So I’ll start with some history of the car. It is a 2014 C7 Z51. It has a magnuson blower and exhaust. I bought the car used at about 12k miles. When I first purchased the car I noticed it was sluggish cranking over but always would start. Figured it was an old battery. After about a month of ownership I swapped the battery and it only slightly helped. I figured if it was still starting to not worry about it. At about 15k miles while driving down the freeway at 70mph the engine seized without warning. About a month later the car was in a shop for complete engine rebuild. They informed me that two rod bearing had spun. Sucked but what can you do? Engine was fully rebuilt, new crank, pistons rods, cam etc along with a new McLeod twin disk clutch. After getting the car back the start up was certainly better but was never quite like it should be. So recently this past month I decided to finally find the cause of the sluggish cranking. Started with a new battery, going to all the positive and ground connections around the battery and making sure they are clean and tightened correctly. Still no change. I found a video on tik tok that it’s a common problem with 5th gen Camaros and a remedy is adding a ground wire from the head to the frame rail. I had high hopes but after doing this still no change. I’ll add that the car never fails to start runs and drives totally fine. The Then I took a deep dive into what could possibly cause this and I found this write up. https://www.corvetteactioncenter.com/tech/knowledgebase/article/2014-2016-corvette-gm-techlink-updated-corvette-driveline-support-assembly-replacement-procedure-1313.html

In short this article highlights an issue with crank shaft end play being caused by the torque tube putting to much forward pressure into the crank shaft. Although the article was based around an automatic transmission I’m curious if the same issue is possible to a manual transmission? I’m also wondering now if this was the cause for the previous motor seizing?
I’m basically all out of ideas on things that I am capable of checking/fixing. If this thrust bearing problem is the issue can someone tell me A. How can I check? and B.how can I fix it?
the motor only has about 1500 miles since rebuild. I’ve been paranoid to even drive it lately incase this issue is in fact what’s wrong. Although it has never not started and seems to run perfectly fine. No weird noises, no problems with drivability.

 

How is the starter? Can you remove it and have it tested and disassembled? I had a lot of slow cranking issues that were fixed by putting a jumper pack on it only to come back after a few days of inactivity. One day, I replaced the battery that was getting old. Each job seemed to make it work for a bit. Can't leave it alone for a few days without having slow crank. One day, I decided to take out the starter and have it checked. Seems like oil leaked from the valve covers and soaked the internals over the years. Rebuilt that and life was good again till I got rid of that "Rickety POS" as the wife called the C4.

 

I considered this but figured if the starter was going bad it would have stopped working by now. I did put a jumper pack on earlier today actually but only on 40amps and it only slightly increased the speed of cranking. I’d estimate about 10 percent. I could try more amps tomorrow but I don’t think that would really narrow down the issue. I’m still hung up on the fact it may be a ground somewhere as I’ve read on multiple threads. Does anyone have a diagram or write up for the location of all the major grounding location on the chassis? Also an update. I was just doing some more research and it seems I was wrong in assuming the torque tube can put excess pressure on the crank shaft since my vehicle is a manual transmission and only on the automatic equipped cars does the torque tube “clamp” onto the crank shaft.

 

If your car is just cranking slowly you don’t need to be concerned with all the major grounds…just the block ground for your negative battery cable and your positive battery circuit from the battery to the starter solenoid…if you know how to perform a voltage drop check on your starting circuit you can narrow down where you may have high resistance in the starting circuit if that is indeed what you have…below is from Service Info for a slow crank…if this electrical testing is over your head seek out an auto electric shop in your area…they “should” be familiar with this testing procedure…being that your battery is in the rear there are a few more connections between the battery and starter that need to be investigated…if you know how to use a DVOM you will need long test leads to go from the rear to the front of the car for testing…if you have a DVOM what does your battery voltage read during cranking ??

 

The blue wave form below denotes how much current my starter is drawing on initial start…about 619 amps which we call “inrush current” and is the current just to get the engine to start turning over…if you can get this checked by a shop I’m certain your inrush current may be well over 1000 amps…after the initial inrush current my starter is only drawing about 152.9 amps.

 

G303 is the ground you should be worried about so it looks like you don’t have an engine block ground…looks like it is on the frame rail so all the current from your starter has to get back to the battery through the engine block, engine mount I’m guessing then to the frame rail and then to battery negative…this is how that works !!…a lot of areas where you can have high resistance in the starting circuit…you can connect your DVOM between G303 and battery negative and while cranking read your voltage drop…should be less than 0.5 volts on your DVOM.

