"mis-Firing" On Cyl 1

[Mike Floutier]

Ok well I tried running on Petrol for a few hundred miles but it makes absolutely no difference - at least this rules out the physical fuel injectors as a problem source.

Next I got a new MAF but again no change. I did consider the knock sensor as I understand this can cause mis-firing but it's so hard to remove that I thought I'd leave that for now - especially as there are no other fault codes.

What I'm really looking for is some change I can make to the system that will give some change in symptoms so at least I can get some idea of where the problem might be.

I do wonder about WHY the code/flashing MIL go away after the engine is warmed up AND also why the sensation of mis-firing remains AFTER the codes go away.???

It's due for an oil change very soon. I've been using a cheap 15W40 mineral oil up until now BUT I've ordered a bottle of Mobil 1 0W40 for the next change. Will probably make no difference but you never know - it can't have anything to do with the rough idle BUT it may make a difference to the cold starting now that winter temperatures have set in.

[steve2006]

Mike have you considered the possibility of valve seat erosion from running on propane, perhaps a compression test would confirm?

[curiousB]

I did consider the knock sensor as I understand this can cause mis-firing but it's so hard to remove that I thought I'd leave that for now - especially as there are no other fault codes.

The knock sensor detects misfiring. The ECU then adjusts timing to compensate. Maybe semantics here but just wanted to be clear on cause and effect.

I have heard of a guys cross wiring the knock sensors from bank 1 to bank2 and vice versa. Easier said than done as you need to somehow splice into the cable harnesses/connectors but that might be easier than disassembling the intake manifold to get to Knock sensor.

I do wonder about WHY the code/flashing MIL go away after the engine is warmed up AND also why the sensation of mis-firing remains AFTER the codes go away.???

Are you sure the engine mis fires? I was thinking a possible theory is everything is OK but the ECU is flagging a problem that doesn’t really exist (false negative) due to some subtle differences in how propane works vs petrol. Recall some of that Toyota dribble that described sensing cam shaft acceleration. Maybe propane doesn’t have the same acceleration as petrol (less energy) so the cam isn’t moving to where the ECU predicts it should. (This begs the question why wouldn’t you see it on more cylinders of course).

Maybe you could swap the camshaft position sensors from bank 1 to bank 2 (and vice versa) to see if the offending cylinder moves with the sensor?

Recall:

To monitor misfires, the ECM uses both the Crankshaft Position (CKP)

sensor and the Camshaft Position (CMP) sensor. The Crankshaft Position

(CKP) sensor is used to measure variations in the crankshaft rotation

speed. On the power stroke, the crankshaft accelerates. If the cylinder

misfires, the crankshaft decelerates. The Camshaft Position (CMP) sensor

is used to identify specific misfiring cylinders.

It's due for an oil change very soon. I've been using a cheap 15W40 mineral oil up until now BUT I've ordered a bottle of Mobil 1 0W40 for the next change. Will probably make no difference but you never know - it can't have anything to do with the rough idle BUT it may make a difference to the cold starting now that winter temperatures have set in.

Rough idle can be caused by dirty throttle body and sticking IACV. Maybe once the engine warms up a sticky IACV starts to move more freely. Doesn’t explain MIL/CEL light but maybe you have a couple things going on simultaneously that is confusing the matter.

[Mike Floutier]

Thanks Guys,

Firstly Steve, I did a compression test on Cyl 1 about 2 weeks ago and it was just over 180psi (the book says 178psi). A lot of folk say that the compression test is not much good and what I need to do is a leak-down test.

Now I understand that the leak-down test is much more specific in that, 1. It is not affected by outside issues such as a weak battery, and 2. You can pinpoint the source of the compression leak by listening etc. However, firstly the Lexus manual specifically says a compression test and gives an exact spec. Secondly, since I have a good result (ie. 180psi) there can be no leak, no weak battery and I don't have to detect exactly where my leak is (since I don't have one).

I guess my question is - can I have a leak but still get a good compression test reading? Surely if that were the case THEN Lexus would not suggest the test.

---------------

Ok Curious, I love your thinking, I'm realizing that I have to start thinking laterally now.

