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92 Ls400 Misfire/lack Of Power Desperate For Advice.


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#1 LS 400 WASTE OF TIME/MONEY

LS 400 WASTE OF TIME/MONEY

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Posted 15 January 2011 - 11:29 PM

We have a 92LS400 since new with 116,000miles.At first it had an obvious misfire up to 3000rpm and lack of power.It may of seemed to clear up because it has 8 cylinders.Heres a list of the things I have done.REPLACED CAPS,ROTORS(Lexus parts)NGK PLATINUM PLUGS and NGK WIRES,FUEL PUMP AND FILTER 8K AGO,CLEANED THROTTLE BODY CARBON,CLEANED IDLE AIR CONTROL STEPPER MOTOR CARBON BUILDUP AND POWERED UP TO CHECK STEPPING IN BOTH DIRECTIONS, TESTED BOTH COILS RESISTANCE,CHECKED TROUBLE CODES,FIRST,AND CODES 25&26 CAME UP MEANING RUNNING RICH AND LEAN.LISTENED TO INJECTERS WITH ELECTRONIC STETHASCOPE,TWO HARD TO GET TO UNDER THROTTLE BODY BUT STILL HEARD CLICKING.HAVE 3M FUEL INJ. CLEANING KIT WHERE YOU TAP DIRECTLY INTO FUEL RAIL,DISCONNECT FUEL PUMP FUSE OR RELAY,PLUG RETURN LINE AND RUN OFF FUEL INJ. CLEANER.COULDN,T FIND 3M CLEANER BUT NAPA CAN FIT MY HOSE KIT AND TRIED TWO CANS.LOTS BETTER BUT STILL MISFIRE BUT SOME WHAT DRIVEABLE BUT NOT RIGHT.USED TO SHAKE BAD WHEN YOU LET FOOT OFF BRAKE.DID FUEL PRESSURE TEST AND GOT 39PSI AT IDLE,JUMPED UP TO AROUND 46 WHEN REVED AND JUMPED UP TO 48 WHEN VACUUM LINE ON FUEL PRESSURE REGULATOR IS DISCONNECTED.FUEL PRESSURE DROPPED TO 25PSI AFTER SETTING FOR ABOUT AN HOUR AND DROPPED TO 8PSI OVERNIGHT.IS THAT NORMAL?I ORDERED A CAN OF 3M INJ. CLEANER AND THE MAJORITY OF IT CAME OUT OF THE CAN AS SOON AS I TURNED THE VALVE ON THE CAN HOSE MAKING ME THINK AN INJECTOR WAS STUCK OPEN LEAKING AND FLOODING THE CYLINDER.IT WOULD NOT START SORT OF CONFIRMING THIS.I RECONNECTED FUEL PUMP AND RAN ENGINE A LITTLE.RE-TRIED INJ. CLEANER AND ENGINE STILL WOULDN'T START BUT VERY LITTLE LEFT IN CAN.RECONNECTED FUEL PRESSURE GAGE,RESTARTED ENGINE AND IT STARTED FINE.IDLES ALMOST PERFECT BUT CAN FEEL A MINOR SHAKE AT IDLE.REVS WITHOUT MISFIRE BUT POWER SEEMS WEAK AND WHEN YOU PUT IT IN GEAR IT BARELY HAS ENOUGH POWER TO GET MOVING,WAY WORSE THAN WHEN I STARTED,BUT NO APPARENT MISFIRE.ACTS LIKE TIMING IS AFTER TDC OR SOMETHING.VACUUM SEEMS STRONG BUT NEVER PUT GUAGE ON IT.ANYWAY TO SHUT OFF EACH INJ. AND CHECK PERFORMANCE CHANGE AND HOW LONG SHOULD IT HOLD FUEL PRESSURE BEFORE DROPPING TO ZERO.PLEASE HELP AS THEY HAVE LONG SINCE RETIRED AND NOW ARE ON SOCIAL SECURITY.HAVE SPENT HOURS AND HOURS RESEARCHING THIS ONLINE AND ONE PERSON WANTS TO SELL THEIRS AS THEY SPENT OVER 3K AND HAVEN'T SOLVED THE PROBLEM.THANKS DUANE

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#2 curiousB

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Posted 16 January 2011 - 08:36 AM

A leaky fuel injector usually has the symptom of poor idle, hard to start, and/or failing emissions test. At higher speeds a stuck injector shouldn't matter as much it is mostly open. Do you get good engine performance at highway speeds and only problems at idle and low engine load? Fuel pump/fuel filter usually shows up as problem on higher speeds initially as fuel demand higher so engine gets starved for fuel. Your pressure readings seem close enough that it should at least run well at idle.


If engine runs poorly across the all speeds it sounds more like ignition to me. If it is only a rough problem at lower speeds and or idle it could be vacuum leak (is an air duct cracked or poorly fitted in place, hose cracked or fallen off port), sticky/broken IACV,

You've done a lot of the right things but not been rewarded for your effort, yet.

#3 hughes369

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Posted 20 January 2011 - 03:42 PM

I would check the fuel pump voltage. Im not sure what it is supposed to run at , but I replaced a pump on my 1992 and fixed a lack of power it had around 225K. Replaced the fuel filter on it too, but that was not the problem, just was peace of mind and thought that would fix it, before replacing the fuel pump, which is located behind the rear seat back. Stupid place to put a fuel pump. It might run around 10 volts or more at idle, and maybe more at higher RPM. But its been a while since i did that job on my 1992. If anyone knows what the manual calls for, voltage or resistance at the fuel pump, please post. Im having issues with a 1991 LS400 missfiring, and looking for advice on it as well.

#4 curiousB

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Posted 20 January 2011 - 11:45 PM

..."92 Ls400 Misfire/lack Of Power Desperate For Advice. TRIED EVERYTHING- NEED GENIUS"...


Actually if you tried everything it would be fixed.....


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