B-Lawrence Posted October 21, 2011 Share Posted October 21, 2011 LS 430 2001 has 145k miles daily driver and has started to ping (detonation) in the last 2-3 months. It usually happens at 1000-2000RPMs when accelerating. Car is serviced at dealer, but before I donate my $1000 this time I'd like to know what the issue is. I use the same fuel stations. It sounds to me that possibly the ECU is mixing too lean in this RPM range; acceleration perturbates the situation by adding more air, making the mixture more lean. Oxygen sensor? There are no EWLs and the engine runs smoothly and gets a city/hwy of 22.5. Quote Link to comment Share on other sites More sharing options...
curiousB Posted October 21, 2011 Share Posted October 21, 2011 What makes you think it is "pinging" (knocking and pre ignition are two different phenomenon)? You need to be careful not to prematurely judge the problem before you jump to any solutions. That said if it truly is knocking(although I can't recall that complaint once on this forum) then it would might suggest fuel mix and/or ignition timing issues. There are knock sensors on the engine so maybe one has gone deaf and isn't detecting the ping and therefore not guiding the ECU algorithm to adjust. There are two such sensors, item 89615 in the diagram below. It is highly unlikely for two sensors to simultaneously fail, but which one? It could get expensive throwing parts at this in search for a solution.. I'm not sure the ECU's ability to diagnose the knock sensors but there are several OBDII codes for the knock sensors so its a bit strange you don't have a CEL and code or two stored. The other possibility is one of the two primary O2 sensors (the ones before the Catalytic converter). If it were sending a false signal to the ECU, fuel trim would be out of balance. You can check this by connecting an OBDII adapter and laptop and look at the O2 output signal on a graph. Some say O2 sensors have a useful life is 100k miles, after that they get contaminated and the signal output gets lazy (slower moving waveform). This leads to over and under correction of fuel trim since the feedback signal is too slow to react. O2 sensors are about $60-70 on eBay for OEM. Its DIY if you buy an O2 sensor wrench. Dealer will charge you $100+ just to look at them, in this case the soluion is about as expensive as the diagnosis. It could also be an airleak in the intake duct which is leaning out the fuel since that air bypasses the MAF. This would show up as an elevated long term fuel trim however since the O2 sensor feedback will attempt to correct the fuel mix problem. Again OBDII data is helpful to run this theory to ground. A very simple test is to go to a different place for gas with a top tier brand and premium grade. Quote Link to comment Share on other sites More sharing options...
B-Lawrence Posted October 21, 2011 Author Share Posted October 21, 2011 Thank you for the detailed explanation. I had heard about leaky intake and exhaust manifolds causing this problem (for 2 different reasons), but mostly inspired when exploring oxygen sensors for a work project. I guess an oxygen sensor puts out more voltage as it senses more oxygen. Therefore it's safe to assume at the end of its life when combustion remnants coat the sensor it will be sluggish in response as well as sending a lower than normal voltage to the ECU. A low output signal will tell the ECU the mixture is too rich causing the intake mixture to have more air added, thus detonation. I was aware that engines of low HP:in3 ratios are ultra sensitive to detonation and should be addressed quickly before damage occurs. I think I'd like to get in touch with the car since it's been so good to me. These cars are electronic marvels, they're even supposed to detect a knock and report it? With no CEL it may be best to get busy with understanding the situation. Question; what if the knock sensors ARE working correctly and are retarding my timing to offset the detonation, would I still get a CEL in this situation? Thanks for the diagram and background. Much appreciated. Quote Link to comment Share on other sites More sharing options...
jaswood Posted October 22, 2011 Share Posted October 22, 2011 Except for knock/ping due to engine luuging most modern day EFI engines use A/F mixture adjustment, enrichment (not counter-productive timing adjustment) to alleviate knock/ping/detonation. Your's sound suspicously like engine lugging and the engine controling ECU should downshift to alleviate that. Many newer cars now have random "re-acceleration" downshift delay of 1-2 seconds, is that your case? Quote Link to comment Share on other sites More sharing options...
Ancdmd Posted February 10, 2012 Share Posted February 10, 2012 I have the same knocking problem with my '02.. Have you resolved it? Quote Link to comment Share on other sites More sharing options...
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