A. Firstly I have to be honest and say that my concern is that the cause of the problem is valve seat recession caused by the use of propane as a fuel (no lubricant). I've used an upper cylinder lube system for most of the 150,000 miles I've done on propane BUT it's a single point injection system and the main manufacturer have gone over to a multipoint system leading me to believe that the single point system may be missing some of the valves.

The funny thing is that Cylinder 1 (along with 2 ) is the closest to the lube pipe inlet.

B. I like the idea of rewiring the knock sensors - but I don't think I'll try that straight away - lol!

C. I did wonder about this idea of a false ECU deduction - in your post about the blinking MIL it says "When the temperature of the TWC reaches

the point of thermal degradation, the ECM blinks the MIL. " - 1. how does the ECU know that the TWC is too hot, and 2. My MIL starts blinking 10 or 15 seconds after starting the engine from completely cold.???

D. I also liked the idea of the rough idle AND the blinking MIL + P0301 being separate issues - especially since the codes go away after warmup but the rough idle doesn't. Correct me if I'm wrong but I didn't think the LS430 had an IACV - having said that I don't see then how it gets it's air needed to idle and how it's regulated.

I've attached a clip from the manual which may be interesting as it shows a pair of narrow air pipes which apparently help reduce emissions (ie. unburnt fuel presumably, which is what we're principally interested in here anyway) AND improve idling stability; also an issue here. Being narrow, could these tubes be affected by gunk after 300,000 miles? Not that I could do anything about it if they were - lol!

Finally, is it possible to clean the throttle body at all without removing it?

[RICKMARTIN3949]

Thanks Guys,

Firstly Steve, I did a compression test on Cyl 1 about 2 weeks ago and it was just over 180psi (the book says 178psi). A lot of folk say that the compression test is not much good and what I need to do is a leak-down test.

Now I understand that the leak-down test is much more specific in that, 1. It is not affected by outside issues such as a weak battery, and 2. You can pinpoint the source of the compression leak by listening etc. However, firstly the Lexus manual specifically says a compression test and gives an exact spec. Secondly, since I have a good result (ie. 180psi) there can be no leak, no weak battery and I don't have to detect exactly where my leak is (since I don't have one).

I guess my question is - can I have a leak but still get a good compression test reading? Surely if that were the case THEN Lexus would not suggest the test.

---------------

Ok Curious, I love your thinking, I'm realizing that I have to start thinking laterally now.

A. Firstly I have to be honest and say that my concern is that the cause of the problem is valve seat recession caused by the use of propane as a fuel (no lubricant). I've used an upper cylinder lube system for most of the 150,000 miles I've done on propane BUT it's a single point injection system and the main manufacturer have gone over to a multipoint system leading me to believe that the single point system may be missing some of the valves.

The funny thing is that Cylinder 1 (along with 2 ) is the closest to the lube pipe inlet.

B. I like the idea of rewiring the knock sensors - but I don't think I'll try that straight away - lol!

C. I did wonder about this idea of a false ECU deduction - in your post about the blinking MIL it says "When the temperature of the TWC reaches

the point of thermal degradation, the ECM blinks the MIL. " - 1. how does the ECU know that the TWC is too hot, and 2. My MIL starts blinking 10 or 15 seconds after starting the engine from completely cold.???

D. I also liked the idea of the rough idle AND the blinking MIL + P0301 being separate issues - especially since the codes go away after warmup but the rough idle doesn't. Correct me if I'm wrong but I didn't think the LS430 had an IACV - having said that I don't see then how it gets it's air needed to idle and how it's regulated.

I've attached a clip from the manual which may be interesting as it shows a pair of narrow air pipes which apparently help reduce emissions (ie. unburnt fuel presumably, which is what we're principally interested in here anyway) AND improve idling stability; also an issue here. Being narrow, could these tubes be affected by gunk after 300,000 miles? Not that I could do anything about it if they were - lol!

Finally, is it possible to clean the throttle body at all without removing it?

[RICKMARTIN3949]

Hi

Not sure if you have sorted your misfire as of yet, but in the uk, we had the same fault and code cleared its self after a while, it turned out to be 2 vacuum sensors under the inlet manifold, once replaced code no longer appeared, its possible you have the same fault.

Richard

Lexus tech.

[curiousB]

Here is the IACV. I like this idea from Rick Martin though. I'd go down that path first. It seems to match your symptoms well.

[Mike Floutier]

The more you look, the more electronic bits this car has!

