HEI distributer module failures
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
HEI distributer module failures
I'm on my third module in about 3 years, luckily they all have failed in my garage when I try to start the car after driving the night before. This is a GM HEI that came with the engine, the original has failed plus the Echlin I replaced it with.
In both cases there was plenty of thermal grease under the part.
I'm wondering if there's something with the alternator that might be causing this, I know these things fail but for the amount of driving I do, the failures are crazy.
Several years ago I rebuilt the alternator (a 10SI 3 wire) which I believe was the original. New brushes, bearings, diodes, voltage regulator. I've also replaced the voltage regulator in the alternator twice, once because it went open and wouldn't allow the battery to charge and the second time because the voltage fluctuated all over the place.
I thought all 10SI alternators were the same but the more I read I'm finding out they come in various outputs. I wonder if the parts I put in the alternator the first time were not correct?
I'm kind of ready to spring for a new alternator but it's kind of shoot from the hip move. Anyone have any ideas why these modules keep self destructing?
In both cases there was plenty of thermal grease under the part.
I'm wondering if there's something with the alternator that might be causing this, I know these things fail but for the amount of driving I do, the failures are crazy.
Several years ago I rebuilt the alternator (a 10SI 3 wire) which I believe was the original. New brushes, bearings, diodes, voltage regulator. I've also replaced the voltage regulator in the alternator twice, once because it went open and wouldn't allow the battery to charge and the second time because the voltage fluctuated all over the place.
I thought all 10SI alternators were the same but the more I read I'm finding out they come in various outputs. I wonder if the parts I put in the alternator the first time were not correct?
I'm kind of ready to spring for a new alternator but it's kind of shoot from the hip move. Anyone have any ideas why these modules keep self destructing?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
You must have some other problem with the distributor cap and/or coil that is causing the module to see too much current....or it is getting too hot....or it's a 'gypo' part from 'the Zone' which isn't made the same as the "official" GM part.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Check out the "caution" about the tach wire circuit in this diagram. Just a thought.
http://willcoxcorvette.com/product_i...ducts_id=26748
http://willcoxcorvette.com/product_i...ducts_id=26748
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Here are a couple of shots of the original that came with the distributer; you can see the wire open in the second shot so it's probably an over current issue.
7T1...It's an Echlin module from NAPA but no doubt made in China. I have the original "white" one in there now that was in the car when I got it, probably the original GM part.
Roger.... Thanks for the schematic. Wonder if the tach filter mght be defective and is shorted to ground......Although it sounds like it would be an instantanious failure by the way it's worded. Not sure, but I'll check the filter tonight.
Edit: Just thinking...maybe I'll take the second one apart and see if the same failure appears.
7T1...It's an Echlin module from NAPA but no doubt made in China. I have the original "white" one in there now that was in the car when I got it, probably the original GM part.
Roger.... Thanks for the schematic. Wonder if the tach filter mght be defective and is shorted to ground......Although it sounds like it would be an instantanious failure by the way it's worded. Not sure, but I'll check the filter tonight.
Edit: Just thinking...maybe I'll take the second one apart and see if the same failure appears.
Last edited by TopGunn; Aug 22, 2011 at 09:55 AM.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Check out the "caution" about the tach wire circuit in this diagram. Just a thought.
http://willcoxcorvette.com/product_i...ducts_id=26748
http://willcoxcorvette.com/product_i...ducts_id=26748
It is odd that yours are failing. GM & Wells (said to be OEM supplier) seem to last about 10 yrs.+.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Mine is bolted to the intake manifold right next to the dist. Odd for sure......something going on here for sure.
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Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
I thought for a while it might be from high vibratiion but after seeing that wire open that's encapsulated it seems more of an electrical failure than mecanical.
This last time it failed after some high rev runs the night before; that's what got me on the overvoltage/alternator idea. I'll take the Echlin apart tonight.
Ganey....Yes good idea, I have been riding around with a spare after that first one went just in case.
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
I have read that grounding the tach wire will quickly blow the module. I suggest disconnecting the wire at the cap and checking for continuity bettween the connnector to ground. Try wiggling the wire where it goes through the firewall, etc.
P.S. I would guess that high voltage would blow the tach circuit board before the module.
P.S. I would guess that high voltage would blow the tach circuit board before the module.
Last edited by Rich's'78; Aug 22, 2011 at 01:34 PM.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
I have read that grounding the tach wire will quickly blow the module. I suggest disconnecting the wire at the cap and checking for continuity bettween the connnector to ground. Try wiggling the wire where it goes through the firewall, etc.
P.S. I would guess that high voltage would blow the tach circuit board before the module.
P.S. I would guess that high voltage would blow the tach circuit board before the module.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
It's not the tach filter, there is a high resistance to the input and even IF the thing shorted internally, all you loose is the tach signal....it would take a arc over on the structure of the thing itself to kill the dizzy, and then it would fry the output COIL itself, not the sending/control module....
