(84 vette 74k miles) shortly after replacing plugs, wires and rotor, my car started running terribly. Constant misfiring and 'popping sounds' from exhaust. Not 2 minutes down the road I turned around and broke down infront of my house. Tested spark and confirmed I do have spark. Noticed injectors not firing. Checked fuses, replaced relay, and no power was being sent to fuel pump. Hooked the pump up to 12 volts and started working. OK so electrical issue. No check engine light comes on when I turn the key to accessory. Cant test any codes what so ever. Prob an ECM issue. I do some research and find the 1227747 is a great replacement. More reliable and adjustable. Got one from a junkyard today. Apparently I am gonna need a HAM (Harness adapter module). Any idea where to buy one? I found this site that has a general guide how to go about swapping it (http://www.technovelocity.com/chevyh...m/8746ecm.html). Anyone know of a youtube video explaining and demonstrating the steps. Still new to working on cars.

Any suggestions where to get a HAM board and where I can get a better tutorial about swapping it in.
Or maybe I could be wrong about my ECM hunch, any suggestions.

If this doesn't work I'm gonna throw a carb on it

 

It should just connect right in the plugs are the same

 

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Not even the same. The 84 ECM uses card edge connectors, think back to the Nintendo game cartridge that you blew on as a kid. The 7747 is a pin type harness, like any aftermarket radio and nearly all ECMs are now days


If you really want/have to convert your harness over be prepared for a very long day. I literally just did this this weekend


7747 harness ready to splice into the 84. I tried to splice it as it was, but the harness just wasn't long enough for me to see what I was doing laying upside down in the seat and using a flashlight to try and read the pin markings so I had to extend the 7747 from 3" to 10", which made it so easy then I could move wires around without ending up with a knotted mess, while sitting up

To splice yours here is the pin out from 84 to 7747, the 84 has a white and a black connector, with 22 and 24 wire slots which are numbered onthe sides of the connectors. The 7747 has 2 connectors with side A, B, C, & D stamped in the plastic about 1mm in size or less. You will need to add 3-6 pin crimps to the 7747 harness depending on the vehicle your harness came out of. They can be bought online for like 30-60 cents each depending on the source


84 Black connector:

1 - C9 --------- 12 - C4
2 - B5 ---------13 - C3
3 - B3 ---------14 - N/U (C2)
4 - C10 ---------15 - D6
5 - C13 ---------16 - N/U
6 - C7 ---------17 - C5
7 - C1 ---------18 - C6
8 - D7 ---------19 - D4
9 - A3 ---------20 - C11
10 - D5 ​​​​​​​---------21 - C12
11 - A11 ​​​​​​​---------22 - A4

84 White connector:

1 - N/C ​​​​​​​---------13 - D1
2 - A10 ​​​​​​​---------14 - D2
3 - A9 ​​​​​​​---------15 - B1
4 - B7 ​​​​​​​---------16 - A6
5 - B10 ​​​​​​​---------17 - B2
6 - N/U ​​​​​​​---------18 - A1
7 - A8 ​​​​​​​---------19 - A7
8 - D14 ​​​​​​​---------20 - A5
9 - D15 ​​​​​​​---------21 - B8
10 - C16 ​​​​​​​---------22 - C7
11 - C14 ​​​​​​​---------23 - N/U
12 - A12 ​​​​​​​---------24 - N/C

N/U is not used. This is where there is an ECM function that is no longer used or wired into. Such as the cold start timer module (W23). N/C is no connection. As even GM didn't use that connection.

There will only be a wire in W-22 or B-6, not both, sometimes neither. W-22 is TCC high gear (auto), and OD request for the 4+3 on B-6


IF you go this route, you better have experience with doing electrical work! And buckets of patience to test every step and double check every connection multiple times. Wire nuts are never acceptable in vehicles! And please, use heat shrink wrap. I prefer marine heat shrink for the glue that helps seal the now exposed insulation connections from the elements. Green corrosion from a heater core failure, or other HVAC issues, or heck even rain since these things are known to leak when they hear it's raining outside, would be a very bad thing on ECU wiring.

​​​​​​​Unhook your battery before you begin, ohm everything out once spliced to ensure you have good connections, and if at all possible use the same color wire for your jumpers. The wire colors and stripes between the 84 and the 1227747 are surprisingly almost completely the same other than like 6 of them. I spent hours researching and ordering wire and a 7747 harnesses and just getting everything ready to splice into the 84 harness, then spent a full 14 hour day tapping into the 84 harness and ohming everything out before sealing it all up. You may want a magnifying glass to see the markings of pin locations on the harnesses. Quadruple check every connection to the correct location!
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I'm hoping this weekend I can slap the 7747 in and see if all the work paid off. If not since I spliced into the harness vs completely replacing the 84 harness connectors I can still use my factory ECM if I screwed up the job
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All that said, have you followed the FSM trouble shooting to make sure the problem is the ECM?

