Knock Sensor Wiring Gone Bad??? Please Read

**TurdsOfMayhem** · 08-18-2007, 01:00 PM

A brief history of repairs/mods to cars so you can have improved input.

Recently was lucky to have to replace my slave cylinder again on my 02 Formula. Had it replaced at Midas by my apt that I've been going to for years and have a good reputation with the GM.

While it was there I had him scan my computer to see why the engine light had come on, and yet again it was my cats...

So I had MTI (motorsport technologies) here in Houston install Kooks Headers, Y-Pipe, Hi Flow Cats, MSD wires, and NGK TR55 Plugs installed. Shortly after picking up my car at MTI the engine light came back on...

So on the way home I stopped back at Midas and had him rescan it, and it showed some error msg for both knock sensors. But he was busy and just said I believe that it showed they were unplugged? I may be mistaken. So I went back upto MTI so they could check it out, and said when the scanned it, they seemed to think the wiring was bad for them. So I've been trying to figure out how that is possible. They claim they do not come in contact with these wires/sensors during install. Which looking on the net appears to be true. Salesman at MTI told me the wires run thru the firewall and above the bell of the transmission. Is this true? Trying to figure out where they run to, so I can find someone responsible for this dmg caused.

I currently have a feeling it might have been done at Midas when my trans was pulled to put a new slave cylinder in. Any insight is MUCH appreciated, and if I was unclear or jumped around alot sorry, let me know if you need any further information. I do not want to be paying to have my intake pulled (where I was told the sensors actually are) to start tracing wires to see what happend...

Thanks so much in advance!

Jonathan

**Redphoenix1998** · 08-18-2007, 03:13 PM

Knock sensors are under the intake manifold. There is a single connector that connects the two knock sensors to a wiring harness that does not come close to the hears. It does run closer to the firewall. There's a chance the wire could have been pulled when Midas messed with the master cylinder because the wiring runs next to the vacuum brake hose. There is a metal, sharp, hose clamp on the back of the manifold that could have rubbed the wires bare passed the insulation or the ground might have been messed up when they were messing with the vacuum booster line. That's my best bet. Check the ground and wiring for that sensor for sure. The ground is on the back of the drivers side head. There should be a bolt connecting the wires. Or pull the manifold out yourself and check the wires visually. That's the best and easiest thing to do

**TurdsOfMayhem** · 08-19-2007, 08:26 AM

Originally Posted by Redphoenix1998

Knock sensors are under the intake manifold. There is a single connector that connects the two knock sensors to a wiring harness that does not come close to the hears. It does run closer to the firewall. There's a chance the wire could have been pulled when Midas messed with the master cylinder because the wiring runs next to the vacuum brake hose. There is a metal, sharp, hose clamp on the back of the manifold that could have rubbed the wires bare passed the insulation or the ground might have been messed up when they were messing with the vacuum booster line. That's my best bet. Check the ground and wiring for that sensor for sure. The ground is on the back of the drivers side head. There should be a bolt connecting the wires. Or pull the manifold out yourself and check the wires visually. That's the best and easiest thing to do

Did they have to mess with the master cylinder to change out the slave cylinder and flush out the clutch fluid system? Sorry, I'm familiar with lots of things on my bird, but not this area.

Not to sure if I'll pull the manifold off myself, I'm pretty comfortable doing some stuff like that, and have a history of MEI (mobile electronics installation) so am good at paying attention to detail and remembering how things came off.

Thanks so much for the feedback, if you have any other info you could provide me with, so I have a lil more fire to throw at midas... Wish the GM could always work on my car himself! Everytime he does, it comes outta the shop perfect. LOL

**Redphoenix1998** · 08-19-2007, 12:04 PM

Why was I thinking Brake Master, I mean your slave cylinder

My bad. In that case, the wiring loom is bolted to the top 2 bellhousing bolts and there's a chance they didn't know this, yanked the Trans out and pulled the wire out of whack. Also theres a chance you don't have a good ground when they reinstalled the wiring loom and didn't clean the grounding points.

**TurdsOfMayhem** · 08-19-2007, 12:20 PM

Originally Posted by Redphoenix1998

Why was I thinking Brake Master, I mean your slave cylinder

My bad. In that case, the wiring loom is bolted to the top 2 bellhousing bolts and there's a chance they didn't know this, yanked the Trans out and pulled the wire out of whack. Also theres a chance you don't have a good ground when they reinstalled the wiring loom and didn't clean the grounding points.

No worries!

Just thankful for your help. I will be sure to call him in the morning and let him know that I believe one of his mechanics caused the issue.

On the other hand, love the way my car sounds with my Kooks and SLP LM

**0rion** · 08-19-2007, 05:53 PM

ls1howto has a good write up on pulling your intake if you decide to go that route. It's much easier than you might think to pull it off. You can also reach back behind the intake on the drivers side and feel for that connection at the base of the intake and see if it's unplugged back there. I'm wondering if they didn't pull your intake to get at those top 2 bolts on the bellhousing. I personally didn't do that but I've read where others do that. If they did then there's a chance they unpugged that connection and didn't plug it back in.

If you decide to pull the intake yourself pay close attn to the torque specs. They're in IN/lb's and not foot lbs. Hate to have you strip out one of those bolts. Other than paying close attention to the small things it's a piece of cake compared to some of the intakes I've pulled. My 4.3 comes to mind. That job sucked compared to the LS1.

**TurdsOfMayhem** · 08-20-2007, 07:45 AM

Thx, found the article on ls1howto. I just called Midas and explained to him what I think happend (thanks to every1's help) and he seemed to agree, gonna drop it off tonight after work, and hopefully pick it back up tomorrow after work... Wish me luck!