cured an intermittent ignition miss

Grumpy

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
some of you members may remember that my brother-in-law bought a cobra replica ,
well over the last few weeks he was complaining about an intermittent ignition miss, and the electrical cooling fans don,t seem to keep up full rpm,air flow, so he brought the car over to my shop and inside of about 10 minutes of testing , with a decent quality multi meter.

http://garage.grumpysperformance.com/index.php?threads/multi-meters.3110/#post-59136

http://garage.grumpysperformance.com/index.php?threads/how-altenators-work.355/#post-62266

http://garage.grumpysperformance.com/index.php?threads/battery-or-alternator.10003/#post-43220

http://garage.grumpysperformance.co...lem-getting-the-engine-started.63/#post-37970

http://garage.grumpysperformance.com/index.php?threads/chasing-a-crazy-electrical-glitch.986/

I found that the battery had only 12.2 volts and when the engine was running it never got to over 12.4 volts.
I ran a test on the alternator and its absolutely on its last legs and failing.
(in my B.I.L's. opinion)
(actually its failed completely ALREADY in my opinion )
I strongly suggested he, research, find, and buy and aftermarket 140 AMP-160 AMP replacement alternator we could install.
but my B.I.L. decided that researching that would be far to much effort,
so he bought a stock 75-90 amp alternator which ,at the local advance auto parts...
yes it cured the intermittent ignition issue , as it puts out a steady 13.6 volts once the engines spinning over 1200 rpm, and it gets to 14 volts by 2400 rpm, but hes missing out on a great deal of the alternators potential.
if he had simply purchased a 160 amp alternator I'm reasonably sure his cooling fans would run noticeably better, the battery would fully charge faster the starter would work better and the ignition would produce a better spark!
yes, the stock replacements cheaper and available the same day vs waiting two-to four days for the auto parts to arrive if ordered on-line, but at least too me the wait and expense would be well worth the minimal inconvenience!
after all the car would run noticeably better, rather than just returning it to basically functional


cob2.jpg

I don,t know why some people resist doing even minimal research
its not like it takes over 10 minutes to find several options

https://www.dbelectrical.com/alternators/automotive/ford/mustang/5-0-liter/

http://garage.grumpysperformance.com/index.php?threads/battery-or-alternator.10003/#post-43220

http://www.americanmuscle.com/paperformance-ho-alternator-8793.html

https://lmr.com/products/Mustang-200-AMP-Replacement-Alternators

https://www.summitracing.com/search...nators-and-generators/make/ford/model/mustang
 
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Sounds like he didn't want to make an upgrade project out of it and spend an extra $100.00-$300.00? Other than fans/ignition/gauges/lights there probably isn't much electrical in that car anyway. It's not like he's running AC, power windows, an electric water pump, and has big stereo amps with giant subs in the trunk. I'd think a 75 would probably be fine. Biggest draw will be when the fans kick on and that'll can take 100 Amps if they're high performance Spal fans and both kick on at once but only for a second till they're up to speed then 50 Amps. Most fans don't require that much juice and if he's got kick ass fans like that he should have them come on seperately. I only run a 100 amp Powermaster in my car with electric fuel pump, full MSD ignition etc. no problems.

Basically functional is probably more than enough for him. He's not racing is he? Is it a stock 5.0? What cooling fans? Any other high draw items?

I'm a bit confused. Lets say the stock type alternator keeps the battery fully charged so its 12.6-8 volts when shut off and 13-14 volts while running. By installing a higher amp alternator: The starter would work better? How? The ignition would produce a better spark? How? The car would run noticeably better? In what way?
 
In car stereos we always did the big three upgrade also I still do this to any car I modify you may not be adding amps and audio but ignition and fans!!!