Apparently although it is an IACV, it's not an Idle Air Control Valve BUT rather an Inlet Air Control Valve. In point of fact, it's not even the Inlet Air Control Valve BUT the Inlet Air Control Valve actuator (part of the Acoustic Control Induction System (ACIS) - see attached pic from the manual. A description of the system can be found on wikipedia. I seem to remember reading somewhere in the manual that it opens at around 4,500rpm to give better torque or something.

I'm still not sure how the idling is regulated, maybe it's just a function of the Throttle Body.

-----------

Thanks Richard,

Do you have a link to the thread, I'd love to read it. It certainly sounds interesting. Also I've not heard of Vacuum sensors on the LS430 before, do you know where in the manual I could find them? We were expecting to find a vacuum leak behind the problem because as well as the mis-firing I was getting very high, although slightly sub-code-setting Long Term Fuel Trim readings. I guess a faulty sensor could mimic a vacuum leak.

[landar]

Something I should also perhaps reiterate is that the problem - ie. P0301 & flashing Engine Light ONLY happens whilst the engine is warming up AND, even whilst it's warming up it will go away under a light load.

Oftentimes when facing a mysterious problem, I find the little clues to be most revealing. And you do reiterate the above clue as well...so it might merit more investigation. If this misfire goes away as soon as you put a load on the engine then it has me thinking injector or slight manifold leak. On the other hand, you mention that P0301 happens with petrol or propane, correct? Are there two separate injectors for each fuel system? If so, then the injector most likely is not the culprit. If the injector is shared, then perhaps the injector "sticks", when cold and lightly used, until it gets a bigger electrical "kick" from the ECU, which would happen under load.

Then again, perhaps there is an air leak at the manifold at cylinder #1 that seals when the engine warms. Under load, the air leaking in would be insignificant compared to the throttle air which might make the misfire disappear for the moment. I know you have performed the propane test once but I would encourage you to grab that bottle again and specifically concentrate on the intake manifold sealing surfaces of cylinder #1.

I may not be understanding your comments because I just noticed in your first post that you say "This would happen ONLY when the engine was completely cold AND under load - eg. pulling uphill at low revs." Seems to be in conflict with the quote above. Can you verify/clarify? Thanks.

[Mike Floutier]

Hi Landar,

Sorry I may not have been that clear. The mis-firing/blinking MIL starts when the engine is completely cold; any kind of load promotes it and it disappears during coasting. Then, when the engine is warmed up it disappears entirely except for occasional situations of high load, eg. pulling uphill at low revs for a longish period.

The problem is the same whether on propane or petrol; they have separate injectors so it's not the injectors.

I have considered doing a cylinder leak-down test but I would need to spend quite a bit on equipment that would only be used once. There is little point as in doing this since it would not be economic to repair the cylinder heads. The only value would be the ability to give up pursuing the problem; on reflection maybe that's not that trivial - lol!

[landar]

Mike,

Thanks for clearing that up. I sometimes wonder if the ECU might be the problem. Generally, and certainly in your situation, the computer is clearly functioning because the engine is running relatively well. However, the coils and fuel injector actuator need a "driver" circuit such as a power transistor(which is a peripheral circuit to the computer) and I wonder if perhaps your ECU driver (either fuel or spark) could be malfunctioning at times. Due to the misfire under load, I would have to go with the spark as it may not be driving the coil hot enough for the richer mixtures that a loaded situation would demand.

[Mike Floutier]

Hi Landar,

I take your point about drivers. The thing with the LS430 is that the transistor that switches on the LT supply to the coil is actually integrated into what we tend to call the COP coil on plug unit. Lexus call this combined unit an "Igniter". It's a 4 wire unit. The wires are, 1. Ground, 2. Battery voltage (constantly live), 3. ECU coil firing signal, and 4. A feedback signal to the ECU confirming that firing has taken place (A P13nn code is set if this misses).

I've tried swapping igniters so it's not that.

-------------------------------------------------

I'm still wondering about Richard's suggestion about 2 vacuum sensors under the throttle body. I've not seen any mention of vacuum sensors in the manual, can anyone throw any light on that?