I have found the HV cap coils have been crimped right through that brown formvar insulation all mag coil wire comes with....it's lacquer based product painted on bare wire and so to scrape the copper wires and solder the ends to the connector tabs....Red and white maybe yellow....
then to make damn sure the coil frame itself is grounded to that middle wire to the dizzy base on the 3 wire plug in.....
then to replace that pesky sending coil in the middle/down under the rotor shaft....a super PIA as it demands dizzy dizzembly outta the car, note the dimple on the gear lines up with the dizzy rotor output end....
may as well send dizzy end play while at it....
or if too much I know a guy who does them.....PM for details...
I have found the HV cap coils have been crimped right through that brown formvar insulation all mag coil wire comes with....it's lacquer based product painted on bare wire and so to scrape the copper wires and solder the ends to the connector tabs....Red and white maybe yellow....
then to make damn sure the coil frame itself is grounded to that middle wire to the dizzy base on the 3 wire plug in.....
then to replace that pesky sending coil in the middle/down under the rotor shaft....a super PIA as it demands dizzy dizzembly outta the car, note the dimple on the gear lines up with the dizzy rotor output end....
may as well send dizzy end play while at it....
or if too much I know a guy who does them.....PM for details...
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Make sure your tach wire is not grounding out anywhere on the back of the head/block!
I had this happening a long time ago on a 350....It will kill modules every few weeks...I could never figure out why...changed different distributors, modules etc etc....I was keeping spares and tools in the glove box..... One day I was rushing on a side of the road change and forgot to hook up the tach wire....I ran it like this for a few weeks and had no issues....Finally I hooked the tach wire back up and 2-3 days later it killed the module. Suspecting the tach wire, I found a slight slight burn spot on it deep down by the tranny tunnel where the wire had rubbed through on the edge of the block and was occassionally grounding out.... Took 3-4 months to figure that one out. Never had another problem though...
I had this happening a long time ago on a 350....It will kill modules every few weeks...I could never figure out why...changed different distributors, modules etc etc....I was keeping spares and tools in the glove box..... One day I was rushing on a side of the road change and forgot to hook up the tach wire....I ran it like this for a few weeks and had no issues....Finally I hooked the tach wire back up and 2-3 days later it killed the module. Suspecting the tach wire, I found a slight slight burn spot on it deep down by the tranny tunnel where the wire had rubbed through on the edge of the block and was occassionally grounding out.... Took 3-4 months to figure that one out. Never had another problem though...
Cruising
Joined: Feb 2006
Posts: 11
Likes: 0
From: tx
i had this same problems years ago. went thru 2 aftermarket modules. the gm module would go out but the next morning it would work again. go figure. bought new dist. same thing. finally ohm'd the spark plug wires. seemed pretty high. bought some from jegs that have almost no resistance. no problems since. or maybe i got luckey, still using that same gm module since 1981. go gm!!
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Thanks for all these good ideas, looks like I'm not alone with these darn things! I performed an autopsy on the failed module but didn't learn anything, it was built different inside and it sort of self destructed when I took it apart.
Anyway, I should have some time tomorrow night to look deeper, sounds like I may have a short to ground poping up every once in a while from the similar experiences you guys are having. I'll check all the things mentioned and report back.
Thanks
Anyway, I should have some time tomorrow night to look deeper, sounds like I may have a short to ground poping up every once in a while from the similar experiences you guys are having. I'll check all the things mentioned and report back.
Thanks
Thread Starter
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Well, I took things apart tonight carefully looking for frayed wires etc. I hooked up a DVM to the tach wire and jjiggled the heck out of moving it all around, looked as far as I could to where it went into the harness and didn't see anything or get any reaction on the meter.
A couple of people mentioned the ground inside the cap, I pulled the one shown here off, checked the connection, reinstalled it, checked continuity from that metal shield all the way to the connector and found it to be good.
I'm unsure by the comments regarding the ground wire inside the distributor. The module is grounded by virtue of the screw at the end attaching it to the base. Is there supposed to be another ground? There is a "G" wire that comes off the end and travels under the weights, is that what you are referring to?
Gene, pulling that thing apart to change that pickup doesn't look like too much fun, think that really could be an issue?
A couple of people mentioned the ground inside the cap, I pulled the one shown here off, checked the connection, reinstalled it, checked continuity from that metal shield all the way to the connector and found it to be good.
I'm unsure by the comments regarding the ground wire inside the distributor. The module is grounded by virtue of the screw at the end attaching it to the base. Is there supposed to be another ground? There is a "G" wire that comes off the end and travels under the weights, is that what you are referring to?
Gene, pulling that thing apart to change that pickup doesn't look like too much fun, think that really could be an issue?