1998 Lexus LS 400- Extremely poor gas mileage

[M.Yasir]

Hello everyone

Its been a long time since i posted a problem with my car, i have to say it, maybe it is only happening with me but since 2015 the ownership of my 98 LS 400 is a nightmare, if i look back at the history and calculate how much i have spent, or maybe i just bought a totally non maintained car considering its now a 20 years old car and can beat a S-500 in a race from 140 to 200 kph

Problem 1

My car suddenly died on the road, i switched off the engine while i was waiting for my wife to pick her up from her office, when she came and sat in the car and i turned the ignition key a bummer!, sound coming was like hissing or when something is turning but slipping, i was at that time 99% sure that the starter motor had died, and is not engaging with the fly wheel

I called recovery and went to a random garage which was open at around 8 PM in the night, the mechanic there told that please leave the car and i will open the intake manifold to see what is the problem

When everything was opened and intake manifold was removed, it appeared that the bearing which holds the 9 teethed shaft which turns the flywheel had gone for good and it broke so while i was turning the ignition key the 9 teeth shaft was somehow rotating and was not moving forward to engage with the flywheel

Anyway, the headache of finding the right bearing for the started motor, i went to the scrap market here and bought a LS 430 started motor due to the fact that the wiring harness clip in the engine bay was big when compared to an original starter motor of 1998 model, see the picture below of the clip which i am talking about

The clip which i am holding is big, well maybe my car is all screwed up anyway, moving forward

As you can seen in the below post the magenta color ice cream is being generated since the water bypass gasket was leak and it was reaching to the starter motor

 

Moving forward, i managed to procure all the gaskets and done, mechanic put everything back together and made 1 click start

After driving the car for a day or two, i noticed that the fuel economy was extremely poor, you see we have four dividers displayed at the fuel gauge in the dashboard, in my personal experience one box of divider should give atleast 100 miles, so as a total by the time your fuel is almost the E symbol you should have clocked 350 miles

But to my surprise in two full boxes of divider lines i.e. in half of the fuel i have only clocked 100 miles which is just ridiculous, gas mileage is reduced to flat 50%

Yes there is a check engine light, i pulled out the code, it is giving me P 0330

 

I dont have a clue from where to start

I am trying to pin point the following

1. Knock sensor are damaged (which i want it to be the last resort since the whole intake manifold needs to be open up again)
2. Clogged fuel injectors
3. Any one of the Ignition coil not working properly

Please help

[M.Yasir]

[M.Yasir]

Please someone help me out here?

Should i prepare to replace the knock sensors? or i should point to somewhere else

[sha4000]

I would definitely replace BOTH knock sensors while your in there since it's throwing that code. What is all that soot inside of the intake? clean all that up and change the manifold gaskets as well as the coolant pipe gaskets. It looks like a very bad coolant leak which probably killed the knock sensors as well as the starter IMO. I would also test the connectors before I did any of that to make sure they are not damaged.

[M.Yasir]

Unfortunately Craig now the engine is all sealed pack and car is in running condition, soot? you mean that pink color residue? coolant pipe gasket was leaking and radiator coolant came inside the V bank,

Starter motor got killed because of its own wear and tear in my opinion since the bearing of the shaft (which engages to the fly wheel) of the starter got broke

Is there any alignment involved to install the knock sensors?, i just cannot believe that car runs so smooth now but drinking petrol like mugs of beer, in half fuel tank i got only 100 miles

[sha4000]

What do you mean by alignment? The intake has to be removed again to change the sensors, this is why you should change both of them. I've read where someone suggested you could go through the spaces on the side of the intake but I would not attempt it because I could have the whole intake removed in 30-40 minutes. This is likely the cause of your poor gas mileage.

[M.Yasir]

Hi Craig

I have to say it knock sensors are expensive! i believe this is the part number for knock sensors? " 89615-12040"

Is there any part number for the wiring harness also?

I am planning to buy from the below link, but which one? option 1 seems inexpensive

1. https://www.amazon.com/dp/B01D30L72S/ref=sxbs_sxwds-stvpv2_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=2708083022714283574&pd_rd_wg=n3AhK&pf_rd_r=QKEHJMZ60XYQ8Y3895NR&pf_rd_s=desktop-sx-bottom-slot&pf_rd_t=301&pd_rd_i=B01D30L72S&pd_rd_w=BwYto&pf_rd_i=8961512040&pd_rd_r=030dcb6e-5918-4e6e-afc1-56877036a7e2&ie=UTF8&qid=1525432624&vehicle=1998-75-1003-20--1-6-7-3976-1783-1-1-1895--1-0&sr=1
2. https://www.rockauto.com/en/moreinfo.php?pk=945088&jsn=1102
3. https://www.amazon.com/Genuine-Denso-Sensor-89615-12040-Toyota/dp/B073MSLMQJ/ref=sr_1_12?ie=UTF8&qid=1525436335&sr=8-12&keywords=89615-12040

Thanks so much for helping me out, i am having so much of headache right now, here in this country a new engine (from scrap market) will come if i will buy the one from rockauto

 

[billydpowell]

if you are going to follow Craigs advice, be sure and clean that intake up... (I did not follow all your links) and new gaskets also..that's a mess.. 

my knock sensors were under 15$ each.. Denso.. 

