1977 Grand Prix lj

[Grandprix723]

Took the car out to the casino at spirit mountain today. Going up the mountain on the way home at 50 mph I punched it to pass another car near the top. It downshifted to 2nd and accelerated it shifted to 3rd then started this up and down surge. I got off it and it smoothed out. Sounded like some top end engine noise also. It's got the 400 and high octane non ethanol fuel in it.

[64 kiwi boni]

5 hours ago, Grandprix723 said:

Took the car out to the casino at spirit mountain today. Going up the mountain on the way home at 50 mph I punched it to pass another car near the top. It downshifted to 2nd and accelerated it shifted to 3rd then started this up and down surge. I got off it and it smoothed out. Sounded like some top end engine noise also. It's got the 400 and high octane non ethanol fuel in it.

Drive it some more and see if there is  a pattern to whats happening... climbing a mountain will be lots of different things, how does it run on the flat high way ? does it do it some times or all the time ... its kinda like being a detective ! you gota work out all the possibles and eliminate the variables . BUT

 do the basics, up down surge to me sounds like fuel. but it could be electrical too. float level in the bowls too high ??, points in the dizzy ??

i would give her a tune up, plugs,points, check dwell, replace your fuel filter, cap, rotor, leads if they are old.....all these parts are cheap and once you have replaced them you know where your at. 

also your carb, how long since it was cleaned/ rebuilt?... is it the factory jobbie ? ... 72 i am thinking its a carter? FROSTY  ... please enlighten us .

justA my fifty cents.. oh thats nzd 

 

Edited May 17, 2021 by 64 kiwi boni

[Grandprix723]

Thanks for the reply. I just limited it home but on level it seemed fine. I didn't romp on it any more though. All ignition parts were replaced by me not long ago with careful precision. No points on this car and a reman carb was installed by me and dialed in by ear and nose. I did time it with a light. It used to screem any time I romped on it any where any time so this is of concern. The fuel filter will be the first thing I look at. But it was replaced a couple months ago with the carb. It has a new fuel tank and pump too. After work today I'll run it again and try to figure it out. Thanks

[Frosty]

I am wondering if the new carb is properly tuned for high altitude conditions. The surging sounds like it is leaning out under a combination of heavy load and high(er) altitude. The carb may be fine closer to sea level but gets lean in the mountains as the air thins out.

Edited May 17, 2021 by Frosty

[Grandprix723]

I tuned the quadrajet myself with no special tools other than a timing light and rpm meter. The window on the air fuel mixture is very small. Half a turn too far in and its lean and half a turn out you can smell the richness. So it's pretty close unless there is another adjustment specific to altitude??? It did seem like a lean condition to me as well. 

[Grandprix723]

Just back from a test drive. First I leaned the air fuel mixture screws about a half turn. It smells cleaner running now. 

Did the 50 romp it downshifted to 2nd secondaries kicked in then at around 65 or 70 shifted into 3rd and there's a problem. It starts to bog or surge up and down. Once I get off it and run on just the primaries it works great. So it seems for some reason the secondaries are not functioning correctly under load in 3rd gear. How far are they supposed to open. When I open the throttle manually they barely open after a few seconds. Oh maybe the float is off and I'm draining the bowl?

 

Edited May 18, 2021 by Grandprix723
Addition

[Frosty]

Those are all good possibilities. Also I am wondering if you are ever getting to full wide open throttle. Perhaps have a friend or family member step on the gas for you while you watch the throttle cable on the carb and then have them gun it to the floor. Is the gas pedal opening the throttle all the way open or does it need to be adjusted? I would expect the car to bog under hard load if the throttle is not opening up all the way, or if the secondaries are too small.

Edited May 18, 2021 by Frosty

[JUSTA6]

Have you checked your fuel pressure?   Could be a bad pump.  Manuel or Electric?  In the mountains you experience Rich conditions as the air is so thin for what your carb is dumping in, but you seem to think it's a lean problem. 

[Grandprix723]

The coastals are only 1500 feet. It does the same thing at sea level. It ran fine till a couple days ago. It's a mechanical fuel pump and it's fine. It's narrowed down to an issue with the secondaries. Frosty suggested  checking to see if the secondaries open all the way. I don't think they are and as a result it's too rich for high gear.

[Frosty]

Out of curiosity - was this originally a 4-barrel engine car or a 2-bbl? I didn't believe it until Indyman Joe showed me the part number, but on A-body's there is a replacement throttle cable when you convert from a 2-bbl to 4-bbl. I'm stretching but it is another possibility.

[Grandprix723]

It's a 4-barrel. I replaced that little in line fuel filter last night. I didn't have time to take it out yet. Since I was running pump gas,  I think the filter wasn't designed for ethanol, it was slowing the flow of fuel. Also I'm going to reach into the wallet and buy a vacuum gage and pump to check manifold pressure and my egr to pinpoint that unsteady idle. I replaced the egr a couple years ago. It's only held on by one bolt, not a good design. I sprayed brakleen around it yesterday and smoothed the idle for a minute. I'd like to just block it but there's only one bolt.

[Frosty]

If the engine smooths out or speeds up with you spraying brakleen around the cab and manifold, then chances are good you have a vacuum leak some where. That won't help you solve your problem. Do you need a new gasket or gasket sealer for the EGR valve?

[Grandprix723]

I will investigate that later after work. I installed it right but there is a leak at the manifold where the egr mounts to it.

[Grandprix723]

So left work early to look at this egr valve see photo. I remember last time I took it apart a couple years ago that the transducer had been braised sometime many years ago. It does not hold vacuum. The egr is good I was hoping to find a chunk of carbon holding it open, nope. Any thoughts about the transducer.

[Grandprix723]

I omitted the transducer and put it back together. It still stumbles at idle and running without the transducer it also hesitates when you take off. Guess I'll reinstall it now. I haven't opened it up yet to see if I cured that problem yet. I don't get how that transducer is so important.

[Grandprix723]

Runs nice and smooth with backflow transducer installed. I romped on it and it goes like it should. Paper inline fuel filter went bad using pump gas in two months.

[Grandprix723]

Thanks for being there everyone who tried to help me figure this thing out.