Swapping ECMs is a massive undertaking (mostly your time) and I'd hate for you to go through the work and cost to find out it was a fusible link or a faulty new ignition part

 

You do NOT want just my HAM board for this ECM conversion. It IS a rather tedious job installing it without trashing your ECM. That is the issue I'm having now that Dynamic EFI is not installing my HAM board anymore. I'm actively trying to solve that issue, and may have a fix, but it will be another two weeks to find out. Had a meeting today with a couple of engineers on this subject. If you decide to splice your harness, also as mentioned, it is NOT for an amateur and you can not be off even one wire or you can run the risk of destroying everything. Triple and quadruple everything is a MUST.

As far as connectors goes, as mentioned they are NOT the same as the 85 corvette and up ECM connectors or anything else 85 and up except the 350 block and SBC heads. If you don't know the CFI system, please refrain from giving owners information, it just confuses everything.

As far as your issue goes with the no start and NO CEL light. There is a very good troubleshooting chart in the 84 service manual on pages...6E2-14 thru 16. If you don't have the manual, get one. It IS VERY good and a MUST have item for CFI. GL

 

I was told the owner that did the ebl flash2 and 4 injector modification is shutting business down because of his death in September.

 

Sounds like he was a talented person. Dead but still able to "shut the business down".

 

The business is in probate court I was told. Not sure what's going in there. Never dealt with probate court.

 

Since Bob is no longer an option for me to ask questions, I'll ask it here. When replacing an 84 corvette ecm with a 7747 ecm, how to get around vats on 7747. My understanding from reading lots of post, without vats input to computer, the vehicle will not start. Most post have to deal with taking readings and finding out resistance of key and then using a resistor to bypass or trick computer. 84 doesn't have vats to use resistor. What's the trick? Programming memcal to disable vats? Thanks for any information.

 

Years ago I converted my 84 to a 7747 and used it to run a 383 I built. Vats wasn't an issue. The 84's don't have vats. I know the truck I pulled the ECU out of didn't have vats either. So that ECU may be able to offer vats if you really wanted it to. But I didn't have to mess with it.

The biggest problem I had with the 7747 was standing on my head for hours putting the new plugs on my factory harness. That wasn't fun.

In today's day in age I think you would be way better off with an aftermarket ECU. They're not expensive anymore and so much easier to work with.

 

The 7747 I have came from an 89 350, 700r4, 3.91 rear truck. Not sure if it had vats, but all the schematics I have show the 7747 with vats on pin B6. The connectors that came with my 7747 has a wire on B6 of connector. So not sure if it actually has vats in program. Still taking old parts off corvette, so a long, long way before ecm comes to play, but just planning ahead. Thanks for reply.

 

B6, a blue and white wire, has no wire to splice to on an 84 pin out. I want to say I removed the B6 pin and used it in another location that I needed one

 

But if the ecm had vats, wouldn't just leaving that pin out since 84 doesn't have one, create a no start scenario? And after looking closer, I might be looking at 16198259 connector. Going to dig out other connectors. Hoping other set doesn't have vats on B6.

 

No matter what you need to burn a chip for the 7747 to work in your car. So when you do that just turn vats off. So then you won't need to do anything with that wire. Even if the truck tune would run the car your constant for injector sizing would be off and the car will run like crap. That's what I ran into with mine anyway.

 

Thanks. I checked. I had wrong schematic and connector. Found other connectors, looked on line for 7747 schematic, and it all matches. No vats. But as mentioned, I will have to have a bin file for my car. Hopefully someone can help with burning one I will buy from them, or help me do it. I'd prefer not to do it. Not very intelligent on electronic stuff. Just trying to get car up and running for son or nephew.

 

Another question. My 7747 connector is missing pin B8 ac signal and B10 park/neutral signal. Since I have other connectors with correctly colored wires, how do you unpin the terminals to repin in other connector. Thanks

 

I always used a pick. A safety pin can work too. It's really hard to explain how to do it through text. I wonder if you could find a youtube video? Molex connectors are similar but shaped different. Maybe watch a video on those to get an idea. But the gist of it is you need to insert the pin or pick into the connector and press the little tab that's holding the connector pin inside the plug housing. While doing that you need to gently pull on the wire. Once you get the tab pressed far enough it will just pull out.

 

Thank you

 

How to repin

 

Thanks flannel man. Ended up using a small long finishing nail. When I pushed it in, nothing happened, but I could wiggle it as I pulled it out and the wire would come out. Bought a re-pin kit from Temu years ago. Has all kinds of gadgets. Square ones, round ones, flat ones, forked ones, etc. If I could only find it. Such is life. Thanks again.