Home » Public Forums » GMCnet » How to test distributor modules
| How to test distributor modules [message #368169] |
Wed, 22 December 2021 19:15  |
Bruce Hart
Messages: 1500
Registered: October 2011
Location: La Grange, Wyoming
Karma: 5
|
Senior Member |
|
|
I took four modules to O'Reilly's to have them checked out. Only thing they did was to check for resistance.
Is this really a good way to verify if the modules are any good.
Bruce Hart
1976 Palm Beach
1977 28' Kingsley
La Grange, Wyoming
|
|
|
|
| [GMCnet] Re: How to test distributor modules [message #368170 is a reply to message #368169] |
Wed, 22 December 2021 19:42  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
|
Senior Member |
|
|
We have an instrument for that, but it does not put an load on it so it
does not show what happens when it has been running for long period.
Some will assemble the distributor with the cap , rotor and coil and hook
up the positive and ground and rotate the shaft or the distributor and
watch it arc from the posts.
Not good to do but once.
On Wed, Dec 22, 2021 at 5:15 PM Bruce Hart wrote:
> I took four modules to O'Reilly's to have them checked out. Only thing
> they did was to check for resistance.
> Is this really a good way to verify if the modules are any good.
> --
> Bruce Hart
> 1976 Palm Beach
> La Grange, Wyoming
>
> Genetically Modified Chevy
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
|
|
|
|
|
|
| [GMCnet] Re: How to test distributor modules [message #368172 is a reply to message #368171] |
Wed, 22 December 2021 21:18 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Sure will. Particularly if the screws that hold the coil inflate are even a
tiny bit loose. One of those 4 screws has a ground terminal under the head.
If loose, it will toast modules regularly. I fixed one at our last rally
for an owner that had failed 4 modules in about 2500 miles. Tightened those
screws and no more failures, yet.
Jim Hupy
Salem, Oregon
On Wed, Dec 22, 2021, 6:15 PM Ken Henderson wrote:
> Here's a pretty good procedure for an installed module, as well as the coil
> and pickup:
>
> https://www.jalopyjournal.com/forum/threads/is-there-a-way-to-test-an-hei-module.706237/
>
> And this leads to a more complete, complex and entertaining one:
> https://www.gmcmi.com/wp-content/uploads/2014/05/HEI-Testing.pdf
>
> Here's a pretty complete review of different HEI modules which will show
> you that the part store's use of a multimeter is essentially useless --
> module models vary widely in the resistances that are expected:
>
> http://gpzweb.s3-website-us-east-1.amazonaws.com/Ignition/HeiModules/HeiModules.html
>
> Frankly, I think testing modules alone is pretty much a waste of time,
> considering that they will sometimes allow the engine to start and run OK
> but later cause problems in performance. There are numerous Google
> articles about how to test one to determine whether missing spark is due to
> module failure -- those are valuable for getting the engine running but
> also cannot predict whether the engine will run well.
>
> One other comment: Any time you have module problems, check the coil and
> its connections -- the coil CAN and often does cause module failure.
>
> Ken H.
>
>
>
>
>
>
>
> On Wed, Dec 22, 2021 at 8:15 PM Bruce Hart wrote:
>
>> I took four modules to O'Reilly's to have them checked out. Only thing
>> they did was to check for resistance.
>> Is this really a good way to verify if the modules are any good.
>> --
>> Bruce Hart
>> 1976 Palm Beach
>> La Grange, Wyoming
>>
>> Genetically Modified Chevy
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
|
|
|
|
| Re: [GMCnet] Re: How to test distributor modules [message #368173 is a reply to message #368172] |
Wed, 22 December 2021 22:37 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
|
Senior Member |
|
|
!0 or 15 years ago I went through 3 modules at one or two thousand miles each time. At Dick Paterson's recommendation I re-gapped the plugs down to .040" and have not blown another one since.
They always quit in the most inopportune time. One on an interstate in heavy traffic. Another on a narrow 2 lane country road with ditches on both sides. One an unfriendly cop called a wrecker and by the time the wrecker got there I was long gone.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
|
|
|
|
| Re: How to test distributor modules [message #368174 is a reply to message #368169] |
Thu, 23 December 2021 08:04 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
The fact that those dual thread ramp coil screws thread into plastic presents an added challenge. What takes out modules is excessive Voltage rise on the coil secondary. This causes excessive (proportional) Voltage rise on the coil primary at the moment the module is shutting off current to the primary and the field collapses. If you keep all secondary parts in good shape and connections good, the spark event completes with less coil Voltage rise. I’ve mentioned before I’ve been driving GM HEI since 76 and never lost a module. Also it might be good to clean and replace the white heat sink compound under the module every 10 years or so as it shrinks as it dries out. Do not use dielectric grease which is not heat sink compound. Most better tool companies make a briefcase type tester. This will give a go/no go test to confirm the semiconductors are switching. I don’t think they stress the module compared to a true high road load situation that might be encountered, but will weed out dead units.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Thu, 23 December 2021 08:05] Report message to a moderator |
|
|
|
| [GMCnet] Re: How to test distributor modules [message #368175 is a reply to message #368174] |
Thu, 23 December 2021 09:07 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Yes, care is needed when tightening any fastener in plastic. Plastics vary
widely in strength, but unless they are reinforced with carbon fibre or
other similar products, they are nowhere close to the strength of the
fastener itself. Dick Paterson is my go-to guy when it comes to "tricks"
that can be used to insure that those fasteners don't loosen up due to
heat/cool cycling and/or engine vibrations. He blames loose fasteners as
the #1 cause of module failure. I tend to agree with him.
