Bypassed esc now truck runs awful.

[Jcj1986]

I recently bypassed the esc on my 86 because the box was bad and would not produce spark. The truck ran very smooth before the box went out but now has a miss. Ive adjusted the timing like a few guys suggested but it still misses. New plugs, wires, cap, rotor, coil as well. Ive also made sure the firing order was correct and it is. When you rev it up it clears up and then returns to a smooth idle but after a couple seconds it starts stumbling like a plug is knocked out. The vacuum lines are also in good shape. It also wants to die when you put it in gear. Is there anything controlled by the esc that can cause this from bypassing it? Thanks.

 

[RoryH19]

I've done this bypass before on my k5 before I LS swapped.
It worked well. The ESC died and the truck didn't start until I bypassed.
Here is link:
http://www.73-87.com/7387garage/drivetrain/escrepl.htm

toward the bottom.

 

[Jcj1986]

I did the exact same bypass but its running horrible.

 

[QBuff02]

Have you taken the distributor apart and inspected the weights, pins and bushings underneath the rotor inside the cap? A lot of times exactly what you're describing is the weights over-traveling when returning to idle and it retards the timing way too much (late) and makes an engine sound like you describe. The components underneath the rotor get so ate up and worn that it simply can no longer hold the correct timing. but when you blip the throttle it clears up, until there is a drop in rpm (such as putting it into gear) and then the weights will actually go over center the wrong way and the timing goes late and makes it sound like **** until you put your foot into it again. Don't have a lot of experience with esc, but I'd put my money on the distributor being the problem. Rebuild the distributor or replace it and I bet the problem goes away. Most times a new one is cheaper and more cost effective than rebuilding though, just fyi.

 

[4WDKC]

Have you checked the spark gap? I read this was a problem with the 96-01 vortec 350 and cause the truck to idle poorly but ran fine. Reducing the gap corrected the issue.

 

[Rusty Nail]

before I LS swapped.

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[Jcj1986]

Have you taken the distributor apart and inspected the weights, pins and bushings underneath the rotor inside the cap? A lot of times exactly what you're describing is the weights over-traveling when returning to idle and it retards the timing way too much (late) and makes an engine sound like you describe. The components underneath the rotor get so ate up and worn that it simply can no longer hold the correct timing. but when you blip the throttle it clears up, until there is a drop in rpm (such as putting it into gear) and then the weights will actually go over center the wrong way and the timing goes late and makes it sound like **** until you put your foot into it again. Don't have a lot of experience with esc, but I'd put my money on the distributor being the problem. Rebuild the distributor or replace it and I bet the problem goes away. Most times a new one is cheaper and more cost effective than rebuilding though, just fyi.

I believe ill take your advice .Im just gonna replace the distributor. A mechanic that has worked at chevy dealerships since the mid 70s told me they used to swap the 80-86 distributors with ones from earlier models because the esc systems are very efficient when they work but aren't very dependable. He was surprised the esc box in mine lasted this long.

 

[Jcj1986]

Have you checked the spark gap? I read this was a problem with the 96-01 vortec 350 and cause the truck to idle poorly but ran fine. Reducing the gap corrected the issue.

The plugs are correct gap. I saw your reply and pulled every one to check gap. They're at 35.

 

[Rusty Nail]

That was a great idea @4WDKC .

 

[Dana W Iverson]

It you bought the truck or swapped to a 350 and used the original 305 carb and distributor on from the original engine, the truck will have no balls and run like crap, no matter what you do to the rest of the 305 motor, the 350 is not designed to run that electric carb and distributor ****, it's that AFR/timing thing (AKA 305itis), buy a nice vacuum advance distributor from a pre 80s or so without all the electronics The stock intake is for a spread bore so if you use a square bore carb you can just buy an adapter plate for 35 bucks or swap out the intake to a dual plane edelbroc performer or street dominator and a holley 650 if the 350 motor stock, completly eliminate the electronics that run the electric carb and timing............so if in fact you have a 350 in your truck that originally came with a 305, look at your carb and if it has wire connectors on the front that connect to your distributor do as I said above, you'll be happy you did. D

 

[Dana W Iverson]

It you bought the truck or swapped to a 350 and used the original 305 carb and distributor on from the original engine, the truck will have no balls and run like crap, no matter what you do to the rest of the 305 motor, the 350 is not designed to run that electric carb and distributor ****, it's that AFR/timing thing (AKA 305itis), buy a nice vacuum advance distributor from a pre 80s or so without all the electronics The stock intake is for a spread bore so if you use a square bore carb you can just buy an adapter plate for 35 bucks or swap out the intake to a dual plane Edelbroc performer or street dominator and a vacuum secondaries Holley 650 if the 350 motor stock, completly eliminate the electronics that run the electric carb and timing............so if in fact you have a 350 in your truck that originally came with a 305, look at your carb and if it has wire connectors on the front that connect to your distributor do as I said above, you'll be happy you did. Did I miss anything?
Later, D

 

[85 CA SIERRA 1500]

Try richening up the idle mix a bit, the ESC system uses a very lean idle mixture to cause the emissions to run a bit cleaner. Does your carb have the electronic solenoids that richen the idle mix? If so then it is definitely too lean cause the solenoids use the ESC of the distributor to tell them when to activate

 

[Jcj1986]

It you bought the truck or swapped to a 350 and used the original 305 carb and distributor on from the original engine, the truck will have no balls and run like crap, no matter what you do to the rest of the 305 motor, the 350 is not designed to run that electric carb and distributor ****, it's that AFR/timing thing (AKA 305itis), buy a nice vacuum advance distributor from a pre 80s or so without all the electronics The stock intake is for a spread bore so if you use a square bore carb you can just buy an adapter plate for 35 bucks or swap out the intake to a dual plane edelbroc performer or street dominator and a holley 650 if the 350 motor stock, completly eliminate the electronics that run the electric carb and timing............so if in fact you have a 350 in your truck that originally came with a 305, look at your carb and if it has wire connectors on the front that connect to your distributor do as I said above, you'll be happy you did. D

It you bought the truck or swapped to a 350 and used the original 305 carb and distributor on from the original engine, the truck will have no balls and run like crap, no matter what you do to the rest of the 305 motor, the 350 is not designed to run that electric carb and distributor ****, it's that AFR/timing thing (AKA 305itis), buy a nice vacuum advance distributor from a pre 80s or so without all the electronics The stock intake is for a spread bore so if you use a square bore carb you can just buy an adapter plate for 35 bucks or swap out the intake to a dual plane edelbroc performer or street dominator and a holley 650 if the 350 motor stock, completly eliminate the electronics that run the electric carb and timing............so if in fact you have a 350 in your truck that originally came with a 305, look at your carb and if it has wire connectors on the front that connect to your distributor do as I said above, you'll be happy you did. D

I found the culprit. A vacuum leak in the carb. I rebuilt it and solved the issue. Its got a 290 hp GM crate in it. It always ran great before the esc went out, before as in a daily for 6 years, but since i bypassed it, adjusted the timing and rebuilt the carb its back to normal.

 

[Jcj1986]

Try richening up the idle mix a bit, the ESC system uses a very lean idle mixture to cause the emissions to run a bit cleaner. Does your carb have the electronic solenoids that richen the idle mix? If so then it is definitely too lean cause the solenoids use the ESC of the distributor to tell them when to activate

The carb had a vacuum leak. I rebuilt it, adjusted it and the the timing and now its running solid. Appreciate it