JekHawkins

Hi all,

I'm completely new here and completely unfamiliar with working on cars, much less my 1999 Trans Am.

I had to replace my knock sensors, so I decided to take a bunch of pictures and make a definitive write up on the topic, with pictures so newbs like me can be assured they're doing the right steps.

Bad knock sensors seem to be a fairly common issue with pre-2000 F-bodies due to a flaw in design that allows more water than you would really prefer to come into contact with the sensor, causing rust over time. I also learned, during my operation, that oil will also foul the sensor, though my cases in general tend to be fairly exceptional. So without further ado, a complete write-up on how to replace your knock sensors.

Thanks to ls1howto for setting me on the right path with their LS1 => LS6 intake manifold swap-I used their guide with great success but wanted to expand on their writeup with pictures.

15mm socket/wrench
8mm socket/wrench
10mm socket/wrench
22mm deep socket
Flathead screwdriver
Pliers
40 or 50 hex key (don't remember which)
Knock sensors (2) ACDelco 213-3521
Knock sensor harness 12601822
Torque wrench (optional)
Gloves (optional)


1. Disconnect your battery's negative terminal
by Jek Hawkins, on Flickr

2. Remove your strut tower brace. (If you don't have one, skip this, obviously.) Loosen the nuts holding the brace to your chassis and pull up. My SLP bar required me to pull driver's, then passenger's side.
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr

3. Turn your attention to your intake lid and bellows. Pop your lid, then unscrew the hose clamp connecting the bellows to the throttle body.
by Jek Hawkins, on Flickr

Remove 2 sensor harnesses connected to your MAF. The purple is 3-pin.
by Jek Hawkins, on Flickr
The blue is 2-pin.
by Jek Hawkins, on Flickr
Pull the lid, MAF, and bellows off.
by Jek Hawkins, on Flickr

4. Throttle body is next. Remove the sensor harnesses on its right side.
Orange 4-pin
by Jek Hawkins, on Flickr
Purple 3-pin
by Jek Hawkins, on Flickr
Remove the throttle cable.
by Jek Hawkins, on Flickr
And the cruise cable...
by Jek Hawkins, on Flickr
The ls1howto mentions some coolant hosing running through the bottom. Mine wasn't connected at all, so if you have these, remove them. You can see the nipples for the connections in the above pictures.
Unbolt your throttle body. There are 3 screws, as pictured:
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr
5. Time to pull the injector harnesses. They look something like this:
by Jek Hawkins, on Flickr
And there's one for each cylinder, so guess how many there are? Press up on the shiny metal and pull straight up on the harness. Should come off very easily.

The harness wiring goes through these hoses. Pull these hoses from their clips. My car had 4. I opened the clips by slightly twisting them.
by Jek Hawkins, on Flickr
by Jek Hawkins, on Flickr
6. Brake booster line. Easy enough, and something you'll need to know for the Seafoam process (still have to do that myself...).

JekHawkins

by Jek Hawkins, on Flickr
My hose clamp was already pushed down the hose, but if you have a normal Trans Am, use a pair of pliers, press the tabs together, and move the clamp off the nipple. Then just pull.

7. I haven't got a clue what this is, but I have a hunch it has to do with the fuel rails, since it's in the same loop as they are. Take it off the right side of your intake manifold.
by Jek Hawkins, on Flickr
To do so, press the grey ring, then pull the connector.
by Jek Hawkins, on Flickr
8. Pull this off too. This should be on the other side of your intake manifold. Mine had oil in it, but don't ask me what it is, because I don't know!
(EDIT: After being a little more familiar with cars, I'm almost "positive" this is the PCV valve for the LS1. I later replaced this with the LS6 valley cover mod. )
by Jek Hawkins, on Flickr
9. Remove your throttle cables. Do this by pressing the button and pulling up. Should note that they're guided by a piece of metal on the manifold too. Just slip them out of it.
by Jek Hawkins, on Flickr
10. Remove the EGR. Mine took a hex key.
by Jek Hawkins, on Flickr
11. Another thing I don't know what it is but remove it anyway is the red/blue plug in the picture below. Leave the white one alone, since you don't need to remove it.
by Jek Hawkins, on Flickr
12. Time to unbolt. You'll be unbolting 10, (count 'em) 10 bolts, the ones without thread sticking up. In the picture below, there's 2 of them. Ones looking like the loner with the thread sticking upshould be left, well...alone. 4 of the bolts are waay under the black plastic cowling. BE CAREFUL unbolting these, or the sharp cowling retainer pins will punish you for your arrogance. The cowling can also prevent these 4 bolts from coming completely free, but we can work around that. If you want to torque them back on, use the 2-pass method and torque values as posted on ls1howto.
by Jek Hawkins, on Flickr
13. Pull on the manifold gently and slowly, bringing it up and toward you. If you couldn't free the 4 bolts in the back, just try to get them to stay upward a little before removing them. (Sorry, no pics here.)
(EDIT: I haven't any idea what I meant by this. I would guess you could get a ratcheting box wrench on these, maybe? I do know they don't need to come all the way out. That's probably what I was trying to say.)
14. BEFORE you get too far, though, as soon as you're able, reach behind the manifold and unhook these 2 connectors. There's a sensor harness and a very thin vacuum line.

Here they are when you've gotten the whole manifold out.

15. Set your manifold down, letting it sit where it naturally wants to. Why do I say this? You don't need to get it any further-you only need to access the valley, and the fuel rails are still attached. Don't want to damage those! For me, the manifold seemed comfortable on the airbox.
16. In the valley, you'll see the 2 sensor boots. Pry time! Get those things gone.