Jim Hupy
Salem, Oregon
On Thu, Dec 23, 2021, 6:04 AM John R. Lebetski
wrote:
> The fact that those dual thread ramp coil screws thread into plastic
> presents an added challenge. What tajes out modules is excessive Voltage
> rise on
> the coil secondary. This causes excessive (proportional) Voltage rise on
> the coil primary at the moment the module is shutting off current to the
> primary and the field collapses. If you keep all secondary parts in good
> shape and connections good, the spark event completes with less coil Voltage
> rise. I’ve mentioned before I’ve been driving GM HEI since 76 and never
> lost a module. Also it might be good to clean and replace the white heat
> sink compound under the module every 10 years or so as it shrinks as it
> dries out. Do not use dielectric grease which is not heat sink compound.
> Most
> better tool companies make a briefcase type tester. This will give a go/no
> go test to confirm the semiconductors are switching. I don’t think they
> stress the module compared to a true high road load situation that might
> be encountered, but will weed out dead units.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
|
|
|
|
| Re: [GMCnet] Re: How to test distributor modules [message #368176 is a reply to message #368175] |
Thu, 23 December 2021 12:03 |
rjw
Messages: 697
Registered: September 2005
Karma: 4
|
Senior Member |
|
|
James Hupy wrote on Thu, 23 December 2021 10:07Yes, care is needed when tightening any fastener in plastic. Plastics vary
widely in strength, but unless they are reinforced with carbon fibre or
other similar products, they are nowhere close to the strength of the
fastener itself. Dick Paterson is my go-to guy when it comes to "tricks"
that can be used to insure that those fasteners don't loosen up due to
heat/cool cycling and/or engine vibrations. He blames loose fasteners as
the #1 cause of module failure. I tend to agree with him.
Jim Hupy
Salem, Oregon
I had a module fail on my way to the Fall 2006 GMCMI convention held in Berrien Springs, Michigan. "The motorhome" stopped running Westbound on I94 within coasting distance of a closed rest area. I was able to coast in and parked well away from the traffic. While in that safe place I figured it might be a module so I replaced it, as well as a distributor cap and rotor that I had as spares. It started right up and away I went.
While at the rally I tested the module I replaced with a module tester that Paul Bartz carried in his coach. Yes it tested bad. Upon examination of the rotor I noticed a burned area and a tiny hole. Also, the cap was missing one spark plug terminal which I found in the distributor. The missing spark plug terminal explained why for thousands of miles why I couldn't get a smooth idle. Every time that spark plug was supposed to fire, instead of going to the spark plug it jumped from the terminal to the rotor eventuality burning a hole which then killed the module. The distributor cap was from Spring Field Ignition and Dick Patterson was at the rally. I showed it to him and he promptly gave me a new one he had for sale.
I now carry a module tester with me in "the Motorhome" and several brand name modules.
Richard
76 Palm Beach
SE Michigan
www.PalmBeachGMC.com
Roller Cam 455, TBI+EBL, 3.42 FD, 4 Bag, Macerator, Lenzi (brakes, vacuum system, front end stuff), Manny Tranny, vacuum step, Tankless + OEM water heaters.
|
|
|
|
| Re: How to test distributor modules [message #368177 is a reply to message #368169] |
Thu, 23 December 2021 14:30 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
More likely it failed because the missing terminal caused the coil voltage rise to go to maximum as no reachable path to ground. That spark may jump to the next available terminal as it nears. That gives that cylinder a grossly advanced spark. This can hammer out ring lands or head gasket. I think the rotor/button fail is simple wear item. They do that over time or if contact is bad. The rotor could have initially whacked the cap if not perfectly homed or poorly made. I have seen caps where the terminal(s) were not cut and the rotor would collide. On HEI that flat terminal if rotated can grab.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Thu, 23 December 2021 14:32] Report message to a moderator |
|
|
|
| [GMCnet] Re: How to test distributor modules [message #368178 is a reply to message #368177] |
Thu, 23 December 2021 14:52 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
I have only one thing to say about caps and rotors. Genuine GM parts are a
cut above the aftermarket stuff. Particularly when it comes to primary
circuit contacts. Frequently the aftermarket stuff will move instead of
interconnect with the plugs. That will fry a module quickly.
Goes without saying about the secondary circuit. Make all plug wires
connect where they should, and keep the plug gaps no greater than .045".
You know that funny looking plastic ring that you couldn't figure out where
it went? It secures the secondary conductors to the cap. Use it. Good
insurance policy.
Jim Hupy
Salem, Oregon
On Thu, Dec 23, 2021, 12:31 PM John R. Lebetski
wrote:
> More likely it failed because the missing terminal caused the coil voltage
> rise to go to maximum as no reachable path to ground. That spark may jump
> to the next available terminal as it nears. That gives that cylinder a
> grossly advanced spark. This can hammer out ring lands or head gasket. I
> think
> the rotor/button fail is simple wear item. They do that over time or if
> contact is bad. The rotor could have initially whacked the cap if not
> perfectly homed or poorly made. I have seen caps where the terminal(s)
> were not cut and the rotor would collide.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
|
|
|
|
Goto Forum:
Current Time: Sat Jun 15 20:31:01 CDT 2024
Total time taken to generate the page: 0.01134 seconds
|
GMCforum
Search
Help
Register
Login
Home