 

wow great thank you. I’ll give this a try. Just ordered a DVOM from Amazon

 

You can even voltage drop between the right frame rail and engine block….i believe your positive battery cable goes from battery B+ to the fuse block and then to the starter solenoid…you can check the connection even removing, cleaning with emery cloth and reconnecting….an engine bay mounted battery is much easier to voltage drop.

 

Just so I’m clear on the instructions. I run the negative probe to the negative terminal on the actual battery and then hold the positive probes to the connection point for the ground cable on the driver side frame real correct? Or do I have to hold the probe to the actual cable itself?

 

can you explain a little more on how I go about this?
are you saying I probe the negative ground point on the frame rail and then run the other probe to something on or around the fuse block in the engine compartment? I have a pretty limited understanding of electrical circuits

 

Don’t worry cause most here have limited knowledge as well as 999 out of 1000 repair shop and dealer techs…I like to start out by voltage dropping between the battery POST and terminal…I screw in a small sheet metal screw into the post so I don’t have to hold the DVOM lead…I use alligator clips…between the post and the terminal I have .023 volts which is fine…next I went from the battery terminal to the engine block…0.404 voltage drop…more than I like to see so I’ll be checking and cleaning the other end of the negative battery cable and cleaning the block ground which is above my starter…a PITA…like I mentioned an auto electric shop would be the place to take your car…the DVOM reads the difference in voltage potential between the 2 leads…in my last .404 pic let’s say I have say 12.4 volts at the engine block but 12.0 volts at the negative battery terminal…just the difference between the voltages !!…all these reading are while CRANKING the engine over.

 

ok thank you for breaking it down for me. As far as the engine block ground connection point, would it be easier to access from underneath by reaching into the space? Also thank you for the pictures👌. That makes things much more clear

 

I to chased a slow start condition for a long time after my orginal motor dropped a valve and locked up tighter than a drum . Dealership put a new motor , but I was told the tech did replace the 350 amp fuse because they tried to crank the car. While I knew that this could have damaged my starter .... I was assured that they checked it

if it was hot out and I shut the car off for just a few minutes, like when getting gas , the car would be slow to start . If I let it sit for 5 to 10 minutes . Car would start normally . I checked the power draw , bought a new and bigger battery , measured the resistance in the positive cables along with all the grounds and even added the ground wire like you did . While all of this lessened the hot start issue ....from time to time it would still start slow . All of this was pre headers .. pre procharger , car was completely stock

I finally got tired of holding my breath when I would start it and just broke down and bought a new OEM starter . The LT1 part number now crossed over to one that fits a ZO6 and it was cheap ....... I wrapped it with a tight heat resistant cover along with the factory shield . I should have complained when it first happened, but I was happy the dealership got my car back to me in 5 days and to have warranty pay the $14,000 engine replacement bill along with the towing bill

My car now starts as it should , cold , hot .... if it sits for a long period of time I no longer use put the trickle charger . I wish I broke down sooner and switched out the starter

Dave

 

If you can reach a bolt from above that would be easier… most DVOM’s only have the probe type tips…Amazon sells kits with alligator clips, back probes and piercing probes…also like I said it good to have 20 foot test lead extensions and a DVOM with a “MIN-MAX feature…if you miss seeing the highest recorded voltage that feature will store it !!

 

One more question for you. To extend the leads from the dvom to the necessary points would some 10gauge wire be sufficient combined with some gator clips?

 

Thats fine !!

 

awesome. I really appreciate the clear instructions on how to get this done. I’ll report back hopefully Thursday when I get my dvom and wire in the mail. Fingers crossed I can track the issue down 🤞

 

No DVOM ??…ok, anyone who does anything on their car should have a DVOM and a 12 volt incandescent test light…not LED !!

 

If your just measuring voltage you don't need a 10 Ga wire.

Almost all DVM's have a 10 Mohm input, they don't draw much current.

Just match the wire size the same as the meter's wires. There will be virtually no IR drop.

I just use 1/2 of a 16 Ga zip cord for long runs, I add a banana plug on one side and a alligator clip on the other. ~10 feet should do.

 

This isn't an issue with M7's because the shafts float on splines. The auto's have a locking collar which requires careful measurement of clearance to avoid damaging the thrust bearing.
Since your original failure was related to rod bearings I don't think it's relevant.
So ... don't bark up this tree, and keep looking at wiring and the starter unit itself.