86 timing/idle issue
Thread Starter
Heel & Toe
Joined: Aug 2015
Posts: 17
Likes: 0
86 timing/idle issue
I have an 86 pace car and just rebuilt the engine and got everything up and running again. The only issue I am having at this point is the timing. I did the steps that the FSM says to do and still around 1200 in Park and 79 in drive.
When I set the timing at 0 with the timing connector unplugged everything is perfect all the way around. It is sitting at 72-78rpm in Park and 64 in drive. As soon as I plug the wire back in and crank it, it jumps right back up. I also disconnected the battery to clear codes.
Just put a new computer and prom in it also. Am I missing something? Why does it change as soon as that timing plug gets plugged back in...
When I set the timing at 0 with the timing connector unplugged everything is perfect all the way around. It is sitting at 72-78rpm in Park and 64 in drive. As soon as I plug the wire back in and crank it, it jumps right back up. I also disconnected the battery to clear codes.
Just put a new computer and prom in it also. Am I missing something? Why does it change as soon as that timing plug gets plugged back in...
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Because the ECM takes over the timing adjustment and sets it to 20°.
That's why you disconnect the EST connector -- to prevent the ECM from changing the timing. What you are doing is setting the base or mechanical timing -- the relationship between the distributor and crankshaft.
That's why you disconnect the EST connector -- to prevent the ECM from changing the timing. What you are doing is setting the base or mechanical timing -- the relationship between the distributor and crankshaft.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
I have an 86 pace car and just rebuilt the engine and got everything up and running again. The only issue I am having at this point is the timing. I did the steps that the FSM says to do and still around 1200 in Park and 79 in drive.
When I set the timing at 0 with the timing connector unplugged everything is perfect all the way around. It is sitting at 72-78rpm in Park and 64 in drive. As soon as I plug the wire back in and crank it, it jumps right back up. I also disconnected the battery to clear codes.
Just put a new computer and prom in it also. Am I missing something? Why does it change as soon as that timing plug gets plugged back in...
When I set the timing at 0 with the timing connector unplugged everything is perfect all the way around. It is sitting at 72-78rpm in Park and 64 in drive. As soon as I plug the wire back in and crank it, it jumps right back up. I also disconnected the battery to clear codes.
Just put a new computer and prom in it also. Am I missing something? Why does it change as soon as that timing plug gets plugged back in...
The timing should be set at 6 degrees not zero.
Thread Starter
Heel & Toe
Joined: Aug 2015
Posts: 17
Likes: 0
Because the ECM takes over the timing adjustment and sets it to 20°.
That's why you disconnect the EST connector -- to prevent the ECM from changing the timing. What you are doing is setting the base or mechanical timing -- the relationship between the distributor and crankshaft.
That's why you disconnect the EST connector -- to prevent the ECM from changing the timing. What you are doing is setting the base or mechanical timing -- the relationship between the distributor and crankshaft.
Thread Starter
Heel & Toe
Joined: Aug 2015
Posts: 17
Likes: 0
I cranked it cold this morning and the idle was great, right around 750 and then once it reached around 120 degrees it jumped up to 1200.
Thoughts? I'm so close to have this damn thing running right again....
Thoughts? I'm so close to have this damn thing running right again....
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
You set it to 6° and the computer adds 14° to get 20°, which is where it should be at idle. The computer changes the timing depending on RPM and load.
Racer
Joined: Apr 2003
Posts: 426
Likes: 0
From: Detroit MI
After setting the timing then setup the IAC.
It sounds like you have too much minimum throttle using the set screw and the computer can't adjust the idle using the IAC valve.
If you have a scanner look at the IAC counts.
It sounds like you have too much minimum throttle using the set screw and the computer can't adjust the idle using the IAC valve.
If you have a scanner look at the IAC counts.
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Melting Slicks
Joined: Jun 2013
Posts: 3,065
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It's sounds like under 120* is where you're problem is. Cold starts need to have high idles. Set the timing to 6* instead of 0*. The ECM retards timing by 5* when the engine is cold, probably why it's idling low when cold and higher when warm.
Drifting
Joined: Aug 2010
Posts: 1,704
Likes: 8
Since you have your engine rebuild and freshly mounted into your engine bay,you need to set the timing at 6 degrees mechanical ,as said above.That said, you need to adjust the base idle as x factory specs at .54 V at TPS sensor on the throttle .there is a procedure to do this,serch the FSM.only when your TPS is adjusted at .54 v and timing is set at 6 degrees you can evaluate your idling.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA