| Author |
Message |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 873
Registered: 12-2001
| | Posted on Friday, August 01, 2003 - 8:42 am: | |
I appreciate it. I tend to think that myself. Anything else to check? |
Greg Rodgers (Joechristmas)
Member
Username: Joechristmas
Post Number: 785
Registered: 3-2001
| | Posted on Thursday, July 31, 2003 - 4:13 pm: | |
I think you are down a cylinder. It doesn't seem to be electrical to me from your input. You do have a 55A alternator. Your battery test idea would be a good idea just to try but I still think a cylinder is missing. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 872
Registered: 12-2001
| | Posted on Thursday, July 31, 2003 - 4:06 pm: | |
TTT |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 871
Registered: 12-2001
| | Posted on Wednesday, July 30, 2003 - 8:01 pm: | |
I can hear the difference. Believe me 500 or so rpm difference is noticeable to the ear. See my V drop. I would think that I would see a much larger drop if it was clutch related, electrically speaking. I do see a V drop but I would expect a drop with electric fans and clutch engaged. |
Steve (Steve)
Member
Username: Steve
Post Number: 446
Registered: 2-2001
| | Posted on Wednesday, July 30, 2003 - 7:55 pm: | |
I set my idle at 1100 rpm and when I turn on the AC it drops to 1000rpm. 1 year old compressor new belts and carbs all sync'ed up and tuned. I was thinking of adapting the AC idle solenoid like the early carb GM cars but for the sake of uping the the idle it wasn't worth the effort. All FI cars have auto idle adjustment with the IAC valve and the CPU. If you are losing 700rpm you have a AC clutch problem. Also try a tach. in the enging and verify the difference between that and the dash tach. |
Lee Hamner (Tennlee)
Junior Member
Username: Tennlee
Post Number: 123
Registered: 2-2002
| | Posted on Wednesday, July 30, 2003 - 5:41 pm: | |
My rpms drop maybe 100 with the AC in a carb 308. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 870
Registered: 12-2001
| | Posted on Wednesday, July 30, 2003 - 3:47 pm: | |
When A/C is off I am getting 13.67V at the battery. When the A/C is on it is showing 12.60V this also turns on one radiator fan. |
Paul Hill (348paul)
Member
Username: 348paul
Post Number: 345
Registered: 12-2002
| | Posted on Wednesday, July 30, 2003 - 2:29 pm: | |
The external battery test would at least be one more step to finding out what the problem is. You would also be able so see what is happening as well if you can switch the 12v to the clutch.
Paul
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dave handa (Davehanda)
Intermediate Member
Username: Davehanda
Post Number: 1415
Registered: 5-2001
| | Posted on Wednesday, July 30, 2003 - 1:48 pm: | |
As a point of referrence, both my previous 78 308 GTS and current 87 328 GTS drop about 100 rpm when the A/C is turned on at idle. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 869
Registered: 12-2001
| | Posted on Wednesday, July 30, 2003 - 5:48 am: | |
When I purchased the car it didn't have working A/C. After changing the hoses, drier, and other components the system was charged. It has been doing this ever since. I normally bump the idle up in the summer so I can use the A/C. I will test the V at the battery with the clutch engaged (compressor) and when off at idle. The 78' 308 doesn't have an idle up circuit for the A/C.
Hans I balance the air flow at 1000 rpms and I am getting around 3.5 Kg/hr with a synchrometer. When off idle they all increase proportionally/equally. If there is anything else you think I should check please let me know. What about if maybe one cylinder isn't firing well or has a slight fuel obstruction?
Also would my external battery trick work to test the electrical? |
Malcolm West (Ferrari_uk_tech)
New member
Username: Ferrari_uk_tech
Post Number: 6
Registered: 7-2003
| | Posted on Wednesday, July 30, 2003 - 3:24 am: | |
Sounds to me like the a/c clutch is drawing too much voltage out of the battery - maybe a faulty a/c clutch, might also be worth checking that the alternator is performing correctly - what is the charge rate at idle with the a/c on then turned off ? |
Phil Hughes (Ferrarifixer)
New member
Username: Ferrarifixer
Post Number: 20
Registered: 7-2003
| | Posted on Wednesday, July 30, 2003 - 2:41 am: | |
Is this something that just happened one day, or was like it since a certain event or maintenance?
