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Discussion Starter · #1 ·
First I hope I don't get in trouble for posting in the wrong area. "Can you find it in your heart to forgive me."

It seems that my 73 GT does not like to idle under heavy electrical load. Basically if I roll the headlights she will stall only at idle. History

Charging system: stock
Ignition system: use's petronix ignitor and bosch platinum plugs all else stock
Fuel system: stock
Charging system delivers 13.75 volts at idle climbs to 14.25 at around 2500 rpm
Engine timing is correct but hard to verify with the location of the *(#$^ timing mark.
Can the timing being to far advanced or retarded cause this issue.
Its very annoying
 

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Old Opeler
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Low Idle

Sounds like your idle speed is set just a bit too low and there is so little power available that whenthe alternator goes under full load it is too much for the engine to drive. The other thing to check is the vacuum advance - high vacuum at idle "sucks" in considerably more advance which ignites the lean idle mixture much more positively. If the vacuum advance diaphram has a tiny hole in ti then less advance will be "sucked" on and >>>> less fuel will be burnt >>>> giving less power. On most motors you can hear the revs change slightly at idle when the load goes on to the alternator.

HTH
 

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Discussion Starter · #3 ·
Vacuum

O.k Idle speed set at 850
are you saying that i'm not getting enough advance on the dist or to much
 

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Charging system delivers 13.75 volts

Rich,

I would have the charging system load tested to find the charging system amp output. The voltage reading alone doesn't tell the whole story. I've noticed that some part stores have the equipment and will test your charging system- free of charge. If a repair shop charges you anything it wouldn't be much to test. :)
 

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Rich, check your battery voltage in a static condition, engine not running and no load on the battery. The conditions you describe "appears" that you may have a battery going south on you, ie., a dead cell or bad cell. The charging system is putting out just what it's supposed to 13.8-14.2 volts. HTH.
 

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charging system is putting out just what it's supposed

I've had situations in the past where the volt meter would read correctly, but when the system was put underload there was a failure due to high resistance. Its typically caused by bad connection somewhere between the alternater and battery, battery to ground or even (most unlikely) alternator to ground (engine to ground). It would seem most likely that you would have a starting problem in all the above senerios except if you had a bad connection between the alternator and battery. It certainly could also be a problem with the battery internally, but I would think that might cause a starting problem as well? Is there an intermittant starting problem or any other indicators that you may not have thought about?:confused: Good luck!
 

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Old Opeler
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Flicker....

Firstly, have you set your idle speed at 850 rpm with an acurate dwell meter type rev counter or by looking at the original rev counter?
Secondly, Do the dash lights flicker when you turn on the headlights?
Thirdly, do the headlights turn on normally with a bright light which remains on without flickering or shutting down when the engine dies?

With the ignition I am talking about the vacuum advance not the static, position of the distributor advance. The vacuum can on the side of the distributor can be checked by applying a vacuum to it with a special device that a real good mechanic should have - a hand operated device specially made for testing vacuum cans on didtributors.

Try increasing the idle revs to 950 - 1,000 rpm and see if the problem still occurs.
 

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Discussion Starter · #8 ·
Flicker

This is alot of ground to cover. The battery is not new but holds a charge well I suppose it could be going south but I've had no starting problems. car fires right up even when cold choke operates correctly.

Idle speed was set using the tach in the car.
Distributor is new/rebuilt as is the vacuum advance can.
the lights do not flicker when turned on or when the engine dies they are bright and do not appear to dim other than the drop in voltage when the engine dies and the battery takes over.
I adjusted the timing and carb a little and the car would idle with the lights up
I just got back from a drive in the dark and it seems I may have misdiagnosed this whole problem I now notice that the engine will die when engine is at idle head lights are on and brake pedal is depressed. which I think points to a bad brake booster.
 

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boomerang opeler
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it could also just be the pipe to the booster so look there first its cheaper to change first
 

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Hi Flicker, If your battery is good, and you mash the brake and the engine falters, that might indicate a bad vacuum booster. Or it might indicate a problem with your brake light wiring, that is, a small short somewhere.

You might try disconnecting the vacuum line to the booster (plug it) and see if the problem persists. As others have mentioned, connections are very important, make sure they are all clean and solid and that you have good grounds to the engine and the fuse block. And of course, the battery could be going south, how old is that battery and what brand is it?

If the problem is isolated to the brake pedal and it is not the booster, then check the electrical system with regards to the brake lights, as well as connectivity from the battery to the car, alternator etc.

P. Martin
 
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