High rpm misfire but no OBD fault code

[Ballistic]

When the engine reaches @4500 rpm it starts misfiring, the CEL flickers during this event but does not stay illuminated. No fault codes are stored.

I've spent a while searching the forums and I've come up with a few threads that appear to be related but no exact match:

http://www.mr2roc.org/phpBB3/viewtopic.php?f=11&t=9884
http://www.mr2roc.org/phpBB3/viewtopic.php?f=11&t=34816&hilit=rpm+misfire
http://www.mr2roc.org/phpBB3/viewtopic.php?f=11&t=38078&p=453321&hilit=rpm+misfire#p453321

This happens in all gears, driving under gentle or hard acceleration,  or just revving under no load.
Apart from this, performance appears to be unaffected, fuel consumption normal.
No matter how far down the gas pedal is pushed, revs wont go beyond 4500.
There is a little smoke produced during the misfire - I guess that's unburnt fuel vapour in the exhaust maybe?

What I've done so far:
Cleaned the MAF sensor
Changed the spark plugs
Removed and checked the operation of the OCV (that was fun  s:twisted: :twisted: s:twisted:  )
Had a general mooch around for loose connections, hoses etc.

What I'm going to do
Following advice given in the above threads I'm going to give the earth points on the engine block a severe looking at.
Have a closer look at anything air intake related, like the vacuum hose on the throttle body for instance.
Check security of sensors in the way they're physically attached to the engine block, not just electrically.

A little history
Last November, before I had an OBD II code reader, my local garage diagnosed a CEL illumination as a vacuum leak and fixed it. However, the guy who did the job wasn't there when I picked the car up and no-one could show me what corrective action had been taken but the car was performing OK so I didn't follow it up   s:oops: :oops: s:oops:  
The car was serviced by the same garage in December.
Since November I hadnt had the car on a decent run and a couple of weeks ago, the first time on the M6 was when the misfire first manifested.
I'm not convinced the original problem (vacuum leak) and the current misfire problem are unrelated. I wish I'd given the car a proper blast after it had been fixed in November   s:( s:(  

If anyone has any further ideas on how I should proceed I'd be most grateful   s:) s:)

[wotugonado]

What are the long term fuel trim readings ?

[Wabbitkilla]

How exactly did you check the vvti ocv?

[Ballistic]

What are the long term fuel trim readings ?

Sorry, I'm not quite sure of the terminology   s:? :? s:?  

If you mean fuel consumption over a long period it seems normal.
I've had this problem for about 3 weeks now and I normally use 3/4 of a tank on a trip to Plymouth (300 miles).
That hasn't changed.

Just to clarify, the misfire manifested early into my last trip to Plymouth so I kept it below 4500 rpm for outward and return journey.
I used 3/4 tank for each trip.

[Ballistic]

How exactly did you check the vvti ocv?

I took it out, ran a lead from the battery and observed it's operation when I touched the terminals on the solenoid.
I got the info from the workshop manual which I found on t'internet.
I can't remember where i found the link, it may have even been on here somewhere   s:oops: :oops: s:oops:

[wotugonado]

From your post i assume you have a code reader, if you plug that in and read the live data for the Long Term Fuel Trims it will give you
an indication of where to start looking for the problem. ie perhaps to lean or too rich

[Ballistic]

From your post i assume you have a code reader, if you plug that in and read the live data for the Long Term Fuel Trims it will give you
an indication of where to start looking for the problem. ie perhaps to lean or too rich

Thanks but I'm not sure it does that. It's not very sophiscated, just a Memoscan U480.

[Wabbitkilla]

OK so you tested the ocv out of the engine and saw it click. Did you test it in the engine with it running?

[Ballistic]

No, I didn't do that.
Is there a quick and easy method?
I'm thinking it might be quite difficult getting leads onto the terminals with the OCV in place.

It must be working though musn't it?
The performance is unaffected until 4500 rpm.

Or am I missing something?

[Wabbitkilla]

The ocv controls the oil pressure getting to the vvti controller on the end of the intake camshaft. There is also a little filter just below the ocv for the feed too.

