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Old 07-25-2010, 10:07 PM
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how to check 1987 4.3L chevy ignition timing

I just got a 1987 Camino with 4.3L V6. The car runs sluggish in overdrive going up a hill. I fixed a few things and now I want to check the timing. It has a small distributor cap (diameter about like on the old 73 Vega 4 cyl), no vacuum advance, and the sticker under the hood says to disconnect a single tan wire with a black stripe, NOT the 4-wire connector, and set it to 0. I can only see two sets of wires going to distributor - one two-wire connector, and the 4-wire connector. I see no single tan/black wire anywhere. I know timing shouldn't change, but the car is sluggish (like timing retarded) and the distributor clamp was loose. I have a generic Chilton manual (75-90 Buick/Pontiac) that say to short A and B on the ALDL connector, but not sure if this is right.

Any ideas, or good resources for this engine in general? I've had good luck with inet searches about other engines, but not this one - though have learned much changed with 4.3L's between 1985 and 1996.

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Old 07-25-2010, 11:08 PM
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More info. Couldn't wait... so shorted A-B, couldn't see timing marks, got under car and see harmonic balancer has a "step in it" (smaller diameter in front - about 1/2" wide) and mark is on back half (about 5/8" wide). The timing mark is about 3/32" wide, and the manual I have says there are two - "normal joes" should use the "thin" mark, and pros/dealers use the wide mark. I only saw one mark, but didn't check very much.

The timing plate on block is odd - only shows 0-12 BTDC and it extends out about 3/8" where ATDC would be so you can't see the balancer (mark) if it's on that side. And it only looks like the front part of the balancer can be seen anyway (I drew a line on the front part).

I got frustrated (old Pontiacs/Chevys are easy to see timing marks) and advanced the timing a bit (idle sped up), then took it for a ride. No knocking and the car runs MUCH better - no need to downshift from overdrive to get up my reference hill.

I'm not the type to time a car "by ear" and even if I could (or let someone do it) I still like to put a light on it to see where it's at. On older high comp engines, I'll set it to factory spec and if it knocks I'll back it off, but didn't try the opposite with this one (advance it til it knocks/runs bad, then see where it is).

This is a dumb setup for checking timing. There's also a small tube attached to the timing mark plate - I seen that before (on newer cars) and have no idea what it's for. I timed an 86 Cutlass with a 3.8L not long ago and it was easy (pull the 4-wire plug and set timing using easy-to-see marks).
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Old 07-26-2010, 06:16 AM
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Disconnect brown - white wire

The tan wire with the black stripe is a ESC to ECM data wire and it must be disconnected when the intial timing is set or checked.

That wire is looped out of the wiring harness for easy acess. The data wire and a in-line connector is located under firewall insuilation or carpet on the inside of the car, on the passenger side. Disconnecting the wire disconnects the ESC (Engine Spark Contol) module from the ECM (Engine Computer Module). The ESC is mounted under the hood, usually on the firewall. It has a four wire conmnector which must be left in place. One wire goes to the knock sensor, one wire is a ground, a wire is 12V, and the tan-black is the data wire to the ECM. After disconnecting the tan-black wire, set the initial timing at the crankshaft at 0 (TDC). Then reconnect the tan-black wire under the dash.
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Old 07-27-2010, 07:34 AM
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Thanks for info. Connector was behind alternator.

The part of the balancer I can see under the scale has no timing mark on it. I extended the mark from the insulated part of the balancer, but if I set it to 0, the engine dies, which it didn't do before so I know it would run worse (if it advanced enough to stay running when I reconnect the data wire).

I advanced the distributor a bit more and it hit a stop - is off scale but may be about 20 BTDC. I left it there and tested the car. It runs great with no knocking or change in running temp. With a little press on pedal, it will accelerate in OD now - this seems how it should run.

Any input on this?
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Old 07-27-2010, 08:53 AM
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Old school

Old school timing advice is: "Set the intitial timing advance where the engine runs best"

The ESC (Engine Spark Control-knock sensor) tan/black data wire connector is inside the car on the passenger side of the firewall, behind the padding, on my 1991 S10 Blazer 4x4. I don't understand why the tan/blk data wire would be behind the alternator on your pick-up.

Where is your ESC mounted? The ESC on my S10 Blazer is on the firewall on the passenger side (RH) side of the distributor. That is a central location for all four of the ESC connector wires. The knock sensor is on the back of the block, to the left of the distributor. The ESC was found to be retarding the timing as a result of valve train noise, so by at least 1991, the factory moved the knock sensor as far from the rocker covers and valve train as possible.
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Old 07-28-2010, 07:34 AM
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Connector was next to alternator and (I believe) ESC module is mounted on fender well above shock mount. I'm getting manuals for this car.

