Timeing Is Advancing At Idle
Thread Starter
Instructor
Joined: Jul 2005
Posts: 129
Likes: 0
From: Austin Texas
Timeing Is Advancing At Idle
My timeing is giveing me fits it will idle fine and then at the light or were ever I stop it will start off fine then climb to 1500 rpm. When I take off the esc wire the idle goes back to normal. This is on a modifided 85 383 any ideas?
Melting Slicks
Joined: Jun 2004
Posts: 3,032
Likes: 4
You esc system is probably detecting knock (real or otherwise) and is screwing with your timing, but I dont think I've ever heard of that messing with idle speed. I think a high idle like you describe comes from a vacuum leak, correct?
Racer
Joined: May 2006
Posts: 293
Likes: 0
It does if you know how it works. As soon as you set the base timing and plug in the EST, you will see a jump in the timing. The EST is programmed for the engine to idle with quite a bit more advance than the spec 6* base timing. When you disconnect the EST, the timing AND the idle speed drop.
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
An 85 under light load and 1600 rpm will run around 35 degrees advance.
If your idle is capable of reaching 1500-1600 rpm, you will see this much spark advance.
Most likely you have way to much min air, the IAC is stuck open, or you have some big vacuum leaks.
You still need alot of air to support 1500 rpm, independent of the spark advance (approximately 15-20 gm/sec airflow) so I think you have too much throttle opening or min air, another possiblity is high tps voltage adding IAC counts.
The IAC can provide about 8 gm/sec when fully open, so your throttle is adding at least another 8 or so, probably even more, since it is unlikely that the IAC is fully open.
Your min air adjustment should normally be set for around 4 gm/sec or 450-500 rpm. A little more air is desireable on a modded motor, but keep it within reason.
Back off on the throttle stop and readust the tps for proper voltage.
Target something like 10-20 IAC counts in a warm idle at the desired (programmed) rpm.
If your idle is capable of reaching 1500-1600 rpm, you will see this much spark advance.
Most likely you have way to much min air, the IAC is stuck open, or you have some big vacuum leaks.
You still need alot of air to support 1500 rpm, independent of the spark advance (approximately 15-20 gm/sec airflow) so I think you have too much throttle opening or min air, another possiblity is high tps voltage adding IAC counts.
The IAC can provide about 8 gm/sec when fully open, so your throttle is adding at least another 8 or so, probably even more, since it is unlikely that the IAC is fully open.
Your min air adjustment should normally be set for around 4 gm/sec or 450-500 rpm. A little more air is desireable on a modded motor, but keep it within reason.
Back off on the throttle stop and readust the tps for proper voltage.
Target something like 10-20 IAC counts in a warm idle at the desired (programmed) rpm.
