mlacek

Hey all, I have been researching and troubleshooting this issue for awhile and could really use some help. In our 1990 RS 305 TBI Camaro, fuel suddenly stopped flowing to the Throttle Body. Car was running great (less than 90k original miles), and after it was parked for a couple hours, it just cranks and doesn't start. Here's what I know and have tried so far.

1. Fuel filter replaced.
2. Fuel flows through the filter toward the motor.
3. Inline fuse is good.
4. Pouring fuel into the TB allows the car to start & run.
5. TBI injectors are getting power (verified with noid lights).
6. Fuel pump audibly clicks on when key is turned.

Here are some questions:

1. Should I replace/rebuild the fuel pressure regulator, since there is no flow (not low, none). If so, how/where is it?
2. Could it be the fuel pump still?
3. Service manual says the fuel pump is in the front of the engine compartment, but all fuel lines flow toward the trunk, which I fear means it's in the tank (ugly job to replace).
4. How/where do I connect up a fuel pressure test gauge? I do not see a Schraeder check valve.
5. What other fuses are involved that could cause the fuel to suddenly stop flowing?

Thanks in advance for the help!

navy02ws6

First thing's first -- does your car still have TBI, or has someone converted it to a carburetor? If it's still TBI, then it's simply called a throttle body, not a carburetor.

There is no way to connect a pressure gauge directly to these cars as there is no schrader valve on them. The only option is to buy a test adapter, which goes in place of the fuel filter underneath the car, and can be hooked up to a pressure gauge.

IIRC, the pressure regulator is built into the throttle body.

I had similar problems with my '91 RS -- turned out to be a bent fuel line at the intake manifold.

mlacek

Yes, Throttle Body.... sorry, didn't use the correct term.

Ghettobird52

check icm(ignition control module) on dizzy. Mine went out long long time ago far far away when i first got the car, injectors stop spraying when icm goes bad.

Schurkey

HOW do you know that there's no fuel flow?


That does not have to indicate no fuel flow.

HOW do you know?

Good indication that the ignition is functional.

Based on this description, I would test fuel pump pressure, volume, and fuel pump motor amperage draw, and voltage supply.

No. Test the fuel pump first.
Yes. It could be other things, though. It's not guaranteed to be the pump.
WHAT service manual? (Hint: The only service manual that counts is the one GM provides to the dealerships. The official factory service manual is so far above Chiltons/Haynes/whatever that they're only good for asswipe.)

On my vehicle there's a fusible link that powers the fuel pump fuse. You could also have a broken wire, or corroded connections in the harness that supplies power to the pump. This is why you need to test the voltage (near the pump) and the current (amperage) flow of the pump.

Checking for spark is easier. If you have spark, you also have a functioning pickup coil. However, he says the engine runs when fuel is poured into the throttle body--so the ignition system works. Since the injectors are getting both power and ground as verified with the Noid light, the computer knows the engine is cranking.

Either there's no fuel pressure/volume, or the injectors have both suddenly seized or plugged, or the plumbing betweenthe filter and TBI is plugged. My money is on lack of fuel pressure/volume--which could be a failed pump, completely plugged filter sock, failed in-tank fuel plumbing, or a failed electrical supply to the pump.

mlacek

Thanks... to answer your questions,

I know there is no fuel flow to the TB because I cannot see or smell fuel in the TB while it's cranking. But when I pour fuel into the TB directly, it fires right up.

I know fuel flows through the filter because I disconnected the OUT end of the filter and watched fuel flow through it while cranking.

I have pressure test gauge and am currently trying to figure out where/how to install a tee to test it. I think I found where to do it (on the top rubber line up front) but need to find a tee.

Where is the fuse-able link that powers the fuel pump fuse located?

How can I check the electrical supply to the pump?

Thanks again,
-Matt

Schurkey

You cannot see or smell fuel that is contained within the fuel plumbing. You wouldn't see or smell fuel unless it's spraying out the injector(s), or leaking somewhere.

You DON'T know that there is no flow. You know that the injectors aren't spraying.

Unless it was spraying out under pressure, you maybe saw only the fuel flowing via siphon effect.

Two commercially-available styles of tees that I'm aware of. One goes in place of the fuel filter. Another would connect between the fuel tube and the TBI unit. They're available from numerous suppliers.


Beware of the style of connector used to attach the probe for the fuel pressure gauge--the second link uses a style of connector that is unlikely to fit the gauge you have. I can't find a link to the "usual" style.


On my Luminas, it's very close to the battery. I'm thinking the K1500 also has one, but I don't remember for sure. A Camaro may be different. You'll need to trace the wiring diagram to be sure.


I use an inductive ammeter probe, and a normal voltmeter. The voltmeter must be connected to the wire to be tested as close to the fuel pump as practical. Ideally, you'd connect inside the gas tank, directly to the motor--but that's impossible. At least check the harness near the gas tank, since you can't check it inside the tank. The same wire can be used for the ammeter.

If you don't have an inductive amps probe, most multimeters can test up to 10 amps. You could pull the fuel pump fuse, and use the two probes of the multimeter to conduct current through the meter in place of the fuse. You can test amperage anywhere in the circuit. You must test volts as close to the pump as you can get.

You would expect something like 12 volts, 6 or 7 amps WITH THE FUEL PUMP RUNNING. If the pump isn't running, neither volts nor amps can be measured with any accuracy--although if you have volts, the pump "should" be running. If the pump has voltage, but doesn't run, either the pump is defective, or the ground connection is bad.

mlacek

If there is adequate flow to the Throttle Body, but the injectors aren't spraying, what could be some possible causes?

Schurkey

1. Injector screens plugged.
2. Injector internal passages plugged with varnish
3. Injector solenoids failed.
4. Failed fuel pressure regulator
5. Lack of power to the injectors
6. Lack of ground for the injectors

5 and 6 are not the problem, because you've already shown that the injector have both power and ground with the blinking noid light. The others are possible, although somewhat unlikely. Let's be clear--it's unlikely that both injectors failed at the same time, and the fuel pressure regulator is fairly reliable. If the regulator failed, you could have fuel flow but with low pressure. Possible, not common. I fully expect that your fuel pump, or fuel pump wiring has died. My point is, without further testing, you do not know--for sure--what is wrong.

A fuel pressure test--preferably at the throttle body, but at the filter area can work--will answer a number of questions. Either you have adequate pressure and volume, or you don't. This helps you determine whether to look at the throttle body (injectors and pressure regulator) or plumbing, filter, and pump/pump motor.

If the pump is not providing pressure and volume, you must test the power supply to the pump. The pump does not work unless the pump motor has got power and ground, just like the injectors.