Knock Sensor Set-Up

[ROYMAC]

I'm working on my first tune. '96 Tahoe with 383 stroker motor, cam, headers, 9.7:1 compression, 0411 PCM swap, running only 91 octane pump premium. Overall the tune I'm running works pretty well, except at idle, right after I start the engine. It's not as bad once the engine gets to operating tremperature but it still idles like an old tractor - sometimes it will stall seconds after starting it.

I've been doing some logging. Have verified with an old fashioned timing light that the ignition advance showing up on my log matched pretty closely with what the timing light was saying. In my first log I found KR was pulling several degrees out of my timing. This is at idle, sitting in my driveway with the trans in Park. I strongly suspect the sensor is picking up valve train noise due to higher tension springs than stock and higher compression (slightly) than stock. There was no audible knock to be heard.

So I go into my EFI Live and learn that there are 2 types of knock sensors. The LS1 resonant type and the LS2 flat response type. I'm still running the stock sensor that came in the original vortec 5.7 Litre. How do I figure out which I have? It only has one wire attached to it. I am guessing that means it grounds itself through the sensor body to the block?

I don't want to get too far out into left field, but I tweaked B6226 Knock Sensor Frequency from 5.5 khz up to 6.0 khz, B6250 Knock Sensor Multiplier TPS up, as well as B6255 Knock Sensor Multiplier RPM up some. EFI Live says that increasing B6250 & B6255 desensitizes the sensor. I loaded this tune and relogged a short while. Looks like this removed the KR at idle and still no audible knock. However, this update had virtually no change in my poor idle quality.

Does anyone have any advice on how which knock sensor I have, and if my changes make any sense whatsoever? Yes, I'm a newbie at this game! Any and all help is appreciated.

I've spent hours reading through many threads here, all related to knock sensors and settings, etc. but it seems these little devils are a bit of black art - lots of questions, a few answers and many threads that lead nowhere.

[5.7ute]

Single wire are the resononant ls1 style sensor. The flat reponse are two wire & bolt externally to the block in the later engines.
I believe there was a change in the knock sensors for the later 0411 PCM.(not sure where I read that) You might want to verify this.

[LS1_Dragster]

Did the idle problem start after the 0411 upgrade? Also, logs and tune files help a lot......

[johnv]

also check that your headers or exhaust isn't hitting chassis or body anywhere as this can also show up as false knock.

[ROYMAC]

Guys, I really appreciate the feedback.

5.7ute - I will do some more checking on the LS1 style sensor.

LS1 Dragster - The path I took to this set up was a circuitous one! I started by rebuilding my engine at 240,000 miles. My engine builder convinced me to go to the 383 (which wasn't a hard sell anyway), but it turns out he's really only an engine machine shop. He told me my stock computer should run the new package just fine. Turns out he didn't know what he was talking about in regards the EFI system. So after talking to a local dyno shop tuner and spending many hours in forum's like this one I made my way to the 0411 upgrade. Got the thing rewired to work in my old truck. I bought a tune in a 0411 that has got me to where I am now. Overall it's worked fairly well, except for this idle problem.

Short answer - yes, the idle problem surfaced with the new engine and the new 0411 PCM. I never ran the new 383 with the original PCM as it could not be tuned with EFI Live. I was told it would need a whole new chip burned for it and I wasn't interested in doing that.

johnv - I did have a downstream O2 sensor rattling a bit on a heat shield, but I bent the heat shield slightly to clear up that rattle. However, you make a very good point here. I will go back and double check that I don't have any other rattles.

Also, I plan to get the knock sensor PIDs set up in my next data log and see if I can read what the actual sensor is seeing. Also, as 5.7ute suggests, I may need to look at installing a newer LS1 knock sensor.

[joecar]

Hi ROYMAC, welcome to the forum

Can you hear any valvetrain noise while idling...?

[LS1_Dragster]

I've done this upgrade with my 97 Yukon and I too had an idle issue with it. In fact it sounded like I had a huge cam in it. Turns out I didnt wire the EGR correctly and it was on 100% of the time. I just ended up cutting the pink wire going to it and the problem went away. I passed I/M with flying colors so I just left it.

Your welcome to look at my tune, I'm sure it wont work without tweaking especially the injector flow rates since I run more fuel pressure then stock. One is with the MAF and the 016 is the latest without MAF. They both run great so I have no idea which one is really better to stick with!

Lee

[ROYMAC]

joecar, thanks. I plan to be spending more time at this forum so we'll likely be talking.

The whole engine had a different sound since being rebuilt. To the ear I would say it has slightly more valve train noise than stock. Cam has more lift and duration than stock and stiffer valve springs, so I would expect a bit more valve train nioise. Not sure how to quantify it though. You can see above the 5.7ute suggested maybe the knock sensor on the LS1 is different. I did some checking of part numbers and found that indeed the stock sensor in my '96 truck is not the same as a '01 truck that runs the 0411 PCM as stock. A different part number doesn't guarantee a different calibration, but might be worth trying it. Before I do that I want to try a new data log with the new PIDs for the sensor and see what it's doing.

[ROYMAC]

Great feedback! More things to check into.

I did retain the EGR function in my 0411 swap. I got the wiring set up for the 0411 off a fellow on another forum. The instructions for the EGR wiring were quite specific. Said to connect the PINK wire from the EGR valve to C2 (Red) Pin 7 on the 0411 computer. The info says this is a 12 volt supply line to the EGR. I can test this idea by either shutting off the EGR function in the PCM or simply unplugging that wire from the PCM.

Thanks for providing your tune files. I hope to have a chance to look over them tonight and compare with what I've got.