4 wire ECS distributor troubleshooting - El Camino Central Forum : Chevrolet El Camino Forums
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Old 12-23-2016, 10:25 PM
psychlopath psychlopath is offline
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Default 4 wire ECS distributor troubleshooting

So I have an 83 El Camino with a 305 that I'm working on that I think has some timing issues. It's all stock as far as I can tell and I just finished replacing a good portion of the cracked and rotted vacuum hoses and fittings for the smog, choke pull offs and other misc items.

The original problem that I was trying to solve was a high idle (About 1100 RPM) and dieseling during a hot shut-down that I thought was due to the high idle RPMs.

I was also asked to do a tune up so I replaced coil, cap, rotors, plugs and checked timing.

This vehicle has the 4-wire plug off the passenger side of the distributor, not a vacuum advance.

Checking the timing, per the sticker under the hood, I saw that the timing was advanced beyond the range of the indicator over the balancer.

I pulled the 4 wire plug on the dizzy, set the timing to the 2* indicated on the factory under-hood sticker, re-set the idle to 500 RPM and everything was groovy. I did all of this while plugging the port on the carb that goes to the flapper in the air filter housing that decides if the engine gets cool air or manifold heated air.

If the nipple on the carb that goes to the filter housing is left un-plugged, I get higher RPMs by about 300. Since that's basically a vacuum leak, I figured that's normal and set the timing with that nipple plugged...although only the RPMs and not the timing change if it's left open.

When I connect the 4 wire plug while the engine is running, the engine dies, as I think it should. But when I go to restart, the engine runs really rough and dies after about a minute of terrible struggle and won't chooch at all when put in gear.

I'm not sure sure where to troubleshoot next; I'm inclined to think that the ESC module could be bad, but I can't find much troubleshooting online and I don't really want to just throw parts at this thing.

Is there some troubleshooting that I'm missing or something else that I'm doing wrong?

The owner insists that a little dieseling on shutdown is a "Feature," of this engine, but I can't believe that's true. This thing should take off from a stop without a lag and should shut down with no problems as far as I can tell.

Thanks in advance for any help!
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Old 12-28-2016, 11:27 AM
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The ESC distributors only have electrical base and advance components. This means the ECM has full control of engine timing. There is always a base reference signal from the computer. The way to set the base timing is to unplug the tach. reference wire (tan/wht) connector between the distributor and the computer. Most times I have found it in the harness on the passenger firewall. Once disconnected, it eliminates any advance at all. This gives you base reference from the computer for setting the initial timing.Try that first, let me know how it does. I have other input on the original problem diagnostics. Chevy On...
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Old 01-02-2017, 03:14 PM
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I'm not at the car right this second, but I'll get to that tonight.

Is the reference wire that youre talking about the one that plugs in opposite of the 4 plug wire that would run the vehicle tach? If so, there is no reference wire plugged in there; I've been using the pin there to run my old dwell meter so I could use it's tach to set idle and fast idle RPM.

It's going to be a while before I can get back to this after tonight, as I'm leaving the country for a few months tomorrow.

Thanks again for your help...I'll be looking for that wire tonight and looking forward to ironing this out with you later.
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Old 01-02-2017, 04:17 PM
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welcome Dave
sorry I forgot all about your thread

everything for the computer is in the 4wire connector to the dist..
don't forget to clear the codes..

did it throw a code when the 4wire was disconnected??

does it have a knock sensor in pass side block coolant drain hole??

does the timing change with codes clear, and the 4wire plugged in??

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Old 01-03-2017, 10:31 AM
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High idle can cause run-on. definitely not a feature! Timing may be off if the balancer has slipped- a common problem. IF you set the timing with the mark in a bad position, timing can be way off. You can check the TDC mark on the balancer with the #1 piston to confirm if it is still properly indicating TDC.
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Old 01-07-2017, 04:08 AM
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need to verify exact point of TDC #1 on compression stroke. dieseling run-on is a feature that wil damage the engine rod bearings. tell him he is a moron. and hope he doesnt own any desirable engines... some of the early 80s light duty trucks had 3 wire with vac advance. our 82 K10 305 did. EST tag on tailgate and everything. not any more though, carb and distrib i replaced with 79-older stuff. and a 350 engine.

to set timing you unplug the computer side of the ignition control and set base timing then. not to ZERO like you did with TBI engines.
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Old 01-11-2017, 03:11 PM
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Default Base Reference Simplified

The base reference (voltage) I'm referring to, is a minimum voltage sent to the distributor from the computer. This voltage is the minimum setting for the 'RUN" operation of the distributor. Simply put, if there is no voltage to the distributor, it retards the timing below base. This is what it should do when the key is turned off, totally eliminating dieseling or run-on.
The tan/white wire I'm referring to, is one from the computer that advances and retards the timing with the computer's calculations from all the sensors in the system. The computer begins calculations at anything over 400 rpm. By disconnecting this wire only, you eliminate any kind of advance, without removing the "run" voltage. This is how to set the base timing.
I've always found a connector in the distributor harness at the passenger firewall where you can unplug it. It's an odd system... most times I only see this ignition in marine engines. Again, all wires to the distributor except the tan/white must be connected, including the tach wire. This maintains the base "RUN" voltage to the ignition module. I hope this helps makes sense of ESC "electronic spark control" distributors.
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Old 01-11-2017, 05:36 PM
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Quote:
Originally Posted by Fox C. View Post
I've always found a connector in the distributor harness at the passenger firewall where you can unplug it. It's an odd system... most times I only see this ignition in marine engines. Again, all wires to the distributor except the tan/white must be connected, including the tach wire. This maintains the base "RUN" voltage to the ignition module. I hope this helps makes sense of ESC "electronic spark control" distributors.
I've found this connection on my TPI setup, but the G-bodies ( carbed) all had the 4-wire plug that needed to be disconnected. This tan wire is one of the 4, and the only way to get the ECM out of the loop when setting timing is to disconnect this 4-wire plug.
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Old 01-11-2017, 05:40 PM
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no offence Carl
I don't think that's quite right ether..

when the car is dieseling,, the computer or timing or dist doesn't matter..
the key is off... where the spark is, is not the problem,, there is no spark ..
it is detonation or pre ignition, take your pick..

the tan or tan/white or tan/black,, which ever year model your working on??
the tan wire is basicly a reference ground for the computer,, by disconnecting the ground the computer cant do anything,,
it cant switch the relay and control the timing, so the other 3 wires don't do anything..
so the timing reverts to what ever you set it at,, that's what the computer calls no advance..
far as I know??? there is no difference in disconnecting the tan wire or the whole 4 wire connector..
it doesn't need any of the 4wire connector to run, or to set the timing..
and I believe??? on the early models the tan disconnect was behind the glove compartment..pita

this type ignition was used on everything except trucksfrom ~81 to 88ish.. [calif is different]
when everything carb went TBI,, except big trucks..
the TBI cars and trucks uses basicly the same system, with a little different setup, up till 93/96 or so...

the later ones got a knock sensor and the est module..

but I aint no expert ether..
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