Obscene Posted November 14, 2011 Share Posted November 14, 2011 Hey guys, I'm a long time lurker, first time poster. A little introduction: I'm currently and aerospace engineering student and consider myself a weekend mechanic of sorts. I look forward to consuming and contributing to this community. I drive a 1999 RX300 FWD (first gen) with 140,000 miles. I bought it from my grandfather, who is a retired mechanic, for $3000 when it had 100,000 miles on it, and it has been pretty good to me. My grandfather bought it brand new, so I know its complete history. *I know this is very lengthy, but I feel like I need to explain everything I can so that you understand the situation as best as possible. If you want a quick run-down, I included a short-hand version towards the end of the post.* Back story: I am currently experiencing a very light engine misfire that you can only feel during idle, and when the car is lurching with your foot lighly on the brake. It feels vary close to a vacuum leak. The problem started after I changed a knock sensor, the following is a recount of what I've done so far: I changed my knock sensor 6 months ago with an after market brand, and big surprise, it broke about 2 weeks ago. I changed the broken knock sensor with a OEM Denso sensor, torqued to spec, and it's working great. However, after the second knock sensor replacement, I started to experience engine problems. My cars CEL is throwing P0300 and P0305. As you all know, cyl 5 is on the back bank, so getting to it was a little time consuming, but I got to it and decided to changed all my spark plugs. After I changed all the plugs, I swaped the coil from cyl 6 (front right), which is known to be working, with the coil pack on cyl 5 (this way I could chage the coil pack faster if it was broken). I reset the codes, and waited for the CEL to come back, and when it did, it threw P0300 P0305. At this point, I suspect a vacuum leak (maybe I forgot a vacuum line somewhere, or I broke one). I bought some carb cleaner and sprayed it over all the vacuum lines and gaskets I could get to, there was no change in engine RPM. I checked all the vacuum lines with a diagram from Mitchell 1 and it all seemed correct. Running out of options, I suspected the lower intake manifold gaskets to have gone bad since I reused them from the knock senor replacement. So I bought a full set of gaskets from Fel-Pro (lower intake, pellum, and throttle body), and replaced all the gaskets. This still did not fix my problem. I finally caved and took my car to a very good mechanic shop ($100/hr) for a diagnosis. They told me the injector on cyl 5 was bad. So I purchased a Denso injector online and changed it, again the problem was still there (shop refunded my money). After all this I ran a compression test and all my cylinders are strong, ~210psi, with the exception of cyl 5, which was at ~70psi. I started to expect a bad exhaust valve since I drove with a bad knock sensor for ~1000 miles (sensor went bad durring a road trip. It is my understanding that a bad knock sensor triggers the computer to run the engine lean, not sure though). Current situation: All this back story leads to were I am now, I am planing on pulling the rear cylinder head to check it for damage and what-not. I was planning on removing the upper and lower intake, headers, coils and plugs, removing/ losening the rear motor mounts, jacking the engine up (to gain better access to the rear cylinder head), and removing the head. Short run down for those that don't want to read: Changed bad knock sensor Experienced engine proplems after changing Misfire, P0305 P0300 Changed all the plugs and swaped coil pack with Cyl6 Codes still P0300 P0305 Suspect vacuum leak Checked vacuum lines, all good Changed lower intake, upper intake, and throttle body gaskets Problem still exists Had a professional shop diagnose problem Shop claimed bad injector on cyl 5 Changed injector on cyl 5 with OEM Denso Problem still exists (money refunded) Ran compression check All cylinders at ~210 psi, cylinder 5 at ~70psi Suspect valve problem on cylinder 5 Planning to pull the rear cylinder head by removing upper and lower intake, removing rear header, loosening/removing rear engine mounts, jacking engine up (better access to back head), pulling the head off, and checking for leaks .etc on cyl 5 valves. So Lexus Owners Club, my question(s) to you are the following: Do you have any ideas of what my problems could be? Have you ever removed the rear cylinder head, and if so, how? Any tips or suggestions for me in regards to diagnosing problem? Any tips or suggestions for me in regards to removing of the rear cylinder head? I consider any relevant information to be useful information, so don't hold back! On a side note: (not related to previous questions) In the past, I've had trouble finding DIY information on the first gen RX300, so I'm thinking about making a step-by-step, idiot proof, DIY guide with high-res pictures and HD video on how to: (all with accompanying torque specs .etc) Remove the rear cylinder head Change spark plugs & change coil packs Drain coolant/oil & refilling Removing upper and lower intakes & gaskets Removing windshield whipper assembly Changing knock sensors Removing / changing engine mounts Pretty much anything on the way to the cylinder head Do you guys think the community is big enough / will benefit enough from these guides to be worth putting in the hours to make and edit them into a guide? Thank you for any and all help, all information is valuable, some more than others. Quote Link to comment Share on other sites More sharing options...
lenore Posted November 14, 2011 Share Posted November 14, 2011 Wow you did a great writeup of your problem...I was going to say injector, but it is done...However what kind of plugs are you using, I hope Denso, or NGK iridium...If Bosch, get rid of them. The compression really bothers me. Maybe a bad valve or possibly bad rings on piston. A leak down test on the compression would help to determine this. Good luck Quote Link to comment Share on other sites More sharing options...
Obscene Posted November 14, 2011 Author Share Posted November 14, 2011 Wow you did a great writeup of your problem...I was going to say injector, but it is done...However what kind of plugs are you using, I hope Denso, or NGK iridium...If Bosch, get rid of them. The compression really bothers me. Maybe a bad valve or possibly bad rings on piston. A leak down test on the compression would help to determine this. Good luck I use NGK Iridiums for the RX. I would like to run a leak down test, however, I don't own an air compressor. I'll talk to my friend who has a pretty nice personal shop (lift and all) and see if he has a small one lying around. If I get one done, I'll post the results. Quote Link to comment Share on other sites More sharing options...
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