Delco EST High Idle

[itxone]

The deets: 1987 5.7L, Holley Carb (fresh rebuild), Sierra Delco EST Distributor, New plugs, wires, starter, fuel pump.

The problem: After setting the timing to 8 degrees BTDC and removing the timing harness the engine dies. When I start it back up (with timing harness disconnected) it runs fine but idles at about 1300 rpm (20 degrees of advance). Leaving the harness connected and shutting off the engine has the same results.

I've been pouring over various delco est related posts but haven't seen anyone with this particular issue. Anyone have any thoughts as to what the issue might be?

 

[alldodge]

A 1987 350 used TB4 ignition. With the TB4 the shift interrupter grounded one lead on the distributor.

To use the EST the switch needs to apply 12V and not a ground.

Did you change the setup?

 

[itxone]

A 1987 350 used TB4 ignition. With the TB4 the shift interrupter grounded one lead on the distributor.

To use the EST the switch needs to apply 12V and not a ground.

Did you change the setup?

The previous owner had one of those auto MSD ignition setups in it. I ripped it all out and replaced it with the EST. I didn't modify anything around the shift interrupt. I'll check my wiring in the morning and get back to you.

 

[Paintman1960]

The previous owner had one of those auto MSD ignition setups in it. I ripped it all out and replaced it with the EST. I didn't modify anything around the shift interrupt. I'll check my wiring in the morning and get back to you.

Not good, at all !!
Did it a vacuum advance too ??

 

[itxone]

Not good, at all !!
Did it a vacuum advance too ??

It was last fall when i trashed it but I don't recall it having one.

 

[dubs283]

fyi MSD does make a marine ignition system that utilizes the same theory of operation as the thunderbolt ignition system. it is offered as a direct replacement for the thunderbolt system however ime it does not have the same durability as the thunderbolt

as AD stated previously the delco system closes (provides voltage through) the shift interrupt switch to activate whereas the thunderbolt system opens (prevents voltage passing through) the shift interrupt switch

the delco system was commonly (but not always) used on early alpha efi packages

 

[itxone]

Took a couple of pictures of the shift interrupt connection to the distributor. I've also attached a picture of the wiring diagram that came with the new distributor. The one difference I see is that I don't have the "coil to ignition splice lead". I might have overlooked the significance of this step in the directions. Could this be causing the excessively high idle? Seems unrelated to me but what do I know..

 

[alldodge]

A connection needs to be their to be able get the drive back into neutral when on the water. It not being there should not have caused the high idle.

Disconnect the throttle cable at the carb and see if it idles down, or it can be adjusted to idle down

 

[dubs283]

as AD stated previously the delco system closes (provides voltage through) the shift interrupt switch to activate whereas the thunderbolt system opens (prevents voltage passing through) the shift interrupt switch

re reading this along with the rest of the thread i realize i misspoke.

in both instances the shift interrupt switch closes but for the delco system the switch provides voltage to the module for ignition interruption whereas the thunderbolt directs voltage to ground providing the interruption

based on your op, the issue of high idle appears to be distributor/timing/module related in that you are verifying the timing is advanced to 20 degrees BTDC where it should be hovering around 8 degrees in "normal" mode

i am not familiar with the sierra brand delco est system but would guess it is similar to the gm based style if not the same. on volvo carbureted systems the shunt has 12 volts (+) applied to the lead to engage base timing mode. not sure if that helps or if the shunt you are using is the same that plugs into the two wire harness connection on the module

 

[itxone]

A connection needs to be their to be able get the drive back into neutral when on the water. It not being there should not have caused the high idle.

Disconnect the throttle cable at the carb and see if it idles down, or it can be adjusted to idle down

I had the idle screw on the carb backed all the way down until it wasn't touching the throttle.

 

[itxone]

re reading this along with the rest of the thread i realize i misspoke.

in both instances the shift interrupt switch closes but for the delco system the switch provides voltage to the module for ignition interruption whereas the thunderbolt directs voltage to ground providing the interruption

based on your op, the issue of high idle appears to be distributor/timing/module related in that you are verifying the timing is advanced to 20 degrees BTDC where it should be hovering around 8 degrees in "normal" mode

i am not familiar with the sierra brand delco est system but would guess it is similar to the gm based style if not the same. on volvo carbureted systems the shunt has 12 volts (+) applied to the lead to engage base timing mode. not sure if that helps or if the shunt you are using is the same that plugs into the two wire harness connection on the module

You're correct about the shunt. When I connect it to a 12v power source the system does enter base timing mode. When I disconnect it from the 12v power source the engine immediately turns off.

I may have to call Sierra tomorrow and see if their techs can advise me on the situation.

 

[alldodge]

I had the idle screw on the carb backed all the way down until it wasn't touching the throttle.

But still need to remove the throttle cable from the carb. The cable might need adjusting to let the carb idle slower

 

[itxone]

But still need to remove the throttle cable from the carb. The cable might need adjusting to let the carb idle slower

Hey, you were right! Much to my surprise there was a tiny bit of tension on the throttle. Backed it off and I'm now idling around 1K rpm. Still too high but much better... Haven't tackled the shift interrupt connection issue yet.

 

[alldodge]

It doesn't have a return spring so to speak like on a car. Adjust the cable so it just slides on, then remove and add one additional turn to apply a little pressure holding it closed

 

[itxone]

It doesn't have a return spring so to speak like on a car. Adjust the cable so it just slides on, then remove and add one additional turn to apply a little pressure holding it closed

Got it.. I'll do that.. Thanks!

 

[itxone]

Ok, so looking over the wiring diagram that came with the new distributor and have some questions regarding the shift interrupt connection as I suspect I have it incorrectly wired up presently.

• I have the shift interrupt lead going from the distributor to one side of the shift interrupt switch (white wire in the picture).
• The green wire on the other side of the switch is grounded. Should this be rerouted to the ignition lead (as per #6 is the diagram)?

 

[alldodge]

The green wire on the other side of the switch is grounded. Should this be rerouted to the ignition lead (as per #6 is the diagram)?

Yes
As in post 2, you need the other side of the switch to go to 12V power when the key is ON. Meaning it goes to the purple wire that goes to the + side of the coil, or spliced off another purple wire location like the excite lead on the alternator

 

[itxone]

Yes
As in post 2, you need the other side of the switch to go to 12V power when the key is ON. Meaning it goes to the purple wire that goes to the + side of the coil, or spliced off another purple wire location like the excite lead on the alternator

Got it. I was second guessing myself and was worried i might damage something by wiring it up incorrectly. Thank you!

 

[itxone]

Yes
As in post 2, you need the other side of the switch to go to 12V power when the key is ON. Meaning it goes to the purple wire that goes to the + side of the coil, or spliced off another purple wire location like the excite lead on the alternator

Well crap, I think I screwed things up by completely removing the ground when I should have kept the ground and added a second wire from that same connection point and running it to the purple wire. I corrected this but now all i get is a click when trying to start it. Perhaps I fried the starter solenoid?

EDIT: I tried jumping the solenoid. Got a brief spark then seemed to lose all power. Starter did not engage. I had the blower running and it immediately shut off.

 

[itxone]

Side note.. This version of the 5.7 does not have the 90 amp fuse on the starter. I guess my next step is going to be replacing the solenoid relay.