Currently trying to get a GM big block 454 running decent. GM HEI ignition. Old school big block with no computers and such. Carbureted. It used to run perfect. Started backfiring and fouling plugs randomly. At the same time I was hearing what sounded like a bearing going internally in the motor. I didn't think it was the alternator cause it wasn't very high pitched. I notice the whine coincided with a change in the engine running. Popped the fan belt off and it seems like it runs great without the alternator turning and no whining. Spinning the alternator by hand it feels like there is something amuck. New one coming tomorrow. Has anyone ever had a bad alternator interfere with the ignition system causing misfire and fouling plugs?
A bad diode can cause high AC ripple and can sound like a bearing noise. I guess high AC ripple could interfere with electronic ignition.
Did you put a meter on the old one while it was running to see what it's output was? It would make sense to me that anything using the electrical system would start to have issues if the alternator was on it's way out, including the ignition system.
put the belt back on and see what the voltage is when the alt is charging. HEI distributors don't like to operate much under 10 volts. Ive had some do complete wacky timing swings because the low voltage is making the module go crazy, or just not even firing back up after a stop for gas when it was just running fine (although not charging unbeknownst to me).
Sometimes bad luck clouds good judgement. I'm thinking you found the problem of a alternator on the fritz. But without you telling us more details, age and engine condition, last time plugs were looked at or changed, I wouldn't try to guess it to cause backfiring and fouling plugs. I could try to explain it as simple as it rotates to create a field, but randomly it collapses, reverses briefly, then corrects. Miss fire. AC to DC to ac to DC. I do think it was using the noodle to separate the noise from the engine. Most would think engine, bring out a screw driver and try and listen it to a solution. You narrowed it down. That's a bonus point for you bud. High five.
Back in the 80's Chrysler had some alternators with the brush slip rings pushed a bit too far onto the rotor. That allowed the brushes to run slightly off the edge of the slip ring. As the brushes wore they would have a "finger" hanging off the edge and it would eventually hit the solder joints on the slip ring. This would cause the brushes to "bounce" on the slip rings. The electronic ignition did not like the high frequency noise that was generated. Engines would have all kind of strange bucks and/or misfires. Since the Chrysler regulators were external, unplugging a brush connection was easy. If that solved the problem, replacing the alternator was the final solution.
Engine was fully rebuilt in 2017. Everything up to par with new carb, distributer, plugs, wires, alternator, starter and fuel pump. When we purchased in late 2018 it ran beautifully. Then all of a sudden it started flooding out and fouling the plugs. Long story short, found a metal chip on the secondary float needle which didn't allow the fuel to shut off. Fixed that. Wrecked the car on June 2, 2019, bought it back from insurance and restored it. Now it took a good year to get it back to reasonable and this year I finally finished 95% of the restore. But while sitting around, the ethanol fuel ate through the braided stainless rubber fuel line. One day the car was sitting out in the yard and fuel was dripping randomly along the fuel line. I replaced all of the fuel lines with teflon lined braided hose. Cost 470 bucks cause all of the AN fittings needed to be changed also but I wanted it to last. Also rebuilt the brand new carb because of all of the sitting. Had a little aluminum corrosion built up on the metering blocks but overall not bad. Seemed fine after all that but I began hearing a bad bearing sound every so often. Wasn't constant but didn't sound like an alternator. Lower pitch and almost sounded like it was coming from inside the engine. I was going to do a compression test with the thought that something mechanical was amiss. Walked back in the house and had a beer. Then I thought... no this has to be something simple. Went back out to the garage and popped the fan belt off. It seemed like it was running quite well but it's done that before and than all of a sudden backfire and fouled plugs. But I did notice no more whining sound. Spinning the alternator by hand I could feel some strange very light grinding.. not really grinding but not perfectly smooth. The fact that I noticed when it was running with the belt on and when the noise occurred, the engine changed the way it was idling. That's kinda what made me think to take the belt off. The alternator is one of those cheap chrome jobs the guy paid 65 for off ebay. New alternator comes tomorrow. Some really good responses here. Truly appreciated.
You can get a huge amount of electrical interferance from a bad alternator. Anything electronic can be disrupted of its bad enough.
Yes, a bad alternator can cause a lot of ripple, i.e. voltage variation - worst case you can get a quick series of going from the full 14.4 charging voltage, down to around 12V when the alternator gives nothing and everything is fed off the battery, back up to 14.4V and repeat. Such a fast voltage variation is rather much like the signal some electronic sensors give, for example the sensor telling the electronics when to send current to an ignition coil and when to cut it off in an electronic ignition system, and ripple on the feed voltage can bleed over into signal wires. So yes, a bad alternator can absolutely cause electronic ignitions to misfire, and cause a load of other issues in cars with more electronics. Here's a video of an off topic car where the speedometer mistakes ripple for a speed sensor reading. Just one of many examples of how excessive ripple can confuse electronics.
One test and repair at a time. Other wise when problem get’s fixed (or not) one will never know which repair did any good.
Wow this is interesting! Just imagine trying to pinpoint a problem on a late model high tech whatsitmobile!
Bad grounds will do that too. I put a big block into a stock car, we were eager to fire it up and did so. Totally neglected the ground between the engine and roll cage. It ran like crap, missing and the only ground at the battery (rear of car) got real hot. We fabbed up a couple of ground straps and it was the cure.
Very interested in your findings. I'm chasing random rough running and a randomly spiking voltage gauge. Never thought the 2 could be related. Similar chrome alt and cheap hei. Was waiting to hit a swoop meet to get a points dizzy
New alternator arrives today. Went with a Tuff Stuff Silver Bullet. Below the picture is a link to an article about this issue. https://www.iatn.net/forums/13/57134/misfire-caused-by-alternator
Well I just got back from a test drive with the new alternator. Looks like that was the issue. She's running great.
Back in the late 1980’s to maybe the mid nineties, I remember there was a GM TSB concerning excessive ripple voltage causing run-ability problems on electronic fuel injection vehicles.
Bad diode leaking AC will kill the HEI control module and any other electronic ignition, like Pertronix. If you have a good multimeter, you can set it on AC and measure the voltage to check this. It should be near zero. It's possible for it to be putting out 14 volts DC and still be leaking enoughAC to cause ignition problems. I've experienced it at least twice. Once the alternator was swapped out, the problems went away.
Yes it has happened twice to me once about 10 years ago on a pontiac v8 (hei distributor) and the second time was today 383 (hei distributor). Both times the gages read above 19v . Assuming once it puts over 18v from a failed reg it will break up ign either by cross firing under the cap or stalling out the hei module. Felt more like a bad corrected spark plug cap that has went bad from the vortec Era ignition. Nasty missfire
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