No vac dizzy

[VileZambonie]

No, it appears to be an ESC distributor is what I am referring to.

[Chevygold]

Pardon my ignorance but what is a ESC distributor? I have a new cap which is the same as the one fitted, bought it as the contacts in the cap are very badly corroded/burned, I cleaned them as best I could but they're still not great. When I put my test machine on and did the cylinder cut test results were pretty much even except cylinder 4 which didn't drop much suggesting it wasn't doing much.
Graham

[VileZambonie]

Electronic Spark Control. ESC Distributors are to be used with an ECM, Knock Sensor, Vacuum controls and are for retarding the ignition timing if spark knock is detected. What you have is an anti-performance distributor.

You want a standard HEI vacuum advance V8 distributor.

[Chevygold]

Here's a couple of pictures of what I've got, no weights, 7 pin ignition control module and no provision for a vacuum unit so looks like I'm in the market for a new distributor, wish I'd pulled it sooner now! Any suggestions and any to avoid?
Thanks
Graham

[Chevygold]

And another

[bd]

Graham, your earlier narrative regarding ignition timing advance increasing to 11 BTDC at 3,500 RPM caught my attention. 

@ Vile:
Do you know whether an ESC distributor module has a built-in timing curve?  I've never had reason to question this until now and assumed that timing was strictly dictated by external input from the ECM, modified by the ESC module.  If my assumption is true, why is ignition timing advancing with no ESC module connected to the distributor?  Although one might expect a worn timing chain to retard timing, I wonder if validating the timing chain condition while waiting for a replacement distributor is prudent.

[Chevygold]

Hi BD, it was a definate 11 degrees consistently repeatable, timing chain is quiet and timing is dead steady so I can only assume advance is made in the ICM hence the extra connections.
Been looking at replacement units and Amazon have one at a good price with good reviews, Voltstorm, also a Proform from a UK supplier I've used before but that's about a third more. Still looking but not many options, current exchange rates make buying from the USA less attractive :-(
Graham

[Chevygold]

So I won this MSD 8362 Distributor Street Fire on fleabay for £89 needs the ICM replaced which I happen to have so figers crossed it all goes according to plan, I could do with a stroke of good luck for a change, got a set of plugs on order as I broke 2 getting them out, the joys of headers!
Will update once it's all back together.
Graham

[VileZambonie]

The HEI/EST is used on models with Computer Command Control (C-3) or Electronic Fuel Injection systems. The system utilizes a distributor similar to the unit used with conventional HEI systems that has been modified to allow spark advance to be controlled by the fuel control system Electronic Control Module (ECM). Modifications to the distributor include a revised ignition module, with additional terminals to receive signals from the ECM, and the elimination of the conventional centrifugal and vacuum advance mechanisms. In addition, some models use a Hall effect switch mounted above the pickup coil in the distributor to provide a reference pulse to the ECM. The ignition coil on HEI/EST systems is mounted either integral with the distributor, Fig. 1, or remotely mounted, Fig. 2, depending upon engine and application.
Primary current switching in the HEI/EST system is performed by the ignition module based on reference pulses from the pickup coil as in conventional HEI systems. However, all spark timing changes in the HEI/EST system are performed electronically by the Electronic Control Module (ECM). The ECM monitors information from various engine and vehicle sensors, determines the correct spark timing and signals the distributor to change timing as necessary. An EST bypass circuit is incorporated into the ignition module to allow ignition in case of ECM failure and to allow base timing adjustment.
On some HEI-EST systems, Electronic Spark Control (ESC) is used to retard ignition timing when detonation occurs. The ESC system consists of a knock sensor, distributor module and controller. The knock sensor is an accelerometer or magneto-strictive device, mounted on the engine block. It detects the presence and intensity of detonation by vibration characteristics of the engine. The sensor's output is an electrical signal which is sent to the controller. The controller is a hard-wired signal processor and amplifier which operates from 6 to 16 volts. The ESC controller processes the sensor signal into a command signal to the distributor to adjust spark timing. This is a continuous process monitoring and controlling detonation.
When detonation is detected the spark advance command is delayed, providing the level of retard required. The spark is retarded for 20 seconds, then the spark control returns to EST. The amount of retard is determined by the controller based on the severity of detonation. A failure of the sensor would allow no retard, while controller failure would be indicated by no ignition, no retard or full retard.

[VileZambonie]

Make sure you ohm the pickup coil before replacing the module.

[Chevygold]

Ran the following tests on the existing unit and everything tested good pick up was 500 ohms and infinity to ground on both wires, BAT to TAC gave 0.5 ohms and infinity to ground so coil looks good so while I'm waiting for the MSD I'm putting it all back as was just in case I need to move the truck. Will check everything over on the MSD when I get it, all I'm waiting for now is a set of plugs and a selection of plug sockets to deal with the awkward one!
Graham

[Chevygold]

MSD arrived and so far having gone through it from top to bottom I can't find anything wrong with it, only thing I did find was that the centre contact under the coil was wrongly assembled, the brass collar was above the rubber insulator so it didn't protrude down from the underside of the cap to make contact with the rotor!
Coil checked out resistance wise, put a test lamp on the ICM and it pulsed like it should as I turned the shaft, pickup checked out good, still waiting for plugs to arrive so have fitted the MSD so once I get the plugs we'll see if it runs!

Graham

[Chevygold]

Just remembered where should I stop off the vacuum advance and what effect would more or less have?

Graham

[VileZambonie]

https://static.summitracing.com/global/images/instructions/msd-8362.pdf

[Chevygold]

Hi Vile thanks for the link but I'd already found that info, anyway after a false start when no start as no spark even though all the tests I'd done checked out so changed the ICM for the new one I already had and bingo the beast lives! So my MSD cost me about £140 to get me going again, motor revs cleanly to 6K without any hint of the misfire which was there before, ran out of time today so didn't get time to check the timing at full advance and with the vacuum connected so will update tomorrow.
Many thanks for all your help

Graham