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8.1/LS swap no start issues, help needed

Kay86K5

Kay86K5

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Alright, some of you know that I have a crew cab V3500 that I swapped an 8.1 into. Some know I've had some issues with start up, so I wanted to start a thread here in the garage section since not everyone looks at every thread in the driveway. Even though the 8.1 is technically not an LS, as far as the wiring goes its the same as a 5.3/6.0 swap. So here is what I'm dealing with:

I ordered a brand new stand alone harness from Howell Development along with a tune on the computer from them too (the same tune as most others have used doing the same exact swap as me). I replaced the crank and cam sensors on the motor cause these are very prone to failure in the 8.1 and real pain to change with the motor in the truck. Right now the motor will crank and crank forever without firing. I have confirmed I have ~58psi of fuel and the fuel rails, so fuel is not the issue. I narrowed down that each coil pack is getting power to them and the grounds seem fine (this new harness has all the grounds for the computer come together to one point, I have this bolted to one of the studs off the intake that normally the plastic cover would be bolted to...this is aluminum so it should be a good conductor), however each coil pack is not receiving the fire signal from the computer. I have found my 12v switched wire we spliced into for the harness (we spliced to the original wire that went to the ignition coil of the TBI motor as per instructed) has 12v's when the key is on, but as soon as I start cranking it drops to below 9v's. According to my understanding this wire is the power source the computer gets to send the signal to each coil to fire. I replaced the battery with an Optima Red Top, and that hasn't done anything.

Is there anyone else here with LS swap experience that has dealt with this before? Where else could I be loosing the cranking amps that would cause this issue. I'm not an electrical guru by any means, but I have felt like I've checked the majority of the basics and can't seem to figure it out. Any help would be appreciated!

Thanks!
 
How hard would it be to bypass the old ignition wire and run a 10-12 gauge wire off the battery and use that as your ignition power signal to see if it will fire up?
 
I'm not sure how I would be able to run that to connect to the ignition switch on the column then to turn the starter/motor over....
 
You can't just disconnect where you are hooking into the Howell harness to power it up with the old coil wire and run that over to the battery so it powers up that way but still use the key to crank it? Or am I totally off on my understanding of your setup?
 
I am wondering if maybe you have some tired contacts in the ignition switch. Or maybe a that combined with a slightly dirty connection somewhere else in the power to the cab which doesn't like the load imposed while cranking the starter.
And do you know the history of the starter? Could it be pulling too many amps?

I would try to jump power to the ignition wire close to the engine and try to start it.

But I really wonderful about the contacts in the ignition switch.
 
I am with these guys about the direct jump wire from the battery. It sounds like the hot wire from the ignition switch is not cutting it. You might want to throw an inline fuse in the jump wire as well to protect the ECM from too many AMPS. If that does not get it going then maybe something is wrong with the ECM...even though ECM failure is not really a common problem, unless it got damaged from accidentally shorting it out or something.
 
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I guess we can try this, but we kinda already did. We took the main 12v power wire and the switched 12v power wire and held them both together with a pair of plyers and that didn't help it fire. I know that's a real redneck way of trying it, but I figured that would be enough to bump the amps up a couple just to get it to fire up, but no dice.
 
I am not totally familiar with the system you are working on, but does the hot wire that tell the coils to fire come from the ECM or from the position sensors? If you know for sure there is power going into the ECM, then you need to check for power coming out of the ECM. Have you disconnected the ECM main terminal connector and probed the incoming hot wire with a test light to make sure there is power going to the ECM? It is just a matter of using a test light to make sure there is power going in and coming out of the entire ignition system. It sounds like you got the ground wires covered pretty good.
 
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Another thing is the coils. Are these old coils with an old engine? I do not know how the coils are wired....weather they are wired "in series" or wired "in line". If they are wired "in line", then one bad coil at the head of the line is going to kill all the rest down the line. Dyeager535 would be a good person to enter this discussion.
 
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All the coils are the factory coils except for 1 (as 1 was broken when I purchased the motor), however the motor only has 91k miles that are confirmed, so I'm not concerned at all about the age of the coil packs. We did probe all 8 coil connectors to make sure power was getting to each coil and it was communicating back to the computer at the correct ports, which it all is. So there is power to each coil, it's just the computer is not sending the signal to each coil pack to fire. Which after our diagnosis we determined the computer isn't sending the signal because the cranking amps on the ignition wire is dropping below 9 amps (at least that is where we are at right now). And according to my understanding, the computer is supposed to get the power to send that signal from that ignition wire that is dropping amps. So I have a feeling if I can find the source of the amp loss, then I think it will start up....I'm just a little lost on that right now.

