Calling All Electrical Experts.

[Jimmy P]

Thanking you in advance for any answers provided.

The problem: Car starts fine and runs fine without any excess load on car and while car is warming up AMP meter reads 14+. Once load placed on car (ie. A/C on or lights on or both) and car is at operating temp AMPS drop off to 10-11 AMPS and car misfires. (car is MSD ignition equipped) Once external load turned off (AC or lights or both) AMPS return and car eventually returns to normal operation.

Attempts to fix: Have had alternator rebuilt by local shop who believed that once ALTERNATOR warmed internal voltage regulator and diodes failed to perform as normal so they replaced both. Basically they rebuilt entire regulator. BATTERY has been checked and indicated it was putting out 540+ Cold Cranking Amps which is what the battery is rated. Battery is at least 3 years old.

Your thoughts ladies and gentlemen.

 

[Frank Catt]

Jimmy, check the relative voltages against Amps when this occurs, also is the car still fitted with a balast resistor if the car was subsequently fitted with MSD, if so get rid of it ! Frank

 

[Bob MacDonald]

Just in case some confusion exists and to eliminate the possibility -- You do mean Amps and not volts? With the alternator giving out 14+ volts, as it does, this will indicate a load over 200 watts. You mention a no load reading of 10+amps, this is still over a 100 watts ? Bob MacDonald

 

[Seymour Snerd]

Jimmy --

I'm going to assume that the meter your are calling an ampmeter is actually a voltmeter. If so it's range is from say +9 to +16 and at rest the needle is at the low side. If it's an ammeter its range will be from - 50 to +50 (or something) and at rest will sit in the middle. Please confirm.

If so, I suspect a poor connection, most likely at the battery, but possibly elsewhere in the heavy cabling that leads up to the dash; I suggest removing, cleaning, and securely reconnecting the battery cables and any other connections that carry current to the dash. Also carefully check the security of the ground connections, e.g. the heavy cable from the battery to the frame, and from the frame to the engine block.

Also, what does the voltmeter read when the engine is *off* and nothing else is running. If the battery is truly healthy it should read at least 12.5. if it's 12 or lower then the battery may in fact not be healthy, although given your cold cranking amps test results that is unlikely.

 

[Frank3]

I would look for loose grounds .
Use an ohm meter to check across all connections , should see 0 to .3 reading across them . Check for corrosion at all grounds , and use no-ox , or other anti-oxidation grease at all exposed connections .
You can also use your meter set on volts , and test for a voltage at the connections . This would be a voltage drop = loose connection .
These test are done by placing one lead on the cable/wire and the other lead next to the connection , or on the cable / wire on the other side of the connection .
Most common would be loose or insufficient grounding to the engine block .
I have seen new cars with battery ground missing to the block burn the tail shaft bushing out before the electrical troubles got bad enough to bring the car in to get repairs .
Your MSD will keep the engine running at 9 volts , so your looking for a connection on the block , head , or intake .
Remember the alternator keeps the battery charged , and the battery keeps the electrical system working .
And on that note , if you don't find a bad connection , swap batteries . You may have a bad cell that shorts when under load , with engine vibrations .
Good hunting ,
Frank3

 

[Seymour Snerd]

....(car is MSD ignition equipped) ....

A side note: if your MSD is a 6AL2 or similar, they are supposed to be powered directly by the battery. That is, they have a heavy black wire and a heavy red wire that are supposed to physically connect to the battery terminals themselves. So, when you get it working the way it used to, if the MSD box isn't connected according to the instructions, I suggest fixing that. Electronics really like having solid power connections.

 

[(C)arlos]

If your battery is three years, then might one of the cells is gone. I had exact the same problem yesterday, and bought a new one, problem solved. It did start with bad cranking the last days, and turned into a faulty battery.

You might want to buy also an AMPERE Meter at a local shop to check if the power consumption raises unexpected during driving ....might be the case that one of your consumers fails under raised temp...
Did you ever measure the AMPS when all ( also the engine ) was turned off.....?

 

[Jimmy P]

Gentlemen, Thanks for your responses....and YES a HUGE mistake on my behalf it is a VOLT meter and not an AMP meter. No idea where my head was. But your responses are the leads (no pun intended) I'm looking for. Any other ideas? They are much appreciated. BTW the battery as a possible cause comes up from some of my local friends as well. I'll try to see if I can get someone to lend me a new battery for a trial run. Thanks again for all your help.

 

[Howard Jones]

Please confirm that the MSD red(big) and black wires are DIRECTLY connected to the battery + (red) and - black wires. Make sure they are tight and the crimps on the lugs are very tight. Pull on them firmly (not caveman style, just get it a good firm tug) if you can't tell any other way.

MSD's will do exactly what you report if they are CURRENT LIMMITED by bad connections. They will work correctly down to 9 volts or so IF they have plenty of available current.

If the current is limmited, caused by resistance in the + supply line, or by a bad high resistance ground then the pulsed output will be effected. This will cause the intermittent firing of the plugs.Things like running the big red wire through the key switch or grounding the unit through the entire lenght of the car chassis for instance can cause this.

This is why MSD wants the wires connected to the battery. They are trying to eliminate all the hair brained ways that people will hook them up if left to their own devices.

Clean and tight will do you right!

Otherwise anything can fail. The MSD boxes can and do fail. MSD can check it out for you, repair it if necessary, and send it back. Call them.

 

[Tom]

Ditto on the MSD and bad/faulty grounds. An MSD will bring marginal grounding issues to surface. They use approximately 1amp/1000 rpm so right off idle you can be pulling a 2 amp draw.

Check your grounds to/from the MSD and/or battery. If you have crimped/soldered lugs they may appear fine until you tug on them.

Tom

 

[Jimmy P]

Guys,

You're the reason I love this forum and the reason why owning a GT40 is so much more enjoyable. I'll let you know what I discover and thatnks again for those that responded.

 

[Seymour Snerd]

Jimmy --

You mentioned in another thread having solved this problem. What did it turn out to be?

Alan

 

[Jimmy P]

Alan, It looks like the problem was a retaining nut that would come loose (after some miles of driving) on the adjustment bar running from the alternator to the block. Once the lock down nut would loosen the adjustment or tightening bar would also loosen thus causing the belt to loosen and slip thus causing the loss of volts. Its amazing what sitting and thinking (usually with a nice cup of hot tea) will do for me. Essentially I would go back through my mind and determine exactly what would occur prior to the drop of of volts on the meter. The tell tale sign in this case was the smell of burning rubber and rubber residue found on the alternator housing and then finding the belt to have loosened just enough to cause the slipping. Wa Lah! I'm now thinking of putting a small drop or two of Loc-Tite on the nut to prevent this from happening again. I just wonder if I needed the alternaotr re-built which I paid $100.00 to have done. We live and learn my friend.

 

[Seymour Snerd]

Alan, It looks like the problem was a retaining nut that would come loose (after some miles of driving) on the adjustment bar running from the alternator to the block.

Wow, that's a good one; I never would have thought of it. Thanks.

 

[Frank3]

Good to here you sorted it out .
See why its so hard to fix the car that your wife drives !
Mine is actually not so bad at leading me toward the problem .
But ...
Sometimes being there , and paying attention is half the solution !
Its the simple things that get you