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Old 07-15-2004, 04:10 PM
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Reasons for Surging

What are some of the reasons that my engine surges some times? It only seems to do it sometimes and usually (but not always) when my fuel level is low.
I'm suspecting my fuel pump may be going bad or maybe it's time for a filter change. Does this sound reasonable?
Thanks for any help.
-alfie

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Old 07-15-2004, 04:20 PM
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Is it possible your fuel pickup is only getting fuel from one side of the tank, and then you're introducing an air pocket in the fuel circuit? Like if the fuel is sloshing around when you go around corners, or when braking or accelerating.

It depends on if you're running TPI or a carb also.

Basically air pockets shouldn't affect carburetors unless the pickup was deprived for quite some time and your fuel bowl floats are set very very low.

You're right, it could also be a fuel pump issue, but it seems suspicious that it only happens when the fuel level is low.

Also, if you're talking carburetion here, you might have a bad gasket on your accelerator pump or something like that.

I'm sure that someone else here will have a better idea than I do, I'm just speculating here.

good luck

tbw
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Old 07-15-2004, 04:27 PM
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i would say what blndweasel said is a pretty good diagnosis, but if you have FI, then thats probably not your explanation, the low fuel is most likely whats causing it.
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Old 07-15-2004, 05:42 PM
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Fuel pick-up, fuel pump, or fuel filter.
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Old 07-15-2004, 07:23 PM
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Those are all kind of the things I was thinking (except the accelerator pump, I'll check it out).

Driving home today it was pretty hot, I stopped off at the auto parts store, and when I came out the coolant temp was pretty high. Anyway, driving along, I'm pretty sure I felt it surge a little bit... hmmm. I wonder if it could be related to vapor lock?
Any opinions?

BTW, the car in question is a '64 caddy with a 429 and an edelbrock 650.

Thanks
-alfie
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Old 07-15-2004, 07:25 PM
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vacuum leaks..............................
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Old 07-15-2004, 08:30 PM
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A small leak that only affects things once the block and components heat and expand? If you were low on fuel it seems it wouldn't surge but rather do the opposite.

How does it run otherwise? WHen its not surging does it seem kinda sluggish. Perhaps it has a constant leak that temporarily seals off causing a closed system which surges because its running correctly.

Kinda out there right lol?
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Old 07-15-2004, 08:45 PM
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its a vacuum leak and either the tbi or carb is loosing and gaining signal based on the erratic flow from the leak-

K
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Old 07-15-2004, 08:58 PM
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Perhaps, I'm mis-describing the symptoms.
When it "surges" it feels like it doesn't have power, then does, if I keep the throttle steady... Does that make sense?

I was just playing with the idle this afternoon and I had a vac gauge hooked up, the vac seemed pretty steady the whole time I was playing with it....
-alfie
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Old 07-16-2004, 06:00 PM
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Ok, I think I've narrowed down the symptoms.
As I'm going up hill and my fuel is low I have small bursts of power. So I'm going up hill, I've got the accelerator floored and it doesn't pull, then all of a sudden I get a small burst of power, then back to no power, etc...
It was doing this to me the whole way home from work.
I was thinking maybe when the tank is low, I'm not getting much fuel into the bowls? Then when I go up hill, what little fuel is in the carb is sloshing away from the jets???
Sounds a little far fetched, huh?
Please help! I was planning on taking the car on a 3 hr (one way) trip this weekend, but now I'm not sure.
-alfie
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Old 07-16-2004, 09:18 PM
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Jet's are locatd near the back of the bowl. Going up hill will cover them. Perhaps you have a float set to high and the fuel is sloshing over into the carb barrel.
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Old 07-16-2004, 10:10 PM
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Good Idea I'll check.
Thanks
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Old 07-17-2004, 03:48 PM
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Here is a list of the problems I've had and their symptoms.

=============================
Fuel filter clogged.

Symptoms:
1. Start car, runs fine.
2. Drive car.
3. Runs fine, but every time I give it gas, it runs with less power.
4. Keep driving and loosing power till the engine doesn't run any more.
5. Pull over, stop engine.
6. Wait a minute or 2.
7. Restart and engine runs fine.
8. Go to 1.

Explanation (a theory):
The crap in the fuel filter was getting all sloshed up in there and getting caked up against the filter paper every time the engine sucked a lot of gas.

When I stop the engine, all the crap falls down.

The car went from running fine with no problems to barely drivable in about 3 days.

=============================
Bad distributor cap.

Symptoms:

1. Car was running fine.
2. Was driving home from work, and about half way home (about 5 miles of driving) the engine starts to have no power every time I floor it.
3. During the next 2 miles of driving I have to floor it less and less to have no power.
4. After the 2 miles I pull over into a gas station and start pulling spark plug wires while the engine is running. It seemed that each wire had the same effect as the others.
5. After about 5 minutes of messing with the wires, the car wouldn't run at all.

I messed around with this thing for about a week trying to figure out why it wouldn't run. Seemed to have plenty of spark.

I had all sorts of theories about leaking for stuck valves. I had a friend come over, and he said (as he always says) If you can't figure out the problem, fix all the cheap stuff, see if there's a difference, and if not, then worry about figuring out the problem. So, I changed the cap, rotor, and wires.

Problem solved.

Explanation:
I wanted to know what really happened, so I put the old wires back on and it still ran fine, so it was the cap or the rotor.

Upon examination, there was a little (barely noticeable) wrinkle inside the cap.

That wrinkle was a carbon trace that had developed between two of the nodes inside the cap. So, when one cylinder was sparking, the other would also spark. Well, the problem was, the other cylinder was just beginning the compression stroke. And I guess the first cylinder did not have enough power to compress the burning fuel in the second cylinder.

=============================
Bad spark plug wires

Symptoms:
1. Car runs great for 5 to 10 minutes, sometimes for a half an hour.
2. Car runs crappy for 5 to 10 minutes, sometimes for a half an hour.
3. Car runs great again.
4. Then crappy.
5. Then great.
6. Each time it runs crappy, it runs crappier. Pretty soon when it's running crappy, it barely runs. In this case, crappy is less and less power every time I touch the gas to demand power.

Finally the instant it's running crappy, I pull over, jump out of the car to remove the plug wires one by one.

I remove the first one, engine slows down a bit. I pug it back in, and grab the next. Same thing. The the next. Well, that one hurt like hell because the spark was going straight through the wire and was shocking the hell out of me.

Explanation:
Upon examination, the wire was able to flop from one side to the other. If it flopped onto the valve cover, the car ran crappy. When it flopped away from the valve cover, the car ran great.

So, I was loosing one cylinder every time the the wire flopped onto the valve cover.

Replaced wires, problem solved.

=============================

The moral of the story. 90% of the time strange problems like this can easily be the cheap stuff, so replace everything cheap, save the old crap as spares, and if the problem gets solved, figure out which part was bad, then throw it away.

It might cost you $100 to $200 in cheap stuff the first time, but the next time, this same procedure will cost you nothing but a little time.

Then, if the problem is not solved, you can start messing around with theories and crap to figure out what the problem is. But at least you know it's not any of the cheap stuff.
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Old 07-17-2004, 04:48 PM
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Fuel filter is stopped up, or the sock in the tank is stopped up.

Troy

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Old 07-17-2004, 06:41 PM
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Quote:
Originally posted by troy-curt
or the sock in the tank is stopped up.
Sock in the tank?

Could this sock be getting clogged with a bunch of crap in the tank every time the tank is low on fuel, but filling the tank stirs up the crap so that it runs fine until the tank is low again?
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