Slow Down 5-8 and Cam Extension Rebuild

This is a guess, but if that were my car and I was experiencing this issue, here's where I'd start:

- My guess as to what's going on is that in the course of fixing the leaky cam extension, the shop had to remove the distributor cap, etc. In so doing, they loosened one of the ignition wire connections in the distributor cap. (My car is an '87 328, but I assume the ignition wires work the same ... the wires are inserted into connection holes in the distributor cap, then there's a small set screw that's tightened from inside the distributor cap that pierces the ignition wire, creates the electrical connection, and holds the wire in place). So, one or more of the ignition wires to bank 5-8 is intermittently failing, causing a misfire in that cylinder, sending raw fuel down the exhaust, which is then getting converted in the cat, causing the cat exhaust outlet temps to go up, triggering your "Slow Down" light.

Again, this is my initial guess, and it's where I'd start.

- I'd pull the spark plug wires from the plugs cylinders 5-8.
- Then I'd gently remove the 5-8 distributor cap from the cylinder head - don't remove any of the ignition wires from the distributor cap.
- Then I'd clip one lead of an ohm meter to the post that the ignition rotor spins by, and the other lead to the connector inside the spark plug extension at the other end of that ignition wire.
- Then I'd wiggle the ignition lead all along its length, especially at (i) the connector to the extension, and (ii) the connection to the distributor cap.
- If the lead is correctly and tightly fastened, the resistance reading should be some four-figure value (I recently tested mine, can't remember the numbers, but it will be lower for the shorter wires, higher for the longer wires).
- If the reading tends to jump around, especially going to infinity (open circuit) for a particular ignition wire, then I'd re-do that ignition lead connection in the distributor cap.

"But," you say, "the ignition wire set is new." Right, but the wire set is sold separately from the distributor caps, and the wires need to be correctly and securely fastened to the distributor cap in order to install the new wire set. So my hypothesis here isn't about a bad wire set, it's about a failed installation or a clumsy tech who was rough with the distributor cap while doing the leak fix. My limited experience (and maybe my own clumsiness) would suggest that the ignition wire connection to the distributor cap is easy to mess up.

If you do this, let me know what you learn.

 

Post 2 makes sense as a possible cause of the misfire; a "mechanic" putting in a can of fuel injector cleaner and thinking it will fix it does not!

 

I'm not suggesting they were. What I'm suggesting is that when the mechanic removed the caps from the distributor mounts and shoved the distributors to the side, and then likely kept jostling them as he was doing the re-sealing work, that in the course of doing all that one or more wires were slightly loosened in their mounts in the distributor cap.

Basically, yes, if the "readings [you] get" are in ohms, but - and this is probably just semantics - you can't really do a straight "continuity test" on ignition wires because the wires themselves have pretty high internal resistance compared to plain copper wire. It's easier to set your DVM to ohms to read what the total resistance in the wire is. I'm doing this from memory, but my wires were in the neighborhood of 700-900 ohms for the shortest wire and maybe 5000-ish ohms for the longest? What you're looking for are readings in the hundreds or thousands of ohms. You just don't want to see infinity or something in the hundreds of thousands of millions of ohms.

In my mind, a plain "continuity test" is just setting the DVM to give you a beep if there's a closed circuit, and my Fluke won't beep over 40 or 50 ohms (or something like that). Again, to-mahto, to-mayto.