1984 C4 ecm, auto, manual differences
Thread Starter
Racer
Joined: Aug 2014
Posts: 269
Likes: 4
From: Bossier City Louisiana
1984 C4 ecm, auto, manual differences
I have a 1984 Corvette. It runs but always rich. Adjust able fuel pressure and it is running in the middle pressure of high and low. I rebuilt the 2 injectors. I put new bushings in the throttle shafts. I have new temp sensor and o2 sensor. New tp switch, map sensor and have driven it at 40 mph as much as I can but still rich, esp at startups. I am curious about the ECM now. I have an automatic 700r4. The ECM is supposed to match that. What is or are the differences between the manual and auto ECM? I have another ECM laying around but can't tell what it is for.
I know it is ancient tech and should consider myself lucky it is running at all but I have an interest in getting it running correctly. Plugs, wires, cap, module are all basically new too. Air filter is new. No air leaks in the manifold. The TP switch is adjusted correctly according to the manual. New idle air controllers too. Rock auto has remanufactured ECM's for around $100.00. I just need to put in my prom. They don't say if auto or manual or if it depends on the prom. And that is my question, what is the difference and how do I tell?
Help!
Thanks
Russ
I know it is ancient tech and should consider myself lucky it is running at all but I have an interest in getting it running correctly. Plugs, wires, cap, module are all basically new too. Air filter is new. No air leaks in the manifold. The TP switch is adjusted correctly according to the manual. New idle air controllers too. Rock auto has remanufactured ECM's for around $100.00. I just need to put in my prom. They don't say if auto or manual or if it depends on the prom. And that is my question, what is the difference and how do I tell?
Help!
Thanks
Russ
Melting Slicks
Joined: Nov 2007
Posts: 2,830
Likes: 147
From: Gainesville FL
I have a 1984 Corvette. It runs but always rich. Adjust able fuel pressure and it is running in the middle pressure of high and low. I rebuilt the 2 injectors. I put new bushings in the throttle shafts. I have new temp sensor and o2 sensor. New tp switch, map sensor and have driven it at 40 mph as much as I can but still rich, esp at startups. I am curious about the ECM now. I have an automatic 700r4. The ECM is supposed to match that. What is or are the differences between the manual and auto ECM? I have another ECM laying around but can't tell what it is for.
I know it is ancient tech and should consider myself lucky it is running at all but I have an interest in getting it running correctly. Plugs, wires, cap, module are all basically new too. Air filter is new. No air leaks in the manifold. The TP switch is adjusted correctly according to the manual. New idle air controllers too. Rock auto has remanufactured ECM's for around $100.00. I just need to put in my prom. They don't say if auto or manual or if it depends on the prom. And that is my question, what is the difference and how do I tell?
Help!
Thanks
Russ
I know it is ancient tech and should consider myself lucky it is running at all but I have an interest in getting it running correctly. Plugs, wires, cap, module are all basically new too. Air filter is new. No air leaks in the manifold. The TP switch is adjusted correctly according to the manual. New idle air controllers too. Rock auto has remanufactured ECM's for around $100.00. I just need to put in my prom. They don't say if auto or manual or if it depends on the prom. And that is my question, what is the difference and how do I tell?
Help!
Thanks
Russ
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
In most cases the same ECM is used for both automatic and manual transmissions depending on engine. For a 84 prom is the difference, calibration will vary for rpos ie transmission, tires, axle etc. Calibration table would list rpos which are found on SPID label it will have both part number and broadcast code. Broadcast code is the 8 digit alpha numeric code on a prom abcd 1234. The 4 digit alpha code is also on original ECM. SPID label location can vary between model years. With used ECM model number needs to match one in the car. GM dealer or online resources can help id used ECM intended applications.
Crossfire rich - Original coolant temperature sensor connector ( round) failure. Requires new sensor and connector. Vacuum leak(s) effecting MAP sensor, that includes plenum gasket. ECM adds fuel if MAP is low. Synchronization of TBIs is also very important, if it's off crossfires don't run right.
Crossfire rich - Original coolant temperature sensor connector ( round) failure. Requires new sensor and connector. Vacuum leak(s) effecting MAP sensor, that includes plenum gasket. ECM adds fuel if MAP is low. Synchronization of TBIs is also very important, if it's off crossfires don't run right.
