Chevy 4.3 TBI problem - I think

Just thought I'd add a thread to an already growing epedemic of 4.3 fuel problems. All my problems as well have started since running low on fuel. After getting gas, within 20 miles I no longer can drive my new (to me anyways) 1990 astro rs. We have so far replaced or rebuilt the following: fuel filter, air filter, o2 sensor, fuel injectors, fuel pressure regulator and tested the fuel pump. I then hopped on the ol' faithful internet and have came to the conclusion that we could try 100+ things and the problem is still going to exist. People with the same problem have replaced far more to get no where. We've had 3 different mechanics come look at it to no avail. The computer says nothing is wrong - no codes at all. Out of all the threads of "fuel problem" has anyone actually fixed the problem?
My symptoms exactly mirror: http://www.automotiveforums.com/vbu...ad.php?t=212039 .
I'm beginning to believe that no one has an answer. What we have troubleshooted is that in the throttle body there is injector A and injector B as well as plug A(for the injector) and plug B. When watching the injectors while cranking the motor injector A squirts and injector B sort of drips. Obviously we replaced injector B. No difference. So what we did was take plug A and plug it into injector B. Lo and behold, now injector B squirts gas and injector A drips. We have traced and retraced all the wires for wear and tear. Again, this all started VERY soon after being low on gas which is what makes us want to believe it is the fuel pump and I burnt it out or something. We've checked it 3 times and everytime the key is turned on (not started) the pump kicks on and fuel begins to flow. PLEASE... if you have any suggestions I would much appreciate it. I have read every thread on this subject so far as well as other research and have came to the conclusion that until someone can say "THIS is your problem" I am not pouring any more money into this piece of S#$%!! Thanks for your help.

UPDATE: Today I tried unhooking the MAP sensor and it tried to run a little better. Going to replace it tomorrow.

delight, The link is broken, so I could not read the symptoms other than what you wrote. According to you, the injector drip moved with the wiring...thus it's electrical. I'm assuming that you mean the injector drips fuel when you say "We've checked it 3 times and everytime the key is turned on (not started) the pump kicks on and fuel begins to flow." It could be wiring related or ECM related. You'll need to diagnose which. I'd wait on the MAP sensor. By unhooking the sensor, you've sent it full rich which is probably only covering up the lean condition you get with only one injector firing. If you have more info, please post it. Best of luck

It sounds like you lost a coil pack. In my sport(where you modify Suzuki GSXR 600 motors) we are used to using coil on plugs, as such, the ECU sends a signal to the coil to tell it to fire (which holds the charge) We refer to the setup on the ECU as a coil driver (Which sends the low voltage signal to the coil to fire). If one plug is firing fully, you're obviously achieving fuel pressure.

FYI: I doubt this to be your problem because you are running a stock setup, but sometimes when you put a higher flowing fuel pump onto your system, you need to increase the size of your return line. On fuel injection systems, the fuel tank actually gets pressurized. There is also a return line from the fuel rail back to the tank to recycle any unused fuel/pressure. If this line is too small the fuel pump can't pump the fuel back fast enough, as such, the tank eventually builds a vaccum the supercedes the fuel pumps ability to pull from. When this happen, you lose fuel. You generally have to wait about 20 min for the tank to neutralize in pressure.

As such, I would guess something within your coils telling the injectors to fire.


You said you tested the fuel pump, I would like to know how? I would put a gauge on it to see what type of pressure you have and how constant it is.

Another thing, the return valve for the fuel rail pressure is vaccum activated. There is a pressure regulator that works off vaccum to know how much fuel to let circulate back into the gas tank. Perhaps there is a vaccum leak and it is not letting it return fuel, as such, you are building a vaccum in the fuel tank. This is unlikely seeing how one injector is firing while the other isnt... Just a couple of suggestions, I hope work.

I'm not as good as these folks at EFI, but I do know that there are almost always relays that carry the juice for the injectors. The computer sends the signal, but the delicate wiring isn't up to supplying the amperage needed to supply the injectors. I suggest you try testing the signal from the computer, and testing the relays themselves. It sounds to me (as benchtest said) that it has to be the juice coming through that wire that is faulty. Find yourself a wiring diagram and trace those wires back to the relays and computer.

Some computers have the relays built in, and some even are built to supply enough juice without relays, but I'm not sure about GM's stuff. The only EFI experience I have is aftermarket ECMs and my 96 Impala which has not had this type of problem.

RandomTask has a good point with the coils, but I think GM uses a crank position sensor / reluctor ring to trigger the injectors.