-------------------------------------------------

My current checking is centering on the Cam and Crank shaft position sensors which I hope to check tomorrow. I see from the manual that their readings are affected by temperature. Since their operation affect ignition timing, and hence mis-firing AND my problem (mis-firing) comes and goes with temperature changes, I'm most interested to see how they shape up.......

[Mike Floutier]

Still pressing on, both the Crankshaft Position Sensor and the Camshaft Position Sensor returned good resistance readings so no joy there.

My next test will be another compression test on the cylinder with the mis-fire codes. I think I did the original test when the engine was warm (ie. P0301 NOT being set). So I'm going to try it cold and compare readings.

If no joy there I think I will do compression tests on the other cylinders to compare.

If still no joy I may consider investing in a compressor and a cylinder leak-down tester if they're not too expensive.

It's interesting to note that I first observed this problem around 12,000 miles ago and it has not significantly worsened in that time although I think there is a slight but steady deterioration - it's hard to tell???

[Mike Floutier]

Well I did the compression test COLD and the pressure was very slightly lower but not significant. However I am rather put off doing further compression/leakdown tests as I had a lot of trouble getting the tester off the plug hole and there is no way I want that to happen!!

Two other thoughts:

1. In my casting around the site I did notice a procedure involving something called "Seafoam" being ingested into a hot engine via a "brake boost" vacuum pipe. Is this something that I could try on the LS430? Is there a thread about this?

2. Also are there any instructions around on cleaning the LS430 throttle body?

Thanks again!

[landar]

Mike, sorry to hear that you have not found joy as of yet.

As for the Seafoam...surely you jest. There are posts ad nauseam about using Seafoam. Not only on this forum but every automotive forum on the web. Many owners love the stuff but I would not even consider using it on my LS. Seafoam is basically just Acetone in a bottle touted as a magic elixir. Its a volatile subject.

[Mike Floutier]

Thanks Landar, yes I've read all I can find about seafoam; some swear by it and some swear at it - seems you have to be very careful how you use it. I was curious (no pun intended) to see if any respected loc members had personal experience on the LS430.

Anyway, whilst writing a thought occurred to me - would a fractured exhaust manifold or gasket cause mis-firing? I'm guessing this would equate to un-metered exhaust gases which presumably upsets the system. I vaguely remember something like this on my old Ford Scorpio but this was a long time ago so I'm a bit foggy.

Any thoughts on this as a possible cause and how would I test it?

[Mike Floutier]

Ok, well no joy so far but there have been some additional symptoms:-

1. If I start the engine when it's already warm it starts but often just stops straight away - but usually starts ok the second time. The alternative is that it starts but straight away the revs sink to zero but at the last minute it catches and all is well.

2. Usually I only use a small amount of throttle and very rarely kick-down. Today I needed to put my foot down and was surprised at what happened. As soon as the throttle pedal got half-way down I lost most of the power. I took my foot off the pedal and drove as normal and all was fine.

I then experimented with various pedal depressions. With less than halfway it was fine, plenty of power, pulling hard at low revs, easy to get up to high speed.

However as soon as I got over halfway there was very little power, hardly any acceleration.

Funny thing was that the kick-down was working as normal; the harder I pushed, the more it would change down. The revs would increase a lot, just as normal, as the transmission kicked down BUT there was still no power and no acceleration.

If I lifted off to halfway the power would suddenly kick in.

Any idea what's going on?? No new codes btw.

[Mike Floutier]

Ok, I forgot to update this thread as things had got complicated/urgent.

Anyway, as you may have read, it turned out that the very severe problems I had been getting (on top of the mis-fire that I started this thread for) were actually caused by the cheap MAF sensor that I put on to try and cure the mis-fire. The new MAF seemed fine but failed after only a couple of weeks.

So now I'm back to the original mis-fire problem.

Just to recap:

1. I get a P0301 & flashing CEL under load/low revs during warmup. After warmup it will sometimes come back while waiting at lights in drive (not in neutral).

2. I've done all the usual tests to no avail.

3. I should mention that the car has done over 300,000 miles with over half that on propane gas - which is implicated in Valve Seat Recession.

Therefore, I strongly suspect that my number 1 cylinder exhaust valves are not closing properly (the others may be close behind).

To confirm this I would like to do a cylinder leakdown test BUT I'm put off by the cost of a workshop air compressor which I would probably only use this once.