I do appreciate all the feedback, and over the last month and a half of dealing with this, I've thought about and checked just about everything you guys have mentioned....hence why I posted this thread :). But if I posted everything I checked over the last month and a half, the original post would be a novel, haha.

Keep it coming though guys....there has to be something i'm missing
 
does yours have the vats still in the system and if so is the little black box hooked up.found this on one when me and two buddys put a 99 c5 vette ls into a chevy silverado. sounds like thats why the computer isnt giving commands to run.
could be wrong though.
 
I just remember seeing something on a tv show for doing an ls swap you had to get it programmed to unlock the ecm. But I've never done one.
 
Yeah, according to my understanding all the VATS system is completely deleted with the tune Howell did on the computer...so that shouldn't be the issue at all. This is the exact same harness and tune that Larry used on both his K10 and Polar Bear Burban builds that both have 8.1 swaps (I pretty much copied what he did). So all of that has made me think it's not an issue with the stand alone harness or the computer/tune....it's got to be the existing wiring in the truck that is causing this drop in amps somehow...
 
cool when we first did the silverado they told use you could not. glade they do now.
 
Have you talked to Howell at all to make sure you have done everything installing it correctly? I'll do some googling and see what I can come up with for no spark on an 8.1L when I get a chance. What about trying to connect with a scan tool and see what's going on?
 
Have you verified power, ground and signal from the crank sensor with a volt meter. Here is a pretty good instruction on doing it.
http://troubleshootmyvehicle.com/gm/4.8L-5.3L-6.0L/how-to-test-the-crank-sensor-1
I know you changed the sensor but make sure you test everything to see if its making a signal and also see if you are getting a ground from the PCM. That might tell us whether or not your pcm is powering up and working correctly. I would back probe the ground wire carefully with a paperclip and hook up your meter like it says in the t/s and put positive lead on battery positive post and ground lead on paperclip back probing the ground signal to the crank sensor and see if you get a good ground while cranking the engine with the key. You may possibly have an issue with how the harness was built by Howell, like an improperly crimped terminal or something to that effect.
upload_2016-8-29_9-31-5.jpeg
Did you somehow get a short cam sensor instead of a tall one or vice versa? I saw one guy online that had issues with this.
This page explains the years and cam sensor and cover differences. But it sounds like the cam sensor has to do with firing the injectors if I'm reading things right and no spark.
http://www.raylarengineering.com/vortec8100-camshaft-position-sensor-camshaft-gears.html
Hope this gives you a little assistance. If I was closer I'd come check it out for you. I love electrical issues.
 
Yeah, I've read both of those articles and done the checking on both. My cam sensor is the factory one and as far as I can tell it's working correctly. And we double checked all the power leads back to the computer, and we also checked that the crank sensor has power and ground to it.

The only thing I haven't done yet is put a true scanner up to the motor while cranking. As far as I know though, things like EFI live will only really give you readings once the motor is running, not just cranking, so that does me no good. And the only scanner I have will read codes (which I don't have any right now) and just show me RPM's and stuff like that, cause those nice scanners are so much freaking money its not even funny. I did hook up my aftermarket tachometer on the truck/motor this weekend, and it too shows that once I'm cranking, the needle bounces up and down just a little bit which to me says the ECM is getting/putting out an RPM reading, so the coils are getting power.....it's just that the ECM isn't sending the fire signal to them to fire. And once again where we are at is we think the overall cause if the amp drop during cranking from 12v to below 9v.

I wish you were closer too, haha. I'm getting to the point I may need a couple guys who have a little more wiring expertise than me to come over and with all our brains together try to figure it out, cause me by myself for the last month and a half hasn't netted me anything so far, haha.

I think I'm going to double check my grounds again, just because. I have the battery to motor ground, the braid from the block to the chassis, and also the wiring harness ground (multiple wires converse to one point...this is how Howell did it) that I have off the intake. I may try to replace those ground wires with heavier gauge and make sure the connections are correct. And I thought my dad hooked up the ground from motor to frame, but if he didn't, I will do that too (pretty sure he did though)
 
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