excsee fuel consumption

[spritley56]

hi  this is rather a complicated and drawn out post so bear with me 

we have a 1996 ls 400 some weeks ago we lost a secondary 02 sensor had this replaced only to find   we had the dreaded split egr pipe (forgot to say car has been converted to lpg ) we did the delete rather than replace the pipe still have valve connected but blanked off sinc doing the delete car runs OK but will not accelerate properly and uses excessive fuel (like 1 mile to £1 of fuel) not good also wont switch over to gas as quickly as before its an obd1 and have managed to get some codes out which are as follows 21,27,28,29,31.71 replaced air filter and tried to clear the codes but they are still there ordered another maf thinking that might be the problem but am now at my wits end trying to sort this out car ran well before the lambda senser blew out although it had a blow on the exhaust which was welded up heres hoping that someone on here can help please just 1 other thing car used to start 1st time every time before this trouble now it takes 2 or 3 goes to get her going

[steveledzep]

Phew !!!  I'm out of breath 

[runsgrateasanut]

I don't have any expertise on your Questions but a few thoughts

Firstly, sure it isn't running on 7 cyls? not as noticeable as some might think.

Secondly, have you ever cleaned the throttle body?

Thirdly when was the last time you changed the Air filter?

Forthly, was this replacement Lambda sensor a Lexus part or a £20 quid job? Cheapies may be OK of course.

Finally check the Throttle sensor for positioning- beware if removing the throttle body not to disturb. There is a very good vutube video on checking this but sorry I don't have a link on this Computer. If its been disturbed it may need checking.

 

 

 

[runsgrateasanut]

 

 I will give a few further thoughts and have questions.
 
Perhaps your year car is an electronic  "drive by wire" throttle position sensor and not adjustable?  In which case could be a faulty sensor. I put here the link to the manual checking method,

Apols I re-read and see you've changed your Air filter.

£1 a mile is this based on evidence or just a guess?

The throttle body should be cleaned. Perhaps no hot air going into the engine via the EGR pipe may slow down the changeover to LPG as the car may not reach temperature quite as quickly?  (I may be wrong here)

Which side of the exhaust box was the 02 sensor?  When you say it blew out, sounds like part of your exhaust broke away? They are screwed in, Although, after a Garage service I had a Spark plug blow out of a Mercedes 230TE. The guys had obviously not screwed it in. What a Bang as it hit the bonnet. Frightened the life out of me. Left its mark.

Not sure where the Lexus Sages have gone but perhaps someone more knowledgeable will follow this thread and correct me where I'm talking rubbish.

https://www.youtube.com/watch?v=_skVHdgtMTU

[plexus914]

Just an idea.... old and leaking ECU capacitors might be the culprit. Common problem with the LS400.

● Lexus LS400 - 1990-2000 (in 1997 and earlier models, the problem is extremely common)

http://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

 

SYMPTOMS:

Please understand that any one of these symptoms can be a sign of ECU capacitors beginning to fail. - You do not need all or most of them to have this issue!

Your ECU capacitors are strongly suspected if you have at least one of the following intermittent issues on your Lexus or Toyota:

● problems in getting into diagnostic mode or scanner says "no communication"
● random dropping into "limp home" mode
● weird shifting problems
● OBD port is unresponsive, seems dead
● throwing random fault codes
● engine won't rev out/rev limits at 2000 or less rpm
● engine runs like crap, then suddenly runs fine again
● random not starting or cutting out
● low idle or erratic idle
● often very hard to start, requires starting fluid
● transmission will not automatically shift, only manual shift is possible
● transmission jerks from 1st to 2nd gear, and kinda slips from 2nd to 3rd
● no A/C compressor operation
● idle speed rolling up and down, or sometimes too low and sometimes too high
● speedometer not working reliably
● speed (cruise) control not working
● tachometer not working sometimes
● air bag light flickering intermittently
● A/C going into reset with flashing front defog light (front defog light typically flashing 10 times)
● check engine light on sometimes, but no codes stored, often in concert with ECT light
● ECU not communicating with scanners or not displaying codes with jumper installed
● bad sulfur exhaust smell in concert with not running right above

 

 

But before that, diagnose faulty parts and get rid of those OBD-trouble codes you have already stored.

21 - main O2 sensor & heater signal

27 - sub O2 sensor signal

28 - main O2 sensor

29 - sub O2 sensor

31 - air flow meter signal

71 - EGR system malfunction

 

 

[Cotswold Pete]

12 minutes ago, plexus914 said:

Just an idea.... old and leaking ECU capacitors might be the culprit. Common problem with the LS400.

From my experience of Mk3, the ECU capacitor issue meant it kept stalling at junctions after engine warmed up, but never impacted the mpg (as far as I could tell)

With Mk4 I have not experienced any problems that seem ECU related and having just had throttle body cleaned it does seem make a difference to when idle, and a mild improvement in MPG, but my car has never been as bad as 1mpg, even when climbing 18% hill from a cold start (gets as bad as 6mpg when doing this).

[runsgrateasanut]

5 hours ago, plexus914 said:

Just an idea.... old and leaking ECU capacitors might be the culprit. Common problem with the LS400.

● Lexus LS400 - 1990-2000 (in 1997 and earlier models, the problem is extremely common)

http://www.clublexus.com/forums/ls-1st-and-2nd-gen-1990-2000/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html

 

SYMPTOMS:

Please understand that any one of these symptoms can be a sign of ECU capacitors beginning to fail. - You do not need all or most of them to have this issue!

Your ECU capacitors are strongly suspected if you have at least one of the following intermittent issues on your Lexus or Toyota:

● engine won't rev out/rev limits at 2000 or less rpm

 

Interesting list of symptoms.  My engine always seems to run fine /starts fine but struggles under load up hills (or it could be my light foot and a fear of backfire left over from my LPG Mercedes single point system)

Don't think I've ever revved it hard so will give it a try when hot, some time.   A set of Capacitors waiting in the wings for better consistent weather and the courage to tackle the job!
 

 

 

 

[plexus914]

Keep in mind, when disconnecting starter Battery or deleting diagnostic trouble codes (DTC's) ECM/ECU will reset to factory default. To get all the engine's power back ECU needs some time to adjust again and a run on the motorway with some nice KICK DOWNS will help. 

"Resetting the ECU" is the process of clearing all the long term memory from the ECU's memory. These variables trim idle speed, fuel, spark, and more. The ECU will also store trouble codes for diagnostic capability. By resetting the ECU, the trim values will be set to some neutral default value and all of the trouble codes will be cleared.

I reset the ECU, and now the car runs rough! Why? The engine may run rough or idle poorly right after ECU reset. The ECU now has default numbers in its trim memory - it has to adjust them to match the tune of your engine and its sensors and actuators. It might take a day or two of driving in traffic before the engine will settle down again. Now you know why the ECU remembers these values in the first place!"

 

PS: Regarding fuel consumption winter tires driven in temperatures above 7 degrees won't do any good either.