Performing what is known as the “Big 3” upgrade to your vehicle will improve the performance of your electrical system and increase its current handling capabilities. This should be the first upgrade done to your electrical system which will then allow you add more powerful audio system components. Factory wiring is thin and insufficient for running anything but basic audio systems. Larger diameter wires will be added to the existing factory wire (or swapped out entirely), usually 1/0 gauge wire to get the best current flow and least resistance. This new decrease in resistance will reduce light dimming, reduce voltage drops, stabilize voltage and current flow, and decrease the strain being put on your vehicle’s electrical charging system. Additionally, you can then add batteries, capacitors and more alternators onto your system.
http://knowledge.sonicelectronix.com/car-audio-and-video/how-to-big-3-upgrade/
 
I went through the loud stereo era of the late 80's early 90's with teenage kids. Trunks full of giant subs, extra batteries, high amp alternators, and MONSTER CABLE! Ahahaha I could hear my son and his friends cars coming 2 blocks away. They entered those sound off competitions etc. and the ones who could crack a windshield were treated as gods. ahahaha I thought it was kinda dumb but helped them anyway.

From a hot rodders performance point of view the smallest alternator that will handle the requirements will weigh the least and take the least amount of power from the engine to keep everything supplied. Using a larger one is sort of insurance for possible future electrical component installations but at a weight and power consumption cost.

For many years drag guys have switched off alternators during runs or eliminated alternators to reduce weight and free up horsepower. MSD provides this as a guide for their 6AL systems
BATERM.JPG

BATTERY
An MSD 6 Series Ignition Control will operate on any negative ground, 12 volt electrical system with
a distributor. The MSD can be used with 16 volt batteries and can withstand a momentary 24 volts in
case of jump starts. The Ignitions will deliver full voltage with a supply of 9 - 18 volts and will operate
with a supply voltage as low as five volts.
If your application does not use an alternator, allow at least 15 amp/hour for every half hour of operation.
If the engine is cranked with the same battery or other accessories such as an electric fuel or water
pump are used, the amp/hour rating should be higher.

http://www.jegs.com/p/Powermaster/Powermaster-GM-CS144-Style-Alternators/1534945/10002/-1


A 150 Amp alternator uses about 11 HP http://www.zena.net/htdocs/alternators/altspec2.shtml

Our muscle car era cars typically came stock with 42 amp in non AC cars and 63 amp in AC cars.
 
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while that is true enough, if you can consistently see the lights in the gauges dim, as the fans kick in, and stay dim,
until the engine rpm's ,exceed about 2000 rpm, its a damn good indication that your alternator,
battery or the related connections to the cars frame ground, and related current flow is in less than in abundant supply.
my B.I.L. is one of those guys that thinks that as long as the car moves easily everything must be "just peachy"
and things like squeaky brakes, dimming gauges,and drops of oil or coolant under the car are "normal"
 
If you fit better in the car Grumpy I think you should confiscate it in the name of hot-rodding. Cause yes there is an obvious problem electrically related which I doubt is uncommon in a replica car where wiring was completed by a builder of who knows expertise. I have dealt with more wiring issues then you can shake a stick at when I worked on a fleet of R-model Mack trucks and there gas trailers. Most issues as you describe end up in the wiring there is nothing that should over power the alternator I see from the brief description. The battery is either not sufficient or there is a wiring issue. And a battery can be tested and doubting that is it seeing it is holding a charge and cranking over the engine. Either way Grumpy there is an issue and it should be addressed
 
Agreed, dimming gauge lights indicates a problem. Poor ground path is common on home built kit cars. Guys don't clean off paint where things are grounded to frame or engine. They just don't know and think the path through the screw or bolt threads to the frame or engine is enough.

1st thing Id check is to make sure the cooling fans are wired direct to battery power and activated by a relay.
 
While in the hospital this past weekend I watched Speed channel a lot. One of the top running cars for the NASCAR race came out for practice after qualifying and went right back to the pits with an alternator problem. A quick check indicated someone forgot to flip the switch back on after qualifying. Apparently even the top tier of roundy round guys shut off the alternator when they need/want the extra power and one of the former drivers turned commentator said they do it during races sometimes when they need a little extra power.
 
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I believe drag also may be based off draw I am not sure this is fact just an observation. If you look at the fan dyno results you posted that were performed in a scientific test method. The electric fan caused a 1 hp drop compared to no fan. I suspect, not conclude, that may be due to draw.
 
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