"mis-Firing" On Cyl 1

[Mike Floutier]

Hi all,

I have a 2002 LS430 which is just coming up to 300,000 miles.

I had it converted to run on propane around 150,000 miles ago. I have been using an upper cylinder lubrication system but this was not working for around 30,000 miles, on and off.

Recently I started getting a flashing Engine Light along with a P0301 code (mis-fire on cyl 1). This would happen ONLY when the engine was completely cold AND under load - eg. pulling uphill at low revs. Any combination of flat/downhill terrain AND/OR engine warmup and the "fault" would clear.

As the weeks have gone on (I do around 1,000 miles per week) it has got worse; ie. "fault" is more easily precipitated and takes longer to clear AND can sometimes appear WITH a warm engine under load (only very occasionally).

I monitor the fuel consumption quite carefully and I am not seeing any significant increase.

The physical "mis-fire" sensation is only noticeable when stationary, in drive, at idle. To give an idea, on a scale of "1 > 10", if removing the coil lead for 1 cylinder was a "10", then this feeling is around "3 or 4".

I should clarify that although the flashing engine light and P0301 codes are only occasional, the feeling of mis-firing is constant.

There are no other codes.

Around 50,000 miles ago I had a very strange problem with misfire codes on most of the cylinders in No. 1's bank. This would happen on gasoline BUT not on propane and completely cleared up following change of spark plugs and air filter and has been fine ever since.

The present problem is the same whether running on gasoline or propane - each system has it's own dedicated injectors.

So far I have swapped the cyl 1 ignition coil with it's neighbor to rule that out AND I have replaced the cyl 1 spark plug - no difference.

I'm not sure what could be the problem OR what I can try next.

Any ideas would be gratefully received.

Kind regards,

Mike

[curiousB]

Since you have changed coil and plug there is not much left for spark other than plug wire and cap. Simple enough to do. Swap the wire and the cap and see if it stays on #1.

Off chance it could be a bad wire arcing to chassis or a faint crack in cap that has a carbon trail to ground. I'm not hopeful this is it but at least your can rule out a couple more scenarios.

[Mike Floutier]

I have an LS430 like you CuriousB, I guess you may be referring to the Ls400 as I don't think there's anything else I can "swap-to-test" on the ignition front.

I suppose there could be a problem with the low tension wiring, that shows up under high load conditions - pity there's no way of swapping that.

When the propane conversion was done a wire was tapped on to one of the LT wires to coil 1 for some purpose, I guess I should examine the wiring for any cracking that may be leading to shorting.

Apart from that, the only other cylinder specific diagnostic I can think of is compression testing. I hope it's not that as this might point toward valve seat recession which can be a problem with the "lubrication-free" propane.

[landar]

Mike, first off, congrats on the 300k mark. I had to read that twice. You did say "miles" and not "KM". My '02 is just about to turn over 36k miles....still a baby.

Now then, don't you just love these intermittent problems? They can be a real bugger to find as you well know. Just a couple of thoughts: you have swapped the COP and plug but have you carefully examined the low tension connector? Just a small amount of patina or corrosion on the terminals could cause your problem. And perhaps there is some chafing of the wiring harness going on over the miles and years and sometimes the low voltage signal grounds out momentarily.

Seemingly unrelated to the spark, I wonder about your valve timing. Is your timing belt in good shape and changed recently? I would think a slippage there would signal a cam timing related code but perhaps it shows up as a misfire. While on this subject, I wonder about sensors misbehaving. Like Crank and Cam. I do not advocate going in there and replacing those "shotgun" style however. At least not without further detective work. I also wonder if cylinder one is really the misfiring cylinder despite a P0301 code. I would be wanting to hook up some instrumentation to capture several (or all) of the spark timing signals and log them to see if one "hiccups" occasionally. This would however, require an outlay of cash for a real-time data logger that you could hook to a PC.

I like your idea of a compression test, especially @ 300k miles.

I fully admit, that some of these things seem like a long shot, so feel free to dismiss them.

[curiousB]

I have an LS430 like you CuriousB, I guess you may be referring to the Ls400 as I don't think there's anything else I can "swap-to-test" on the ignition front.

OK didn't realize you were 430.

