fuel economy & ISC

[BUSHWHACKER]

I always replace the main O2 sensors with new heated (four wire) ones. I've never had to use resistors in place of the sub sensors.

I think your running problems are to do with the LPG system. Was the engine running perfect before it was installed?

I forget now, but do you have an engine check light wired in?

And have you got a decent exhaust (no leaks) on that truck yet?

[dannyboy77]

i have the 4 wire main oxygen sensors but they arent toyota but universal as i have different exhaust manifolds. the exhaust is still clipped but as far as i know its all sealed now! ?!the check light works as the temp sensor code came up when it was giving 5v. i dont have the sub sensors in at all and i think i read on lexteme to use resistors to give the reading the ecu wants.

i got the lpg done early on so im not too sure on the fuel economy initially
but i am thinking that it does have something to do with it. he said the only signal they take is off one OX sensor, but they do go in the injection system of course. this is in the table of possible causes but i dont understand how that would make it rev at 2000rpm at idle. i thought it would be a fuel air discrepancy???

[BUSHWHACKER]

Did the high idle start after you removed and re-fitted the IACV?
It could be a vacuum leak somewhere.
I use the cheap O2 sensors from Rock auto.

Do you have the original EGR crap fitted?

[dannyboy77]

i think it was always like this as i remember blocking off the ISC and then putting an adjustable valve on it so when it got to temp it idled fine and when the LPG of fitted we did the same. so really im putting an old problem right. i remember blocking off the egr and the different manifolds dont have an opening for it so i will check the egr plate is still on. i will have to check the air temp sensor and the air flow meter and see if the senor readings are OK. is it washing up liquid on seals?? need to check the voltage reading on the OX senors see if there are any problems there. jut got to go though the FSM trouble shoot till i can find whatis wrong??

[BUSHWHACKER]

I block off the EGR system with a piece of shaped aluminium, (you can see the polished blanking piece in the photo below) junk all the rubber pipes, seal the plugs with tape and hide them. All thats left is the PCV hose that goes from the valve cover to the inlet plenum.

Check everything thats connected to the inlet plenum is sound and tight, as this is normally where the vacuum leaks occur.

[dannyboy77]

will do! will check for leaks and loose the pipework! just change one thing at a time to see if that makes a differance!

nice manifolds what are they off?

[BUSHWHACKER]

will do! will check for leaks and loose the pipework! just change one thing at a time to see if that makes a differance!

nice manifolds what are they off?

A 1995/6 LS400 (UCF20) It has the 'hot wire' type AFM too.

[dannyboy77]

just to keep you up dated the throttle position sensor is bust well the idle part is constant 5v and no resistance when checked the VTA reading was OK! next on list air flow meter! think the LPG can fry that with a backfire as the LPG goes in just passed the buttlefly!

not bad another to add to the list O2 sensors (heater part), ISC, throttle sensor no wonder mpg was down and not runnin right! keep me busy going around the engine checking all the sensors! there are a lot!

even though 'engine check' is working i think it needs a 0v or 5v to trip it off?

[BUSHWHACKER]

I would re-new the EFI coolant sensor (the green one) and the main O2 sensors first to sort out the over fuelling. Don't forget to re-set the ECU afterwards and run the engine up to temp a couple of times.
Then the TPS.
Then the ISCV.

The AFM should be OK, just give the honeycomb a squirt of brake cleaner and allow to dry.

[dannyboy77]

sorry vince kind of waffled through the last thread i have replaced the EFI temp sensor, both Oxygen sensors, the ISC and now will have to replace the throttle sensor. will test the air flow this week

with the old LPG conversion there is a small chance of a backfire and blow the air flow meter so thats why going to give that a once over to make sure it hasnt. will disconnect the battery to reset the ECU everytime i add / replace a new sensor! will get there in end

[BUSHWHACKER]

Oh, OK.

You could always mount the AFM further away from the throttle body to prevent any fire damage.
It doesn't matter where you fit it in the intake ducting.

[gary-r]

maybe worth checking - i had a duff cam position sensor which causes a high idle speed and for some reason i also got a tps fault code with it.

changed the cam sensor and the tps fault code disappeared. i guess it was upsetting the ecu.

i also had O2 fault codes with new sensors fitted ( cheap pattern ones). one of the guys in the lexus dealers here gave me 2 ngk ones to try and it cured the faults straight away.

[an1mal_69]

hard work these trucks are..!!

[dannyboy77]

umm still idling slighty high at certain times when at temp?? it does drop revs then picks up again so not sure what is wrong. the TPS i got from second hand place was bust too well the voltage reading on the IDL signal at closed position was 4.5 and needs to be between 2-4v (as resistor reading was low) so going to trick it with a resistor see if that calms it down?? its doing 16mpg around town though so an improvement on what it was and havent pumped tyres up or anything!?!

[BUSHWHACKER]

It'll take eight or nine starts/warm-ups for the ECU to re-learn everything thats been changed before it settles down.