[sha4000]

On 5/4/2018 at 9:16 AM, M.Yasir said:

Hi Craig

I have to say it knock sensors are expensive! i believe this is the part number for knock sensors? " 89615-12040"

Is there any part number for the wiring harness also?

I am planning to buy from the below link, but which one? option 1 seems inexpensive

1. https://www.amazon.com/dp/B01D30L72S/ref=sxbs_sxwds-stvpv2_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=2708083022714283574&pd_rd_wg=n3AhK&pf_rd_r=QKEHJMZ60XYQ8Y3895NR&pf_rd_s=desktop-sx-bottom-slot&pf_rd_t=301&pd_rd_i=B01D30L72S&pd_rd_w=BwYto&pf_rd_i=8961512040&pd_rd_r=030dcb6e-5918-4e6e-afc1-56877036a7e2&ie=UTF8&qid=1525432624&vehicle=1998-75-1003-20--1-6-7-3976-1783-1-1-1895--1-0&sr=1
2. https://www.rockauto.com/en/moreinfo.php?pk=945088&jsn=1102
3. https://www.amazon.com/Genuine-Denso-Sensor-89615-12040-Toyota/dp/B073MSLMQJ/ref=sr_1_12?ie=UTF8&qid=1525436335&sr=8-12&keywords=89615-12040

Thanks so much for helping me out, i am having so much of headache right now, here in this country a new engine (from scrap market) will come if i will buy the one from rockauto

 

Just inspect the harness for any damage in the connector and wire. I googled 2000 LS 400 knock sensor and came up with much cheaper alternatives which I would likely go with at this point in the cars life even though the denso from amazon is not that expensive IMO.

[M.Yasir]

Thank you so much for the help

Well i am trying to find a genuine source to procure the item, the amazon link above there is a comment by one user that this is not a genuine product, so leaving a big question mark on the reliability, i am trying to find something on amazon including the wiring harness

Is there any other possibility apart from the knock sensors which would drastically reduce the gas mileage? i dont have any misfire in any of the cylinder that is for sure but is there something else which i should look into, although there is a clear cut code in my OBD reader but still sometimes the code which is appearing might not necessarily mean the same meaning which it is displaying

Example: before i changed the starter with all the new gaskets, i was getting error codes of P0720 and P0730 that is for catalytic system efficiency and a turbine speed sensor circuit code, but when the starter replacement job was done with new silicone applied all the codes were gone, except of course this knock sensor one which is coming now and also i replaced the fan clutch and the fan blade as well

Will update here once i have the spare parts, i am planning to sell the car after the repairs i had enough troubles but yes i gained good knowledge

[M.Yasir]

Update:

I ordered the sensors from the below link

https://www.ebay.com/itm/232461386365

Well lets see when it arrives, will there be any possibility of bad

1. Fuel Injectors
2. Engine coolant temperature sensor?

[sha4000]

I doubt your injectors are bad and I would also change the coolant temp sensor while your in there since it is such and inexpensive part. The knock sensors mess with the timing of the engine so they can definitely mess up the gas mileage though.

[M.Yasir]

Thanks craig, soon after the starter was replaced and the car was in running condition i test drove it and it lacked that "punch" which it usually used to show when you press the accelerator pedal all the way to the ground at once, i thought maybe i am being too conservative but after 4 days of driving it drank half the fuel tank and gave only 100 miles like i said before

I just want to make sure that once again the manifold will be open so this time i dont want to miss anything else, in this country its difficult to find good garages majority of the ones are only for show with good lighting and customer service but 0 technical and foolishly expensive.

And hey during this time i also managed to get a good fan clutch and replaced my old one and indeed the car became so quieter comparing to the previous

Thanks for the support please do let me know if i am missing something

 

[sha4000]

I think you got everything covered. You can change the PCV valve too if that has not been done but I think the knock sensors are the problem. Maybe they were disconnected when you went in the first time. I have yet to change them on my car and it has 240k on it. I seriously thought about it when I changed the starter though.

