1972 Cutlass 350 automatic. HEI. I've replaced the following: battery, alternator, voltage regulator, coil.
Under the following conditions, I have a "surging" situation taking place:
temp over 180 degrees
RPM 850
headlights and taillights on

The engine speed will fluctuate between 850 and near stall, and will continually cycle like this. Almost stalling, but coming back up to the 850 before dropping to almost stall again. If I accelerate above 850, the car is fine. And if I come to a stop and put the car in reverse when it is doing this, it stalls.
When this is happening the voltage at the battery will fluctuate between 12.85 and 13.50. the voltage at idle (700) is 13.15-13.25.
IF I disconnect the alternator, the problem stops. If I shut off the headlights, the problem stops.

Thanks in advance for any help any one can provide.

 

I want to suggest to you that this is all carb/vacum leak related.

Fix the vacum leak, surging problem should go away. #1 cause in older carbs is sloppy throttle bushings. I think it needs some carb work.

The electrical surges are a by product of your root problem. Actually normal, and nothing to worry about....for now.

 

13.25 volts at idle with no load? that's low. should be in the 13.8-14.5 range, depending on temperature. the 13.5 number is also low for that rpm, with no to light load on the alternator. an internally regulated(10si/12si) is the preferred alternator with hei. it has a much more stable voltage which the hei likes.

i'm only addressing the electrical end with this post.


bill

 

I should have thrown in that I have rebuilt the Edelbrock 1406 carb thinking that was the issue. The alternator is the older style with the external VR.

I only pose this as electrical because when I put a load on the system (turn on the headlights) it happens. If I disconnect the alternator it stops.

"Surging" might not have been a good word. The engine RPM is fluctuating between 850 and stall.

 

how did you wire the hei system in?
with a new 14-12 gauge line? or off of the existing points system wiring?

 

The HEI was in the car when I got it in 2001. This problem came up in 2007.

 

I'm going to jump on the vacuum leak bandwagon. Have you put a vacuum gauge on the car when it's doing this?

 

OK, another vote on the vacuum leak. and BTW, I'm not convinced it's electrical either, but it seems the symptoms point me that way. Not having a vacuum gauge, I haven't used it. Joe, if I should get one, where do I need to connect it to get an appropriate measure?

However, I checked my records because this dawned on me but I wanted to be sure. I replaced the cap, rotor and coil (that had been on the car since I got it in 2001) in April 2007. This problem first happened in June 2007 (my mother-in-law was in the passenger seat; her only time). This could likely be as little as 50 miles later, and certainly at a warmer part of what passes for a New England spring.

Bill, I checked the HEI connection. The person who installed it did indeed just jump off the existing wiring, which I now know is not good and should be addressed. I don't think this is my issue however.

 

The vac gauge is connected to any straight manifold vac port, but the relatively recent tune up brings something else to mind. I had a situation once where a brand new rotor and cap apparently had a manufacturing tolerance problem. The rotor hit the cap terminals and caused the contact to swing around. Needless to say, performance suffered. Since I "knew" the parts were new, I didn't bother to check them for quite some time.

 

ok

 

the fix is in, and Bill Demmer is the winner:

Took the car to a local auto electric guru. His first words were "fuel problem" but when he heard that the problem would stop when the alternator was disconnected, he was intrigued.
A couple of hours of diagnostics and $127 later I had a new 12 gauge wire from the HEI distributor to the plug on the firewall, replacing the spliced connection to the original coil wire ignition system that was in place for at least the last 8 years. He thinks that perhaps when I replaced the coil last year, the new coil voltage draw is higher than the old, and when it gets hot it causes the problem. But he also said this doesn't necessarily make sense and was basically baffled as to what exactly was transpiring, since all his voltage tests showed things to be normal.
In any case, it's fixed.