2004 Ls430 Misfire On Startup

[Greavett]

Just though I would share this with you as some of you may have similar problems, mainly with the 3UZ-FE engine. I started to experience an engine misfire on startup which lasted of all of 1-2 seconds. It always cleared and ran perfectly after wards. I could smell excessive fuel from the exhaust after intial start, but again that cleared after start up. Problem seemed to be less pronounced when cold, but mainly because of the nature of cold start need for richer mixture.

I had my suspicions that the fuel injectors may be the trouble, or maybe the ignition coils or even the engine temp sender for the e.c.u. I ran all the tests on the sensors, including cam and crank sensor checks hot and cold. Still no obvious anomolies! Now, usually with fuel injected cars they run a return to tank line, which after the regulator usually terminates back in the fuel tank. This is really helpful, it enables you to manually restrict return line flow which in turn increases fuel line pressure.

Usually problems with injectors are related to poor discharge patterns, normally caused by a partial blockage, or weak electrical coils within the injector itself. Now on conventional cars if you have a misfire and you suspect injectors, you can restrict the return line with a clamp. This usually improves the spray pattern for the faulty injector and will usually remove the miss for as long as the clamp is installed. Running with the clamp is not desirable due to the extra load it would put on the fuel pump (raised pressure), but your testing has highlighted that it's likely to be an injector. So a clean will normally fix them..........usually!!

The LS430 does not have a return to tank line, and so it's almost impossible to restrict the return line to overcome possible spray pattern issues which will give the miss. I removed the spark plugs after the car had been sitting for a while and inspected which plug was discoloured differently to the others. I found number 8 plug was glazed and swapped it out with another. I let it run for another week or so to do a fair test, then removed them again for inspection. Found the swapped out plug was clean, but the new plug in the cylinder that had given me the glazed plug was now also glazed.

Ok, so I had found the cylinder which was responsible for the miss, could be one of three things from now, mechanical problem, fuel problem, or ignition problem. Starting with the easiest first I changed out a coil pack for a neighboring cylinder and left the car run another week. Removed and inspected plugs again and still the same results. Same cylinder with glazed plug. Next thing to check was the mechanicals, I discarded this check mainly because the car runs well after start up, there is no miss from the exhaust and no lack of power.

Finally I was totally convinced it was the injectors. I got a set of serviced units from the states and installed them. The first two start ups were perfect, and I was pleased with my diagnosis. Or at least I thought I was!!

The next day the fault had returned, not much worse, probably the same, but still there. So I ran all the checks again, and came back to the same conclusion. Injectors.

I've had it one time before where the older model 1UZ-FE had the same sort of issue, only found the injector failing when using and oscilliscope. It showed a lazy coil pattern, easily identified on a scope with a second pulse after the intial activation. The other injectors did not display the same pattern.

So again I ordered injectors and installed them. This time the fix was instant and long lasting. It's been running good ever since. I don't beiieve that the original set were not cleaned satisfactorily, just more that the activation coils may have already become weak.

I read a few posts on LS430 Misfires, but none of them had any answers or fixes for the concern. If your V8 lexus is missing briefly on startup, it might be worth a look at your injectors.

To reduce the likelyhood of failures due to contamination of the fuel circuit, I changed the in-tank fuel filter under the rear seat, (mostly forgotten about).

I only paid around the $35 per injector from the states, all genuine Denso and all brand new, not reconditioned. I will always go new from now on.

I also want to mention that the front four and rear four injectors are a different part number however.....the injectors are exactly the same. The difference in the part number is the little jacket that the rear ones wear to reduce heat soak. These jackets are removable and can easily be fitted to the new injectors. The reason I added this is because the front four injectors use a fairly common Denso injector, and you are going to find them easier for cheaper than the rears.

Any way, I just thought I would share this with the forum, hard problem to find because of the time span of which it actually occured. With a return fuel line, the diagnostic would have been far quicker. Hope this helps out other LS430 owners

Simon