C3 - Help! Engine Problem

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RickStehr

7/7/2007 8:16:49 PM

I know this could be one of a few problems...maybe even as simple as a tune up, but let me run this by you in hope that the specific problem is "common" or has happened to someone before.

First off, the Vette in question is a 1977 L48 4 Speed Manual Transmission. The problems may or may not be related.....

After running for awhile (say 5 miles or so) and with the engine plenty hot, the car seems to miss, or lose power, at low RPM. To be more specific, after coming to a stop at a light, I go to put the car in 1st, hit the gas, and the car wants to stall....and if I catch it right, I can prevent the stall, but the engine power isn't there until she's running high in 1st gear.....the problem does NOT continue through the other gears.

Now, If I don't catch it, and it stalls, its not real easy to start back up....but it does restart. However, the same power problem will be present.

It will go away after it happens and run normally again for another few miles, only to happen again. Its especially noticeable when Im bringing the car into the garage. I have to give an awful lot of gas when backing her up to keep it running.

Now here is the part that may or may not be related....twice when this happened, when I put the car in 1st gear, and let off the clutch, it was as if the car was still in neutral. Nothing happened. I was forced to start in 2nd...but as soon as I do, 1st gear is back. Im thinking this could be a simple adjustment, but transmissions is not my thing, so this I will bring to a shop...but I wonder if anyone else has had similar issues, and were they related??

As far as I know, the car does have only 65K original miles, so it really did not get driven much by the previous owner and I have continued that trend, driving it only once per week for a little bit.

I realize it could be as simple as a tune up, or a vacum leak (but I doubt the vacum leak 'cause I don't hear anything unusual and the problem is intermittent). Keep in mind, the problem only has appeared when the car is hot. It runs perfect until that the first sympton appears each time.

Any idea's????

RickStehr

7/8/2007 5:53:11 AM

quote:

ORIGINAL: cwb

Hangin' choke? Any black exhaust?

Tranny unrelated. Synchros (internal $$), possibly linkage (external). How does the stick feel? I think you have nylon bushings in your linkage. Cheap repair, but painful process.

The stick feels fine. Nothing out of the ordinary, I think (Its been 15 years since I last drove a C3 4 speed, so I don't recall the feeling)...if anything, when that problem happens, there is no resistance at all when putting it in 1st gear (not that there is much anyway, but there is that 'click' if you will, when shifting from gear to gear). Its almost as if nothing is happening at the transmission to place the car in 1st gear.

No black exhaust, but I will look closer next time to be sure.

These problems are such a pain in the a$$ 'cause it could be one of so many different things....Im sure Im not alone when I say I hate the diagnostic part of the repair process the most!

Lee Willis

7/8/2007 9:47:55 AM

The symptoms surely do seem like over rich mixture at low RPM, but they could also be due to the engine running too lean at low RPM, due to a dirty/worn/whatever carb. I'd check vacuum hoses and all that stuff one more time, too, very carefully, just in case: I won't claim to be an expert on emissions controls and so forth from the 70s (is anyone?) but I do recall several cars I owned from that period had driveability problems unless every vacuum hose and fitting was tight, etc. It was often very difficult to find the problems, I recall.

But overall I agree with Starship that your car needs a full tune up, etc. If it were my car it would get a new carb, etc., and a full tune of ignition, plugs, the works, just to be sure (when you aren't certain of the cause, fix everything), but regardless I would want to know what was wrong if possible, so you might try this . . .

Drive it until it is warm, then head home. Drive it at low RPM, etc. -- just on the edge of this problem, then maybe into the driveway and let it stall. Check the exhaust - is there a film of black soot/overrich mixture? Let the engine cool for a bit and then a pull a sparkplug or two and look for the signs of overrich running (and over lean). This won't guarrantee a correct diagnosis but in 2/3rds of the cases I expect you'll see a sign. If you are really expert you could rebuild the carb but its safer to buy a rebuilt of new one, although you may have to re-jet a new one anyway.

cwb

7/9/2007 9:58:30 AM

quote:

ORIGINAL: Lee Willis

The symptoms surely do seem like over rich mixture

Yes it does. That's why we need to find black exhaust at idle. And a very hard warm engine re-start, huh Rick?

So you hate the diagnostic part of the repair, huh? Kinda' forces ya' to think, huh!

Unless you want to pay the mechanic to think for ya'

. And there's no guarantee they will at that!

Air, gasoline, fire. You got too little, or too much, of one.

Check your airflow, check your gas flow, check your ignition [plugs]. Each time you find one that's right, you know it ain't that. AND, you learn how your system works. Next time you got a problem, you'll prbably know exactly what it is.

I do NOT agree with the tune-up suggestion. You won't necessarily find the problem. If you do get lucky tho', and it comes back in 6 weeks, whatcha' gonna' do? Tune-up again?