1999 LEXUS GS 400 HAS A CODE P0171. I SPRAYED THE ENGINE WITH CARB CLEANER,NO PROBLEM FOUND.I, REPLACED THE MAF BECAUSE IT WAS READING BELOW SPECS.REPAIRED A CRACK IN THE AIR INDUCTION CHAMBER.I AM READING MISFIRE IN CYLINDERS 2,4,6 AND 8 AT TIMES BUT NO P0300 CODES
Year: 1999Make : LexusModel: gs400Engine: 4.0l
Thank you for using just answer.
What are the fuel trim readings on bank 1 and 2 long and short term?
I feel like I am missing part of the story here.....what repairs were done on this car right before this issue?
Where exactly did you find this "crack?
REPLACED AIR FILTER,CRACK WAS IN THE AIR CHAMBER BOX NEXT TO THE AIR FILTER COVER
Please answer all questions above so I can properly help you.
I DON'T KNOW FUEL TRIM
You stated code #'s above so by this I assume you have a scan tool and know how to use it correct? Does this scan tool have data lists also?
YES, I DON'T HAVE THE CAR RIGHT NOW
I will need that to help you further.
Did this car recently have a starter replaced by chance?
ok, get me fuel trim readings when you can
OK, IF THE SHORT TERM FUEL TRIM IS LOWER THAN THE LONG TERM THAN WHAT OR THE OTHER WAY AROUND
Get me data and I can offer you the assitance that you are paying for, I do not play any guessing games or give guestimates, thank you
ok.how do I get back with you
Just reply as you are doing right now, there should be a few e-mails in your inbox also to direct you back here, I am mostly online in the evenings, there is another excellent expert here by the screenname of skyvisions that is on during the day and can help you at that time if needed also. I want a list of short term feul trim readings at idle, when revving the motor up and under a load on BOTH banks, thanks
DID YOU GET THE SPECS
hey Peter short term fuel trim 2.3 long term 34.4
Hello again, I just came online.
Clarify these specifications?? Are these from bank 1 or 2 and in percentages?
hi. bank 1 and 2. I perform a smoke test no leaks. checked fuel pressure 28 psi at idle isn't that low
Ok, so the short term % is toggling around zero but at 34.4 long term then correct? What do these values change to when you drive or put it under a load? As last stated by me last night I need values at idle, revving motor and also under a load, thanks
at 2000 rpm bank 1 st trim -2.3% lttrim 24.2 bank 2 st 1.6 lt 27.3 uder load bank 1 st4.7 lt 23 bank 2 st2.3 lt 23.3 the misfire went alway when i checked fuel pressure
Question for you so I can better explain here....do you understand how fuel trim calculations work and what they mean?
short term is whats going on and long term is correcting it.if short term # XXXXX XXXXX the vehicle is lean
Short term is supposed to be around zero on this car, yes long term is correcting but it takes longer for these values to change.....if you are reading near zero on short term this means you are not duplicating the issue currently, this is most likely happening when the car is actually driving. Yes your fuel pressure reading is low, the specification on this car is 44-50 psi when the pump is commanded on and the system is also designed to HOLD pressure above 20 psi once the car is shut off. I would be checking fuel issues at this point if the idle speed is normal and the 02 sensors are responding normally.
yes o2 sensor working correctly.yes fuel pressure was holding for 5 mins
you said fuel pressure was 28 psi though did you not? Did you mean this when running or engine off?
running and it was holding pressure for 5 mins
ok, so pressure when the fuel pump is ON is 28 psi is that correct?
That reading is too low, as I stated above with the pump energized specification is 44-50 psi.
ok,that why when i removed the fuel pressure pulsation damper the vehicle stopped misfiring
My thoughts on this would be to check the fuel pressure regulator on the rail, if this is sticking or bad it can cause pressure issues on this bank of the engine and cause the issues you are describing. I believe you are trying to describe this same part by "dampener"....the round shaped cylinder with the float needle in the middle and the plastic cap on it.
yes, it's two, one for each banks.I thought itwas to damping the pulsation in the fuel line.the fuel pressure regulator is with the fuel pump in the tank
There is a regulator on the pump that holds pressure in the line when the pump is not running but the "pulsation dampeners" also play a vital part of the fuel delivery to each bank, you said the issue went away after you removed this to check pressure, I assume this came back once reinstalled correct?
yes, just the misfire went away and i was starting to feel the misfire come back but the po171 was still there
Your questions to me have been crystal clear and very well worded but every reply I get from you to a question I ask is only 50%, you need to be clear in your replies to my specific questions please
sorry about that ,you have been very helpful ,thank you.how do i contact you to let you know the problem is repaired??
you can just log back in here and reply as you are doing now, I carry a blackberry that is linked to the site but am mostly only available in the evenings, I woudl probably swap the 2 "dampeners" and see if you have any change. Also try flushing the fuel rails, I have seen a lot of issues lately with fuel quality and e85 contamination that can get clogged in the injector ports.
Master Certified with lexus, 8 years experience with Lexus