4.7 VX with Lumpy Idle - Been told burnt valves? - HELP ME!!

[Lionheart]

Hi guys

Just got a early 2002 4.7 VX, which also has a decent LPG conversion.

Gutted as when collecting I noted that it had a bit of a lumpy idle, which completely dissappears when driving. I assumed it was probably the spark plugs as I know LPG burns hotter than petrol and so they get through spark plugs quicker.

Put it in to a local garage and they have advised that the plugs are almost brand new, and they suspected burnt engine valves. They diagnosed this by listening to the 'pop' of the idle through the exhaust, and general experience, and recommended a compression test.

They did a compression test, and all valves were in the 13.5 - 14 range, except one in one bank running 7.5, and one in another bank running 8.

They are inlet and exhaust (different sides/ends).

The labour to strip and replace is 19.9 hours per bank - which is 40 hours labour!!! Gutted!

Has anyone come across this or a similar issues? Will it definitely be down to burnt valves?

Are burnt valves different to stuck valves?

Is there an easy fix???

Help needed! Worried!!!

Thank you

 

[wobbly]

Lpg burns hotter than petrol, so burnt valves are a fairly common issue.

If the vehicle has new plugs I suspect the previous keeper became aware of the problem and outed the truck to avoid the cost.

40 hours, at what an hour? Ouch.

Are they proposing to replace all the valves, or just the two burnt ones?

Pete

 

[Shayne]

A job like this would scare hell outa me so the first thing i would try is a fuel additive , after all burnt usual means carbon build up and that's what fuel additives are supposed prevent . Obviously i'm a novice but would it not be worth Lionheart trying a few treatments with something like the stuff in the link below before getting the spanners out ?

http://www.putoline.com/en/products...system-products/fuel-inject-en-valve-cleaner/

 

[Lionheart]

Hi guys

Yes, the suggest replacing them all at the same time as the valves themselves are not silly money - but the labour is the killer!

Yes,c ould try fuel additive I guess? Couldn't hurt??

Yes, I think also that the previous owner knew damn well the nature of the issue as the spark plugs - the garage said - look out of the box (like a week old!)

Not sure what my options are really?

Is there anything else except the valves that could be causing this lumpy idle, or has the compression test ruled this out??

 

[Shayne]

Simple things , fuel can't burn without air , fuel filter even water in your fuel .

 

[silvercruiser]

how many miles does it have? and would it be worth buying a warranty

 

[Lionheart]

Thanks guys

It has 117,000 miles. Should be nothing for a Land Cruiser (it's an Amazon by the way). Had the LPG since 60 or 70 I believe.

Hmmm... Maybe I'll get it back from the garage and check the filters etc. But what about the compression test showing low compression on two chambers? Could air and fuel filters etc affect this??

 

[Shayne]

I doubt filters would effect compression but i imagine a carbon build up would , the rough idle may be completely unrelated to your valves as you say these trucks are tough , i would change the filters , and treat the fuel before you lay down any serious money for repairs . Another thing i would do is give the truck a severe thrashing rev wise to blow out the cobwebs i think its pretty much accepted that these trucks suffer when used as short trip limo's because the oil never reaches its ideal working temperature .

I should say though i am not the man to advise you my approach is just common sense rather than experience , there's plenty on the forum that that know more about landcruisers than toyota themselves . I find the trouble is these guys think its fun to completely strip and engine and so rarely bother to suggest the most simple solutions .

 

[Paddler Ed]

Is it worth trying one of the premium 98 octane fuels for a couple of tanks of petrol (and only run it on Petrol) and an Italian tune up, holding it in the higher rev range, to try to burn some of the carbon out?

I suspect I know why it's 40hrs labour to do the valves; it'll be both heads off, send off for skim and refurb, and then re-fit. New belt/chain (I'm not sure if it's timing belt or chain) and associated tensioners if belt, and then put it back together resetting the clearances on the valves as well.

Good luck with it.

 

[wobbly]

Converting to lpg can be a great idea, my experiences are with American dayvans, not Toyotas, so I cant comment on engine specifics, but the general opinion is to also use a flashlube when using lpg, this helps prevent valve seat recession which leads to burnt valves etc.

The recession is caused by the lpg running hotter and drier.

It sounds to me like the previous keeper(s) havent done this and you are left holding the baby.

There is a bit of info here: http://www.flashlube.com/gb/products/valve-saver-fluid.html

It could be worth you trying it now and seeing if it helps, but I suspect that the damage is already done.

Good luck.

Pete

 

[Scott]

Do you have any comeback on the sale? As the garage are implying that this was an existing fault.

Not the first time I've heard of burnt valves on an LPG'd engine.

 

[Graham]

A job like this would scare hell outa me so the first thing i would try is a fuel additive , after all burnt usual means carbon build up and that's what fuel additives are supposed prevent . Obviously i'm a novice but would it not be worth Lionheart trying a few treatments with something like the stuff in the link below before getting the spanners out ?

http://www.putoline.com/en/products...system-products/fuel-inject-en-valve-cleaner/

A job like this would scare hell outa me so the first thing i would try is move it on....

