TBI electronic timing advance knock
02-08-2017, 01:54 AM
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TBI electronic timing advance knock
Hey there,
So this is a long one...
I have a 1993 Caprice Wagon with a 350 TBI with 93,000 miles. This problem started recently after doing a tune-up, changing the plugs and wires, new cap and rotor, and new ICM. New coil too.
So what's happening is that I have a knock. Sounds like pinging.. I only have it under slight throttle over idle when in park, or during idle when in drive. As soon as I'm around 1000rpm or so it's gone.
Here's the thing, if I unplug the EST bypass wire and/or also the ESC module the knocking is immediately gone.
I know how to set timing on a TBI and has set it with the wire unplugged and warm motor, right on 0*. Then once the wire is plugged backed in, the ECM reset and motor started again, I have about 16-17* BTDC at idle.
I have tried setting the initial timing at around 5* BTDC which made it even worse. I have also set initial timing at slightly retarded which made the knocking less persistant, but still present.
At this point, I have changed; plugs, wires, cap, rotor, ICM module (TWICE!), tried changing to a new ESC module with no luck, new coil, MAP sensor, TPS, knock sensor, EGR, and even the thermostat!
I have been to countless shops, even the local Chevy dealership to see if they could read OBD 1, which they couldn't. Nobody understand it at this point. Wires and grounds have been checked. Only code I had was 42, which disappeared after I reset the ECM.
Worth mentioning is also that the car runs amazing! No surging or hesitation and lots of power
Hopefully somebody has a clue, because I'm out of ideas!
cheers
So this is a long one...
I have a 1993 Caprice Wagon with a 350 TBI with 93,000 miles. This problem started recently after doing a tune-up, changing the plugs and wires, new cap and rotor, and new ICM. New coil too.
So what's happening is that I have a knock. Sounds like pinging.. I only have it under slight throttle over idle when in park, or during idle when in drive. As soon as I'm around 1000rpm or so it's gone.
Here's the thing, if I unplug the EST bypass wire and/or also the ESC module the knocking is immediately gone.
I know how to set timing on a TBI and has set it with the wire unplugged and warm motor, right on 0*. Then once the wire is plugged backed in, the ECM reset and motor started again, I have about 16-17* BTDC at idle.
I have tried setting the initial timing at around 5* BTDC which made it even worse. I have also set initial timing at slightly retarded which made the knocking less persistant, but still present.
At this point, I have changed; plugs, wires, cap, rotor, ICM module (TWICE!), tried changing to a new ESC module with no luck, new coil, MAP sensor, TPS, knock sensor, EGR, and even the thermostat!
I have been to countless shops, even the local Chevy dealership to see if they could read OBD 1, which they couldn't. Nobody understand it at this point. Wires and grounds have been checked. Only code I had was 42, which disappeared after I reset the ECM.
Worth mentioning is also that the car runs amazing! No surging or hesitation and lots of power
Hopefully somebody has a clue, because I'm out of ideas!
cheers
02-13-2017, 01:52 PM
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Car: 1991 RS Camaro
Engine: 350 TBI
Transmission: 700R4
Axle/Gears: 3.42 Posi
Re: TBI electronic timing advance knock
Is this a stock engine with a stock chip / tune?
Maybe try retarding the base timing slightly?
Maybe try retarding the base timing slightly?
02-13-2017, 05:51 PM
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Car: check
Engine: check
Transmission: check
Re: TBI electronic timing advance knock
Code 42 was set because of the open EST/BYPASS connector, this is normal. And with the SA firing at 0* BTDC, it won't ping.
As for the pinging, there are several reasons. A lot of carbon build up on the pistons raises the compression. A lack of octane in the fuel is another cause.
Getting the spark plug wires in the wrong locations (invalid firing order) is another cause of pinging.
RBob.
02-13-2017, 06:37 PM
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Re: TBI electronic timing advance knock
Yes, 100% stock. I'm the second owner.
I have tried retarding base timing to 4 ATDC. This does help a bit. It's not gone, but there's less knocking then. With the bypass then connected this sets idle timing at about 12 BTDC with it at 4 ATDC with unplugged wire. I can try to set it back even more but it doesn't seem like it's supposed to be like that. Plus I'm worrrid I'll loose too much power...
it idles at 500 in park.
Thanks for for the reply!
02-13-2017, 06:44 PM
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Re: TBI electronic timing advance knock
Unplugging the ESC module should have set code 43. With this code active the ECM also retards the spark advance some. Maybe why it doesn't ping then.
Code 42 was set because of the open EST/BYPASS connector, this is normal. And with the SA firing at 0* BTDC, it won't ping.
As for the pinging, there are several reasons. A lot of carbon build up on the pistons raises the compression. A lack of octane in the fuel is another cause.
Getting the spark plug wires in the wrong locations (invalid firing order) is another cause of pinging.
RBob.
Code 42 was set because of the open EST/BYPASS connector, this is normal. And with the SA firing at 0* BTDC, it won't ping.
As for the pinging, there are several reasons. A lot of carbon build up on the pistons raises the compression. A lack of octane in the fuel is another cause.
Getting the spark plug wires in the wrong locations (invalid firing order) is another cause of pinging.
RBob.
Yes, code 42 was set and I know that's normal... 43 was also set but then disappeared. Obviously because I had disconnected the ESC module... So nothing new or wrong with the codes. Just that whatever helps retarding timing gets rid of the knock.
Have tried up to 93 octane...no change.
I seriously doubt the spark plug wires are in the wrong order. Unless the shop that did it REALLY messed something up. Also, the car wouldn't be running as good as it is then. Again, it's not pinging under heavier load.