Car Stalled when Decelerating From Cruising - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 08-21-2019, 06:54 PM Thread Starter
 
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Car Stalled when Decelerating From Cruising

So my brand new gto had a funny thing happen. My. Rebuilt 400 with over 1,000 miles normally idles very nicely. It is rebuilt, headers, and a bit of a cam but can sit idling forever, and in gear at intersections no problem. But today I was cruising along at about 50 or so, and ahead of me traffic had stopped down a slight hill. I stopped rather quickly, but not unreasonably, when the car stalled - it actually stalled just as I was coming to a stop, and the car should have been changing to idle. I stopped, put into park, then it was a bear to restart. Eventually held my foot to the floor thinking it was flooded, and it did restart. Any ideas what would cause such a thing with a car that actually idles fine? I really don’t think I have a vacuum leak, and I haven’t been able to recreate this. Thoughts? Thanks!

Last edited by Ebartone; 08-21-2019 at 07:58 PM.
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post #2 of 12 (permalink) Old 08-21-2019, 10:05 PM
 
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So my brand new gto had a funny thing happen. My. Rebuilt 400 with over 1,000 miles normally idles very nicely. It is rebuilt, headers, and a bit of a cam but can sit idling forever, and in gear at intersections no problem. But today I was cruising along at about 50 or so, and ahead of me traffic had stopped down a slight hill. I stopped rather quickly, but not unreasonably, when the car stalled - it actually stalled just as I was coming to a stop, and the car should have been changing to idle. I stopped, put into park, then it was a bear to restart. Eventually held my foot to the floor thinking it was flooded, and it did restart. Any ideas what would cause such a thing with a car that actually idles fine? I really don’t think I have a vacuum leak, and I haven’t been able to recreate this. Thoughts? Thanks!

You already answered your own question in my opinion - flooded it. Quick stop caused gas to slosh out from the top of the carb (assuming Q-jet). The secondary rods that go through the top of the carb are not sealed. The trick is to put a piece of cellophane tape on the gasket before re-attaching the top of the carb. Once attached, you push the secondary metering rods through the tape to create a better seal around them so gas won't slosh out on hard acceleration.

Other things could be too high of a float setting.

Idle too low for cam chosen, and aggravated if you have a stock converter.

Check for a vacuum leak if you have power brakes.
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post #3 of 12 (permalink) Old 08-21-2019, 10:19 PM Thread Starter
 
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You already answered your own question in my opinion - flooded it. Quick stop caused gas to slosh out from the top of the carb (assuming Q-jet). The secondary rods that go through the top of the carb are not sealed. The trick is to put a piece of cellophane tape on the gasket before re-attaching the top of the carb. Once attached, you push the secondary metering rods through the tape to create a better seal around them so gas won't slosh out on hard acceleration.

Other things could be too high of a float setting.

Idle too low for cam chosen, and aggravated if you have a stock converter.

Check for a vacuum leak if you have power brakes.
Thanks for the response! Thing is, I burnt a quarter tank of gas this evening, trying to recreate this, with no luck at all. Running up to 50 mph, stopping fairly quickly down hills, with absolutely no problem. But when this happened earlier, it was not about to start again easily (as I was trying to impress the wife with my new car, and we sat out on the middle of a fairly busy road!). I have to say, this engine runs amazingly (except that incident). I was wondering, what about vapor lock? I had always thought that the term vapor lock, loosely translated, means”I don’t really know what the problem is, so it must be vapor lock”, but could that apply here? Yep on the q-jet for sure, but the idle is about 675 or so, and agin normally runs perfectly. Thanks very much for responding!
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post #4 of 12 (permalink) Old 08-21-2019, 10:44 PM
 
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Thanks for the response! Thing is, I burnt a quarter tank of gas this evening, trying to recreate this, with no luck at all. Running up to 50 mph, stopping fairly quickly down hills, with absolutely no problem. But when this happened earlier, it was not about to start again easily (as I was trying to impress the wife with my new car, and we sat out on the middle of a fairly busy road!). I have to say, this engine runs amazingly (except that incident). I was wondering, what about vapor lock? I had always thought that the term vapor lock, loosely translated, means”I don’t really know what the problem is, so it must be vapor lock”, but could that apply here? Yep on the q-jet for sure, but the idle is about 675 or so, and agin normally runs perfectly. Thanks very much for responding!


Yep, it could simply fall under the "shit happens" category seeing you cannot reproduce it. It could have been you took a slug of water just at the wrong time if you run any gas with the ethanol in it. I could have been a vapor lock issue, but this is typically when you go to start the engine after it is already hot, but I would not rule it out with the summer temps we have been getting.

I personally add a little Sta-Bil 360 in the tank in my '73 Fury and '92 S-10 which is said to help pull any water out of the gas. I do find it runs better, but just might be in my head. And if you don't run the car every week (which I don't), it'll help keep the gas fresher longer. There may be other additives that will work just as good, but this is what I use, and have for the past 2 years.

