LS1 Knock Sensor Issue?

**ironfreak247** · 04-05-2015, 03:04 AM

Hey guys...

I have a 2000 Z28 with the LS1. I've only had the car a few months and the previous owner put in a few mods and a custom tune. I've got some dash lights showing because of it, but my main concern is the SES. It will flash sometimes at around 75-80mph (the speedometer is off due to a possible gear change so it will actually read 110-115). I've had the codes run and the main ones that concern me are the knock sensor faults and misfire codes.

Could the knock sensors be causing the misfires? It drives good and smooth at normal speeds up to around 70 and accelerates pretty strong, but I feel like it's got more in it and is being held back.

Another weird thing is that from about 1500-2000 rpm, there's a knock you can hear that goes away when you get outside of that rpm range, and you don't hear it at all when you rev it up to that in park. Strange.

**pajeff02** · 04-05-2015, 09:31 AM

A flashing SES is generally bad and the vehicle should not be driven until the problem is diagnosed and repaired. Misfires can result for multiple reasons - first things to do are clean the MAF, check for vacuum leaks, and check your fuel pressure at the rail. Has the fuel filter been changed recently? After that, you need to consider things like plugs and wires.

To answer your question, yes, the knock sensors are susceptible to issues. Generally they can become corroded from water getting in under the intake - this includes the sensors and the wiring harness. Also, if the intake has been off, the harness may be pinched somewhere and this can cause an issue. If you replace the knock sensors, go with GM replacement sensors and not parts store cheapies.

***SMWS6TA*** · 04-05-2015, 07:59 PM

Also what fuel are you using?

Our motors like 91 or higher octane. Lower stuff tends to cause knocking issues. If the ecm is detecting knock it will retard the timing. I'm surprise you're running as well as you stated.

Agree with all Jeff pointed out. I pinched my wire harness and it set off the lights, I now use a piece of masking tape to hold the harness in position and run a thin bead of RTV around the boot to keep water out. Haven't had an issue since.

You say it only flashes around 70< not anytime else?

Also post up all the codes, by themselves it means one thing but if it's a group of them it could help us narrow down the issue. For example if one code will say multiple misfire while another will say which cylinder the misfire is on. Could end up being a crack plug...

Oh pull your plugs, see how they look, and post. Could be running too lean or to rich.

**ironfreak247** · 04-05-2015, 10:05 PM

Thanks guys...we're taking it to the shop in the morning to see what it needs and get a quote on what it'll cost. If it's too costly I'll just do the knock sensors myself. I've heard changing the plugs can be a pain...if it's anything like when I changed the plugs on my Ram Hemi...Bleh.

**ironfreak247** · 04-06-2015, 01:58 AM

Yeah, it only flashes when I'm going at least around 75 or 80, like gunning it to pass someone, etc. Also like I mentioned, the speedometer is off so while I'm going around 80, the speedo will say 110-115. This is the only time it flashes.

We fuel it with premium fuel always.

**2002ssslp** · 04-06-2015, 04:36 PM

Post the codes when you get them. See if your shop can do a live data stream while the vehicle is on the road.

**pajeff02** · 04-07-2015, 03:08 AM

Agree. Codes would be helpful.

Plugs aren't that big of a deal on our cars -- use a 1-1/2" extension on your ratchet and go at number eight from under the car. Also, be sure to pop up the pins on the cowl seal as they will shred your hands.

**ironfreak247** · 04-17-2015, 09:51 PM

It's been awhile, but thought I'd give you guys an update.

Took the car down to the shop our dealer uses and had them look it over. They came up with $1700 worth of crap. Among the list was various small oil leaks and a 4-wheel alignment (that one made me lol because we just had that done because we just installed new aftermarket wheels and tires). They also said the harmonic balancer was about to fall apart and there was some kind of aftermarket accessory installed on the tranny that they'd never seen before and didn't have a clue about how to solve any potential issues with it. I figured the tranny mounts were bad because of the thump we feel on the floorboard sometimes when shifting, but they said they were fine.

Anyways, looking at the list, I decided to tackle a lot of it myself. Spent the last couple days working on it. I've never done any type of work on an LS1 before lol. I got the knock sensors replaced, put a new air filter in, cleaned the MAF, and replaced the plugs. When removing the intake manifold, I accidentally broke the oil pressure sensor somehow, and had to replace it. Also the little purge solenoid connected to the fuel line broke also. So I replaced it as well. On the plugs, they all looked pretty worn out, and the plug closest to the firewall on the driver's side was actually fouled with some fuel on it. I also cleaned the throttle body.

After a lot of cussing and scraped up forearms, I got everything back together and she started right up. I noticed the oil pressure gauge was buried over 80 and reached back to check the sensor. Even though I had been as careful as possible and checked multiple times to make sure the sensor didn't get broken, somehow the wire going to the sensor ended up getting severed, grr. I have no idea how it happened but I guess that's a project for another day.

The good news is the car is running lots smoother and there is a noticeable power increase. The knocking sound at 1500 rpm is gone as well. The Borla exhaust that was installed previously sounds a lot better now lol. We have a friend that is pretty experienced with LS1's and he says it still needs a good tune to get the HP it's capable of, and I imagine we'll be doing that soon as well as fixing the small leaks. As far as the harmonic balancer, it doesn't look worn to me but I'm no expert when it comes to those. Still getting the SES light even after taking the battery cable off for a while...I know it's throwing something for the oil pressure sensor. Haven't made it down to the auto shop yet to have a new scan run on it though to see what else is there.

**RONS98TA** · 04-18-2015, 05:31 AM

You def wanna get the oil pressure wire fixed. Not something you just let go. Probably 1 of the most important things to moniter is oil pressure. I know from experience on a previous car that I just said, " I will get that later". Motor blew up 1 year later due to a broken oil pressure switch leaking.

**ironfreak247** · 04-18-2015, 05:51 AM

Yeah we don't plan on letting that go unchecked for long. Just wondering if I can reach back there, remove the old connector from the sensor, splice a new one (along with a longer length of wire) onto the wire and reconnect it to the sensor without having to pull the whole manifold off again...man I really don't wanna do that.

**RONS98TA** · 04-18-2015, 06:01 AM

Yes you can. NOT an easy task at all. I did mine laying across the engine and reaching back there. PITA but I think its easier then taking the intake completely back off. Its been several years, but I think I removed the last coil pack on the passenger side.

**pajeff02** · 04-18-2015, 09:11 AM

Sounds like the shop was trying to sell you a certain bridge in New York. Good for you for taking it all on yourself!

***SMWS6TA*** · 04-18-2015, 10:56 AM

it will be a little difficult but loosen the injectors, disconnect the coil pack harness and you may have to also do the temp sensor as well as the rest of that loom to get enough to go over the intake. you'll also need to loosen the 2 grounds on the back of the drv head because it is all in that section off loom