Do you think it would be ok to use a "tire inflator" type compressor to feed the leakdown gear or would I be better off just taking it to my friendly independent Lexus tech?

I also tried to measure the valve clearances but failed even to get to the bolts holding on the 2 x oil dipstick tubes let alone the lower cyl head cover bolts - I guess it helps to have small hands:)

[curiousB]

Hi Mike. You've been battling this for a while. At some point with 300k miles does it really matter? Not trying to sound flip but lets say it is the valve seat. Are you going to pull and head and do a valve regrind on a 300k car/engine? Why not live with as is until it's time to pass the car onto its next life? It doesn't sound like it is hurting you much other than a nuisance indicator while the car warms up on cold days? If the engine dies you can buy a used head from a wrecker or a whole new engine if you are really motivated. Other time for a newer LS.

[Mike Floutier]

Thanks Curious, sorry I've taken so long to reply, you have certainly caused me to think. I guess I could sell it now, the mis-fire is almost un-noticeable (apart from the P0301 & flashing CEL - lol!)

I have thought through the financial side and given that I've just had the cambelt & water pump done, replaced all 4 wheel bearings (cost $2500 in total due to having to replace the steering knuckles as well), and that I save around $5,000 pa by running on propane (cost $4,000 to convert), I think it's probably reasonable to spend a bit to keep the engine running well.

The bodywork and interior are still so good that many customers (I have a car service business) ask me if I've bought a new car. I'd like to keep it for a further two years (120,000 miles).

Ok, having said that, I decided to invest in a leak-down tester and an air compressor. It's been a bit of a learning curve (which I enjoy). I had never had to set a piston at TDC before so that was fun. I read that you should put a long thin screwdriver down the spark plug hole and turn the engine until the handle peaked. Suffice to say I was duly horrified to see the thing disappear down the hole. Fortunately the piston wasn't at TDC and it re-appeared in due course albeit only by 1/4" or so - phew.

Anyway, I tried my new tester on the offending cylinder and was rewarded by something they don't mention in the blurb (well not that I've read anywhere on the web anyway). The leakage rate was showing 55% compared with 18% on it's neighbor.

I checked all the (apparently) usual suspects and, apart from a small amount of air getting past the rings (common to both cylinders) heard through the oil filler hole, what I had was a large amount of air emanating from the spark plug access orifice.

At first I assumed that I hadn't sealed the test lead properly but it was fine on the other cylinder and I had a few more tries to satisfy myself that it wasn't my fault.

Does anyone know what the cause of this could be; I've never had a head off so I'm pretty unfamiliar with the possibilities?

[landar]

The spark plug threads in the head could be damaged or perhaps there is a crack in the head near the spark plug hole. It is far more probable that the leak tester is not properly threaded into the hole or a gasket in the tester is not seated. I am guessing that the leak-down tester screws into the spark plug hole but you might try to get a V-shaped conical rubber stopper to plug the hole as well. Thats a "one size fits all" plugging solution and might eliminate the threads from the test. However, if the cylinder leaks around the tester threads, there is good chance it might leak around the spark plug as well.

You might want to wet the tester male connector with some soapy solution and using a flashlight(er, "torch" in the Queen's English) to peer into the hole and see if you can notice bubbles in a certain area of the threads. You can also buy a small camera on a flexible wand to snake into that area, and indeed the cylinder, to have a close-up look. They are not too terribly expensive and it is a toy for the toolbox. Cannot have too many of those!

Finally, did you carefully examine the #1 spark plug threads for evidence of exhaust gas blowing past the threads? If leaking, it might show evidence of slight charring along a section of the threads.

[Mike Floutier]

Thanks Landar,

I guess that answers my first question, ie. where could it be coming from, it's a relief to be finally getting close on this.

I have only just changed my spark plugs - in a vain attempt to correct this problem (they were 50,000 old so no real loss). I kept the old ones and there is a small degree of charring on the early threads but this is slight and applies to all the plugs to a greater or lesser extent.

One thing I did notice on the offending cylinder's plug was the slight presence of oil on the threads; this was absent on the other 7.

Time for confession. I don't torque the plugs when fitting them, I simply hand tighten then and add 1/2 - 2/3 turns according to the plug manufacturers instructions. Knowing now that the head is aluminium and that I tend to err on the tight side, not to mention the fact that it's had about four plug changes, I guess there's fair chance that I've damaged the head/threads in some way.

