It does't matter whether you put the jumper in before or after the key is on. Put the jumper on first: The tests start when you turn the key on. Turn key on first: The test starts when you put the jumper in.
If you are using the check engine light (or you have a meter in the dash like I do) you put the jumper in first.
If you are working under the hood you do the key first.
When you pull the jumper to clear the codes, leave it out and turn the key off to finish-up the operation.
When you turn the key off, wait until the EEC primary power relay drops before you turn it on again. About five to ten seconds. You can hear it if you listen close. It's in the dash to the right of center.
The caution about not disconnecting the battery is because there are other things stored in the KAM (Keep alive memory) besides the error codes. There are tables with operating parameters stored in them that the computer will have to "relearn". It may run rough until the learning process is complete. Relearning the parameters may be a good idea after you get the bugs cleared up.
Of course we never disconnect the battery with the key on.
The two cylinder Onan engine in my Gravely tractor is built like that. It also has no distributor. The coil has two high voltage wires. one to each plug. The plugs fire simultaneously. One on the compression stroke while the other is on the exhaust stroke. It would be flat on top if the carb wasn't there.
21 and 24 codes, you may not have let it warm up enough before you ran the tests. Try disconnecting the battery for a few minutes. Then start and let it idle for a few minutes to see if you can clearup the 99 code.
Unplugging the jumper while running the KOEO test will reset the memory codes. So will disconnecting the battery.
The TAD (thermactor air divertor) vacuum line controls whether the Smog pump air is put into the exhaust system upstream or down stream from the O2 sensors. I suspect if the air is not going where the EEC "thinks" it is, it could screw up how the EEC interprets the O2 sensor reading.
The priorty sequence for multiple codes is to start with the first KOEO code and work through them one by one in order. Then the KOER codes.
I lost the lens off my tail light about seven weeks ago. I was parked in a tight spot and brushed against another car. I heard a slight click. When I got home I noticed the lens missing. Drove back to the scene of the crime but couldn't find it. Must have just loosened it enough that it blew off on the way home. Had to replace the whole assembly.
Anyway the shop manual says the lens is held on by a strip of butyl seal and you remove it by prying with a screwdriver.
To replace, clean off all the old seal and apply a new one. Taking care not to bunch or tear the seal while going around corners.
I don't know where you can get butyl seal stuff or if there is a substitute.
On your distributor, find the #1 plug wire. Thats passenger side front. Make a mark on the distributor base directly below the #1 wire port on the cap.
Take the passenger side valve cover off.
Take the distributor cap off.
Turn the engine over manualy with a socket wrench. Every other time that the timing pointer points at TDC the rotor should be pointing at #1 and both valves for #1 should be closed.
What kind of electrical trouble shooting tools do you have? Meter, 12 volt test light, anything?
It means the computer may be bad. It takes some very sophisticated and expensive tools to pin something like this down 100 per cent for sure. Especially without a process of elimination to eliminate some of the suspects.
So the best we can do is give you some insite in how it works and suggest what is most likely the problem.
I will say that if it still surges with the SPOUT disconnected and this is really an ignition problem, it is not the computer.
The Hall Effect mechanism in the distributor, that MasterBlaster suggested you check out, generates a pulse. The TFI sends this pulse the PIP (profile ignition pick-up) to the EEC. The EEC after making adjustment to timing, sends the pulse back to the TFI as a SPOUT pulse.
So take the steps suggested and post the results. Then we can buttstuffyze it further.
Spark out (SPOUT) is the wire from the EEC that tells the Thick Film Ignition (TFI) module when to pulse the ignition coil. The TFI is mounted on the distributor. Look at the cable plugged into the TFI. One of the wires has a connector that allows you to disconnect that one wire. That is the SPOUT. This allows the TFI to pulse the coil without control from the EEC. Your ignition timing will stay at the "base" timing of 10 degrees BTDC.
