91 running very bad
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
The FSM shows +12V to the injectors and the ECM switching the return or ground side.
I suggest using a Noid light to be sure that their are no pulses at the injectors. If that be the case, then yep the ECM is toasted.
I suggest using a Noid light to be sure that their are no pulses at the injectors. If that be the case, then yep the ECM is toasted.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The ECM puts out injector pulses when it sees pulses from the module in the distributor. You can verify that the distributor pulses are getting to the ECM by checking the timing. If the timing mark is above the top of the timing tab on the timing chain cover with the EST connector connected, then it's OK. You can check timing while cranking. The engine does not need to be running.
Another possibility is a bad VATS signal to the ECM. If it's not between 20 and 40 Hz then the ECM will not fire the injectors. The VATS module also controls the starter relay, but some people bypass it, so the fact that the engine cranks is not a 100% sure test. See good info on VATS here:
http://www.vatssucks.com
Another possibility is a bad VATS signal to the ECM. If it's not between 20 and 40 Hz then the ECM will not fire the injectors. The VATS module also controls the starter relay, but some people bypass it, so the fact that the engine cranks is not a 100% sure test. See good info on VATS here:
http://www.vatssucks.com
Last edited by Cliff Harris; Nov 23, 2011 at 04:19 AM.
Melting Slicks
Joined: May 2001
Posts: 3,270
Likes: 26
From: Winchester VA
Cruise-In V Veteran
Thread Starter
Melting Slicks
Joined: Jul 2004
Posts: 2,295
Likes: 14
From: Grand Sport #82
VATS might be a good guess here, since I am sure that the injectors have fuel, they just dont open. Also I have Ignition.
BUT, would the VATS not prevent me from even cranking the engine?
I actaully have another 91´corvette avalible to swtch some parts around.What VATS releated parts can a try to switch to verify if its the VATS?
I have no idea if these cars have have same VATS code...
BUT, would the VATS not prevent me from even cranking the engine?
I actaully have another 91´corvette avalible to swtch some parts around.What VATS releated parts can a try to switch to verify if its the VATS?
I have no idea if these cars have have same VATS code...
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
VATS might be a good guess here, since I am sure that the injectors have fuel, they just dont open. Also I have Ignition.
BUT, would the VATS not prevent me from even cranking the engine?
I actaully have another 91´corvette avalible to swtch some parts around.What VATS releated parts can a try to switch to verify if its the VATS?
I have no idea if these cars have have same VATS code...
BUT, would the VATS not prevent me from even cranking the engine?
I actaully have another 91´corvette avalible to swtch some parts around.What VATS releated parts can a try to switch to verify if its the VATS?
I have no idea if these cars have have same VATS code...
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
Did you hook up the light or some measuring device to measure the low side of the injector coils? It should be going between 0 and 12V. If it is not then it is either a bad input to the ECM not requesting fuel or it is a bad ECM output stage. Did you try a coil drive from both banks? if both banks are not driving the injector coils I find it highly unlikely that it is the ECM output - it is more likely an input that is not allowing the ECM to fire the injectors - which could be the input itself or something wrong in the input circuit of the ECM.