You mentioned the tester connector but I've ruled this out in that it works fine in the other cylinders; ie. perfect seal, leakage only heard through the rings (common to all cylinders).

My plan now is to use a little teflon tape on the tester connector and see if the readings change at all. When I bought and set up my compressor/tester/pipework setup I initially had 3 or 4 leaks at different spots but they all yielded to Teflon tape so I'll be interested to see the effect.

Obviously this would affect a cracked head but it might save investing in camera equipment etc.

Will let you know how it goes.

Thanks again.

[Mike Floutier]

Ok, firstly I should have said, "Obviously this wouldn't affect a cracked head but it might save investing in camera equipment etc."

Well, you guessed, it didn't make any difference, anyway I cleaned up the plug seating using a greased screwdriver but it seemed pretty clean and made no difference.

Now it seems that the only thing left is a crack in the head around the plug hole. I will now invest in an endoscope camera, as you suggested Landar.

However, in the meantime I did a little experiment. I coated my leakdown tester hose evenly with dark grease and repeated the leakdown test. Same leakage, as expected, but I got an interesting pattern on the grease - I've upload a couple of photos. One shows what it looks like around 90% of the circumference and the other is a specific little arc.

The pattern in the grease seems to support the crack theory.

I will now order a camera but in the meantime I'd like to canvass for suggestions (apart from a new head) as to how to reduce the leak, even by a small amount. Since I understand that the seal is made by the gasket rather than the threads, it occurred to me that a larger diameter gasket might conceivably help.

Any ideas?

[Mike Floutier]

Ok, firstly I should have said, "Obviously this wouldn't affect a cracked head but it might save investing in camera equipment etc."

Well, you guessed, it didn't make any difference, anyway I cleaned up the plug seating using a greased screwdriver but it seemed pretty clean and made no difference.

Now it seems that the only thing left is a crack in the head around the plug hole. I will now invest in an endoscope camera, as you suggested Landar.

However, in the meantime I did a little experiment. I coated my leakdown tester hose evenly with dark grease and repeated the leakdown test. Same leakage, as expected, but I got an interesting pattern on the grease - I've upload a couple of photos. One shows what it looks like around 90% of the circumference and the other is a specific little arc.

The pattern in the grease seems to support the crack theory.

I will now order a camera but in the meantime I'd like to canvass for suggestions (apart from a new head) as to how to reduce the leak, even by a small amount. Since I understand that the seal is made by the gasket rather than the threads, it occurred to me that a larger diameter gasket might conceivably help.

Any ideas?

[Mike Floutier]

Ok, well this is a learning curve for me.

It turns out that the leak is not from the spark plug hole at all. In spite of using a stethoscope and clearly hearing the air coming from the hole it looks like what I was hearing was the air rushing through the pipe screwed into the plug hole; I guess the plug hole just served as an amplifier of sorts.

How do I know this? Well I didn't wait for the endoscope camera I ordered but found I was able to take these pictures with my trusty iPhone 4. I expected to see a crack or a hole or something but, as you see, it's clean as a whistle. The black bits are the CV joint grease I used to help seal the leakdown hose

So, knowing that this 55% leak was coming from somewhere, I simply fed 60psi into the plug hole and listened at the tail pipes. Well, they say a low frequency sound means a large leak and they are right. In this case I could feel the air on my hand as it blew out of the pipe.

So, no question, I have a leak from the exhaust valve(s) on No. 1 cylinder. In fact the leakage at TDC at the top of the exhaust stroke is only 10% more.

The only question now is, "what do I do next?". My friendly local independent Lexus tech agrees with you Curious, ie. I should get rid of it or just run it into the ground.

Also he doesn't think it's caused by valve seat recession, rather that the exhaust valves are simply messed up and therefore not sealing properly.

However, for the (propane related) reasons I've already mentioned, I believe that the problem is likely to be recession and I'd like to prove this by removing the valve covers and checking the clearances. If it is then I think it's worth getting thinner shims installed in the valve lifters to restore full valve closure. On the figures I have mentioned previously this would be very cost effective.

The problem is that I've not done this before and it looks fairly difficult so if anyone has had the valve covers off an LS430 I would greatly appreciate some guidance.