CODES

This 91 has been here the whole time, through both Computers, so It actually lean, or the 02 is bad. What you can do is, take the 02's out and swap them around in the H-pipe.....Driver side to passenger side and pssenger side to driver side. Then Run the KOER test again, if Code 41 shows, then the 02 is bad, if code 91 is still there, then its in the wiring or an real Lean condition.

Note: dont move the harness with the 02. Actually un plug the 02 from its connector, then swap sides on the H-pipe or what ever is down there, then Plug them back in and code test.

Base idle setting proceedure is in the following sticky...
See the "Surging Idle Checklist for help with all your idle/stall problems. Everything you need to find and fix idle problems is in there.

The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

jrichker said:

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

The V8 computers will post a 4 when the engine is running and computer is jumpered into diagnostic mode. If you are looking to post an 8, it will never happen. A 6 cylinder computer would post a 3 under the same circumstance.

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I know I'm responding to an old post but I'm new to the scene and chasing some gremlins. I did a KOER test and the got an 8 instead of a 4. This is a 5.0. Any ideas as to why its and an 8 if it's supposed to be a 4?

Dart68 said:

I know I'm responding to an old post but I'm new to the scene and chasing some gremlins. I did a KOER test and the got an 8 instead of a 4. This is a 5.0. Any ideas as to why its and an 8 if it's supposed to be a 4?

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I would not worry about that. You may have a slightly different computer or an add on chip on the computer. The computers have what is called a "catch code" on the rear of the case opposite the electrical connector. and it varies by model year and transmission type. That may give you a clue as to why you got a different result.

The other possibility is that the computer did a cylinder balance test and you got the 8 as a result. That would tend to point to #8 cylinder being weak.

To get the cylinder balance test to run, you have to quickly step on the throttle and bring the engine RPM above 2500 RPM and then let off on the throttle. The engine will settle down to 1450-1600 RPM and shut off the injector on 1 cylinder at a time until lit has cycled through all 8 cylinders.. A perfect pass of the cylinder balance test will give you a 9 or 90 when it finishes. A cylinder test that didn't give a 9 or 90 displays the cylinder number(s) of the weak cylinders.