I have an LS400 that is giving me the check engine code Air-fuel ratio lean malfunction and I was curious about whether or not the spark ignition related components could cause this issue or if it's strictly a fuel issue. I checked the fuel pump and it APPEARS to be fine, I doubt it's the fuel filter because the car ran fine two years ago when I last used it (it has been parked for a while). I'm thinking the issue I have is related to the electronics/wiring as the hood was open for a long duration with the sun beating on it every day (long story). So, would bad spark plugs, wires, coil etc. possibly cause a lean malfunction?

The LS400 is a quiet engine so it's kind of hard to hear it, but I believe it is misfiring. When I rev the engine, the problem is less pronounced which according to some sites would not happen if it was a fuel pressure issue. I can't hear/feel the "misfiring" at low RPM under little to no load, but under high load, I can see the vibrating in the shifter and feel the whole car shake pretty badly. The issue gets slightly worse after the car is warmed up and is much worse on a hot day. High RPMS/Low RPMS and high load, lots of vibrating, High RPMS/Low RPMS and Low load, little to no vibrating.

I noticed disconnecting the MAF seems to help the issue but doesn't completely alleviate the issue. I feel like I have a similar issue to this guy: http://www.clublexus.com/forums/ls40...nging-too.html

 

it should cause a rich misfire not a lean, but it kinda sounds like one of the spark plug wires might be arcing like you said. check all the plug wires

 

Nice pictures, man!

 

A bad coil or wire would cause a rich mixture like stated above but it would run bad at idle also. The motor would jump or shake a bit every time it missed. It is possible that the fuel tank got very corroded from old gas sitting in it for 2 years and now the particles in the gas has clogged up the lines and filter. That makes more sense than a bad plug wire or coil. It may seem like a lot of work, but drop the tank and see how it looks. I would bet money that it looks like crap in there.

 

I looked inside the tank and couldn't believe how clean a gas tank could be, especially from a 1994 model! I was expecting little particulates here and there but found nothing. My friend's dad drove with me with the MAF disconnected and said that because the car didn't die when driving up the steep hills we drove it on, that is was very unlikely to be the fuel filter which to me makes sense considering that this wasn't an issue two years ago.

Ok, so how likely is this issue attributed to a vacuum leak near the fuel injectors or a faulty EGR again? Apparently the EGR is an issue with these cars and the EGR line HAS been replaced 4 years ago, though only like 10K miles ago.

 

The MAF sensors on these cars are also really expensive. Good luck with the problem, man. Use this site:http://www.random-misfire.com/ for instructions to check for intake and vacuum leaks.

 

Just to let you know, I checked the MAF with a multimeter and it would appear to be within specification. It'd be great to know where the cam position sensor, or other such sensors are and their ohm ratings so that I could test them. I want to test the spark wires and distributor but it's a very involved job and I don't know if I can see myself doing it.

 

I use this site for my GS. There are all the ratings for all the sensors. I know your car is an LS. However, it may still offer some help in diagnosing the problem. http://bahamutcars.free.fr/workshop/...nts/index.html