1997 Merc 5.7L 2bbl with Alpha I Gen II and Thunderbolt V ignition with no knock sensor module. Engine is a brand new long block at 29.6 hrs. Timing just doesn't seem to be correct when setting it. Incorrectly thought I had a TBolt IV since there was no knock control module and set timing at 10btdc and didn't like the way the motor was running. Compared the wiring at the ignition module with the Merc manual and found out I have a TBolt V. By the way, the 90-823225 manual states 8dbtdc but the cover on my flame arrestor states 10dbtdc.
Grounded the purple/white wire and adjusted the timing to 10dbtdc. RPMs are at 700 on a tach/dwell meter. Still don't like the way the motor runs. When I rev the motor from idle, it's not too hard to get it to pop out the carb before it revs.
Two things: First, the farther I advance the timing (with or without pur/wh grounded), the better the engine runs up to about 20btdc. It's not really missing or even running rough at 10dbtc, but the farther I advance the timing the smoother it idles and the faster the RPMs. At around 20dbtdc, it's idling at 850 RPMs. This doesn't seem normal. My experience back to when we used to set the timing "by ear" was you cranked the distributor till the motor was idling fastest and that was usually pretty close. In my case, this would be way off.
Second, when I remove the ground from the pur/wh, the RPMs actually go down about 50 RPM so the motor is running better in base timing mode. The timing retards about 2 degrees but it's hopping around a little bit also. I thought the ignition didn't muck around with the timing below 1200 RPMs and even if it did, since the motor runs better with the timing farther advanced, I would think it would be advancing the timing instead of retarding it.
Anybody able to explain this behavior or shed some light on this?
Grounded the purple/white wire and adjusted the timing to 10dbtdc. RPMs are at 700 on a tach/dwell meter. Still don't like the way the motor runs. When I rev the motor from idle, it's not too hard to get it to pop out the carb before it revs.
Two things: First, the farther I advance the timing (with or without pur/wh grounded), the better the engine runs up to about 20btdc. It's not really missing or even running rough at 10dbtc, but the farther I advance the timing the smoother it idles and the faster the RPMs. At around 20dbtdc, it's idling at 850 RPMs. This doesn't seem normal. My experience back to when we used to set the timing "by ear" was you cranked the distributor till the motor was idling fastest and that was usually pretty close. In my case, this would be way off.
Second, when I remove the ground from the pur/wh, the RPMs actually go down about 50 RPM so the motor is running better in base timing mode. The timing retards about 2 degrees but it's hopping around a little bit also. I thought the ignition didn't muck around with the timing below 1200 RPMs and even if it did, since the motor runs better with the timing farther advanced, I would think it would be advancing the timing instead of retarding it.
Anybody able to explain this behavior or shed some light on this?
