knocking w/91 octane? - 92Q

[tkd_q45]

I've noticed when the ambient temp gets past 75º F that I hear knocking. I've been using 91 octane (all we can get in SoCal) but it's only recently that I've noticed the knock. I thought that this engine had a knock sensor. What gives?

Thanks in advance,Tom

[Q45tech]

Are your knock sensors working [heat cracked or corroded connectors]? On pre 1996 models they won't turn the MIL on.Is your throttle body, plenum, egr clean as new? Injectors clean as new ?

Assuming that no one has adjusted the crank angle sensor incorrectly and you pass CA emissions test have you tried all available brands.....[did the problem start recently mid September when the fuel blend was changed at the refinery?]

[tkd_q45]

I must assume that my knock sensor are not working being that I'm hearing knock. Don't know where to check the lines for these. Just had a 120k service done by the dealer. I believe that the throttle body, plenum and egr were cleaned/serviced. I know they cleaned the injectors (right after the service one of my injectors went bad, had them replace that too). I HOPE that the dealer DID everything the charged me for - still get crap fuel economy in town. I've been using mostly Chevron gas but I'll try switching.

[DAEDALUS]

Q45Tech posted on the old NICO board the nominal resistance of new knock sensors. I think I recall them being about 440k, but I'll ask Q45Tech to confirm that. Or Heath...seems he has a lot of old info archived. Might also be in the manual. Pull the harness connectors and measure the resistance of both sensors.

[Q45tech]

550,000 [+-50,000] ohms is resistance for KS."I HOPE that the dealer DID everything the charged me for - still get crap fuel economy in town."

If you get a long term average of 19 MPG and 21-22 on highway at speed limit no AC, then pure rural city should be 16 and bumper to bumper exclusively might be 14 mpg........... is normal

[Professor_Mike]

If you just had a service done by the dealer I suggest you ask them to check for codes with Consult, if it's failing the knock sensor code will be in the computer but not turn the light on. Since you had a large service done they should not mind checking codes for free.

[DAEDALUS]

550,000 [+-50,000] ohms is resistance for KS.

So a KS measuring 570k ohms isn't necessarily bad? The +/- 50,000 seems like a pretty wide tolerance. Also, seems like a higher resistance would make it less sensitive to knocking.

[Q451990]

Check out this awesome thread on checking the resistance of knock sensors and fuel injectors. I printed it for my folder... much better than my notes from a few years back!

If they check out OK I'd look for restricted or non working EGR system, dirty throttle body, spark plugs, etc.

Heath

[DAEDALUS]

LOL Thanks, but that's my site Glad you like it. I was just wondering about the acceptable resistance ranges on the KS and at what point and to what degree they begin to impact timing.

[Q45tech]

The ks is just a high impedence piezoelectric microphone.It is tuned to respond to sounds in the 3-7kHz range, when over heated the plastic case cracks changing the tuning and decreasing the sensitivity.

Just because the resistance reads in the range is not a 100% guarantee that the system is working as new. But it is all you can measure.

If the ks are more than 8-9 years old good idea to examine them for stress cracks and replace whenever the plenum is off.

Short of forcing a knock by advancing the CAS timing and watch a Consult for a reduction in WOT timing [a 2-3 hour diagnostic job for someone who knows the Q well.]

[Q45tech]

The other problem is how the 91 octane [blended average] octane is tested...........you don't know if the motor octane portion of the test is adequate [at least 89] it could be 87 motor and 95 research octane which won't cut it in an old Q.

Passing the motor octane is much much harder and more expensive............even 93 blended octane can be jeeped to save a penny and cause terrible knocking.

If you still hear knocking try changing brands [assuming your EGR is perfect].........make sure your CAS initial timing is set no lower than 13 and no higher than 15.

[Q451990]

LOL Thanks, but that's my site Glad you like it. I was just wondering about the acceptable resistance ranges on the KS and at what point and to what degree they begin to impact timing.

Sorry, I couldn't remember who's site it was! There should be a links section here on NICO for stuff like that! Great work! I love how in all of your photo tutorials you're wearing gloves... more like surgery than mechanical repairs!

Heath

[Q45tech]

Any technican who wants to stay married better use gloves as the weekly manacure gets expensive.Since most cars are filthy and never cleaned of oil, slop, and grim there should be a $25 surcharge to punish owners for not keeping engine clean.

[maxnix]

Any technican who wants to stay married better use gloves as the weekly manacure gets expensive.Since most cars are filthy and never cleaned of oil, slop, and grim there should be a $25 surcharge to punish owners for not keeping engine clean.

I think $25 would be cheap for some of the engines I have seen.