The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)

- LSx Swaps (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=206)

- - Knock sensor problems (https://67-72chevytrucks.com/vboard/showthread.php?t=744026)

Knock sensor problems

72k10 with an LQ4 swap
Getting PO327 and PO332
Downloaded the troubleshooting guide
And checked the following:
Sensors to ground ohms out to spec (99.9 and 100.7)
Wiring from sensors to PCM checks out
AC voltage test is good right to connector on PCM

Next step is replacing the PCM
Anything I missed?
Thanks

Re: Knock sensor problems

Replace both sensors and harness

Re: Knock sensor problems

Sensors And harness are new..

Re: Knock sensor problems

Then could be pcm problem

Re: Knock sensor problems

Have you had it tuned, or is everything stock in the engine and tune?

Re: Knock sensor problems

How many times has it triggered? Like if you clear the codes, do you get any period of function before the light pops up?

If you can watch live data, look at what the KR* count actually is, and see where the histograms show the hits counting. If you have a physical interference (things like transfer case, exhaust, trans xmember) touching/vibrating against the motor, it can actually trigger a large single hit of knock. It would show up on the logs as a spike, instead of a plateau like an actual knock condition would.

Even easier....can you hear an actual knock? Because your getting BOTH sensors to trigger the same conditional code, it means there is either; a problem with the hardware (loose pigtail, partially shorted wire that only contacts under certain conditions), a kr threshold set oddly (unlikely unless tuner got ambitious, or sloppy), or an actual knock severe enough and frequent enough to trigger both sensors at the same time under the same circumstance.

The only time replacing the PCM is a logical step is when there is an actual internal board failure, driver failure, component mismatch..or pissing off my tuner. If you think the PCM could be a cause, then try hard grounding the case. Probably best to check your grounding straps on the head and block as well, or consider adding some if you've streamlined the factory layout.

Re: Knock sensor problems

Quote:

Originally Posted by BR3W CITY (Post 8010476)

I can drive the truck for about 4-5 Miles (sometimes further) with some hard acceleration then the check engine light comes on. The PCM is not original to the truck, I bought it from a member here. I do have the original but would need to be programmed.
I can't hear a knock or detonation but exhaust is loud..and I am slightly deaf..
I have added additional alligator clip grounds to PCM case and block..

Because the truck is a 4x4 and runs 35's it can be a rough ride over some bumps...I did disconnect the PCM this morning when I checked wiring so maybe the connection wasn't good? I read somewhere that plug gap could cause the KS to trigger? Just got truck on road so we will see this week.

Re: Knock sensor problems

don't go cheap with sensors and senders. I have learned multiple times already with my ls swap, temp, oil, crank and knock sensors. don't get the cheap stuff, you will have to replace shortly after!!

Re: Knock sensor problems

^ very true when it comes to knock, cam, and crank sensors especially.

If you baby the truck, can you go farther? Does it seem like there is a certain situation in which it will always happen? Again, live data from a scanner or HPT would tell you if its "real" knock or not.

Whats the story on the motor? If there was a ton of blowby, or something like assembly lube from break-in, its possible even new sensors can get fouled out.

Re: Knock sensor problems

Quote:

Originally Posted by BR3W CITY (Post 8011251)

You posted this just after midnight, so I think you're getting sleep deprived! :lol: Pretty sure its not possible to foul out a knock sensor. ;)

Re: Knock sensor problems

i repalced the knocks in my 02 suburban didnt make it 200 miles kight back on i pulled the pos advance bwd sensors out and used ac delo and a dorman harness light never came back

Re: Knock sensor problems

Quote:

Originally Posted by ls1nova71 (Post 8011441)

You posted this just after midnight, so I think you're getting sleep deprived! :lol: Pretty sure its not possible to foul out a knock sensor. ;)

Midnight, after a friends 3 day wedding weekend. I havent slept in about 50 hours. Time for bed.

Re: Knock sensor problems

Ok still having knock sensor issues..
I moved my OBD port into the cab so I can watch live data while driving.
The one thing that I noticed is the vehicle speed says 0mph...
I installed a Dakota Digital SEN-01-4L60 AND A SGI-5E speed sensor to cure a missfire I had (haven't had a misfire since)..should the speed data that the DD is giving the PCM show up on my Bosch 1100 reader? Or do I have an issue with the vehicle speed setup.

Re: Knock sensor problems

are the knock sensors torqued to spec?

Re: Knock sensor problems

Quote:

Originally Posted by v30crewcab (Post 8018090)

are the knock sensors torqued to spec?

No they are not...I am going to re-torque to 15ft pounds this weekend. I know they are much tighter than that.

Re: Knock sensor problems

Quote:

Originally Posted by suburban99 (Post 8018098)

No they are not...I am going to re-torque to 15ft pounds this weekend. I know they are much tighter than that.

The torque spec is so you don't over tighten them. They can be damaged by doing so. If they are damaged then re-torquing them wont help.

Re: Knock sensor problems

Quote:

Originally Posted by ls1nova71 (Post 8018507)

The torque spec is so you don't over tighten them. They can be damaged by doing so. If they are damaged then re-torquing them wont help.

I'll replace them with GM sensors...live and learn:)

Re: Knock sensor problems

Changed out the sensors for GM sensors...my Son's an apprentice Tech and gets parts at dealer cost..unfortunately he works for a VW dealership...they were $90.00 each (CDN) holy crap. Well hopefully it's the fix. Torqued to 15ft Lbs..we'll see tomorrow.

Re: Knock sensor problems

I feel the parts cost hurt. I actually was just going to tell you to check amazon.ca
I got delphi knock sensors for $57.73 each and free shipping.

Re: Knock sensor problems

Quote:

Originally Posted by 72MARIO (Post 8019345)

I feel the parts cost hurt. I actually was just going to tell you to check amazon.ca
I got delphi knock sensors for $57.73 each and free shipping.

I saw those but wanted to get it fixed as I am travelling next week. I only live 9 miles from the border and have a US PO box too...most if not all my parts come from the US. Good news is the problem is gone! Drove 80-90 miles today and no check engine light...Thanks to all for your help!