Engine Misfire Diagnosis

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.

When the engine misfires, high concentrations of hydrocarbons (HC)

enter the exhaust gas. High HC concentration levels can cause increased

exhaust emission levels. High concentrations of HC can also cause

increases in the Three-Way Catalytic Converter (TWC) temperature,

which may cause damage to the TWC. To prevent this increase in

emissions and to limit the possibility of TWC thermal damage, the ECM

monitors the misfire rate.

The misfire monitor is designed to detect increases in emissions caused

by cylinder misfires, not to reduce driveability concerns.

Misfires are counted when the crankshaft rotation speed variations exceed

predetermined thresholds. When the temperature of the TWC reaches

the point of thermal degradation, the ECM blinks the MIL. If the misfire

exceeds the threshold levels, and could cause emission deterioration, the

ECM illuminates the MIL and sets a DTC.

The engine misfire monitor is a continuous monitor.

The catalyst temperature is calculated by the ECM based on driving

conditions and percentage of misfire.

Use the following steps to diagnose a single cylinder misfire:

1) Duplicate the misfire using Engine Live and Freeze Frame data.

2) Compare the spark plug firing tip of the misfiring cylinder to spark plug firing tips from cylinders with no misfires present.

3) Swap the igniter from the misfiring cylinder to a different cylinder with no misfires present (swap the igniter with cylinder # 4).

4) Swap the spark plug from the misfiring cylinder to a separate different cylinder with no misfires present (swap the spark plug with cylinder # 6).

5) If the misfire moves to a cylinder with a swapped component, replace the component (e.g. if cylinder # 4 begins to misfire, replace the igniter, etc.).

6) If the misfire stays with the original cylinder, check the cylinder compression pressure and fuel delivery.

7) The diagnostic procedure outlined here is for training purposes only and may not be effective for every issue. Always refer to Service Bulletins (SB) and Repair Manuals (RM) for information on specific vehicles and issues.

[Mike Floutier]

Haha Landar, you are so right about the Coil Pack Multiplug problems; I have a funny story about one of mine. My No.2 threw up P1305 soon after I bought the car with 143,000 miles on the clock. I had no code reader in those days and simply went though taking each plug off it's coil, cleaning it and putting it back along with a good wiggle. Obviously I would start the engine as I took each one off until I discovered which one made no difference.

As you can imagine, I left good ol' no. 2 until last as it's buried beneath the air intake resonator box (not to mention my propane injector rail and injectors for that bank). Anyway I was glad to discover that no. 2 was the offender (ie. causing the mis-firing). I duly cleaned and wiggled it and was rewarded with 110,000 trouble free igniting.

However around 40,000 miles ago it started acting up again and the usual wiggling etc. would only give me 1,000 miles or so until it started missing again. This gap got shorter and I got fed up with all the dismantling just to wiggle the plug.

So, I tied a bit of string around the wiring, led it around various bits of the engine and tied it off at a suitable point where I could tension it with a piece of towel which also prevented the string chaffing against the replaced resonator over which it ran.

Lo and behold, this constant tension on the plug combined with the ability to remotely wiggle it when failing tension allowed the plug to fail to connect properly has giving excellent service ever since.

Still not really sure what is wrong with the thing, ie. is it the connector or the wiring??

Anyway, I'm just agreeing with you really, these things can give trouble. However I'm not sure if any part of the igniter (circuitry) can be implicated as surely any failure would prompt a P13nn code. Also, I've had a good look at the plug and it's wiring and it's in very good condition as it's always been well protected. The wiring is still supple and intact.

CuriousB, thanks for the diagnostic info, I have done all the swapping as it suggests so that now leaves the compression test - I guess I can get a standard figure from the manual somewhere.

Ok, while I was driving home from work just now I had the following thought:-

1. I am focusing on diagnosing a "specific cylinder" problem - ie. ruling out other cylinder specific causes.

2. My question was, "If I have a general problem (eg. a vacuum leak) that is fairly slight and only justsufficient to cause a mis-fire, then, since not every cylinder's condition (compression, igniting, etc) is exactly the same, it is possible, presumably, that only one cylinder will be bad enough to trigger a DTC.

