[kride]

real short just purchased a 1984 corvette, doesn't start, runs with starting fliud, found bad fuel pump and replaced, still no fuel out of ejectors, purchased a noid tester and no pulse noted. tried to hook up a code reader but it tells me that no cable is attached to the ECM ?
Question can someone tell me if the problem is just a bad ECM.

[toobroketoretire]

Originally Posted by kride

real short just purchased a 1984 corvette, doesn't start, runs with starting fliud, found bad fuel pump and replaced, still no fuel out of ejectors, purchased a noid tester and no pulse noted. tried to hook up a code reader but it tells me that no cable is attached to the ECM ?
Question can someone tell me if the problem is just a bad ECM.

First of all each of the injectors have their own separate fuse in the fuse block so check those first. Second when you turn your key on the ECM will turn the fuel pump relay on and then the fuel pump will run for only two seconds if it doesn't receive an oil pressure signal from the sender. If the oil pressure signal is received the relay will remain operating and the fuel pump will continue to run.

So first verify the fuel pump runs for two seconds when you turn your key on. I have been told the fuel pump relay is mounted under the dash on the passenger side and you can feel it "click" when the key is turned on. But just clicking doesn't tell you it's any good because it's contacts can be burned and wouldn't send current to the pump.

[Slicktop]

Originally Posted by toobroketoretire

First of all each of the injectors have their own separate fuse in the fuse block so check those first. Second when you turn your key on the ECM will turn the fuel pump relay on and then the fuel pump will run for only two seconds if it doesn't receive an oil pressure signal from the sender. If the oil pressure signal is received the relay will remain operating and the fuel pump will continue to run.

So first verify the fuel pump runs for two seconds when you turn your key on. I have been told the fuel pump relay is mounted under the dash on the passenger side and you can feel it "click" when the key is turned on. But just clicking doesn't tell you it's any good because it's contacts can be burned and wouldn't send current to the pump.

Not exactly correct. On an 84 the fuel pump is turned on by the relay only and is not wired thru the oil pressure switch. Also, on an 84 the fuel pump relay is in the engine bay by the master cylinder or on the firewall by the windshield wiper motor. It is part number 14078915 identified by big white numbers on its side..........

The fuel pump relay

The ECM controls the fuel pump through the fuel pump relay. When the key is first turned on without the engine running, the ECM will turn the fuel pump relay on for two seconds. This builds up the fuel pressure quickly. If the engine is not started within two seconds, the ECM will shut the fuel pump off and wait until the engine starts. As soon as the engine is cranked, the ECM will turn the relay on and run the fuel pump.

The oil pressure sender unit

As a backup system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure sender. The oil pressure sender has two circuits internally. One half of this sender is a normally-open switch that closes at about 4 psi (a normal cranking oil pressure) and remains closed while the engine is running. It should open when the engine is shut off. The other half of this sender is for the oil pressure indicator in the instrument cluster. So, if the fuel pump relay fails, the oil pressure sender will close and run the fuel pump.

In 1985 this was changed so that if there was no oil signal the fuel pump would shut off...........

With this in mind if the fuel pump is not coming on I would check for 12 volts thru out the system to find out what is going on. Start with the fuel pump fuse. Is it getting 12 volts on the power side and is the fuse good. Next pull the relay and check for 12 volts on the control side, etc........check the fuel pump positive wire, does it get 12 volts when it should, etc. The relay is controled by the computer so if you bypass the relay and it then runs you might have a bad computer, or lack of continuity between the relay and the computer........both of which can also be tested for.

If the fuel pump works and you have good fuel pressure then check to make sure that the injectors are firing....also check the computer for codes, there is a self test function that works by flashing the check engine light. A haynes repair manual will tell you how to use it. FYI the ecm has a prom in it that can be installed backwards, which will ruin it, or taken out and left out by someone, the car is new to you so everything has to be checked.
Haynes repair manual and/or FSM are your best friends.