how often should the fuel injectors be replaced on the LS400? I've got an LS400 with 124K miles which I've been running after having it sit for 2 years and it's misfiring pretty badly. It has no power, had a lean malfunction code of 25, and shakes the car pretty badly under high load. I replaced the fuel filter, checked the MAF and came to the conclusion that the injectors are the issue. This car hasn't been getting very good mileage for a long time leading me to believe the injectors are the issue.

 

Don't just throw parts, either diagnose it correctly, or let someone else diagnose it correctly. Me personally, I would bet that the injectors themselves are ok, I haven't seen to many issues around these injectors. I would look elsewhere. 124k is nothing. Have you tried new gas? Have you checked the air intake or exhaust for leaks?

 

This site is what helped me draw the conclusion that I have: http://repairpal.com/what-does-the-term-misfire-mean

"Lean Misfire
The lean misfire is another common reason for an engine "miss"—this is due to an imbalanced air/fuel ratio (too much air).....lean misfire may decrease or disappear as the engine speed increases.... An EGR valve that is stuck open, a leaking intake manifold gasket, a defective mass air flow sensor, a weak or failing fuel pump, or a plugged fuel filter are some of the many causes for a lean misfire." -- Yet replacing the fuel filter barely helped the issue and in some cases seemed to make it worse

"Mechanical Misfire
Mechanical problems can also cause an engine to misfire. Common causes of a mechanical misfire are—worn piston rings, cylinder walls, or lobes on a camshaft, a leaking head gasket or intake manifold gasket, damaged or broken rocker arms, defective fuel injectors (and/or the electronics that control them), and a slipped or incorrectly-installed timing belt or timing chain. Generally, this type of misfire has more of a regular thumping-type of feel to it. It is usually noticeable regardless of engine speed; in fact, it may even intensify as the engine speed increases."

From the exhaust, I have a thud thud thud sound much like an older diesel would be indicative of a cylinder or two not firing quite right. This is inline with the description this site had for the issue. Would a vacuum leak and check engine code go away from giving the car an italian tuneup? I mean I drove the car for like 300 miles, filled it with new gas twice and still had the issue, and check engine light. Gave the car an italian tune up, turned off the car and when I turned it back on a while later, the check engine light went away and never came back, not to mention running a bit better. Changed the fuel filter and things got a little better in some cases and worse in other cases. Overall the car still runs like crap and seems to vibrate more now which would mean it's misfiring in one cylinder and not in two plus before.

 

do a search for "seafoam" if y0ou think the injectors are clogged. cheaper than replacement.

 

I don't trust seafoam, not to mention having to change the oil again after just changing it (500 miles ago). What about redline fuel system cleaner?

 

Try some Chevron Techron fuel additive for one or two tankfuls.

 

+1 for seafoam. iinjectors don't have a replacement schedule, but you could always take them out and have them cleaned and rebalanced.

 

i doubt it's an injector issue. more like a vacuum leak.
get some carb cleaner and start spraying it around anywhere the engine has intake gaskets or ducting or vac. lines. if the engine smooths out in any particular area, you have found your leak.

 

i say its ur 02 sensor(s) before the cat...a vacuum leak will have no effect once the engine is up in rpms,fuel filter if really clogged will cause the car to have no power under load going up hills,and its def. not ur injectors, u can have a coil that is going out thats causing a misfire and putting injector cleaner in will take the misfire away because its causing the gas to burn cleaner...

 

an 02 sensor won't cause the rough running though...
could be a coil going out though, youre right about that if it is a coil on plug car. i didn't see what gen LS he has... the lean code could just be a stored code frm a minor vac leak.

 

02 sensor will cause rough running....trust me i went through all of this, a bad 02 sensor sends a lean code to the ecm and then it corrects what it thinks is the problem by putting out the incorrect fuel air mixture....been there done that, i thought the same thing until this very same problem happened to me

 

i disagree.... i've spent the better part of this decade working on cars for a living and i've never seen an 02 make an engine run rough. no offense meant here, i'm just discussing...
here's why:
let's say the 02 is faulty and sends an incorrect signal to the ecm saying the a/f mixture is lean. the ecm then adds fuel to the mixture until the 02 sends an acceptable signal back. in this case, the engine would be taking in too much fuel for the amount of air, causing an actual rich mixture. rich mixtures actually run well, very smooth and quiet.
of course, there's a limit as to howmuch fuel the ecm and add or subtract. this is called the fuel trims. it can't keep adding fuel over and over. this would be the case in which a lean code would be stored.
the opposite coudl happen as well, the ecm would pull out fuel until it gets what it thinks is a good signal from the 02 but then a rich code would be stored. in this case, the engine would run badly but that doesnt' fit with the lean code that the OP states he has.

 

Agreed with 19psi. Also if you add injector cleaner, it isn't burning any cleaner, it just has increased the amount of octane in ones tank, which resist detenation and burns hotter. I would also have to think that its not an o2 sesnor because if it were the case that it was constantly sending a rich/lean signal, there is a CEL code for staying rich or lean for too long, not a lean misfire code, something is happening with your ignition system.

 

yeah but if it was the ignition system, it would be putting out a rich code which it hasn't. The best part is that I disconnected the MAF which seemed to improve things but when given a high load, it would still vibrate pretty badly and STILL had no power, so if it was the O2 sensor, you can be assured that it isn't now since a disconnected MAF also makes readings from the O2 sensor void. Furthermore, O2 sensors arent' read when first started up and the car runs rough all the time.

For those who are insisting it's the coil and annoyed I'm disregarding it, here is some good news... For me to get to the injectors, I'll probably have to remove a bunch of covers, intake manifold, etc. which would be necessary to check the spark plugs, distributor, coils, etc. so I'll be checking with a multimeter both the injectors and plugs since it'd be conveinent to do so.

 

The intake doesnt have to come off for the injectors, as the injector rails must come out before the intake does. It will take you at most 30-45 minutes to have the covers, TB removed and replace the dizzys, rotors, and plugs. It's pretty easy actually, you don't even have to take the serp belt off.