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8.1/LS swap no start issues, help needed

Team208Motorsports said:
If you are dropping that much voltage on the old coil circuit the tbi engine never would have ran. Do the jumper see whats up. What does the voltage drop to on the old coil wire while cranking?
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The old TBI 350 ran like absolute shiznit before pulling the motor to do this swap...so this could have been a problem. The voltage is dropping between 8.5v and 9v right now on that old coil wire while cranking....everything is leading me back to this is the problem and if I can figure out why that wire is dropping then I think it will fire right up.

I will try the straight 12v from the battery on the 12v switched wire and see if that does that trick...fingers crossed
 
Sorry, the TBI will run like crap with 9 volts at the coil while cranking. Cuz it will fire and then the volts come up after it goes to the run position. That was only running the coil, not the ECM.
Seen it..
But once again, just my experience.
 
Would a TBI coil have some kind of a resistance wire powering it,instead of it getting a full 12V?...I suppose not,or the wiring harness makers would not reccomend using that wire to power the ECM.

I know HEI uses full 12V feed,but that's about as "new" as my experience gets..
 
I wouldn't be surprised if your system voltage dropped to 9V while cranking. A starter draws a ton of current! That said, 9V should be sufficient to get you up and running regardless. The entire system runs on a 5V reference architecture and should technically run on anything more than 5V of supply potential.

If I had to guess, I'd go with a poor power or ground connection somewhere. I'd start with checking every single connector that has a power or ground going to it to make sure everything is good. From there I'd be checking point to point on the harness from every engine side connector to the PCM. If that pans out, you really need to get yourself access to a Tech 2 or MDI so you can check your cam / crank sensor counts while the engine is turning over to verify if you've got signals from the both of them as well to verify a believable reading on the rest of the engine sensors. You require both the cam and crank sensors operating correctly for the PCM to know where it is in the timing cycle and to fire the coil packs accordingly.

If you don't mind a couple weeks wait for shipping, I'd be happy to do the point to point wiring check on your harness for you. Your connections to your truck should be pretty straight forward and the heavy gauge pink wire that ran to your old ignition coil is perfect for the ignition input to your PCM.
 
Russell said:
I wouldn't be surprised if your system voltage dropped to 9V while cranking. A starter draws a ton of current! That said, 9V should be sufficient to get you up and running regardless. The entire system runs on a 5V reference architecture and should technically run on anything more than 5V of supply potential.

If I had to guess, I'd go with a poor power or ground connection somewhere. I'd start with checking every single connector that has a power or ground going to it to make sure everything is good. From there I'd be checking point to point on the harness from every engine side connector to the PCM. If that pans out, you really need to get yourself access to a Tech 2 or MDI so you can check your cam / crank sensor counts while the engine is turning over to verify if you've got signals from the both of them as well to verify a believable reading on the rest of the engine sensors. You require both the cam and crank sensors operating correctly for the PCM to know where it is in the timing cycle and to fire the coil packs accordingly.

If you don't mind a couple weeks wait for shipping, I'd be happy to do the point to point wiring check on your harness for you. Your connections to your truck should be pretty straight forward and the heavy gauge pink wire that ran to your old ignition coil is perfect for the ignition input to your PCM.
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According to Howell, they said if cranking drops below 10v, it's not going to start (just going off what they told me).

I tried this weekend the trick that @Team208Motorsports and Howell suggested of hook the 12v switched wire directly to the battery and see if that get's it to start, and no dice. Still just cranking with no start....

Thanks for the offer Russell...I have two buddies who are going to come over most likely this weekend and try to help me track it down (both are good with electrical and very familiar with 8.1's). I'm just hoping its something I've overlooked or something simple....but at this point I'm kinda at a loss with it.

We will make sure to double check grounds (for the 15th time) and all the power supplies to the crank/cam sensors again.
 
The 10v thing is BS. I have race cars that fire with less voltage than that due to battery size.

Don't just check the cam and crank. You need to get a scanner on it and see if they are working.
 
Not yet. The truck is at my dad's shop which is 45 min away from me, so I'm limited to working on it only on the weekends. So this Saturday going to head over there and try a few more things to see what happens
 
Update...I had a buddy come over who has EFI live that he hooked up to my computer. We looked at the tune and didn't find anything that should cause issues with start up or running...we kept trying a couple different things. With his scanner hooked up to the computer, we were able to see good tach signal, injectors, ext all looked real good, but still no start. Come to find out...I only have 1 coil pack firing....there is 1 other coil pack that is intermittent, but nothing on the other 6 coil packs.....that is where we are very confused. My buddy even brought over a full other set of coils off a donor 8.1 he has and we put them....still the same exact thing. He even had a different ECM we put on it...still the exact same thing.....we are getting pretty confused as to what is going on....Now I wondering if the harness from Howell is bad. They will be getting a call Monday morning...
 
I told him hey I know a guy that could probably use your help. Then it turned out he already knew you.
 
Yeah, we swapped tranny's for my crew cab build. So my crew cab now has the tranny in it that was in his Tahoe....small off-road world we live in huh? haha

Alex is a really good guy and is very smart when it comes to electrical and all this stuff. We were all starring at it for about a half hour scratching our heads trying to think what the heck is going on....
 
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