensor with a heated o2 but no difference.

I ran some more tests today with the engine filly warmed up.

 

Can you take your data after about 5 minutes of running. This latest one is only 91 seconds in and you're still showing open loop. But at least monitor the Loop Status before starting to take data (should show closed). Until you get into closed loop, the ECM is not making corrections for the operating conditions. Learn Control should also show Enabled as well.

The data won't be useful until this above is correct.

 

Okay, I let the engine warm up and have attached readings at around 8-9 mins. The loop status is now closed but cannot get the learn control to show enabled? Below are the readings for 1500rpm and Idle. It will not rev beyond 1500 and just backfires constantly.

 

Your fuel trims (BLM and INT) don't appear to be affected by the problem. But since the ECM only sees the driver side (only side with an O2 sensor), it won't react to a problem on the passenger side.

I'd start by

1.) Looking at all the spark plugs for any fouled ones

2.) Inspecting and measuring the resistance of all the plug wires. The resistance will increase with longer wires, but if you see one with a resistance that's WAY out of family with the rest, that would be problematic.

3.) Measure the impedance of your injectors (again, they should all be in family with one another). You can also put a piece of hose to your ear and put the other end to each injector body while the engine is running and see if you can hear clicking. Maybe you have a dead injector.

4.) Could also be a bad vacuum leak on one of the intake runner connections. Maybe take the same hose and start listening for hissing around the passenger side runner flanges.