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Diagnostic Problem


Mike Floutier
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Hi,

You may recall that I had a problem with mis-firing on 1 & 3 - where the "mis-firing" only occurred when running on petrol but not on propane.

The problem was intermittent and appeared to have been solved by changing spark plugs, cleaning the Air-flow filter and adding a bottle of injector cleaner.

However, after a few weeks (around 2,000 miles) both 1 & 3 started mis-firing again today (again only on petrol) - this is confirmed by pulling the coil leads on 1 & 3, performance on petrol & propane identical under these conditions.

It has been suggested that the injectors need changing - my response to this is; "how can both 1 & 3 injectors start misbehaving (and stop misbehaving) at the same time?".

However, I don't know where else to look - surely if it were a general problem (eg. Air-flow meter) it would affect other injectors as well.

Does any one have any thoughts.

Kind regards,

Mike

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Well its probably more work than you like but you could swap the injectors and see if the problem follows them..... use new O-Rings though.

Also wonder if it is knock sensor related. Maybe those cylinders are furthest from the sensor????

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Well its probably more work than you like but you could swap the injectors and see if the problem follows them..... use new O-Rings though.

Also wonder if it is knock sensor related. Maybe those cylinders are furthest from the sensor????

Thanks Curious, good point about moving the injectors, I guess maybe I hadn't thought of that for the reason you hinted at...I've not removed injectors before, they look well buried. Do you need any special tools or just patience and care?

I'm very interested to understand the role and location of the knock sensor - as you can imagine I'm particularly interested in any component that affects more than one injector and is liable to intermittent failure - would you mind explaining your thoughts about the knock sensor.

Thanks again.

Mike

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I'm no knock sensor expert but my understanding is it is essential a microphone that listens for predetonation of fuel in a cylinder prior to ignition. Since the ECU commands the timing of ignition it can tell if a detonation is pre-ignition just by comparing it in time to what was supposed to happen. If the detonation is early then a knock is detected. After this I am sure it gets pretty complicated in the algorithms used to adjust fuel and timing to reduce knock. It’s probably highly secretive and proprietary by Lexus.

If the sensor was not hearing any detonation (either regular of pre detonation) then the ECU probably flags that as a missing fire and if it gets enough it figures out if it’s a missing cylinder or a bad knock sensor...

So my "theory" (more of a guess really) could be one of your knock sensors is marginal. The closer cylinders naturally create a stronger output signal but maybe 1 & 3 are further away and just fall short of a good signal out. I'd look to see the sensor is firmly attached so it gets a good "ear" to the patient and failing that maybe try swapping the knock sensors and see if problem moves to the other bank. Again maybe more work than you want but what else to do have to do on a bank holiday when its misting all day...

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Hi Curious,

Many thanks for helping me think this through, we will get there.

1. Regarding the knock sensor, it's located fairly centrally but slightly closer to 3 than 5 so the cylinders furthest away are in fact 1 & 7. Therefore I'd like to rule that out for the time being, especially as it is so hard to get at.

2. Today I started it up with 1 & 3 igniter coils disconnected - by the way I do this as it stops the engine light flashing (cat damage!!), I still get loads of white petrol-smelling smoke out the back once it's warmed up but no flashing engine light. A QUESTION here is; "does disconnecting the coil cause the ECU to turn off the relevant petrol injectors?"

Anyway after it was warmed up it switched to propane, I pushed in the coil connectors and we're running normally on propane; no mis-firing.

Now I stop the engine and clear the DTC codes - I do this because my plan is to swap over the Petrol Injector Emulators (one per bank)- the role of these btw is to 1. divert the petrol injector signal/current to the propane injectors (on switchover to propane), and 2. To let the petrol ECU know/think that the petrol injectors are still working normally - ie. to stop it throwing up injector codes because they "don't seem to be working" which of course they are not.

Ok, so I clear the codes. I then start up again on petrol but this time it runs perfectly smoothly. I switch back and forward between petrol and propane but it still runs perfectly. I drive around for a while on petrol, re-scanning for codes as I go but no codes!

3. What I think this tells us is that the fault does not lie with the injectors themselves. Something may be causing them to misbehave but they themselves work fine; this must be true because they would not both fail at the same time and certainly not recover together.

4. So, what I have done is to swap the Injector Emulators - fortunately incredibly easy. I will keep driving and see what happens; naturally if the problem behaviour switches banks we'll have the culprit.

5. Finally the thing that is very interesting, and I think well worth further thought, is that the problem simply went away when I cleared the DTCs. Taken on it's own I would not be so keen to persue this BUT exactly the same thing happened when I was originally working on this problem with my propane installer a few weeks ago. ie. whatever we tried, nothing made any difference until the DTCs were cleared and then, as now, the problem just stopped immediately the codes were cleared.

