Hey everyone!

Have an '84 Conquista SS here. A good "20 footer" Love it even though it seems to be a tinkerer's hobby truck. Lots of little things to do on it.

Biggest problem so far seems to be that the computer and distributer are mismatched. The check engine light gives me code 41 which tells us that the computer is not recieving timing pulses from the distributer through the electronic spark timing circuit.

But the distributer is one with vacuum advance, not the est circuit.

The truck originally came from Washington and had since then been registered in California.

It has the 305 V8 (maybe it's a 350. I'll have to find the engine stampings and decode them) and it runs very well. I would be quite satisfied with it if I could only make the check engine light happy.

So, what I would like to know is which type of distributer would give better performance, reliability, availability of replacement stuff later, etc.

Probably either type would pass smog here. (One smog repair guy told me that the est is not required on my '84, but that does not mean that it couldn't or didn't have it at some time.) On the other hand, if the computer is expecting to have control of the timing through the EST circuit, then that'll have to be provided or a different computer that won't be so controlling.

So, that's why I was asking which type of timing control would give the better performance?

Also curious about performance chip sets for this one. What are some good reliable performance chipset suppliers?

By the way, yes this one does have the four wire connector to support the est type distributor. So the easy fix would be to replace the one I have with an est type. That would satisfy the check engine light.

But since it has been so difficult to find good information about the Electronic Spark Timing circuit it makes me wonder if it might be worth upgrading it to something else?

Well, ok.
Ask around enough, eventually you will find some answers that actually make sense. Here's what makes sense for California smog requirements as they relate to my ignition system:

If the vehicle originally had the Electronic Spark Timing (ETS) or at least the currently configuration (computer) expects it to be there, then it won't pass smog with any other distributor timing system.

It may be possible to change out the computer for one that does not expect the EST circuit, but that would be at least as expensive as getting the distributor with EST and would no doubt be a downgrade in performance anyway. Can't afford to lose any bits of performance with this litle old 305.

So, the new problem for me to solve seems to be that there are (according to the trusty parts guy) some 6 different timing modules. (Not interchangable. ) and I will have to figure out which one my computer control module is wanting, or the whole timing curve will be wrong, etc.

So, does anyone here have any suggestions for decoding something that will tell me which timing module my truck is wanting?

Seishin, if you do not have a code 12 with your 41 then you have an intermitent problem. Check to see if the MAP or VAC sensor voltage CHANGES with LOSS OF VACUUM SUPPLY.
A good EST sensor will change voltage at terminals A AND B (the top two wires, your colors may be white, and purple and white.
You may have an open ground in the distributor circuit.
Check the terminals of your MAP and VAC SENSORS, MAKE SURE THEY ARE CLEAN. If these two sensors have the same voltage outputwhen the engine is running and when the ignition key is just "on," then it will have no reference signal.
To properly check terminals A and B you may have to remove them from the connector (the four prong flat connector from the distributor.) Hope this helps

I doubt there is a non-computer controlled distributor in your engine. You will have to trouble shoot six potential causes of the service engine light staying on. They are : 1) Cam sensor (CAM) failure, 2) Cylinder select error, 3) tach input error - no reference pulses during engine run, 4) Electronic spark timing (EST) circuit - open or shorted to ground during engine run, 5) Direct ignigion system (DIS) fault - bypass circuit open or shorted to ground during engine run, 6) ignition system fault - loss of 1X reference pulse signal.

Your best bet is to find a professional mechanic who professes to know how, and has the equipment, to check each of these problem areas. Look him in the eye and ask him if he has any experience. Don't pay anyone to experiment and learn. Keep looking until you find someone who tells you he has the experience. These days, mostly the "old heads" will have the experience you are looking for.

It is an interesting problem, so please let us know what you find out.

This distributor thing is crazy!

I've found an '85 model with the distributor that my '84 wants. It has no mechanical timing advance parts anywhere and the four wire harness connecting the EST module to the engine harness. That engine looks dead original. So one would think that the dist. could be found on some supply house?
But the parts supply places (even Chevrolet) can only find the distributor with vacuum and centrifugal timing advance stuff. They list no other dist. ever being on a chevy.

Go figure!

Well, at least the dist will have some part number stamping on it somewhere. That'll get me closer to making the check engine light happy.

Seishin,

Sure wish I hadn't thrown that distributor away. I can't understand why parts said they didn't have one with out vacuum advance cause that one did not.

Any ho you said "I would be quite satisfied with it if I could only make the check engine light happy". You also noted there would be no smog problems. You therefore must be happy with performance. In that case if I were you I would just take that light bulb out, cut the wire or whatever. Now I know every one isn't like me, but for me, if it works and I'm happy with it, I do it.

L.D.

I appreciate that sentiment, brother.

Thanks, but as for disconnecting the light, that would also fail smog tests here, because the first test they are supposed to do is to make sure that the light does actually light up when you first turn on the key.

And besides, if something is not working right, while we may not notice it in the drivability of the vehicle, the fuel economy may suffer and that could in turn shorten the life of our ride.

Have you noticed how much longer vehicles live these days as compared with the pre-smog days? Used to be that 100,000 miles was about it. But nowthat's just another scheduled tune up point!

Well, I went out today to spend some quality time at the local auto recycling centers. Found quite a few Gm vehicles of the right year and engine configuration. (suspiciously few with a 350 engine though. Did they not put 350s in anything back then?) In fact, I found that while most of the distributors were of the mechanical advance type, there were a significant number of the computer controlled ones.

That means that I could configure my ride either way, just as long as the computer matches the distributor (and everything else is consistent with one configuration or the other) That's what I meant about there being no problems with the smog test in either configuration.

And yes, the power and performance of this one makes me think that someone has already slipped in a 350 under the hood for me. I'll have to locate the block casting numbers and stamps to be sure, but untill then , , ,Way cool!

So that brings up my original questions:
Which would give a better performance, the mechanical timing setup or the computer controlled timing setup?

I'm suspecting that the preference for mechanical advance setups is because of how easy they are for the average mechanic to tune up the timing advance curve. Also, the high performance ignitions (Accell, Mallory, etc.) are all configured for mechanical advance curves. But for the question here, let's compare only standard Delco-remy HEI.

The computer controlled distributors would need a prom chip reprogrammed to alter the advance curve. That's not so easy to do, (and can lead to damaging the computer and maybe even the engine if mishandled) but potentially could give much more accurate timing curves since they can also include many other factors like air temp, mass air flow, absolute air pressure, fuel quality, engine knocking, etc..

So it's a much more dynamic timing curve that can be right up to the edge in more engine load situations. I'll go with that and see about a performance chip set for the computer. Maybe I won't feel the difference, but if we see better fuel economy, then the wallet will be a little happier at least. :D

Anyway, while I was out there poking about the parts yards, successfully picked up a couple of the right distributors for $40.oo each(out of 84 and 85 malibus), and a computer for $25.oo. Plan to go again soon for a few more interesting things I saw there.

So things are looking better. Thanks Brothers! :-D