Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Car came in with knock sensor code p0330 and when test driving at half throttle and under seemed to perform okay under higher load above half throttle it seemed to fall on its face. I scoped the knock sensors one looked good the other showed nothing just a flat line. Contacted customer and sold them both knock sensors and the wiring harness after clearing codes I drove it around the block a few times then code popped back on and car started doing the same thing. I notice in the data stream the a/f sensors are responding to lean and rich as they should also the rear o2 sensor looks good LTFT is showing at idle 32 percent bank 1 23 percent on bank 2 under load or wot they go to around zero on LTFT I have searched and searched for a vacuum leak with out any luck.
Test I have performed
1 Fuel quality appears good
2 back pressure check on both cats 0 psi idle and 3k rpm
3 a/f sensors seem to be working properly when I force rich with brake clean they go down to around 1.97 volts on scan data force lean I have seen them go around 3.9 volts
4 fuel pressure is 52 psi it drop maybe 1 psi under load spec says 45-55psi
5 I do not feel or see a misfire on this car and we replaced o.e denso plugs and one coil about 4 months ago.
Things I am questioning
1 Even before the knock sensor code comes on the fuel trims are always between 20 and 30 percent at idle and come down with higher rpm/load
2 what else could be causing this lean condition at idle
3 I feel I need to Chase the lean problem and that will hopefully fix the knock sensor problem.
I am sure there is something I forgot that I did any help will be appreciated as always I will update this post as soon as I get more information
Your trims definitely suggest Vacuum Leak, are you able to smoke test a cold engine and then a warm engine?
Your fuel pressure didn't seem right, was that scan data or a physical gauge? On snap throttle, you should see a gauge rise 5-10 psi then fall back to no less than 5 psi of standalone pressure. NO pressure rise and a drastic fall on a snap test indicates bad regulator or restriction or for volume a bad pump.
I'm thinking your Knock sensor issue may be a symptom of your fuel trim issue. It would also be good to check the MAP PID at WOT against the BARO.
eg if you BARO is 29. You want to see the MAP Pid go high up to 27 inhg or better, anything less and you've got a breathing issue.
If you are able to record some scan data and save it as .csv file take it for a ride, do some power tests,and post a file.
I think there are 2 or 3 little vacuum lines that go onto the air cleaner box those are often forgotten to be put back on after a air filter change and I’ve seen them cause lean codes
Topic Author