I would not be overly concerned unless it repeats itself. I am not promoting AAA, but they have a nice towing program. The Gold membership like I have allows for 2 tows a year up to 100 miles for free. You can typically get a roadside package/towing through your insurance agent pretty cheap, but you have to ask for it. My buddy with a '67 Chevelle has a policy through his insurance agent. Peace of mind in my book, and takes away some of that frustration if you have a problem. Just make the call and get towed to home or a repair shop. AAA will also bring you a new battery and install it if yours dies (personal experience) or gas should you run out. You have to pay for the battery or gas, but not the road call - beats walking!! LOL
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post #5 of 12 (permalink) Old 08-22-2019, 09:45 AM Thread Starter
 
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Thanks Jim! I think my approach for now will be to see what happens, and at least now I'm super aware of it. All said, I think my head is back to your original thought on it being bowl related. It makes sense, braking down a hill, and what appeared to be a flood. If this happens again I'll pop the top on the q-jet, check out the gasket, look at the float level. Maybe I'm being picky, but it just seams that I should be able to expect the car to stop quickly on the downhill without flooding, but I guess I have high expectations!

Thanks allot - I always enjoy reading your posts!

Ed
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post #6 of 12 (permalink) Old 08-22-2019, 05:11 PM
 
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Ebar, yeah I think Pontiac Jim has got this one nailed down with the most likely cause, high floats and or gas sloshing out. as PJ said your hard start, where you thought it was flooded would coincide with that diagnosis.

most likely it is a carbuereter stall and those come in 2 forms "rich stall" or "lean stall." A common "lean Stall" comes when the throttle plates are tight when closed at idle...

but now are open and driving and suddenly slam shut...... this causes an over lean condition, you can see it on the air fuel meter if you use one, but if it is too lean for too long it will stall the car.......so the car manufacturers put on an "anti-stall dashpot", on the side of the carb which is basically a plunger that prevents the throttle from slamming shut.......it eases it down, and does not stall.

Some cars and carbs had them not all it depended on engine and trans combos, also many hot rodders took them off. One way to prevent that lean stall is just a little more opening of the throttle plate at idle, very little. but just enough to prevent the over lean stall.

it it happens again when you come off the gas real suddenly and the throttle slams shut, and no hills involved or hard braking, it could be that. But I think PJ is right, it is a rich or flooded condition most likely.

Vapor lock does not need any rapid deceleration, rather heat alone while driving, will cause the fuel in the suction side of the pump,...between tank and pump ......

to boil and vaporize because the vacumn created by the pumps suction lowers the fuel's boiling point, and today's gasoline already has a low boiling point.

with vapor lock you can be cruising along and the car just stops, no fuel and no hard stop needed. A return line to the tank is the is the cure for vapor lock.

Float height is critical on all carbs, you need that set right before you can deal with anything else, does not sound like you are having it regularly. i would follow PJ's plan check float height and go from there.

and I always recommend a bottle of ................"Redline S1 Complete Fuel System cleaner", drop a bottle in your gas tank when full. It will clean up the carb and intake even remove carbon deposits on the pistons. It contains the only chemical that will do that...PEA... Poly Ether Amine....the trade name is Techron.

It was developed by Chevron Chemists. Redine also has octane boost and upper cylinder lube as carriers for the PEA, so you win all around.

Nothing comes close, it has the most PEA of any of the very few products on the shelf that have PEA......

If it does not have PEA..it is just Voodoo,....others that have it are Amsoil PI, Gumout Regane, (not all Gumouts, only Regane) Techron,.....a couple others.

anyway your car sounds cool! keep driving it! Garage Queens just rot out anyway.....
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post #7 of 12 (permalink) Old 08-22-2019, 07:12 PM
 
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Oh and I should clarify because PJ mentioned Stabile gas stabilizer"........a great product, but a different purpose

I was referring to fuel systems cleaners.......with PEA

I also like stabile, but my favorite is the “Stabile 360 Marine”....It is a little stronger, has a vapor element to help reduce phase separation...water and fuel....and is recommended for not just storage but as an ongoing additive.....

Those are my favorites, I like em in small doses regularly.....RedlineS1.....and Stabile 360 Marine....

Others like different stuff.....
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post #8 of 12 (permalink) Old 08-23-2019, 11:30 AM Thread Starter
 
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Awesome LG, thanks! Ever hear of a product called Sea Foam? Any thoughts on that? I would definitely want to add something that would deal with water too, if that's the case. When I had the car delivered (about a week ago), it had about an 1/8 of a tank, and I bet that had been sitting for a year or so with only occasional starts, no driving to speak of (I know this from the previous owner). I immediately filled it up w 93 octane at the station, but don't know what surprises may still be there from that 1/8 tank. So a crazy gulp of water is a real possibility, although admittedly a bit coincidental - I'm still leaning to the bowl I think. Thanks!
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post #9 of 12 (permalink) Old 08-23-2019, 12:57 PM
 
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Not a fan of sea foam, it was developed in the 30’s to clean boat motor carbs......hence the nautical name...

Makes a lot of white smoke, so if you have a rock band and need white smoke I guess it is ok for that...

Bottom line is the only chemical cleaner that will clean off combustion deposits is PEA,...because the chemists at chevron developed it to withstand the high temperatures of combustion...for a cleaner....you need PEA....Seafoam does not have any...

Redline S1 to clean and a little octane boost......”Stabile Marine 360”for water phase separation,.......is what I like in small regular doses
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post #10 of 12 (permalink) Old 08-23-2019, 01:05 PM Thread Starter
 
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Awesome, thanks!
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