17. Disconnect the harnesses. (No pics, sorry.) This is a tad tricky. I had to examine my new harness and sensors to figure this out. The harnesses are longer one way than the other. If you press on these longer ends, just pull and they snap out easily. I did that with one with pliers, but screwed up the other one and destroyed it. Be VERY careful, particularly if you're using the stock harness again! (I wasn't.)
18. Swap those new sensors. You'll need a 22mm to pull the old ones and install the new ones. Remember, righty-tighty, lefty-loosey! I would strongly recommend that you carefully wipe down the valley and sensor wells before installing the sensors. This allows any crap that accidentally goes into the sensor wells to pile up on top of the existing sensors, so you can (CAREFULLY) remove all the junk at once. If you're brave, you might use a shop rag wrung out with degreaser, but be CAREFUL. Anything that goes into the intake goes right into your beloved engine! Here are my sensors. I actually also wiped down the inside of the sensor wells without the sensors in-I'm not sure if that's a good idea, but I thought it was at the time. If you want to torque things down to spec, 11 ft.-lbs. will do.


19. Alright, so you've gotten the new sensors into their new, clean homes. If you're like me, and you bought a new knock sensor harness, never fear, off we go....I'd like to point out that your stock harness may be underneath that metal piping. I opted to take a pretty serious risk and cut out the old sensor harness in lieu of the new one. (Keep in mind I'd already broken mine by this point.) If you do this, you better pray your harness is ballin', because you won't have another if it isn't. I cut the old harness out with wire cutters. (No pics, sorry. But here's the new one!)

20. Connect up the harness (You should find that pretty easily, just follow your old harness to the connector.), then clip the sensors into it. To do so, just get the connection straight onto the sensors, then press down. Simple! (No pics, sorry!)
21. RTV that stuff in! I used Hi-temp RTV Sensor Safe for the boot. Here you can learn from my mistake! Take the boot and apply the bead of RTV to it, as opposed to my idiot self who tried sticking it in the hole first. (Can I sue if it's not sensor safe? > ) Stick the RTV'd boot in, then give it time to set.
22. To prevent this ever happening again, GM suggests you create an RTV "dam" around the sensor boot. I figure it'll be fine if I just put another bead on it. (I'm not going to hang around and wait for an hour between 3 or 4 beads. You gotta be kidding!)

23. Guess what! You're actually done! Once everything has set up to your satisfaction, put everything back together (look up there and work backwards if you need to), let the RTV set over the next day or so, and hit the streets! See you out there!

The author of this post will not be responsible for damage caused to any vehicle during the following of these steps for any reason.

LS6427

iTrader: (2)

Man...those runners are black.

Good write up.....

.

JekHawkins

Thanks man, and yeah, I was absolutely shocked. Seafoam inc....luckily I don't need to write that up.

LS6427

iTrader: (2)

If I were you I'd take all 8 spark plugs out and stick a rag in each hole...then buy a couple cans of MCCC and fill up each runner and cylinder with it. Let it soak over night. Bump the key so the valves all barely open so each cylinder gets filled up all the way to the runners.
Your pistons are probably pretty bad since they are so hot, burnt oil really builds up on them.

Or SeaFoam...that will do great also. Just don't ever use SeaFoam to clean the top end with the engine together and running, like people do through the brake booster hose. It cleans almost nothing that way. Maybe the rear two cylinders a little bit.

If you can't find MCCC, GM makes a good cleaner too. But SeaFoam is fine since the intake is off and you can actually fill each cylinder all the way up and let it sit and soak.

.

RARON455

iTrader: (35)

You forgot to tell the folks about torqueing the sensors,, they only go to 11 ft. lbs I believe,, IF you overtighten them you will screw them up, and they can cause false knock... and You dont need to put RTVB on the harness well plugs,, If you have oil in there that means your seals are bad on the valley that the sensors go through. Great write up with pics BTW

mbaker3

Great write up! Since I bought my 2002 Z28 a little over a month ago I am getting a knock sensor code when I nail it hard. I reset it and it stays off until I get into it again. I wanted to change the sensors and check everything else out and this will help get me there.

JekHawkins

Thanks for the info-adding that in right now.

Fosnot

iTrader: (15)

Sticky worthy.

bobbyd

iTrader: (10)

wouldn't using MCCC through the intake also clean the runners up? any symptons of having dirty runners?

Camarosteve44

iTrader: (8)

thanks a ton for the write up, great pics and description

ISMELLRICE

iTrader: (22)

What a man! Thanks

loyolacub68

iTrader: (16)

Unless I'm so tired I can't see it, it looks like you got most every step except for removing the main fuel line from the rails. This was a difficult step for me for whatever reason.

JekHawkins

I actually didn't remove the fuel line. My fuel line was slack enough to allow me to just move the intake manifold, rather than take it off completely.

And thanks for the compliments, guys! Definitely encourages me to keep making these.

HoLLo

iTrader: (17)

Great writeup but I highly recommend anyone doing this to go ahead and put on a 2004+ LS6 valley cover. It greatly reduces my oil consumption. I used to add a whole quart between oil changes, but now it does not require a drop.

patSS/00

iTrader: (6)

There's a special tool for this, any parts store should have it, should be really cheap and makes it totally simple.

loyolacub68

iTrader: (16)

I did buy that tool and ended up bending the crap out of it. I guess I don't really understand how it comes apart.

However, much like the OP, I was able to switch out my intake without disconnecting the line due to extra slack. Although it would have made the job a lot easier.

38DD2436

WOW, Excellent post. Great detail!!!!

sjsingle1

iTrader: (1)

anytime the mani is off........you should check the knock sensors.......and if you change them out put a new on a new harness too........cheap insurance.......ask me how i know

JekHawkins

So I went to find MCCC at the local MOPAR dealer. They have cans, but not ones with the aerosol heads. The tops are threaded, and they say I need a machine to use them. What's up with that?