3. So, let's say no. 1 cylinder is most susceptible to mis-firing and along comes a general problem that doesn't bother the others BUT tips no. 1 over the edge - does that make any sense?

4. So, what would be the general problems that could lead to mis-firing - ie. usually in the "multiple/random mis-fire" section of the diagnostic manual?

Anyway,and finally for now Landar, I did have the timing belt and water pump replaced earlier in the week. It had done 165,000 miles and I was only spooked into doing it as my serpentine auxiliary drive belt failed totally without warning the other day. I did hope that the mis-firing would go away with the new belt but it made no difference at all - in fact the old belt looked like new to me although the guy who did it thought it was starting to crack a bit.

Ok enough for now, thanks for your thoughts guys!

[landar]

3. So, let's say no. 1 cylinder is most susceptible to mis-firing and along comes a general problem that doesn't bother the others BUT tips no. 1 over the edge - does that make any sense?

That makes a lot of sense, Mike. Keep an open mind for other things that are perhaps, seemingly unrelated. At 300k miles, your machine is in the heavy-use category. Connectors of all sorts can be very temperamental with age/use and could be the source of your headaches. That goes for sensors as well.

It might be a good idea to invest in a good OBD scan tool for your PC. You can buy a handheld unit but those just give you the "idiot" codes. With the PC app, you can get more data and possibly glean more diagnostic info to pinpoint the misfire.

If I were in your situation, I would R&R all of the plugs if you have not done so already. Despite the guessing game, I always like to start with the assumption that an issue is fairly basic and try those things first. Because they usually are simple.

[Mike Floutier]

Thanks Landar, as you thought I've already looked at all the plugs.

Thinking about general misfire diagnostic, I wanted to check for vacuum leaks and EGR. Would I be correct in thinking that there is NO EGR on the LS430?

[landar]

Thanks Landar, as you thought I've already looked at all the plugs.

Thinking about general misfire diagnostic, I wanted to check for vacuum leaks and EGR. Would I be correct in thinking that there is NO EGR on the LS430?

I believe you are correct, no EGR valve. Did you actually replace the plugs? Or just look at them? Sometimes you can not tell just by looking.

[Mike Floutier]

No, I just cleaned them. I have tried to get new plugs but Lexus want £60 each - that's around $800 for the set!!

So, no EGR. There do seem to be several vacuum hoses connected to the air intake body but most of them disappear down below so I'm finding it hard to check them for leaks.

There is a thing called "VSV for EVAP" which seems to operate a valve allowing/or not a connection from the air intake to the charcoal cannister. At least I can test this fairly easily.

I've looked at all accessible vacuum hoses/connectors which seem ok.

I will bite the bullet now and test the compression on No. 1.

Thinking back 40,000 miles to when I last had a "mis-fire" problem along with flashing Engine Light, I remember that this was accompanied by loads of whitish smoke from the tail pipes which smelt very badly of gasoline. I have had no such symptoms this time.

I wonder if it's possible to get the flashing Engine Light without unburnt fuel entering the TWC. I guess you can have a mis-fire code set even though the igniter fires correctly - eg. poor compression.

The reason for all my wondering is that I really need to be pragmatic here; my main purpose is to keep the car going NOT to solve all it's problems (it is very old after all). My primary concern, I think, is to avoid ruining the TWC; I can live with a little rough idling for the last year or so of it's life.

Anyway, I'll report back when the latest tests are done.

[curiousB]

I was wondering how they determined misfire in the ECU. I thought maybe some strange property of propane measured differently that the ecu was declaring a fault when in fact none existed might be something to consider. But as you can see they looks at acceleration of camshaft after firing. I think it would be hard to spoof that reading. Either the cylinder fired and sped up or it didn't and it continued to slow down. Seems pretty black and white. Now that you see misfires with both fuels its even more compelling.

So I think you probably do have a misfire just not clear on the cause.

As for plugs if you had them out to reclean them I assume you liekly didn't put them all back in the same cylinders. If you did its easy enough to swap a couple. Not to likely that is the issue but guess better to be certain than have all these unclosed possibilities floating around.

I think you should do compression test as next step per Lexus. You might have a burned value or damaged head gasket. Its easy enough to do especially on cylinder 1. Maybe you just do #1 and a couple other nearest neighbors which are easy to get at.