Yesterday I asked a mechanic about this and he said to do what I did (chalk a line for timing mark from back of balancer forward, disconnect the tan/blk wire, set to 0, then expect it to run crappy until the computer learns the new setting). I know it will run crappy like this/ESC won't compensate because it was probably set to +3 or +5 before. And the distributor hits another "stop" when I set it to 0.

I did find out there was no "stop" where I had it set because it was knocking bad when I left - backing it off a bit, I could feel a "resistive" spot where I'd had it set. I left it there since it runs good again with no knocking (using 87 octane).

Big mystery is it runs bad when set to 0. Is possible the ESC is bad because I've got it set around +20 with the plug disconnected, but it runs great so I'll leave it alone for now.

Took it out for a run again and is amazing how much better it runs. Easily accelerates up mild inclines without kicking down to Drive. Gas mileage will be much better. Now I know why people say the 4.3L is a good engine.
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Old 07-28-2010, 07:57 AM
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Quote:
Originally Posted by 60smotorhead
I just got a 1987 Camino with 4.3L V6. The car runs sluggish in overdrive going up a hill.
You're in overdrive going up hill, of course it's gonna be sluggish.
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Old 07-28-2010, 09:48 AM
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I agree it'd be sluggish going uphill in Overdrive, but it was chugging/slowing down fast and I had to push acc pedal halfway/downshift to Drive to make it up a moderate (2-3 degree) hill at 60-65 mph. Now it runs fine - slight push on pedal and it will slowly accelerate in OD up the same hill.

Will learn more about this/how to test after I get the GM manuals.
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Old 07-28-2010, 09:53 AM
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The wire you are looking for is a tan wire with a black tracer. It will be located either on the large harness by the dizzy in the passenger side firewall area, or in the car behind the golvebox, or at the passenger side carpet line area. If the initial is coming up at 20*, you do not have the right wire unplugged.
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Old 07-28-2010, 10:56 AM
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I'm fairly sure I have the correct wire because engine speed decreases when disconnected, and when set to 0, timing stays steady when disconnected, and jumps between 0 and +10 (as engine speed changes) when connected.

Attached is a photo. The wire/connector is in center and what I think is ESC module is just above reservoir.
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Old 07-28-2010, 11:24 AM
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Correct wire

That appears to be the correct tan/white data wire and the appropriate butt connector. However, I don't recognize the ESC module in that photograph. The tan/white wire looks as if it enters the wiring harnes next to the A/C drier/accumulator and the harness continues back towards the firewall. I cannot imigine where the tan/white wire would go in the direction of the alternator. Maybe it is just loops in and out of the wiring harness as it is supposed to do. That access location is more convenient than location on my 1991 S10 Blazer.

Anyway, you have found and disconnected the ESC data wire if the initial timing advance drops back to zero (TDC) and the idle speed decreases.
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Old 07-28-2010, 01:01 PM
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timing

I had the same problem. I could not find the PCM under the "glove box". i put a timing light on the mark to see where it was set to now. It was in the second notch. No timing numbers were visible so I guess this by normal timing marks to be 6 below 2 deg a mark with the furthest from the inductive ring being '0'. I understood the PCM controlled the timing after it is set to zero with the data wire disconnected so changing timing without disconnecting this wire was worthless. Where does BS come into the conversation??
I moved the distributer the small amount to get a 4 deg movement and got a 4 deg advance on the timing mark with the data wire still connected. How does that happen?? If you move the contacts on the distributer then the PCM has to comply with the move or the engine quits running. afer the distributer adjustment my mark is steady at "0" ?? I presume if the first mark is Zero. engine runs better and the stall at idle is gone.
OH yea it is a 89 4.3 with 192,000 miles on it. Must be the timing chain is a little stretched. Hope it holds for a while.
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Old 07-28-2010, 04:20 PM
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the ecm doesn't know where you set the distributor. it assumes at zero. if you moved it 4 degrees and the spark moved 4 degrees, the knock sensor didn't pick up any pings so the ecm has no reason to back the timing off a bit
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Old 02-27-2014, 11:27 AM
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Long delayed reply....

Ended up that some yo-yo had installed the harmonic balancer misaligned (keyway to timing mark) after they pulled the outer ring off at the rubber isolator - they must have hammered it back on. This car has a HB that needs a puller/installer to R/R it - I'd never seen that before.

With new HB, mark was easy to see and set when tan wire was pulled.
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