Question: Car dies temporarily going around corners

[gmhowe]

1985 4+3, when about 1/4-3/8's of a tank of gas turning corners ( doesn't matter left or right ) car will die as soon as I turn the corner. I can't figure it out. If it was the fuel pump I would think it would take a little bit before dying, but its as soon as I turn. Any ideas ?
Thanx
Gordon
Just got the 85 back from being freshly painted, came out real nice

 

[aklim]

Check the fuel pump. The pickup might not be where it should be so it sucks air around the corners. Also the "modulator" or whatever it is called might be substandard at this time. When replacing the pump, I deleted the thingy

 

[Jeb]

One would think that if it were a fuel pickup issue, the car would not "die" instantaneously, it would pop and gurgle for a couple of seconds at least, and even then it would take a second or two to draw the fuel load from the fuel lines.

Also, since it happens with both left and right hand turns, the pickup must be in the center of the tank and there must be an amount of fuel in the tank which would be less than enough to reach the pickup. I find that hard to believe if you have as much fuel remaining as you state.

Is it possible that there is a critical wiring loom which, when turning, moves ever so much to the left and right that it would aggrevate a short or open in the wiring? This sounds more like an electrical problem than a fuel problem.

 

[Hib Halverson]

One would think that, if the car exhibits this characteristic only when the fuel level is lower than 3/8-tank, that the problem is fuel level in relation to pick-up location and not electrical.

If it was electrical, the engine would cut out abruptly, regardless of fuel level.

The fuel starvation sets in fairly abruptly because the fuel system is a bypass type with no short-term reservoir (like a "float bowl" in a carb) so the injectors loose fuel flow almost as soon as the fuel pump does.

Note that early C4s do not have the tank baffling installed later as a result of Chevrolet's experience in showroom stock road racing in the mid-90s, and once fuel level gets below 1/4, the car will starve for fuel (though not cut out abruptly) in high-g turns.

 

[aklim]

Note that early C4s do not have the tank baffling installed later as a result of Chevrolet's experience in showroom stock road racing in the mid-90s, and once fuel level gets below 1/4, the car will starve for fuel (though not cut out abruptly) in high-g turns.

So would my 91 have tank baffling? I can't remember but I THINK that it is a circular wall around the pump??:confused

 

[Hib Halverson]

So would my 91 have tank baffling? I can't remember but I THINK that it is a circular wall around the pump??:confused

A 91 tank is baffled.

 

[vetteboy86]

1985 4+3, when about 1/4-3/8's of a tank of gas turning corners ( doesn't matter left or right ) car will die as soon as I turn the corner. I can't figure it out. If it was the fuel pump I would think it would take a little bit before dying, but its as soon as I turn. Any ideas ?
Thanx
Gordon
Just got the 85 back from being freshly painted, came out real nice

I think it may be worth noting that it is possible that gauge is off, and the fuel level may be lower than the gauge indicates, which would increase the likelihood of this issue being low fuel related.

 

[GerryLP]

Is the pump self regulating or is there a pressure regulator as part of the system?

Also, Hib, I don't get your meaning about the by-pass feature. Is the fuel by-passed at the injectors? I am guessing that there is a check valve on the fuel rail that maintains the desired pressure at the fuel rail (closest to the injectors). And most system have a by-pass/return feature -do they not?. My L81 fuel pump has a return for the excess fuel, so if there is pressure between the pump and the injector, wouldn't there be enough fuel to prevent the engine from dying instantaneously?

Also, as a side note, it is amazing that the early C4's did not come with a baffle in the tank, for it seems that I have read in here from members saying that the 1982 Vette fuel tank is baffle'd (I think that it was in discussions of converting carbureted cars to fuel injected cars. Or am I off? :confused

GerryLP :cool

 

[Hib Halverson]

The 85 system has a tank-mounted pump and an engine mounted fuel pressure regulator. The regulator is non-linear-referenced to MAP.

Fuel flow is from the tank, to the injectors, to the regulator and back to the tank.

The longer the injector pulse width, the less fuel is bypassed back to the tank.

All fuel systems used on EFI Corvettes up until very recently, were bypass systems.

I didn't mean to imply that early C4 tanks had no baffles. I do not know for sure that the early tanks had no baffling. The later C4 tanks had improved tank baffling and pickup design to mitigate the effects of fuel starvation at low fuel levels during endurance road races.

 

[boomdriver]

The 85 system has a tank-mounted pump and an engine mounted fuel pressure regulator. The regulator is non-linear-referenced to MAP.

Fuel flow is from the tank, to the injectors, to the regulator and back to the tank.

The longer the injector pulse width, the less fuel is bypassed back to the tank.

All fuel systems used on EFI Corvettes up until very recently, were bypass systems.

I didn't mean to imply that early C4 tanks had no baffles. I do not know for sure that the early tanks had no baffling. The later C4 tanks had improved tank baffling and pickup design to mitigate the effects of fuel starvation at low fuel levels during endurance road races.

The first sevral yrs of C4 do not have baffles in the tank.
What GM did do, was glue a tiny 3"x5" pan thats about 1" deep to the bottom of the tank and the pump pickup assy sits inside that.Its about 1/2 cup of fuel, or less.
The assumption was that the tank being shallow and wide, that there would never be a long enough time where the fuel would be held to the side of the tank from G-loads. They were wrong....