[Mike Floutier]

Thanks CuriousB, I'm sorry I've just realized I might be at cross-purposes here. When I said I hadn't changed the plugs, I meant the igniter coil multiplugs. I have changed the No. 1 spark plug and also swapped igniter coils around.

I'm going to do as you confirm and check the No. 1 cylinder compression next - I understand it should be around 178psi.

Will let you know how it goes.

[curiousB]

I'm going to do as you confirm and check the No. 1 cylinder compression next - I understand it should be around 178psi.

I think I'd just concentrate on cylinder #1 reading vs its neighbors. If there is a valve or gasket problem it should read significantly lower than the others. I wouldn't get too hung up on the absolute value as this is an engine with many miles on her. Cylinder to cylinder variance is most relevant here.

My wife's Lincoln had a problem with bad cylider head (burned exhaust valve). Ford prescribed a cylinder leakdown test instead of compression. I think this is why:

Cylinder leakdown test-

While a compression test is a dynamic test (engine moving), a cylinder leakdown test (C.L.T.) is a static test (engine at rest). The compression test measures how much pressure the engine can produce while cranking; in contrast to the C.L.T., which measures how much pressure is lost in the engine. In a C.L.T. the engine is placed on TDC of the cylinder in question and using a similar type of connector as the compression test, we fill the cylinder with pressure. The tester then measures the volume of air needed to maintain a predetermined pressure in the cylinder. This reading is expressed in a percentage. Good cylinder leakdown readings should be below 5-8%.

The great thing about C.L.T. is that it deals with how well the cylinder is sealing and nothing else. The readings are not affected by carbon deposits, cam timing, or even engine cranking speed.

Another great feature of the C.L.T. is the fact that you can hear where the air is leaking out of the cylinder. When a cylinder has high percentage of leakage, first check the oil filler cap. Do you hear a hissing sound? If so, you may have pressure leaking by the rings. Is there air escaping out the exhaust? Is it escaping out the intake system? Then a burned valve may be the problem. If two adjoining cylinders have similar low readings and you hear leakage out the other cylinder, then a failed head gasket may be the problem.

Being able to pinpoint the exact source of the compression loss will tell you where the problem is; and not just that you have one. This knowledge will greatly assist you in the next step… the repair.

I am not sure how expensive a CLT setup is in the UK but they are reasonable here.

http://www.harborfreight.com/cylinder-leak-down-tester-94190.html

[Mike Floutier]

Wow, never heard of that, seems like an excellent idea for pinpointing the source of a cylinder leak. We can get them over here but my problem is lack of easy access to compressed air.

Anyway, I did the standard compression test this morning and it was 180psi so it's certainly not a compression problem.

I would like to try a diagnostic idea to be certain it's the No. 1 cylinder causing the blinking Engine Light and P0301.

Since I always get these two things happening under load whilst the engine is warming up what I thought I would try is removing the multi-plug from the N0. 1 coil pack before setting off.

I've got a feeling that IF a P1300 is set (for the coil pack) THEN a P0301 will not be set (even though a separate misfire condition is present on that cylinder) UNTIL the P1300 (coil fault) is remedied. However I'm assuming that, 1. A separate misfire would still be recorded, and 2. A blinking engine light would still occur in the event of unburt fuel getting into the TWC.

Also, my understanding is that, if the coil is not firing (P1300 in this case) then the ECU will turn off the fuel injector to that cylinder.

Will try that and report back.

[Mike Floutier]

Ok, this is taking a little time as I wanted to be certain and I have to let the engine go completely cold between each test which takes around 8 hours.

Well I've tested it 3 times - ie. removing the No. 1 cyl coil pack multiplug - and on each occasion I fail to get a flashing Engine Light. Correct me if I'm wrong but the only deduction possible from this is that the unburnt HC (fuel) is coming from No. 1 cyl (ie. when the coilpack multiplug is on).

So, what could be the problem?

I've read that it's possible for the Crankshaft Position Sensor to give trouble if there is dirt on the teeth of the wheel it reads. My feeling is that this would be unlikely as I've have been changing my oil every 5,000 miles and every other change I've been using engine flush to keep things clean.