Gra.

 

[clivehorridge]

My experience of burned valves in petrol engine is just that, as its written on the tin.

Despite all the above suggestions, which may work, usually 50% compression is not just some carbon build up. Once a valve lets any compression past it, the heat in that leak is concentrated on a very small part of the valve, maybe less than a mm. Full force of the ignition is then being forced through this tiny gap and huge temperatures are achieved which literally burn the steel, like in blacksmith's forge.

Over time (and that doesn't have to be long) there will be a missing piece of the valve, usually complemented by a missing piece in the cylinder head (or valve seating if it has inserts) which can only be cured with a new valve and a new seating. If there's no inserts, new seatings can be machined, or new inserts can be pressed in. I've seen inserts used on heads that didn't have them originally. Alternatively, if the seatings are too bad, the head is scrap.

The only way to properly find out is to have the head off.

Isn't there a friendly scrappy that has a 4.7 engine with a broken crank or con-rod with a good head for sale? The cost of a complete s/h head and the labour to replace it would be a fraction of the cost of reworking yours.

Alternatively, move it on before it gets noticeably worse. Sadly, you were duped, and you'll have to dupe a potential buyer. Or you can take the seller to court or set his house on fire.

Either way, you have a problem.

I'd go the replacement complete second hand head route if it were mine.

Calling KARL... !

Sorry to be the bearer of bad news. Lets hope I'm wrong.

 

[Lionheart]

Hi guys

Many thanks for the feedback - very, very much appreciated!!!

Slight update on this - not sure if it affects much but I found this quite interesting.

I bought Wynn's EGR & Valve cleaner, which is a spray product which goes into the air intake whilst holding the revs at 1,500.

After doing it I noticed it's actually freed up a lot of power in the car, and it has a lot more pep again. Better acceleration. I really, genuinely noticed a BIG difference!!

Also, it's made a tiny difference to the lumpy idle. Just a slight reduction 10-15% better maybe. But it's not solved it.

BUT - I was playing around and noted that the RPM sits at 6,000 when idling. If I touch the accellerator to 6,500 it almost dissappears and starts to become smooth, and at 7,000 it's gone completely.

Does anyone know what the correct idle speed is for a 2002 Amazon (4.7 petrol)?????

Thanks guys!!

 

[chadr]

Interesting results with the EGR /valve cleaner......

I'm sure you mean idling at 600 rpm ?

 

[Shayne]

I think every engine has its own personality with regards to idle speed so there is no correct answer . The improvement brought about by the cleaner suggests to me that your engine is just dirty from doing too many short runs and being driven gently . My truck got its first real thrashing at Lincolm recently rev wise and everything since seems to feel somehow better , its hard to explain but its probably a very similar improvement to the results you got from the cleaner . What i would do is - after a long run when the engine is already hot take the rev counter up to 4000rpm and hold it there for the count of 5 , and i would do this 5 times in the hope it would cause the truck to cough up some of the crap that has accumulated over the years .

An old fashioned theory maybe and i will probably get shouted at now by engineers , but its what i would do .

Have you tried removing the air filter altogether to see if the idling problem improves ?

 

[chadr]

Yes, an Italian tune-up does wonders sometimes - my petrol 90 feels a lot more spritely following some high speed/rpm runs on the French autoroutes recently.

 

[Lionheart]

Hi Guys

I've found a very good thread on this. It seems that a fair few people have experience an indentical issue:

http://forum.ih8mud.com/100-series-cruisers/436010-vibration-shake-idle.html

I think this is actually a quirk of the car - and good to see other people experiencing exactly the same issue.

I noted when idling at traffic lights it drops to between 610 and 590rpm and it's a bit lumpy, but then it automatically pops up to 700rpm and smooth as a whistle.

Then the revs slowly drop down to nearer 600 again and it's a bit lumpy.

It's almost like it's idling too low and getting near to the point of stalling so starts to struggle a bit.

Unfortunately you cannot change the idle speed (I've been informed) as it's not cable controlled like the the old days, but ECU controlled so without reprogramming an ECU you can't change it.

The solution would be to set the idle at 680-700rpm and that's solved!! But can't be done.

So - I have a feeling it's a quirk and so we'll all just have to live with it! It does not affect the drive of the car at all and only noticed when stationary.

My conclusion - especially as it seems that it's affected a fair few people - is that it's just a quirk of this particular model.

 

[chadr]

They did a compression test, and all valves were in the 13.5 - 14 range, except one in one bank running 7.5, and one in another bank running 8.

Have you identified/resolved the cause of this?

 

[Shayne]

Can't the idle speed be altered at the carb ? just a suggestion because i used to do it on bikes maybe someone who actually knows what a cruiser carb looks like can tell us .