Now the vvti is constantly adjusting across the whole rev range. But like any engine there is a cross over in the power and torque curves which just happens to be around 4500 to 4700 rpm on the 1zz. So a vvti issue could show up odd behaviour especially in this area of rpm. The service manual says to run the engine and put 12v across the ocv, the engine should just about die if the vvti is working. If nothing happens then it is either the ocv, the filter, or the vvti controller on the camshaft. Yeah I know it's a bitch to get to. I had a couple of wires with the mini spade connectors on them for testing the vvit, works a treat.

Of course this kind of issue has also been diagnosed to a faulty crank position sensor or the wires to it. The cps is located just behind the crank pulley before the oil filter. It gets plenty of weather chucked at it.

It may be easier to check the cps wires before you struggle with the vvti test.

There is also the cam position sensor but they're normally not a problem.

Anyway, more diagnostics for you.

[Ballistic]

Ah, thanks very much for that Wabbitkilla.

Plenty to get on with there - that's my Sunday sorted out then   s:D s:D

[Ballistic]

Just in case anyone's checking, I'm still working through this, albeit slowly.

I'll post the outcome, good or bad.

[Ballistic]

I've checked the OCV with the engine running and yep, the engine does indeed almost die when 12V is applied.
Running the engine without the OCV connected produced a CEL fault code P1656 which doesn't appear in my generic code list. Is that a Toyota specific code? Anyway it was easy enough to delete once the OCV was reconnected.
I couldn't get at the OCV oil filter because of the dipstick tube - there must be a way though...

I was able to give a reasonable visual inspection of the Crankshaft Position Sensor and associated wiring and it all looks in good nick, no corrosion or obvious loose connections but with such limited access there wasn't much else I could do. Most of my half-decent tools (including ramps and axle stands) are at home in Plymouth. I've just got a small socket set and a few basic tools here in Leyland.

So, the problem remains.
I don't know if this is relevant but under no load conditions I can slowly rev to 5000 but if I push the pedal down quickly it misfires all the way up the revs until it reaches 4500 - 5000.  Anything to do with throttle position maybe?

I took the PCV valve out a while ago but it seemed OK. Now I'm wondering- how strong should the spring be? Mine only takes a very light pressure to get it moving.

Any further ideas would be much appreciated.

[Ardent]

I took the PCV valve out a while ago but it seemed OK. Now I'm wondering- how strong should the spring be? Mine only takes a very light pressure to get it moving.

I bought a new one thinking the same. The new one was the same.

When the ocv is operated to its max, the engine should stall. Coughing and spluttering is good as it indicates it is at least moving. If it was getting full movement freely it will normally stall the engine.
Maybe a bit sticky. (but then you have had it out if I recall)
Maybe a semi blocked ocv oil filter?

Still not sure either of these would account for a misfire though.

[Ballistic]

I disconnected my test lead before the engine stalled.
I'm pretty sure it was about to stall though.

I think I'll have another bash at the OCV filter tomorrow - although I'm a little worried about damaging the dipstick tube   s:scared: :scared: s:scared:

[Ardent]

I wish you the best of luck.

I trust you have the hands of a child with the dexterity of a speed cuber and the flexibility of a contortionist.   s:shock: :shock: s:shock:

I would worry less about damaging the tube and more about not rounding the head of the nut/bolt you wish to remove and not losing the filter it carries.

[Wabbitkilla]

tbh the ocv filter is rarely blocked and you've proved the supply by the testing you've done.
So now I'm switching to an electrical problem, you should be able to run with the pcv pipe closed off (to the throttle body) but again i have a feeling it's a red herring.
P1656 is to be expected from the testing you've done and this shows the crank position sensor and cam position sensor are working  m http://www.autocodes.com/p1656_toyota.html m  as their relative positions tell the ecu if the ocv and vvti function.

With you getting no codes for the misfire it's obviously difficult to track down.
Some codes take a number of events to show up, there are stored codes on the ecu which are waiting for the even count to add up ... but going by the number of events you're experiencing they should have popped up by now.

I wonder if you've checked all the earths on the engine and gearbox (there is even one under the airbox believe it or not)

[Ballistic]

Thanks for the suggestions guys.