The other thing that is suspect has to be the low tension electrical supply to the coil pack. As I've said the multiplug and wiring at the coilpack end seems fine and I've cleaned it and refitted it. However, I'm wondering if the connection at the Engine ECU end may be suffering under load. Would I be right in thinking that the ECU is located behind the lower glove compartment (I'm RHD remember)?

One thing that I'm also wondering about is, "why does the problem happen when the engine is cold BUT it goes away when it warms up"? What could this be about?

[Mike Floutier]

Well I found the engine ECU under the hood and cleaned up the relevant connector BUT no change.

I don't really have any idea what to try next.

I was looking through the "live data" on my scanner and a couple of readings may give some ideas (hopefully!!)

1. The reading for the MAF with the key on BUT the engine off was 0.56 grams/sec (compared to around 6 when idling). Since the figure obviously ought to be ZERO that makes me think the MAF needs re-cleaning or replacing - I guess it's only a smallish error but I don't have the experience to know how significant it may be - any ideas?

2. The Long term fuel trims were around -3% for one bank and + 14% for the other. That sounds like a significant difference. I read (http://repairpal.com/OBD-II-Code-P0171-and-P0174) that anything over 15% was likely to throw up a code (P0171/174??)

So, my reasoning here would be -

a) I'm not getting a code because the lean-ness is just too low,

B) This level of lean-ness is sufficient to cause mis-firing AND a flashing Engine Light due to unburnt fuel through the engine.

I guess I should perhaps look at possible causes of P0171.

All ideas very welcome!

Regards,

Mike

[curiousB]

1. The reading for the MAF with the key on BUT the engine off was 0.56 grams/sec (compared to around 6 when idling). Since the figure obviously ought to be ZERO that makes me think the MAF needs re-cleaning or replacing - I guess it's only a smallish error but I don't have the experience to know how significant it may be - any ideas?

I wouldn’t be concerned with MAF reading when engine not running. I am not sure it is considered a valid state. In any event it is less than 10% of idle reading (which is already small) so not very material.

2. The Long term fuel trims were around -3% for one bank and + 14% for the other. That sounds like a significant difference. I read (http://repairpal.com/OBD-II-Code-P0171-and-P0174) that anything over 15% was likely to throw up a code (P0171/174??)

This might indicate a vacuum leak on the +14% side. The ECU is detecting a lean condition at the O2 sensor and commanding the EFI to send more fuel in to compensate. Vacuum leak could be head gasket related, intake manifold leak, injector gasket leaking or maybe a few other areas.

My wife’s car had a +14% long term fuel trim. It was due to a sizeable vacuum leak. The root cause was a ruptured vacuum hose to the crankcase ventilation system. With the engine running the leak was significant and quite audible. So I have to think there is something significant going on for a 14% LT fuel trim.

[Mike Floutier]

Thanks CuriousB, to be honest I've only really had a cursory look at vacuum leaks as this is an area where I have no experience at all.

I think I understand the theory, ie. the introduction of un-metered air leading to a leaner mixture which the ECU spots via the O2 sensors and compensates for - hence the +14% LTFUEL trim.

What I haven't done is identified exactly which pipes I need to pull off and examine. Would I be right in thinking that there is crankcase ventilation pipe for each bank (PCV)?

Since bank 2 (btw I'm assuming that Bank 1 is the lefthand bank as viewed from the driving seat) fuel trim is normal, I'm guessing I only need to look at pipes that only serve one individual bank.

Finally I should reiterate that by turning off the coil pack to cylinder No. 1, the mis-firing report AND flashing Engine Light stop happening. I don't know how significant this is but my assumption was that it means that the cause of the problem is related to that specific cylinder.

I have to say I'm struggling to think this through in terms of cause and effect.

[curiousB]

I think I understand the theory, ie. the introduction of un-metered air leading to a leaner mixture which the ECU spots via the O2 sensors and compensates for - hence the +14% LTFUEL trim.

Yes that is the mechanism. The O2 sensors say the engine is lean and the ecu bumps up the fuel map to compensate. Its the unmetered air which is creating the problem.

