Most swap harnesses have problems. I wouldn't install one without doing a thorough pinout test and inspection of it. They tend to be more of a starting point than a finished product.Originally Posted by Obvioustoaster
But remote trouble shooting something like this is hard and is mostly a guessing game. We have no way of knowing what you have done/checked or if you know anything about electrical trouble shooting. Maybe this is a tune issue, but most swaps tend to have wiring issues.
I have 0 experience trouble shooting EFI cars, like I said, this is the first. I can rebuild and tune a carb with my eyes closed which makes this all the more frustrating. Put an LS in it they said... its cheap and easy... lol its been nothing but a money pit. Thank God I didn't try this with my Nova. Unfortunately, I live in a very rural area with no nearby shops that deal with hot rods and race cars.
Thanks for all the help guys. I guess I will remove the harness, look for some kind of diagram for the ECM and start testing pins.
Side note, its not throwing any DCT's. Not sure if it needs to run first to throw codes or not.
Most of what we are discussing are not EFI principles but automotive electrical principles, which are really just basic electrical principles. With EFI there are just more "points".
If you are trying to do a swap without some sort of wiring diagram, you are in for a world of hurt. You need the diagrams for the donor ecm as well as the C4 if you are trying to mate the two together. No way I would trust a swap harness company to get that right.
But again, it might be in the tune like Alvin said. Or it might be all of the above. It's hard to say, since without more experience than what you profess, we have to try and read between the lines of what you are telling us. You might tell us something checks out, but you might not be testing things correctly.
Its a road race car, the engine harness is basically the only wiring it has. Interior is completely gutted, no dash, no side windows, etc. Was going to use the OBD port for gauges.
Why didn't you go with an aftermarket ECM?
Trying to a "cheap" LS swap. An aftermarket ECM costs more than I have into the whole project
Does that mean you went cheap on the harness? It's not a made in China ebay/amazon is it?
To be completely honest, I dont remember where I got it. Most of my parts came from Speedway, but I have been on there recently to see if I can find documentation for it and was not able to find that particular harness. I am an OTR worker and progress on my projects is slow. This one got pushed into the corner about a year ago out of frustration. I recently got HPtuners thinking if I could to hook up to it, it would make things more clear.
I am assuming the ECM needs to know it's in park/neutral and your foot is on the brake to start. Anyone know what pins those are and if they should be 12v or ground?
dont assume.
no the ECU doesnt care if your foot is on the brake, or if its in park
OK, Why can't you start your car in gear with your foot off the brake?
3 of my LS swaps i can start without foot on brake, and in drive or reverse. It has nothing to do with the ECU
It’s typically handled on the starter relay and maybe on the key circuit. Maybe at the bcm. Look at the wiring diagrams for your donor ECM. Having those diagrams is pretty much mandatory for trouble shooting.
And it won’t crank in a stock setup because of the park/neutral and brake. It will usually start if you were to jump the relay in gear.
I found the harness at Speedway. It shows a park/neutral wire and a brake signal wire, these are not needed?
Can’t say without wiring diagram for both the donor and for the wiring harness. There are other things that a park/neutral and brake signal is used for other than “will it run”. Cruise control needs the brake signal. It may use different idle settings for park/neutral than in gear.
Well, I guess I will go through the harness. What sensors are required to make it start? I will start with those and move on if I find issues. I can eliminate the crank sensor, I do see RPM while cranking.
Your VE table (which is your main fueling table) is filled with the highest possible number you can put into that table. I've flagged this three times now. I promise you that is a major issue and if everything else was right on the car it wouldn't fire.
If everything else was correct it still would not fire this way. You should fix that ASAP and especially before trying to diag anything else.
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Wow. No offense OP but it is exponentially difficult to guide someone with no electrical or EFI tuning experience through diagnosing a no start condition in a swap vehicle with aftermarket everything.
Do what Alvin says first. Before anything else.
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That's not the results of a voltage drop test.
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