Help! C4 starved for fuel

[DudleyB]

Ever since I replaced the original fuel pump, if the tank level gets below 1/2 full, my '86 starves for fuel and stumbles badly when floored, especially when cornering. Recently, it's been doing the same thing at full throttle even when the tank is full. I've burned up half-a-dozen pumps since then; so I keep the tank at least 1/3 full; but the stumbling is still a problem. What can be done? This didn't happen with the original pump. The replacement ones look just like the original. Advance swears they're just as good.

By the way, I burn up alternators too. They run hotter than a popcorn fart. If you spit on the alternator it will sizzle--way too hot! I'm fed up with these marginal designs!

My C4 has a "track" chip, a matching thermostat, and a bigger fan that keep it at an appropriate 160F rather than the brutal 195F or 215F that some idiot at the factory came up with.

 

[JimBobC4]

Ever since I replaced the original fuel pump, if the tank level gets below 1/2 full, my '86 starves for fuel and stumbles badly when floored, especially when cornering. Recently, it's been doing the same thing at full throttle even when the tank is full. I've burned up half-a-dozen pumps since then; so I keep the tank at least 1/3 full; but the stumbling is still a problem. What can be done? This didn't happen with the original pump. The replacement ones look just like the original. Advance swears they're just as good.

By the way, I burn up alternators too. They run hotter than a popcorn fart. If you spit on the alternator it will sizzle--way too hot! I'm fed up with these marginal designs!

My C4 has a "track" chip, a matching thermostat, and a bigger fan that keep it at an appropriate 160F rather than the brutal 195F or 215F that some idiot at the factory came up with.

How much fuel pressure do you have ? Maybe you have a restriction in the fuel line creating extra stress on the pump?

When was the last time you put a fuel filter on it ?

As far as the alternator is concerned I would check the wiring and connectors. Obviously its under much more of a load than it was designed to handle.

You don't have big zillion watt stereo amps in it do you ? Maybe some killer weed burning rally lights up front? Tv microwave ?

Also I don't think the designs are marginal. I think you have an individual issue with your car. Keep in mind about 35 thousand 86 vettes were made, I doubt they all have the same problems as yours.

Personally I think you have a chassis to engine ground problem.

However, that is theory and conjecture at this point.

 

[gmjunkie]

How much fuel pressure do you have ? Maybe you have a restriction in the fuel line creating extra stress on the pump?

When was the last time you put a fuel filter on it ?

As far as the alternator is concerned I would check the wiring and connectors. Obviously its under much more of a load than it was designed to handle.

You don't have big zillion watt stereo amps in it do you ? Maybe some killer weed burning rally lights up front? Tv microwave ?

Also I don't think the designs are marginal. I think you have an individual issue with your car. Keep in mind about 35 thousand 86 vettes were made, I doubt they all have the same problems as yours.

Personally I think you have a chassis to engine ground problem.

However, that is theory and conjecture at this point.

I agree 100%!!!Sounds like some great places to start!!

 

[DudleyB]

I've changed the filter a couple of times without any noticable effect; and it didn't look bad when I cut it open to inspect it.

The connectors to the alternator are OK. I've had other ground problems in the past; so this might be it; but even so, where else would the current go? I'll check into it.

I don't have any additional items demanding power. I even have the original sound system.

The alternator problem may be entirely due to buying remanufactured items. Of course, I only paid for the first one I think what they do is just replace the faulty items and leave everything else alone. The alternators burn out in 3 stages (one for each phase), each time getting weaker. This most recent one burned out a rectifier in less than 5 miles. I've checked the current and voltage. The voltage is normal and the current isn't anywhere near the 90 to 105 rated capacity.

I'll check on that ground thing. How about the tank pressure system as a culprit? Perhaps the fuel pumps I've been getting require more net positive suction head than the original; but why would that be the case?

 

[gmjunkie]

Be sure to check the eyelet on the big red wire to the alternator!!
They sometimes get corrosion where there crimped to the wire and you can't see it!! It can make the alternator voltage go wild and pop diodes,over heat and cause other electrical problems!!

PS Also check the rubber hose in the tank at the fuel pump,they'll sometimes leak and by-pass fuel in the tank and cause your exact problem!!

 

[DudleyB]

The connection at the alternator is clean. I only have 50,000 miles on the car and it's spent most of it's life under cover. There's some corrosion in some places, but not there.

There is no rubber hose in my gas tank. Metal tubing connects to the fuel pump through a funny little push-on fitting which I've replaced several times too.
The best I can tell the pump is either not sucking up the fuel or it's not producing adequate flow. If it's stuck down in the tank at the proper level--which it must be, seeing as it's the same size as the original pump, there's nothing below it except for a dippy little plastic strainer, which I've also replaced, and it only fits one place on the metal bracket that hangs down into the tank.

The anti-slosh baffels are built into the tank and appear undamaged. So what's their excuse?

I don't know what would keep it from sucking up the fuel other than that the fuel pumps are scat. Also, seeing as there isn't fuel spewing all over the car, I can't see what's preventing it from producing adequate flow--other than the fuel pumps being scat.

Even if the fuel regulator was bad, that might let too much fuel in or might not let enough in, but how could it possibly know what the level in the tank is unless the porking pump weren't sending it adequate fuel?

I just think the whole design is scat. What with this tiny [but shockingly expensive!] little pump shoved down in some stupid place [like the gas tank] that uses something really stupid [gasoline] for cooling? How about a metal tube coming out of the bottom of the tank, going to a pump about the size of a starter mounted on the frame sending fuel through a hose up to the engine? Nah, that would be too easy to fix and way too cheap!

 

[minifridge1138]

What is the fuel pressure when the car is running?

 

[DudleyB]

I posted "C4 Starved for Fuel" back on 9/17/08. I finally got around to fixing it. I thought this might help others. The fuel pressure gauge held steady at 40 psi except under full-throttle with less than half a tank, when it dropped to 10 psi. I replaced the fuel pump with a 225 lpm Holley unit ($180) that's supposed to be for a Mustang! It fits perfectly and works great. The after-market unit I got at Advance ($70) was basically a piece of crap and noisy too! The Holley pump is quiet as a mouse.

 

[LVMYVT76]

Is your alternator still running hot? or have you fixed it?

 

[DudleyB]

Is your alternator still running hot? or have you fixed it?

It comes and goes depending on ambient temperature and how long the engine has been running. For instance, on a frosty morning I turn on the headlights, windshield defroster (fan and compressor), the rear window defroster (resistance tracks on the back window), and the radio. For the first few minutes the alternator can keep up with this demand. Not only do I watch the volts display, but I also notice the brightness of the headlights and console. By the time the engine warms up to 120F the alternator can no longer keep up with it and the voltage drops as low as 10.3 at an idle, but will pull up to 14 if I keep the rpm above 2000. If I don't turn the rear window defroster off at this point, by the time the engine heats up to 160F the alternator can't keep the voltage above 13 regardless of the rpm. That sounds like a malfunctioning alternator to me! This is par for the course with rebuilt alternators for me. They just keep getting worse in steps until they die alltogether. Seeing as they are entirely self-contained (internal rectifiers and voltage regulator), it must be the fault of the alternator. I guess I'll just have to buy a "good" [expensive!] one as was the case with the fuel pump. I don't know about you all; but I haven't gotten my $10M bail-out check yet; and, seeing as I'm not a CEO, I'm not likely to get a $100M exit bonus either!