L-78 starting problem update

[mike hom]

I know there was some interest on the board regarding the outcome of my dilemma. Good news, bad news. Good news is that I believe I have found the problem. Bad news is cost. I called Dave Fiedler as suggested here and by my mechanic Bob Ruth. Anyway, it turns out that the magnetic pickup unit in the distributor is bad. $195 for NOS parts! If I pull the distributor Dave will restore it for $175, but that doesn't include the parts. Oh well, the continuing saga of buying parts for a rare bird I guess . . .

For those interested in the diagnostic procedure, here it is:

1. Look for poor connections at distributor "pig tail" connector.

2. remove pulse amlifier and do the same. Ths requires removal and disassembly of the unit.

3. ensure pulse amplifier is securely connected to ground when reinstalling.

4. disconnect distributor "pig tail" connector. read resistance of the magnetic unit with an ohmmeter. Looking for 500 to 700 ohms (mine was 650).

5. Hook up volt meter at same connector while cranking engine. Looking for minimum of 1 volt ac (mine ws 750-800 mv). This was the end of my journey. This is also exactly what Dave predicted when I gave him the symptoms.

step #6 would be to reconnect pig tail, remove amplifier and remove the back cover (again). Ground the case of the amp, crank the engine, and look for 1vac there which would check the cable and connections. Again, I didn't have to go this far as step 5 told me what the problem was.

Hope this info helps someone else in the future. Dave gave me this step by step procedure. He is very cooperative, as I have found most members to be. Thank all of you for the input. I will send a follow up message after repairs are campleted. Thanks all again.

[Jack H.]

Re: L-78 starting problem update

Thanks for the feedback, Mike. Sounds like check air/gas/spark worked again and it was spark....

On replacing your magnetic pick-up coil, you should be aware of an original parts issue. Factory original coils of the era had 2-wire 'harness' exiting bottom of distributor routing to plug-in connector. Judges check for originality here (are wires correct color code/striping pattern/length) since 'NOS' (often means GM service spare) assemblies have subtle difference in wires.

Initial reaction is to discard original pickup coil with its correct wiring that will cost concourse points later. Even if the coil is 'fried' -- it's preserving the original lead wires since they can be moved onto replacement coil and spliced in....

[Jack H.]

Re: L-78 starting problem update

Thanks for the feedback, Mike. Sounds like check air/gas/spark worked again and it was spark....

On replacing your magnetic pick-up coil, you should be aware of an original parts issue. Factory original coils of the era had 2-wire 'harness' exiting bottom of distributor routing to plug-in connector. Judges check for originality here (are wires correct color code/striping pattern/length) since 'NOS' (often means GM service spare) assemblies have subtle difference in wires.

Initial reaction is to discard original pickup coil with its correct wiring that will cost concourse points later. Even if the coil is 'fried' -- it's preserving the original lead wires since they can be moved onto replacement coil and spliced in....

[John]

Re: L-78 starting problem update

If I may ask, why so much money to rebuild a distributor? How much are the parts? By magnetic unit I believe you are referring to the pick-up coil. It should not be exspensive unless it is particular to the Vette engine. Isn't it a standard GM part? Why rebuild the entire distributor if all else checks good? I would check the bearings and bushings and only if neccessary replace them. Thanks for your patience in answering these questions.

John

[John]

Re: L-78 starting problem update

If I may ask, why so much money to rebuild a distributor? How much are the parts? By magnetic unit I believe you are referring to the pick-up coil. It should not be exspensive unless it is particular to the Vette engine. Isn't it a standard GM part? Why rebuild the entire distributor if all else checks good? I would check the bearings and bushings and only if neccessary replace them. Thanks for your patience in answering these questions.

John

[mike hom]

Re: L-78 starting problem update

Yes, spark, gas, etc - except in this case the spark is there sometimes. Not your typical "old cars are easy to work on" stuff. Not rocket science either, but the key is to find someone who knows what to look for. Now I know, and I understand the system. Thanks for the advice regarding the leads. Will be splicing . . .

As far as why so much is charged for distributor resto - same reason a dog licks himself I guess suspect.

[mike hom]

Re: L-78 starting problem update

Yes, spark, gas, etc - except in this case the spark is there sometimes. Not your typical "old cars are easy to work on" stuff. Not rocket science either, but the key is to find someone who knows what to look for. Now I know, and I understand the system. Thanks for the advice regarding the leads. Will be splicing . . .

As far as why so much is charged for distributor resto - same reason a dog licks himself I guess suspect.

[John]

Re: L-78 starting problem update

Mike, I thought this board was for people interested in the same hobby to try to help one another with info. Your last sentence was uncalled for and who would know what it means anyway? The point to made was that you anyone with basic tools and knowledge could rebuild the dist. for alot less.Good Luck to you!

[John]

Re: L-78 starting problem update

Mike, I thought this board was for people interested in the same hobby to try to help one another with info. Your last sentence was uncalled for and who would know what it means anyway? The point to made was that you anyone with basic tools and knowledge could rebuild the dist. for alot less.Good Luck to you!