Och

iTrader: (3)

Well, as many of you read in my previous treads, I purchased a 94 LS400 with nearly 100k on the clock in July. The car has three problems: rough idle and stalling which I fixed by cleaning throttle body; pinging at midrange RPMs and lack of power. In an attempt to resolve the last two problems I replaced the fuel filter, air filter, cleaned out PCV valve, used various inject cleaners and octane boosters, did a full seafoam treatment (oil, crackcase, and intake). Did a full tune up including new spark plugs, wires, distributor caps and rotors. All to no avail.

Well today it stuck me... what if.... And I proceeded to remove my ECU fuse, unplugging the MAF sensor, and reinstalling the ECU fuse. Needless to say the check engine light is on, traction controll is off, BUT the car now has goabs, and I mean literally goabs of power. Step on the gas halfway from a dead stop, it kicks you back in the seat, chirps tires and pulls like a V8 should!!! On top of that, the pings are now rare, and occur rather random, more at part throttle than at full throttle. They are also very distinctive, loud pings, compared to the pinging I have with the MAF connected, which sound like a rattle.

So I conclude that my MAF sensor has come to the end of its life. Even though its not completely dead, it's lying to the ECU about the amout of air coming into the engine, most likely reporting too little air, so the ECU isn't supplying enough fuel, therefore I get what most likely to be a lean condition, thus no power and pings. With the MAF disconnected I guess the ECU is supplying excessive fuel, therefore the car is probably running rich, thus the random pings. However the engine is making a lot of power.

That being said, I believe most of us with a first gen LS400 are suffering the symptoms of a faulty MAF, without even knowing. And needless to say, I am EXTREMELY disappointed in Lexus for charging nearly $1,000 for a new unit. There should be no reason for this sensor to cost so much. We should file a class action lawsuit against Lexus on behalf of our CL community.

NewLSlover

Nice find, och...but can someone chime in with how healthy this is for our cars?

I am thinking of doing the TB cleaning this weekend, possibly..to fix my random low idle stall problem.

But if this disconnecting the MAF sensor thing isn't bad for the engine, I may try it...

dfkd

I think it would only be bad for emissions and maybe your mileage.

MASS AIR FLOW (MAF) SENSOR

The mass air flow sensor (MAF sensor) is located between the engine air cleaner (ACL) and the throttle body.
Uses a hot wire sensing element to measure the amount of air entering the engine. Air passing over the hot wire causes it to cool.
Sends an analog voltage signal to the powertrain control module (PCM) to determine the intake air mass. The powertrain control module will then calculate the required fuel injector pulse width in order to provide the desired air/fuel ratio.
The mass air flow sensor hot wire sensing element and housing are calibrated as a unit and must be serviced as a complete assembly.

It seems that it's more about efficiency than anything else. The pinging would be my only concern.

Lexmex

I have been pulling that EFI fuse every week before I head up to the track. Last Saturday I forgot and it was slow city. Good idea to use electrical contacts cleaner to clean up the MAF.

Och

iTrader: (3)

So I cleaned the living crap out of the MAF with QD electrical cleaner, dried it with a hair dryer and plugged it back in. Got a check engine light that stayed on for about half hour, and the car ran like total crap. RPMs were jumping up and down. I guess the cleaner didn't dry up completely, so it was triggering CEL. Then the light went off, and the car is running pretty much the same as it used to be. The acceleration under very low throttle seems jerky, it was somewhat jerky before, seems jerkier now.

I was also told that this may not be the MAF, it could be bad oxygen sensors, which work in conjunction with MAF, and when MAF is disconnected the ECU does not take read input from oxygen sensors. I'm gonna have my oxygen sensors tested when I go for the next oil change.

Och

iTrader: (3)

If I could get rid of the pinging with the MAF disconnected, I would run it without the MAF all the time. I dont pay for my gas, I get it from my work, so I dont really care if gas mileage suffers.

Suneet

Hey Och, can you tell me more aobut the Seafoam treatment? My 94 LS has about 191K on it and I'm planning to keep it for a few more years. I think its time for a seafoam treatment. Where exactly did you put it in, how much, etc, what was your full procedure? Thanks!

PureDrifter

iTrader: (10)

here ya go buddy

https://www.clublexus.com/forums/sho...hlight=seafoam

how to thread
https://www.clublexus.com/forums/sho...hlight=seafoam

Och

iTrader: (3)

The easiest way is to put half a can into your oil, and then SLOWLY suck half a can into your intake chamber through the PCV valve hose. Mind you, when you disconnect the PCV valve hose, the car is gonna start chocking, and even more so when it starts sucking in Seafoam, so you might wanna have a buddy in the car stepping on the gas, keeping RPMs at around 3k. Drive around maybe 150 miles, and change the oil.

You can also add it to your gas tank to clean injectors, but from what I heard Lucas injector cleaner is more effective.

Brandicus

iTrader: (6)

hmmn... so the only solution to the problem is a $1k fix? thats not cool

looks like im going to have to hunt through some junkyards

Och

iTrader: (3)

I wouldn't - chances are they are malfunctioning.

lorenzo816

och:
What codes were u getting?

trouble codes

o2 sensors do come up with a code on OBDI and OBDII.
Its just a little hard sometimes to pinpoint what the problem is with OBDI because sometimes you get a MAF code when it indeed is your left or right bank1 sensors.
Do the sensors first. If they are bad. Then reset the ECU drive 3 cycles and if the MAF comes back on I would be surprised. These things dont really go bad all the time. (correct me if I am misled fellas)
But spraying it with cleaner I would not do. May change the rate of which the element cools thus fooling the ECU into thinking crazy things.

Och

iTrader: (3)

Well, actually I'm not getting any codes, so whether its the MAF or O2 sensors, they are not completely dead. I was thinking about replacing O2 sensors, because when I unplug the MAF, the reading from the MAF and O2 sensors are no longer being sent to the ECU, so it really could be either the MAF or O2's. But right now I'm still trying to put my car together after it was stolen and stripped, so its the least of my problems now.

lorenzo816

check the AFM - MAF resistance and then check the O2 sensors resistance.

In the manual it says that even though codes do not come up, a car can still be diagnosed by the symptoms it is presenting.



and look here for the o2 sensors check....

mainoxygen.pdf

hope this helps bro.

Bradster

May i make a few suggestions to really smooth out the ride on a high mileage LS400.... replace the 2 front motor mounts and the tranny mount,manually scrub the throttle body,do a fuel injectors cleaning treatment using the BG high pressure system which can be found at most dealerships (and other shops..$70-$120) I guarantee a great improvement.