Knock sensor for timing issues!

[Hitani]

Anyone with twin turbo setup had to ask their tuner to desensitize (lower) the sensitivity of their knock sensor for timing? I have an 18 with twin turbo top mount that is freshly installed. Shop went over the installation multiple times and couldn't find any issue with piping. we aren't sure what is causing the knock sensor to go off on the dyno pulls. we tested the runs on both 93 and e85, same thing. So now my shop wants to ask the tuner if they can lower the sensitivity of the sensor to at least half. anyone had to do that to trick their sensors ? should I go for it or not ? my tuner wants me to sign a disclaimer. Please help. I should mention that my turbos have the screamer mod, so im not sure if the loud turbo whine could be causing a false trigger.

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[NGOT8R]

Are your IMRCs locked out? If so, did you secure the connectors to the main wiring harness with zip ties to keep them from rattling around and being detected by the knock sensors? I kept the brackets for the two blue connectors and just plugged them back up on mine to prevent rattling. The two off-white ones I zip tied.

 

[Cobra Jet]

They also want you to sign a disclaimer because if the engine ventilates they can say "not our problem"....

Is there anything at all that is causing vibrations against the block - any header primaries touching A/C hard lines, bad motor mounts, any vibe being caused by the trans to engine spacer plate?

 

[dead_inside]

Welcome to Hell

 

[K4fxd]

I would not turn them down unless I only ran E85 or race gas.

 

[Zrussian13]

If you go that route you need to run octane booster or meth all the time when your on pump gas and I'd probably limit boost or timing a hair on e85. (Just speculating on e85 I've only ran pump to this point) Detonation is the big killer for these engines. I had a similar issue after going twins. Except my car was happy on single gear pulls. Everything looks great except on the shifts. I went through my set up over and over for a year with no luck finding the cause. Went as far as replacing the clutch and shocks based off different vendors recommendations. Eventually I had Lund make me a KR tune. Should have done it way sooner. The car rips and always has 16°- 19° of timing now. I run 14 gph of meth that comes on at 6lbs of boost and 16(ish) oz of boostane per tank. I had always planned to run some octane booster because our gas is crap so upping it wasn't a huge deal. I've got 84k miles on the car now, 36k of that boosted.

OP Curious how many miles you have on your 18? I always wondered if my false knock was due to having 48k hard miles on it before going boosted. I've never been one to baby this car.

 

[illtal]

It's definitely from resonance, metal to metal contact, or something loose. First I would put a filter on the turbos or quiet them down some kind of way to eliminate if that's causing the problem. Manual cars seem to have more problems with false knock but since you've done a major mod everything needs to be investigated.

If you can put some insulation around the piping that is close to the frame and insulate your AC lines as well.

If that doesn't work then you need to check wiring which is going to be a pain since you didn't do the install. The first response post is a great start.

 

[Hitani]

Are your IMRCs locked out? If so, did you secure the connectors to the main wiring harness with zip ties to keep them from rattling around and being detected by the knock sensors? I kept the brackets for the two blue connectors and just plugged them back up on mine to prevent rattling. The two off-white ones I zip tied.

Yes im IMRC locked out. I will double check with my shop on this. thanks !

 

[PC_GUARD]

Yes im IMRC locked out. I will double check with my shop on this. thanks !

You may also want to beat on your exhaust with a mallet and see if there something rattling there.

Including your turbos, and make sure there isnt something in one rattling. Most likely its the turbo plumbing

 

[Hitani]

It's definitely from resonance, metal to metal contact, or something loose. First I would put a filter on the turbos or quiet them down some kind of way to eliminate if that's causing the problem. Manual cars seem to have more problems with false knock but since you've done a major mod everything needs to be investigated.

If you can put some insulation around the piping that is close to the frame and insulate your AC lines as well.

If that doesn't work then you need to check wiring which is going to be a pain since you didn't do the install. The first response post is a great start.

if its metal to metal contact and could never find it, do you think its a good idea to turn down the sensitivity or possibly eliminate the sensors ? who knows, my shop may give up in the next 2 days and tell me that they couldn't find anything wrong. what should I do in this case ? I'm def going to check all what you guys have mentioned here. I just want to be prepared for the worst case scenario as well.

 

[illtal]

if its metal to metal contact and could never find it, do you think its a good idea to turn down the sensitivity or possibly eliminate the sensors ? who knows, my shop may give up in the next 2 days and tell me that they couldn't find anything wrong. what should I do in this case ? I'm def going to check all what you guys have mentioned here. I just want to be prepared for the worst case scenario as well.

I don't recommend turning off knock sensors even if you're running e-85 full time.

Depending on how that tune is done it could be running into knock. If you desensitize them it won't detect minor bangs. Where are you located?

 

[NGOT8R]

If you eliminate or turn down the sensors, it would be very wise to use extremely good fuel (perhaps even race fuel, if not E85). It could also become a hassle of a ritual to do with a daily driver.

My brother had a built Cobra motor back in 98 and he was required to run 110 octane race fuel in it. He would spend $250 in fuel just to drive/race it a little between Friday nights and Sunday evenings. He could run 93 octane in it, but he could not apply heavy throttle at all like that, not to mention it was just risky in general because he wasn’t even testing his fuel back then.

I would keep searching for the source of the noise. Patience will be required, but I’m hopeful that you will locate the source of your problem.

 

[Zrussian13]

Including your turbos, and make sure there isnt something in one rattling. Most likely its the turbo plumbing

Good idea! I can honestly say I've gone through my car front to back 100 times but never thought my false knock could be in the turbo itself.

 

[mejohn50]

I would change, or get rid of, a problematic component (in this case it appears to be an entire forced induction system) before I’d disable, remove, or limit the sensitivity of the knock sensors on one of these engines in a street application. It‘s just not worth it to lose the functionality they provide. Plenty of people are making big power with fully functioning knock sensors.

You need to find and fix the issue.

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