You can search for intake leaks with a simple propane torch. With the car idling (outside on in garage) run the torch (without flame just gas flowing) around suspicious points of the engine. If there is a leak it will suck in the propane and engine should surge a bit from the hit of fuel. Just be careful because propane is heavier than air so in a still garage it would settle to lowest spot and be an explosion hazard. Hence doing it outside.

[Mike Floutier]

Thanks, sounds like a great idea, I'll try it tomorrow and let you know how it goes.

[Mike Floutier]

Ok well I tried a propane torch but couldn't find any leaks - it certainly seems to work ok though as I pulled my upper cylinder lube hose off the inlet manifold and squirted some propane in; you sure can hear the effect on the engine!

Anyway I checked the Fuel Trim readings and it turns out that it is Bank 2 that is rather high - it's fairly stable at around +10% (Long term) AND this is the same at a variety of RPMs and Loads (including idle). The problem cylinder is on Bank 1 which is showing around +2%

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.

I can't think what else to try. I see you can get MAFs quite cheaply on ebay so I thought, since mine has done nearly 300,000 miles AND suffered my none too gentle cleaning (ie. Brake Cleaner), it wouldn't do any harm to try.

[curiousB]

I can't think what else to try. I see you can get MAFs quite cheaply on ebay so I thought, since mine has done nearly 300,000 miles AND suffered my none too gentle cleaning (ie. Brake Cleaner), it wouldn't do any harm to try.

Very strange. Puzzling for sure. I can't see how it would be MAF because that is common element for all cylinders so it doesn't play favorites. I wonder if it is some strange condition related to propane. What if you just run on petrol for a week or two to see if it heals itself at all?

[Mike Floutier]

Mmmm, yes I take your point about the MAF not playing favorites BUT my feeling is that some cylinders will be more susceptible to the effects of a poor sensor reading than others and if the sensor problem has just reached the fault threshold of the "weakest" cylinder...

Anyway, bearing in mind I spend around £10,000 on fuel each year and the MAF costs £31 I'm going to replace it.

The other thing I'm wondering is about the fact the problem goes away when the engine is warm - well the fault codes go away but the rough idle (in drive) remains.

Could this be a problem with the coolant temp sensor? Again they're very cheap so if the MAF doesn't work I may replace that next.

I know you don't like the "suck it and see" approach but comparing the value of the car to me in my business with the cost of these small items I may press on with this.

However, I will do what you suggest and try running on Petrol for a few hundred miles, I've got a bottle of injector cleaner spare so I'll pop that in before filling up.

[curiousB]

I know you don't like the "suck it and see" approach but comparing the value of the car to me in my business with the cost of these small items I may press on with this.

I did the same thing recently on an emissions issue I had. Eventually you get tired of developing theories and feel like you have to try something even if it isn't relevant in the end. Closing off theories is helpful too.

I know you changed the coilpack for the suspect cylinder to no avail. I wonder if your pulled the connector at the COP pack and spray bother ends with electronics contact cleaner. Plug it together and pull it apart 5-6 times (this is called wiping action and gets fresh metal to metal contact). Then trace wires back to ECU and do same thing at that connector. Maybe you just can a marginal driver wire to the COP and when things warm up it just moved into tighter contact. Just a guess, but costs nothing to give it a go.

[Mike Floutier]

I know you don't like the "suck it and see" approach but comparing the value of the car to me in my business with the cost of these small items I may press on with this.

I did the same thing recently on an emissions issue I had. Eventually you get tired of developing theories and feel like you have to try something even if it isn't relevant in the end. Closing off theories is helpful too.

I know you changed the coilpack for the suspect cylinder to no avail. I wonder if your pulled the connector at the COP pack and spray bother ends with electronics contact cleaner. Plug it together and pull it apart 5-6 times (this is called wiping action and gets fresh metal to metal contact). Then trace wires back to ECU and do same thing at that connector. Maybe you just can a marginal driver wire to the COP and when things warm up it just moved into tighter contact. Just a guess, but costs nothing to give it a go.

Thanks, I've tried this already, both ends (including the multiplug at the ECU). I also swapped over the propane system's fuel injector emulator units in case one of them was causing fuel injector problems.

Will let you know how it goes over the next week or so.

Thanks for sticking with me!