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77 Trans Am rough idle and engine pulsation
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jyank
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Jul 1, 2016, 4:38 PM
Post #1 of 15
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77 Trans Am rough idle and engine pulsation
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Had 77 T/A since new. 59000 miles. All original or stock. Engine idles rough and there is a pulsation ( the best word I can use) when at speeds from 55 and up. All new electrical from the spark plugs to the pick up coil in the distributor. Problem must be in the carb. Never rebuilt. I will purchase a rebuilt if need be. Any ideas please. If it could be something else then the carb. Engine is 400 cid. 6.6 liter quadrajet carb auto trans.
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Discretesignals
Ultimate Carjunky
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Jul 1, 2016, 4:45 PM
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Re: 77 Trans Am rough idle and engine pulsation
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Is the pulsation repetitive such as if you disabled a cylinder? Is there a way you record the sound of the engine and upload it to a video hosting site and paste the link in here?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 1, 2016, 4:46 PM)
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jyank
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Jul 1, 2016, 4:55 PM
Post #3 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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It's not repetitive. Does not feel like a miss fire. When you step on the gas hard the car accelerates without skipping a beat. It is a random pulsation at highway speeds.
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Discretesignals
Ultimate Carjunky
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Jul 1, 2016, 5:05 PM
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Re: 77 Trans Am rough idle and engine pulsation
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It possible you could have a carb problem. Qaudrajets had their issues such as leaking metering wells, clogged up air bleeds, and etc. It is important to be sure the engine itself it is good shape mechanically. The cylinders need to have good even compression and no vacuum leaks or a sticking open EGR valve. With the mileage it probably wouldn't have engine mechanical issues, but wouldn't hurt to run a compression test. Also possible there could be cylinder head valve problems. Valves sticking in the guides or sealing issues could cause random misfires.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Jul 1, 2016, 5:13 PM)
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jyank
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Jul 1, 2016, 5:24 PM
Post #5 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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Thanks for the reply. Will look into to what you suggest. thanks.
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Discretesignals
Ultimate Carjunky
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Jul 1, 2016, 5:31 PM
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Re: 77 Trans Am rough idle and engine pulsation
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Another possibility is that the rubber of the engine mounts have turned to stone and you can feel excessive vibrations through the body. Really the car needs to be driven by a professional to get an idea what is going on.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Tom Greenleaf
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Jul 1, 2016, 8:56 PM
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Re: 77 Trans Am rough idle and engine pulsation
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Note on this carb: Big bucks rebuilt and many worse than what you have. Learn or find the right person as they are about the best fuel mixing carbs ever made just getting one right is a total pest.
They are a maintenance item by '77 if OE you can buy the parts and are mostly just cleaning it. '77 or close is also when they tamper proofed chokes and idle mixture screws. You need to know how to remove that stuff properly just to clean them or ruin them. Just FYI,
T
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Hammer Time
Ultimate Carjunky
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Jul 2, 2016, 3:53 AM
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Re: 77 Trans Am rough idle and engine pulsation
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Nobody independent does a good job on these any more because there is just no demand. There are carb suppliers online that specialize in this stuff and that is about the only place to get a goo rebuild these days.
Here is a Google search that turned up dozens of suppliers.
https://www.google.com/...e=utf-8&oe=utf-8
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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jyank
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Jul 2, 2016, 4:05 PM
Post #9 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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Thanks for all the help. I searched on line for a carb and called numerous suppliers. Serial number 17057266. The only place that got one is Carburetor Exchange out of California. Can ship right away. About $345 including shipping. Has anyone done business with them? I don't care about spending the money if it solves the problem.
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Hammer Time
Ultimate Carjunky
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Jul 2, 2016, 4:08 PM
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Re: 77 Trans Am rough idle and engine pulsation
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I think I may have done some business with them in the past. I don't recall having any problems. I assume that price probably includes a refundable core charge.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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kev2
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Jul 2, 2016, 4:35 PM
Post #11 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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no testing and ready to spend 300+ for a guess -
lets slow down - on the spending that is.
lets look at engine vacuum -
how is EGR ?
You sure its engine , not trans, driveline, AC makes no difference,
Any starting issue- cranking more than normal? Puff of smoke at start?
Was the issue there before plugs, and other work?
pick up a copy of Rochester Carburetors by doug roe, that and some youtube* tutorials should get a better feeling for them.
*"quadrajets overhaul youtube"
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Hammer Time
Ultimate Carjunky
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Jul 2, 2016, 4:40 PM
Post #12 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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The carb is 40 years old. I'm sure it is very gummed up inside and should have a rebuild, regardless of any other issues.
Rebuilding it yourself is not really an option. You you have none of the tools or chemicals needed to do that.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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jyank
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Jul 2, 2016, 5:36 PM
Post #13 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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$75 off the 345 if I return the core.
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jyank
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Jul 2, 2016, 5:54 PM
Post #14 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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I am having a mechanic or tech do some of the work on the car. I like to do the work myself or with a friend. Vacuum lines have been checked. There is enough of them. Not sure on EGR. Will check. Same with AC on or off. Good point on trans. I did think of that. Trans appears to be functioning properly. No starting issues. A couple of pumps on the gas and fires right up. Starts the same as when new. No smoke. Issue there before plugs and fuel filter change. That's why I changed the plugs and fuel filter. Old plugs and fuel filter looked great. Haven't been changed in 25 years. The car is stored and only driven about 2000 miles or so a year. Live in upstate Michigan. Tech told me the problem is most likely the carb. Carb looks wet around gaskets.
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Tom Greenleaf
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Jul 2, 2016, 10:45 PM
Post #15 of 15
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Re: 77 Trans Am rough idle and engine pulsation
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Just FYI - many will just bolt on and may not be adjustable for each vehicle. "1705WXYZ" suggests design was complete for a 1975 model year and some years beyond.
It's just leaking - that's easy stuff. Keep the core if not broken hopelessly as you won't find just easy small parts for most whether you do it or a shop.
Trouble is new or rebuilt final adjustment are made on the car while running, some while not. Takes time and shops don't want to spend all the time or plain can't make time for that - the whole reason the carb ended - too much service, no time and wait for parts isn't practical.
Whole vehicles new you went back at 500 miles for final settings just mostly idle speeds cold then warmed up. That really can't be set off car new accurately but close and most never touched is a problem or was when new. New dealer nor customers wanted to deal with taking a new (vehicle or machine back in a couple weeks and most never did.)
Once perfect you really want that carb not another, new or rebuilt rather than a fix when possible.
IDK - your call now but for a '77 would want the "core" for parts later,
T
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