Monday August 18, 2025
Engine Troubleshooting (Firewall Forward)
2.0 Hours

So the two main problems as of the end of yesterday were (1) a big RPM drop and rough running during the mag checks and (2) very rough idle that got worse throughout the day.

Here are the things I did today:

• Checked the manifold pressure sensor line and branches to the PMAGs to make sure it was all sealed up.
• Checked all of the fuel injector restrictors. None were broken or clogged.
• Checked resistance on all of the ignition wires...they were all okay.
• Double checked the ignition timing...it's still right on.
• Replaced all of the spark plugs with new plugs. I also cleaned the auto plug adapters and annealed the copper gaskets.
• Did another PMAG pull-through test. All plugs fired at the times they were supposed to.
• Torqued the new plugs/adapters and made sure the ignition wires were all really well seated.

Then I ran the engine again. The RPM drop during mag check is now ~100 RPM and there is no significant roughness. My suspicion is that one or more of the spark plugs were bad (like I dropped them or something) or some of the ignition wires weren't firmly seated.

Unfortunately, the engine was still idling like garbage. I plugged the sniffle valve drain line and ran the engine one more time without any change. So I gave up for the day and went home.

I figured I would start looking for induction leaks as the next step...

Previous - Index - Next





---

This work is licensed under Attribution-NonCommercial-NoDerivatives 4.0 International