The cure is easy. Pull the pump assy, make a small "can" that pulls up around the pump and pick-up AND return tube, secure the can to the tubes/pump so its all clear of the float arm and insert the whole mess back into the tank. Plastics work best.Bottom half of a Lucas qt bottle of oil stabilizer is near perfect. Be sure to make a small hole in the front bottom and rear bottom of the new can / baffle assembly. I also cut a slot for the screen to lay flat and out of the can. Keep any cuts or openings on the sides as tight and small as possible so fuel is not lost while cornering. This can/baffle also needs to be about 4 to 5" deep so the return flow is what keeps it full, so side loading cannot rob that fuel thats readily available to the pump. The small holes in the bottom allow same level to be maintained when there is no side loading. When there is more than 1/4 tank the "can" is covered so there is not an issue. This also helps keep trash away from the pump suction screen.

The instant that your pump pulls air the pressure drops off and the engine stumbles. It feels like a key off situation because the same instant that pressure reappears, so does the engines pulling power. These don't sputter and spit because running out of gas means there is some gas getting thru until the time there is no gas, thats when the engine dies. When we side load a 1/4 tank of gas, that instantly takes away all the gas until the G forces are relieved and gas can return to the suction screen on the pump.

 

[Jeb]

Hib - If the pump was not picking up fuel, it would immediately drop fuel pressure at the fuel rail, correct?

If so, that would explain the instantaneous nature of the engine stoppage.

Thanks for the correction.

 

[GerryLP]

I have not ever released fuel pressure from a Corvette fuel system, other than messing with the carburetor in my L81; however, I have done this in other vehicles, and the fuel running pressure, depending on the system, is anywhere between 35 PSI to 50 PSI (not including those of our cars which we're always doing changes in search of more power... ).

So, the amount of fuel present is sufficient to keep the motor going a few seconds...So if the symptom described is trully cutting the engine instanteneously, then there's got to be some sort of sensor in the system that tells the computer that the fuel pressure has been lost, right?

One example I can think of is my F-150 pickup truck. It has dual tanks. And that means dual fuel pumps and dual fuel sourcces. I can be cruising at 75 MPH in that thing, and if I switch fuel tanks with the fuel tank selecting switch, the only thing noticed is an ever so slightly stumble if I do not back off the gas pedal. So this makes me think that there is got to be some other factor or sensor tying computer involvement to make the engine die instantenously while making a turn...do you guys see what I am saying?


GerryLP:cool

 

[gmhowe]

After a full tank there is no stumbling going around corners, I will pull the fuel pump this next weekend since it will finally be below 100 here in Phoenix, I will check all things out and let everyone what I find, I do have a new Sock for the fuel pump and new fuel filter.
Thanx for all the responses
Gordon

 

[boomdriver]

After a full tank there is no stumbling going around corners, I will pull the fuel pump this next weekend since it will finally be below 100 here in Phoenix, I will check all things out and let everyone what I find, I do have a new Sock for the fuel pump and new fuel filter.
Thanx for all the responses
Gordon

when you get to the filter portion, pull the fuel pump plug and let the engine run until it dies from starvation. Then, use caution when removing the filter....its at the bottom of the system and all the fuel in the lines on either side will drain down in your face...Thats why I run it to try to use as much of that as possible and minimize the spill. If you look closely at the lines, somewhere it says BP...otfl

Below 100 in Phx? wow...finally some cool weather ! 90's is sweater weather in AZ.

 

[Hib Halverson]

Hib - If the pump was not picking up fuel, it would immediately drop fuel pressure at the fuel rail, correct?

Yes...along with a rapid decrease in fuel flow.

 

[vee93]

...if you whip around a corner too fast, it will slosh the fuel and momentarily starve your Vette....especially if your fuel is low.

 

[gmhowe]

Finally found the problem, the very hard vacumn line running from the fuel pressure regulator to the plugin under the plenium was cracked. Replaced and all is better now. Was a really hard one to find since its so hard to root around under the plenium without taking it off.
Thanx for all your help

 

[CharlesBrown]

" thingy?"

 

[Schrade]

This was the only problem???

Vacuum to the FPR makes for enrichment under pedal down conditions - fuel pressure in the line INcreases. And the opposite - en-lean-ment when vacuum DEcreases, and pressure decreases when you let off of the pedal. There's not much delay here, if the pump pressure is up to spec.

How this would affect turns is strange, because you've let off the gas before you entered the turn.

 

[boomdriver]

This was the only problem???

Vacuum to the FPR makes for enrichment under pedal down conditions - fuel pressure in the line INcreases. And the opposite - en-lean-ment when vacuum DEcreases, and pressure decreases when you let off of the pedal. There's not much delay here, if the pump pressure is up to spec.

How this would affect turns is strange, because you've let off the gas before you entered the turn.

No way thats the problem.....

Fuel pressure would go UP with a leak at the FPR, manifold vac would increase letting off the gas...If gas were still applied and an increase in lateral forces were to take place cornering....it's the other end of the car thats got the problem.

That hard-line has probably been cracked for yrs.