[M.Yasir]

Sure will do that as well about the PCV valve

Well i received the spare parts from ebay, looks good and i can indeed see denso on the sensors, costed me around 26.48 $ for 2 sensors and wiring

 

I am planning to buy the following as well before i take my car to the mechanic

1. PCV valve
2. PCV valve seal
3. Fuel Filter (i can bet that the current fuel filter is around the same age as of the car 20 years, so i will replace it as well)
4. Coolant temperature sensor

I will try to find the above parts locally here since these appear to be inexpensive

 

1998 Lexus LS 400- PCV valve seal-ACDELCO CV5006C.pdf

1998 Lexus LS400- Coolant Temperature sensor-ARNLEY 1580520.pdf

1998 Lexus LS400- PCV valve- FRAM FV401.pdf

1998 Lexus LS400-Fuel filterARNLEY 0431008.pdf

[sha4000]

Hopefully those work out and you report back with a success story.

[M.Yasir]

Hi All

Well reporting back, following things got replaced

1. Valve cover gasket
2. Knock sensors (unfortunately the wiring harness was not used by the mechanic i think he was not able to connect it, well i will keep it for future)
3. Fuel filter
4. PCV valve with the gasket
5. Two transmission coolant hoses which are below the radiator

Some pics

 

And the flashy new one installed

Now the knock sensors and ECT sensor

PCV valve old

Replaced the two transmission hoses which are below the radiator which were cracked and were leaking with new ones

 

Okay now the car starts and what a bummer, Check Engine Light (CEL) is glowing in its full glory

As you can see in the above dash pic, i have consumed half of the gas tank and was only able to get only 114 miles! well this was before so i will test drive and lets how much i will get now, i should get atleast 100 miles in 1 box of the fuel gauge meter,

Ok now coming back to CEL, i already erased the DTC's right after the car started, took it for the test drive and again the CEL popped up ok so this was the result

Well from the above, the P0715 is haunting me since i purchased my LS in 2015, i replaced the trans speed senor (which is near the trans foundation/ mounting) but still i failed to rectify this DTC

Anyway now the car runs smooth and better than ever i just hope i get a good gas mileage now, i am attaching the new spare parts photos with part numbers just for reference

Next steps

I have some vacuum hoses which are cracked on the Intake Manifold pictures as below and also the intake air valve assembly (the whole plastic part) since it is cracked where it connects to the IAC valve, maybe i am losing some HP there and fuel efficiency there, will buy that whole assembly from junk yard

 

Ok that sums it up, once i have these i will replace them myself and will report back again here,

Well to be honest since my ownership since 2015, i have invested a lot in this car which makes me think that is it worth? well lets see if i recount i have changed the following

1. Starter motor (from junk yard it was of LS 430 which fitted in just perfectly)
2. All 4 oxygen sensors (Bosch from rockauto)
3. All 8 spark plugs
4. Alternator (purchased from rockauto)
5. Radiator fan belt
6. Power steering pump (from junkyard)
7. Exhaust gaskets
8. Exhaust center Y pipe (from junkyard)
9. Front right and left lower ball joints (from junkyard)
10. Front right and left control arms (from junkyard)
11. Front right inner tie rod (genuine toyota)
12. Rear upper control arms both right and left (from junkyard)
13. Radiator fan clutch
14. Radiator fan blade
15. Starter motor (yes 2nd time since the bearing was shot of the 1st one)
16. Intake manifold gaskets
17. Water inlet coolant gasket
18. Valve cover gasket
19. PCV valve
20. Engine Coolant Temperature sensor
21. Fuel filter

Phew!

[M.Yasir]

Hi

Ok reporting back after a short drive, well it appears that the problem is solved now, and yes check engine light is also gone by itself after driving at slow and constant speed, so from the pictures below, exactly 1 box of fuel is remaining and it is showing 100 miles range which is normal, we can say this a success story!

[sha4000]

Check out my thread on the code P0715.

https://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/732312-lexus-gave-me-a-new-to-me-ecu.html

[M.Yasir]

Hi Craig

Yes i saw your post sometime back, but do you think that if i reach out to Lexus at this point of time they will entertain? considering that the car was imported to UAE, i will try to reach them and will report back, 

From your post what i can understand you did managed to change it in the year 2014, so i am guessing i still have a chance

Looking at the PDF of the SSC, my VIN number falls within that range which is specified as compared below

campaign-ssc-wl2-1998-gs400-ls400-sc400-ecm-replacement.pdf

[sha4000]

I did not think they would change mine either. The key is to call corporate first and get the approval. Then you can go into the dealership.

[M.Yasir]

Hi Craig

The thing is unfortunately in this part of the world (middle east) no body cares and customer feedback have 0 value, and yes there is no lexus corporate here

Can i buy an ECU from a junkyard for a lets say 2000 LS? will it work with mine?

[sha4000]

On 6/1/2018 at 6:37 AM, M.Yasir said:

Hi Craig

The thing is unfortunately in this part of the world (middle east) no body cares and customer feedback have 0 value, and yes there is no lexus corporate here

Can i buy an ECU from a junkyard for a lets say 2000 LS? will it work with mine?

I doubt many cars have the updated ECU If you do try a junkyard make sure the part numbers match up.