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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 20 Apr 2009 :  10:11:44 AM  Show Profile  Reply with Quote
Dear Pontiac Aficionados,

My 1970 455 Bonneville is having hot weather engine issues:
Running rough at lower than usual idle rpm (500-550 rpm in park), stalling if trans gets put in drive
Symptoms come and go, though are more likely right after hot start, especially in hot weather.

Could this be the original high altitude Quadrajet, not suitable for hot weather at sea level? Or is it just heat soak? How do I find out about the cause and how do I correct the situation? Do I need to recalibrate the carburator (idle mixture screws, power valve spring, change jets/rods), insulate the engine compartment fuel lines? Install a smaller fuel filter?

Any help or advise is greatly appreciated.


Very best regards,

Rick

Christ
Howling Wind

USA
1805 Posts

Posted - 20 Apr 2009 :  10:37:15 AM  Show Profile  Visit Christ's Homepage  Reply with Quote
Well first off make sure you do nothave vacumn lock! Second check your plugs for light tan color. If there white to lean. Black to rich. Also use a vacumn guage to adjust carb! idle seems low to me. I never went below 650 but I don't have the spec's for your car!

Wht type fuel you running 92 octane?
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Bill Boyle
Horse Feathers (Charter Member)

USA
4010 Posts

Posted - 20 Apr 2009 :  11:55:41 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
I've experienced the same malady in years past. In hot weather (really hot)--90+ degrees F, my idle would drop 75-150 rpm. I'd come to a stop light and the engine idle would be 600-650 rpm. (Stick car with clutch engaged). Then at night in cooler air, 75 degrees, the idle would be a normal 750-775. Same gas, same carb, different temperature, different humidity. The engine temperature was under 200 during the day and less than 190 at night. This occurred in California where it is rather dry. It does the same thing here in South Florida. As the temperature here is not very drastic in terms of day and night time temperatures during the summer, I adjusted the idle so it would run a little faster at idle. As a result the change from day and night driving is pretty consistent. I did not change the air fuel mixture--I have it on the rich side.

I sense your air fuel mixture and idle needs a minor adjustment.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 21 Apr 2009 :  09:14:37 AM  Show Profile  Reply with Quote
Dear Pontiac Aficionados,

Engine Vacuum at normal idle (750 rpm in Park, T<<25 deg. C) approx. 18.5" Hg
Engine Vac at erratic idle (550 rpm in Park, T>25 deg C) approx. 14.5" Hg, though needle is a little "bouncy"
Always using Shell 98 RON V-Power with additional lead substitute (officially running 10.25 iron head compression ratio)

Additional info: the engine can even stall when coasting to a stop at low speed (veh. sp. < 15 mph)


Very best regards,

Rick
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Christ
Howling Wind

USA
1805 Posts

Posted - 21 Apr 2009 :  3:01:27 PM  Show Profile  Visit Christ's Homepage  Reply with Quote
quote:
Originally posted by dr. Rick Riviera

Dear Pontiac Aficionados,

Engine Vacuum at normal idle (750 rpm in Park, T<<25 deg. C) approx. 18.5" Hg
Engine Vac at erratic idle (550 rpm in Park, T>25 deg C) approx. 14.5" Hg, though needle is a little "bouncy"
Always using Shell 98 RON V-Power with additional lead substitute (officially running 10.25 iron head compression ratio)

Additional info: the engine can even stall when coasting to a stop at low speed (veh. sp. < 15 mph)


Very best regards,

Rick





Ok Rick. Check for small vacumn leak or leaks? around carb and intake. Use 4d 40 spray it in area to see if it sucks it in! This what it sound slike to me!
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bnorris_74
Crazy Horse

USA
1412 Posts

Posted - 21 Apr 2009 :  7:21:56 PM  Show Profile  Reply with Quote
How up to date is your ignition system?

Maybe heat soak in the ignition coil could be a problem.

How about the valve train? Adjustable? Just throwing out the idea that once it gets heated up you are losing your lash.

Brian
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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 22 Apr 2009 :  12:38:04 PM  Show Profile  Reply with Quote
Dear Pontiac Aficionados,

The ignition system has been upgraded right after purchasing the car, approx. 4 years ago now, by fitting a Pertronix Ignitor II trigger and matching new coil and RS plug cables. Except for an occasional relocation from the small to the big shed (getting car away from agricultural unloading/stocking/loading activities) under her own power, the car hasn't been driven much 'till last fall, when I finally got her registered. Up to now, I've done a few fair weather cruises, cumulating slightly over 600 miles. So ignition system wear is very unlikely in my opinion.

As far as heat is concerned, the engine never really gets hot. I know the stock in dash (rallye cluster) temp gauge isn't very accurate, though the needle never gets past 180F if you drive the car in a civilised way. If you pretend every stoplight is the starting grid of a drag strip, the engine temperature steadily climbs towards 210F, though even in hot weather doesn't seem to go past this T milestone. The car is an original airco equipped model, although I ditched the condensor, compressor and all airco lines, so cooling capacity isn't an issue at all. I can verify the engine's T with an infrared thermometer, I've purchased recently, if that would be helpful, though would like to know what to aim for (siamesed exhaust ports of cylinder head, upper radiator intake tank, timing chain cover, water crossover intake manifold) and what values would be OK. The radiator is equipped with a 16 psi overflow cap and spits out approx 0.5 litres of coolant during warm up. No amounts worth mentioning get added to that during trips. All gets sucked back in after cooling down.

The original one snorkel closed case air cleaner has been replaced with a large reusable deep drop base air cleaner with directly exposed filter. Probably this slightly increases the temperature of the intake charge, though as far as I'm concerned this must get compensated by the larger amounts of air that can be drawn in.

The valve train consists of stock hydraulic lifters and press in rocker studs with stamped rockers. So not much adjustability here, though maybe it makes sense to pop a rocker cover or two and have a closer look?

I'll give the vac leak search idea a try. Will WD40 do or need I an agressive brake cleaning agent to do this?

Thanks a whole lot in advance for your concern, ideas and feedback.


Very best regards,

Rick
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Vanmor
Cochise

USA
572 Posts

Posted - 22 Apr 2009 :  12:57:51 PM  Show Profile  Visit Vanmor's Homepage  Reply with Quote
Rick,

This may sound silly, but you may not be driving the car enough and your fuel my getting a bit stale. Maybe try a fuel stabilizer ?

Vance

"A man has got to know his limitations." Dirty Harry
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dr. Rick Riviera
Sitting Bull

Belgium
214 Posts

Posted - 23 Apr 2009 :  07:44:55 AM  Show Profile  Reply with Quote
Dear Pontiac Aficionado,

That's actually not silly at all! My car can sit in the garage for up to 3 months, waiting for a sunny afternoon to hit the road. I try to just fire her up and have the engine reach normal operating temperatures before shutting her down again every now and then, though that doesn't really freshen up the gasoline that's in the tank indeed. I'll give her a shot of fuel stabiliser right after filling her up with fresh fuel again and see what happens.

Just out of curiosity, what would a sticking valve do to engine vacuum, idle speed and low and high speed vehicle behaviour? Would a bad lifter cause the same kind of issues? How do I isolate a bad lifter/sticking valve?


Very best regards,

Rick
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