Air is needed to ignite the fuel you have just introduced. The '85 and the '89 are both mass air cars (MAF), but use different mass airflow sensors. Not only are the sensors different, but also the burn-off relay for the '85 is not the same relay as the '89. To go a bit further with MAF, the car starts by the ECM calculating mass air flow and engine coolant (ECT)
Spark is going to be the most complex issue. There are many conditions that will need to be met to get the ECM to provide the spark. The distributor provides the spark; but the ignition system requires power to the coil, an operating HEI and ESC module. The HEI module is the same for both years, but they have different pin-outs at the EST.
Timing is not as critical to get the car to fire, but to keep an idle. To begin with, set the timing at somewhere around 12-16 degrees. When making conversions like this you have to do a lot of homework. I have found wiring mistakes in service manuals with regard to pin-out connections. It's best to research as many sources as you can to verify connections, pin-outs, and proper sensors for that conversion.
Need More Input
I recently purchased my first Corvette: a blue '90 six-speed coupe. I know this is ambitious, but I would like to do all the mechanical work on the car myself. Since I am not a mechanic, I recognize that I have a lot to learn. I have read in your magazine about ECMs, codes, chips, replacement chips, and code readers. Is there a comprehensive reference that deals with this aspect of the car? Also, can you recommend a code reader that I can use for diagnostics? my Vette has an indentation in the upper rear right back bumper assembly. Can this part of the car be repaired or do I have to replace the entire bumper?Fred Hefter, Via e-mail
There are many C4 books available for tuning, maintenance, troubleshooting, and general information. One book that might help you a lot is Fuel Injection & Engine Management by Charles O. Probst. This book will guide you through emission problems, engine codes, ECM wiring, and sensor testing. This book is available through Corvette Central, PN 114083; www.corvettecentral.com. While you are searching their web site you will find other books and manuals that may also be a great help.
As far as your rear bumper, once they become damaged they are impossible to get to look right again. I don't know of anyone out there who can repair and guarantee that it will withstand the years or look correct after the repair.
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