Will let you know how it goes but in the meantime if you have any thoughts I'd love to hear them.

Kind regards,

Mike

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Hi Curious,

Many thanks for helping me think this through, we will get there.

1. Regarding the knock sensor, it's located fairly centrally but slightly closer to 3 than 5 so the cylinders furthest away are in fact 1 & 7. Therefore I'd like to rule that out for the time being, especially as it is so hard to get at.

2. Today I started it up with 1 & 3 igniter coils disconnected - by the way I do this as it stops the engine light flashing (cat damage!!), I still get loads of white petrol-smelling smoke out the back once it's warmed up but no flashing engine light. A QUESTION here is; "does disconnecting the coil cause the ECU to turn off the relevant petrol injectors?" _____>>>>>>>>>>>>> I doubt it. The coil is controlled by an ECU output. There is no spark signal feedback input to the ECU. Therefore I doubt the injectors gets controlled individually based on a spark status input.

Anyway after it was warmed up it switched to propane, I pushed in the coil connectors and we're running normally on propane; no mis-firing.

Now I stop the engine and clear the DTC codes - I do this because my plan is to swap over the Petrol Injector Emulators (one per bank)- the role of these btw is to 1. divert the petrol injector signal/current to the propane injectors (on switchover to propane), and 2. To let the petrol ECU know/think that the petrol injectors are still working normally - ie. to stop it throwing up injector codes because they "don't seem to be working" which of course they are not.

Ok, so I clear the codes. I then start up again on petrol but this time it runs perfectly smoothly. I switch back and forward between petrol and propane but it still runs perfectly. I drive around for a while on petrol, re-scanning for codes as I go but no codes!

3. What I think this tells us is that the fault does not lie with the injectors themselves. Something may be causing them to misbehave but they themselves work fine; this must be true because they would not both fail at the same time and certainly not recover together.

4. So, what I have done is to swap the Injector Emulators - fortunately incredibly easy. I will keep driving and see what happens; naturally if the problem behaviour switches banks we'll have the culprit.

5. Finally the thing that is very interesting, and I think well worth further thought, is that the problem simply went away when I cleared the DTCs. Taken on it's own I would not be so keen to persue this BUT exactly the same thing happened when I was originally working on this problem with my propane installer a few weeks ago. ie. whatever we tried, nothing made any difference until the DTCs were cleared and then, as now, the problem just stopped immediately the codes were cleared. ----->>>>> Probably just means its an intermittent issue and it will take a bit of running to reoccur

Will let you know how it goes but in the meantime if you have any thoughts I'd love to hear them.

Kind regards,

Mike

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I'm not sure if we're at cross-purposes here but there is feedback to the ECU regarding a successful spark or no. There are 4 leads to each igniter coil pack, the 9-14v live feed for the coil, the earth, the ECU igniter signal (that switches a transistor in the coil pack and like a relay turns on the power to the coil) and finally the feedback signal wire to the ECU that advises the ECU if the spark plug has successfully fired.

It is the absence of this feedback signal that triggers the P1300..series DTC in my case although I notice that it's a P0351... series on your model which is later than mine (see page 05-152 of your workshop manual for full details)

So it is possible for the ECU to shut down an individual injector, I'm just not sure if it does or not.

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Ok, the story continues.

I have continued driving with the petrol injector emulators swapped over. Finally the "mis-firing" fault re-appears. Slightly disappointingly the problem remains in Bank 1 - so I can rule out the Emulators.

Another thing I noticed while test-driving this morning is that the "mis-firing" fault comes and goes "by itself"; it was merely a coincidence that it dis-appeared when I cleared the DTCs so I've lost interest in that angle too.

One thing I did notice today, that I haven't heard before is a sound coming from the petrol tank. As well as a normal fuel pump sound (barely audible) I could clearly hear what I can only describe as a "sloshing" sound; and it's not always there. At first I thought it was the fuel slopping around (but it's not), then I thought it was the guy working on his house (but it's not). Any ideas?

Anyway, I'm going to keep the scanner plugged in and as soon as I get the "mis-firing" again (never does it when I want it - lol!) I'll record a fuel trim data series along with a "normal" one for comparison.

Are there any other Bank-specific sensors that could be involved. I'd love to clean the knock sensor's multi-plug but it looks so hard to get at.

So far in the life of this car the only problems I have had have all been caused by electrical connections.

Kind regards,

Mike

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Sloshing is probably the fuel return line spilling back into the tank. This way the pump can run at a nominal flow even if injector draw is less that it. The surplus flow is returned to the tank.

The return flow is also used to run some sort of liquid fed inner tank pump. This is basically a pump that transfers fuel over the hump of the tank so you don't run dry on the side with the main fuel pump all the while leaving fuel on the other side blocked by the hump.

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