Or did you just buy the car and it was already like it?
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Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1599
Registered: 4-2002
| | Posted on Wednesday, July 30, 2003 - 2:19 am: | |
I'm not sure about model years, but most, maybe all, carb F-cars don't have an idle solenoid. But I know what you mean, as 1970 vintage GM cars had them. Late 1970 F-cars had a "dashpot", which was a shock absorber-type device which prevented a snap closure of the throttle. But even if Richelson's car is so equipped, this wouldn't explain a steady state idle problem.
I'd still suspect the carbs, but if you are not convinced, check the high/low A/C pressure. It's a real cheap deal, providing you use a competent A/C specialist. They should be able to tell you in 5 minutes. (And if they tell you that they don't do R-12, then they aren't competent. ANY decent A/C shop uses all of the common refrigerants.) |
Eugene Angelo (Eangelo)
Junior Member
Username: Eangelo
Post Number: 62
Registered: 8-2001
| | Posted on Tuesday, July 29, 2003 - 9:12 pm: | |
I'm not sure about F-cars, but many older domestic cars use an idle solenoid (sp?) that kicks up the idle just a little to compensate for the extra drag on the motor from the AC compressor. These solenoids are normally mounted on the side of the carbs. If this solenoid is not working, the idle will drop significantly. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 868
Registered: 12-2001
| | Posted on Tuesday, July 29, 2003 - 7:20 pm: | |
It could be electrical. I am just not sure how to go about narrowing it down. My carbs are in good balance. This is a drastic draw or drop in rpms. I appreciate the help. I could take an external 12V battery and start the car and power the clutch (a/c that is) through the external 12V battery to see if it is an electrical draw. Would that work? I have a feeling it is something else though. |
Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1597
Registered: 4-2002
| | Posted on Tuesday, July 29, 2003 - 7:14 pm: | |
Total Wild-Ass-Guess: Maybe if your carbs aren't well sync'd you could have a few cylinders doing most of the work at idle. Add a load, and rpm drops, as these few cylinders can't handle the extra work.
Less likely: Extra Heavy Duty Drag in your A/C compressor. I kind of doubt this, as I would suspect that you would notice some problems with the A/C system itself. But, just in case, you might have the high and low side pressures checked. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 867
Registered: 12-2001
| | Posted on Tuesday, July 29, 2003 - 6:44 pm: | |
It has a new A/C belt. Car runs fine with the A/C on except for the idle. If I bring the idle up to 1000 rpm with the A/C on it drives normal.
Do you have any ideas on what it might be? |
Mike Procopio (Pupz308)
Member
Username: Pupz308
Post Number: 460
Registered: 10-2002
| | Posted on Tuesday, July 29, 2003 - 6:44 pm: | |
Agreed. No change in RPM for me.
Anything that represents excessive resistance for the spinning of the crankshaft will drop the RPMs... Your AC compressor should not represent this resistance, but it apparently is.
How does the AC Compressor belt look (see owners manual for location)?
How does that car run otherwise, for example, under heavy acceleration with the AC on?
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Hans E. Hansen (4re_gt4)
Intermediate Member
Username: 4re_gt4
Post Number: 1593
Registered: 4-2002
| | Posted on Tuesday, July 29, 2003 - 5:28 pm: | |
Hmmm.... *something* is haywire. I don't notice any rpm drop at all. |
Richelson (Richelson)
Member
Username: Richelson
Post Number: 866
Registered: 12-2001
| | Posted on Tuesday, July 29, 2003 - 4:09 pm: | |
When I turn the A/C on in my carb 308 the rpms drop much more than they should. I have the idle set to 1000 rpm and when the A/C is turned on the rpms drop to around 300-400. What would cause this? Would the carbs need to be rebuilt? |