07 tahoe no crank

Alright I messed up, I really really messed up. I strive my best to not be a parts changer but this one has given me a run for my money. I'm gonna try and shorten this the best I can but leave as much detail that would be needed, so bare with me some.
07 tahoe came in with the typical DOD lifter tick, I removed the valve cover to inspect the rockers while turning the motor over. I used one of my relay/circuit testers. The ones that go in place of the relay then the relay goes up top and you can access all the pins. This setup uses a permanent ground with a computer 12v output for the control side. I had my little cheap push button starter switch hooked to bat + and then to the control side of the relay. Well the janky alligator clip fell over and connected to the ground pin while I was operating it ( here's where I screwed up BAD!), the fuse box instantly started smoking and caught fire. We put it out quickly with minimal damage but it still needed to be replaced. Any how I did the repair that It came for and sourced a fuse box. Installed it and and changed one burnt connector and rewired a few wires for the pins were melted into the connectors. I get the job done and take it back, she calls me 10 mins later stating it won't crank. Before I even get the shop closed up she shows up, she finally got it to start and it was doing great so she went on. Any how few days later it leaves her stranded and won't crank again, on level ground.  She finally gets it started the next day and brings it by. After the repair I had wrote a tune thru hptuners to delete the DOD, I thought maybe just maybe this is caused by the tune, maybe it was a corrupt file. So I rewrote it and drove it myself for a few days without issue. Take it back to her house and park in her driveway which is very steep. Sure enough it won't crank again, we ended up letting it roll forward to get it out of the way of her garage so she could take me home in her other car and we could try again later. At this time it's on level ground and cranks. So I take it back the shop. Over the course of the last month I have been messing with this car. A few times it's gave me trouble on an incline but 99% of the time it won't crank on a heavy decline. When you turn the key it just clicks like a bad starter. You get in it and hold the brake on a heavy decline and put it in neutral or just unload the drivetrain it cranks everytime, but let it roll forward and load the drivetrain and it just clicks. I thought neutral safety switch, turns out there's no adjustment, I even replaced it thinking maybe the contacts arnt making great connections. Anyways I installed my relay tester again and used my breakout lead set this time to connect to all 4 pins of the relay to see what I was missing when the no crank happens. Turns out it's the 12v control feed from the ecu to the relay. It will spike 12v and quickly drop out, only on a steep decline tho, at this time it will start great on level ground. I don't believe a heavy incline or decline would cause more load on the starter as I would figure the torque converter would relieve it of that? Not sure tho insight needed. Any how for the sake of trying something I went with the theory it was putting more strain on the starter and the starter was weak. So installed a new starter, now it won't crank at all, on level ground in neutral nothing. So I probed the 12v control from the ecu at the relay again and it's doing the same thing 12v then immediately dropping out. Installed the old starter and it cranks fine (on level ground) Thought maybe I got a faulty starter and tried another new one, still no crank on level ground. At this point I'm thinking my wiring from the ecu to the relay is bad so I probed at the ecu and the relay, they both match, 12v the immediately drops out, just like a spike. Now changing nothing but pulling the relay out I get a steady 12v. This seems like a load issue internally to the ecu. I'm thinking I've damaged the ecu and need help in my thinking here but need clarification on a couple things.

1. Is it possible that my new starters are pulling more amperage than my old starter which is my the car cranks with the old and not the new?

2. Would more load on the load side of a relay also cause more load on the control side some how? Which would then cause my no crank?

3. Does drivetrain load cause the starter to have to work harder?

I've got a computer ordered for this car and perfectly fine with that being the fix, in all reality I don't car if this cost me 1000 bucks to fix I just want to fix it and move on. I've def learned alot from this mistake but at this point it's really starting to cost me alot of money and time as well it may cost me a good customer if this rocks on much longer. Thanks for your input!

Have you done a voltage drop test from battery negative to engine block? When it turns to a no crank perform that test. You want less than 200 mv. If you have anything higher it’s a bad ground. Also have any codes?

I have no since it was an issue on the control side of the relay I didn't see a need for that? But I will try it. Only code is for an evap issue. Has a yaw sensor code too in the ebcm

1. Is it possible that my new starters are pulling more amperage than my old starter which is my the car cranks with the old and not the new?

2. Would more load on the load side of a relay also cause more load on the control side some how? Which would then cause my no crank?

3. Does drivetrain load cause the starter to have to work harder?

1.) The new starter could definitely be pulling more current. But, like Cheryl mentioned, if there's a voltage drop across the starter main B+ or ground, then neither starter really has what they need to work correctly. I'd second the suggestion to check starter voltage drops during your incline/decline/loaded drivetrain condition AND during normal cranking.

2.) It shouldn't, especially the way this circuit is designed. If you substitute an incandescent test light in place of the relay, does it behave the same way? With your description, I'd expect it to flash briefly before going out with the key in crank.

3.) Again, shouldn't. Technically, the starter shouldn't care if the whole car is upside down in a tree. :silly: I was actually picturing a condition where the engine/trans rotates slightly on its mounts with drivetrain load. That could cause the right wiring harness/connection to flex in just the right way to get your issue. Allowing everything to neutral out makes the problem go away.

Which engine are you working with? You mentioned DOD, so I'm gonna figure LMG. Are there any codes set when it doesn't want to crank?

For whatever it's worth, you might check this thread. Another member did the same thing you did. :silly:

www.scannerdanner.com/forum/post-your-re...100-p0615-p1682.html

If it makes you feel any better, I own the exact same Lisle relay testers. I'm ALWAYS scared of crossing up the pins. :ohmy: 

Did you check the 12volt feed signal for the relay control side at the ecm side? Do you have a starter request pid in the data stream?

You may want to compare the current consumption of the old and the new starter....

If you had a 4 channel scope hook it up to b+ at the battery, b+ at the starter (solenoid in), solenoid out to starter and the 4th channel to the starter housing. That way you'll see all possible VD's in a sole capture.

So I'm an idiot and left this part out intentionally as I realized how stupid it was now. I pulled the relay and tried a bulb that I know pulls 3amps inline. It didn't light with the key in crank. I realize now this could fry the driver. Circuit is still giving 12v like before tho. I will try the test light next chance I get. No there's no new codes during the no crank.

I did check the 12v from the ecu while using another channel of my scope to check at the relay. They matched with 12v spike and immediately dropping out.

Using a light in place of the relay only gave a brief flash of the bulb as you figured. I can crank this thing over with out issue using a test light hooked Bat + to the control side of the relay. It will crank all day that way. That should prove out the relay,

I accidently posted my last reply without finishing, that should prove out the relay, starter, wiring to the starter, control side ground. The only left is ECU, and control wiring to the relay from ecu?

Is there any chance the ignition switch itself could be the culprit?

wrote:

Is there any chance the ignition switch itself could be the culprit?

This is absolutely possible. As mentioned before he might want to look at the start request pid in scan data while holding the key in the crank position or check the voltage signal from the ignition switch to the bcm.

Don't forget the park/neutral safety switch on side of tranny