Engine spits and misses @ high rpm

[soth122003]

I think I got a handle on this, but I would still like some opinions. Last week I started putting the spurs to my 48. I got her up to about 65 mph and she was doing good with just a little strain. On average she likes 50-55 mph the best. The engine was smooth other than a exhaust leak which I temp fixed until I get a new manifold. That was last Friday, and I put about 60 miles on it. This past Saturday, I put about 100 miles on it, and found out my gas gage is not working right, and I ran out of gas about 35 miles from the house. I thought it was the fuel pump at first, because I put and Airtex on it about 4 months ago. Should have tapped the bottom of the tank and saved myself the tow to the house. The engine still ran fine at this point.

 

Anywho, Yesterday (Sunday) I drove about 80 miles round trip and the engine started missing (but no backfires) every time I got to the high end rpm of each gear. 1st,2nd and 3rd. It started raining so I turned on my lights and the car about died. this was at about 45 mph. By the time I got home, the misses were starting to occur at the mid range rpm's.

 

I talked with my buddy and we came to the conclusion it might be the generator. If it is not putting out a good current flow, the battery will slowly drain. With the high demand for electric power at higher rpms the spark would become weaker and erratic resulting in the misses in the engine, especially with the parking lights on in the rain, I couldn't use the headlights because it would have stalled the engine out.

 

The battery is about 2 months old and I cleaned the armature on the genny about 4 months ago. I don't know how old the brushes are, but if they are old and leaving residue on the armature, it will cause a current loss to the voltage regulator and not charge the battery very well. I know the genny hasn't been serviced for at least 2-3 years, plus it sat outside for at least a 1 1/2 years before I bought it. When it sits at idle it purrs like a kitten at about 500 rpm's.

 

Any thoughts as to if I am on the right track or not would be appreciated.

 

Joe

[Don Coatney]

What does your amp gauge tell you?

[soth122003]

Amp gage sits at zero. will not show a positive charge, but will show a negative, like when the key is turned on -1 amp. parking lights -3 to -5. headlights -10 to -13.

 

Joe

[soth122003]

Meant to add will show a slight +, maybe 1/4 amp when reved high.

 

Joe

[Niel Hoback]

Loose fan belt? 

[soth122003]

Just replaced the belt. Tightened jenny to allow the 1/4" deflection in the belt. As mention in post 3 and 4 the amp gage has always read that way. there was a brief time 2 days maybe that it did read about 2 amps positive. then it went back to zero.

 

Joe

[soth122003]

Just replaced the belt. Tightened jenny to allow the 1/4" deflection in the belt. As mention in post 3 and 4 the amp gage has always read that way. there was a brief time 2 days maybe that it did read about 2 amps positive. then it went back to zero.

 

Joe

[Young Ed]

At least briefly after a start up the amp gauge should go to +15-20. Mine dont stay over there long but they do go at first

[ptwothree]

How does it run with a fully charged battery?  How about some voltage readings taken at the battery at around 1200 rpm with and without a load.  That might tell you something........

[Lloyd]

Amp gage sits at zero. will not show a positive charge, but will show a negative, like when the key is turned on -1 amp. parking lights -3 to -5. headlights -10 to -13.

 

Joe

 

Does it show these readings with the engine running?

Seems the amp gauge should read more than 0 when its running. Pushing over to the negative side would that mean its drawing from the battery?

If the engine is running off the battery then it should die if you pull a cable off the battery while its running.

[soth122003]

ptwothree: Battery is on the charger now. with a full battery it runs great. My multi meter is at work and the shop is closed on Mondays. I was waiting for a friend to get home so I could use his but he got home around 7 o'clock which made it a 12 hour day for him. I wasn't going to bother him after a long day like that. I'll check the readings with a meter on Friday. Last time I checked the meter readings I was getting about 8 volts at the battery @ about 1500 rpm's but that was a few months ago after I cleaned the brushes and commutator.
 
Lloyd: Those are the amp gage readings are with the engine running. I'll check the battery cable idea on Friday. ( I work Tuesday, Wensday and Thursdays)

 

When the engine is running turning on any load will show a negative ammeter reading no matter what rpm the engine is at. This is leading me to look at the genny and the voltage regulator.

 

I understand I might have problems with either the genny or the voltage regulator, but my question still remains: Will a low battery with the charging system out of whack, cause the engine to miss and stall at high RPM's?

[Don Coatney]

ptwothree: Battery is on the charger now. with a full battery it runs great. My multi meter is at work and the shop is closed on Mondays. I was waiting for a friend to get home so I could use his but he got home around 7 o'clock which made it a 12 hour day for him. I wasn't going to bother him after a long day like that. I'll check the readings with a meter on Friday. Last time I checked the meter readings I was getting about 8 volts at the battery @ about 1500 rpm's but that was a few months ago after I cleaned the brushes and commutator.

