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I recently had a very strange issue with my timing. While driving the truck started running strange, idle was high, IAC was closed, then it started to detonate above 1/4 throttle. Everything else looked normal on the touchscreen. I limped it into the parking lot at work. Shutdown, then it cranked really hard when restarting. I suspected a timing issue. I had a timing light with me, and when I checked the timing was ~50° advanced! It was past the end of my timing marks running about 75° at idle. The cap & rotor were both tight.
Vehicle Specs:
'71 Chevy K30
427 BBC
Terminator EFI upgraded to the latest firmware.
GM small cap HEI controlled by Terminator.
Distributor: GM Performance with ACDelco ignition module.
Coil: ACDelco
Cap Rotor wires: MSD
I've been running the Terminator since 2016 and changed to the small cap with electronic timing control in 2017. I put several thousand miles on this setup with no issues.
About a year and a half ago the truck was running poorly, down on power, missing, backfiring under load, and making the exhaust manifolds glow red. It sat for a year before I started fixing it. I attributed it to a bad intake gasket fouling the plugs. After I changed the gasket out and put everything back together I verified the timing. It was very retarded. I thought that I had made a mistake marking the distributor before removing it. So I moved the distributor to bring back timing to 25° BTDC. After this the truck was running great. Likely the issue was always the retarded timing. Now it's jumped ahead last week. Seems like it’s probably the same issue causing the timing jumps in both cases.
Any ideas what could be causing these drastic and sudden timing swings? Cap & distributor are tight and not moving. Rotor is installed all the way, very little play. When the distributor was out a couple months ago the gear was in good shape. Didn’t check the roll pin that holds the gear to the shaft. So maybe. Could a loose cam chain allow the cam to skip and cause this? Seems like that would be making a ton of bad noise all the time so unlikely. Thanks for taking the time to read all this.
Vehicle Specs:
'71 Chevy K30
427 BBC
Terminator EFI upgraded to the latest firmware.
GM small cap HEI controlled by Terminator.
Distributor: GM Performance with ACDelco ignition module.
Coil: ACDelco
Cap Rotor wires: MSD
I've been running the Terminator since 2016 and changed to the small cap with electronic timing control in 2017. I put several thousand miles on this setup with no issues.
About a year and a half ago the truck was running poorly, down on power, missing, backfiring under load, and making the exhaust manifolds glow red. It sat for a year before I started fixing it. I attributed it to a bad intake gasket fouling the plugs. After I changed the gasket out and put everything back together I verified the timing. It was very retarded. I thought that I had made a mistake marking the distributor before removing it. So I moved the distributor to bring back timing to 25° BTDC. After this the truck was running great. Likely the issue was always the retarded timing. Now it's jumped ahead last week. Seems like it’s probably the same issue causing the timing jumps in both cases.
Any ideas what could be causing these drastic and sudden timing swings? Cap & distributor are tight and not moving. Rotor is installed all the way, very little play. When the distributor was out a couple months ago the gear was in good shape. Didn’t check the roll pin that holds the gear to the shaft. So maybe. Could a loose cam chain allow the cam to skip and cause this? Seems like that would be making a ton of bad noise all the time so unlikely. Thanks for taking the time to read all this.
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