However, disaster has struck. The OCV filter bolt came out relatively easily with a 14mm ring spanner but I dropped the filter! AAARRRRGGGHHHH!
Despite my precautions of placing a piece of kitchen roll underneath as I was removing the bolt, the filter popped out, was caught by the kitchen roll but as I pulled it out it snagged and away the filter went - somewhere...

I spent all Saturday afternoon trying to find it and eventually spotted it lying directly underneath the hole it came from but hidden from view, being really close to the body of the cylinder head,or maybe lower down, hard to tell. It was only visible using a small mirror at a weird angle.

Today, as I was retrieving it using a bit of wire with a blob of grease on it I heard a light clunk as it fell and it once again disappeared from sight. Spent all day searching but access is so limited I can't do any more without some serious dismantling - and I don't have the tools for that.

I'm going to call MrT tomorrow and order a new filter. Really regretting the decision to do this now but I learned/made up some new swear words.

Meanwhile I'll continue checking earth points - might as well, I'm not going anywhere   s:cry: :cry: s:cry:

[Ardent]

I feel your pain.
Might just be as easy to buy another as you suggest.

But failing that one of these might be useful
 m http://www.screwfix.com/p/monument-tool ... ArsB8P8HAQ m

Just a thought

[beavisrules]

First of all I assume you have also checked air filter and put fresh petrol in maybe check for blocked fuel filter?.

The 1zz manual I have says (First to admit manual can be full of BS) the timing is continuously varied (and also says will throw a CEL if it inst) , so not sure it would suddenly manifest a problem at specific rpm?.

Anyways-
It says "check valve timing" at the beginning of all the OCV and VVI diagnostic flow diagrams.

If your ECU inst keeping an error code , it might be worth making it have one on purpose to check it's working.

The ECU output to the OCV is easy to check if you have an oscilloscope , even a hand held one.
It uses a 'Pulse with modulation' starting at 1ms with 2ms gap.

As you'd expect the end of all the diagnostic flow diagrams end with "replace ECU"  lol.
but if there's any test procedures for specific things you want I don't mind copying bits 'for fair use' or whatever.

[Ballistic]

Thanks for the reply beavisrules.

The air filter was my first check, followed by cleaning the MAF sensor.

I've done about 650 miles since the problem manifested so there's been plenty of fresh fuel through the system - I haven't checked the fuel filter though.

I've made the ECU register fault codes, so I know that's working OK.

No, I don't have an oscilloscope, I've barely got a socket set - pretty much flying by the seat of my pants until I can get home to my proper tools. (I do have a small multimeter with me).

It's very kind of you to offer to copy the test procedures for me. I'll take you up on that when I can think of something specific I want to check, if that's OK?

Meanwhile I'm continuing to check underneath for any electrical wiring anomalies/corrosion etc. and waiting for a new OCV filter to arrive.

[Anonymous]

Try a new maf, no error codes for a broken one. Also the random flashin eml is telling you it is multiple missfire. Had it on mine due to really old petrol

[ChrisGB]

First up, VVTi OCV will generally not cause misfire. The way the VVTi system works is to fill out low end and mid range torque and part throttle EGR functions. At full throttle and high revs, it's not doing anything anyway. Failed system would give poor cruising economy and drop in lower mid range torque. A cam position fault would show.

An air leak is a distinct possibility, but my money would be on an earthing fault. Historically, some people with the same issue have found the earth connection for the CPS to be the issue. That's where I would look first. Generally, small air leaks cause rough idling but have less effect on heavy load running.

[Ballistic]

At long last I've found... something

The earth connection on top of the gearbox was loose, not quite finger tight. It's in a good material state, no corrosion or dirt and this could be the biggest red herring ever but it's the first actual anomaly I've found.

I now have to wait for the postman to deliver my OCV filter before I can check if there's any difference.

[Ballistic]

Well,that was disappointing but not entirely unexpected   s:( s:(  
Fixing the loose earth connection on the gearbox made no difference and I'm back to square one. *

Fitting the new OCV filter was even more fun than getting the old one out but that's done now and I never want to see it again!

Meanwhile I've got myself a WiFi ELM 327 OBD2 gadget to see if I can get any more data on my laptop.
Are there any decent software recommends to make the most of it? Any to avoid?

* On a positive note, I have found a loose bolt that no longer has the potential to fly around the engine compartment   s:) s:)