 

Lloyd: Those are the amp gage readings are with the engine running. I'll check the battery cable idea on Friday. ( I work Tuesday, Wensday and Thursdays)

 

When the engine is running turning on any load will show a negative ammeter reading no matter what rpm the engine is at. This is leading me to look at the genny and the voltage regulator.

 

I understand I might have problems with either the genny or the voltage regulator, but my question still remains: Will a low battery with the charging system out of whack, cause the engine to miss and stall at high RPM's?

I may be wrong but I believe you answered your own question. The lower the battery charge the worse the engine will run.

[Dave72dt]

Yes and fortunately, you could still limp home.  New cars when they get below a certain voltage simply quit.  You may get a mile or two of poor running or enough time to get it off the road but that's about it.

[Robert Horne]

Since you ran the car out of fuel, I would check the fuel system.

[greg g]

Simple test for Genny output is to ground the field terminal at idle. If the amp gauge pegs to full charge, the gen is OK.

What is the condition of your gen's brushes ?

Edited August 19, 2014 by greg g

[soth122003]

Hey guys,

 

Thanks for the thoughts. The fuel system is fine, just the gas gage was wrong and I didn't realize how many miles I put on the car. The tank was bone dry. had about 200 miles on the tank

 

I'll check the genny later on this friday.

 

Joe

[1940plymouth]

I have been having the same problems as you have been describing, here is what appears to be the problem.  Knowing enough to be dangerous, I am thinking that the armature is no longer functionable

[Dave72dt]

It looks like you may have burned the insulation off the armature windings. With a VOM, place one lead on the steel core of the armature and the other lead on each of the commutator bars. If you get continuity on any of them, it will need rewinding or replacing. Next test is to place one lead on one of the commutater bars and the other on each of the commutater bars. This time you want continuity on each of them. That's 2 of the 3 tests done on an armature and without a growler, you can't do the third. If it passes the first 2, likely will pass the third also.

[Merle Coggins]

 Next test is to place one lead on one of the commutater bars and the other on each of the commutater bars. This time you want continuity on each of them.

 

You wouldn't want continuity with all other bars on the commutater, only on the one on the opposite side. Each pair of commutater bars connect to each end of one loop of wire. There shouldn't be continuity between the loops.

[Dave72dt]

They've always worked when I've tested them that way.  Maybe I've been doing it wrong for all these years. Live and learn.  I've hooked them up to a battery charger and motored them too as a quick test.

Edited August 20, 2014 by Dave72dt

[iowa51]

I will throw this out as I had the same high speed miss issue that seemingly appeared out of nowhere. Check the distrbuter cap and rotor. My looked all "sooted" up on the inside and replacement of both fixed the problem.

[soth122003]

Hey Guys,

 

Well it 90 plus degrees with a heat index to 106 and 60 percent humidity. That being said, I went out to check the readings on the genny and the voltage regulator. It was putting out voltage but it was erratic at best. The battery was reading 6.35 after the charge. Started the engine, it ran fine. Pulled one of the battery cables off and the car died. Cleaned the commutator and the amp gage started working pretty good. At idle it was showing a slight negative draw. At about 1500 rpm it showed about 15 amps positive. At 2500+ rpm it was reading about 25 -30 amps positive. Turned on the lights and the amp gage went to about 10-15 pos. Back down to idle and it read about 15 neg amps. Turned the lights off and the amp gage went back to 0.

 

I took the voltage reg out and checked the gap clearances on the breakers, they good and the VR looked brand new inside. No burnt smell or visual damage.

 

I'm thinking the brushes in the genny are semi-toast. Plus I haven't pulled the genny and cleaned it yet. I'll wait till I get the brushes and do everything at once.

 

I still have a spitting and stalling at high rpm, I mean pretty high reving the eng in neutral. I think the timing might be off a bit. Should the timing wait until the genny is fixed or can I set it with just the battery? Something else to note as well, I installed the pertronix ignition module in the distributor. I am wondering if this may be a factor at the high end rpm range with a faulty genny?

 

Thanks again for all comments and suggestions I really appreciate it. And Don? I really did answer my own question, but its nice to have it verified.

 

Joe

[Jeff Balazs]

Joe;

I think it is very likely that the Pertronix unit would be sensitive to the voltage of the system. You probably have not damaged it but you can call their tech dept. for verification on this subject.

[Silverdome]

How much play do you have on the ditributor shaft? An excess amount could cause the miss at higher RPM's.

Edited August 22, 2014 by Silverdome

[Plymouthy Adams]

Silverdome, on 22 Aug 2014 - 3:49 PM, said:

How much play do you have on the generator shaft? An excess amount could cause the miss at higher RPM's.

could you explain this logic for me please...