Heads

[SRK]

The compression is fine - that has been established. Don't forget that for 99% of driving, the throttle is nearly closed, and the engine does not see maximum compression because you are limiting the amount of air to control power. Cranking compression is high as a function of the test itself, but operating compression is not while the throttle is less than wide open. So carbon or compression is not responsible for whatever may be wrong.

[daffy]

The compression is fine - that has been established.  Don't forget that for 99% of driving, the throttle is nearly closed, and the engine does not see maximum compression because you are limiting the amount of air to control power.  Cranking compression is high as a function of the test itself, but operating compression is not while the throttle is less than wide open. So carbon or compression is not responsible for whatever may be wrong.

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Hi SRK,

Well, I am relieved that the heads don't have to come off. And it is nice to know that at 390,000 kms, the compression is pretty good. I just finished taking the throttle valve body off and cleaned it out. Boy was it ever dirty! I don't think that's the problem, but might idle better now. So what's left? I am going to replace distributor and rotor because they are probably original. Thanks for your input, it confirms that this engine is in pretty good shape. I am not giving up on it just yet. I'll bet it is something simple that is wrong with it. I am back to work tomorrow so I probably won't get it back together until this weekend. I sure miss it already.

[ArmyofOne]

this is baffling, im thinking the carbon is your issue though, especially if you run ~89 octane or less on a regular basis.

[daffy]

this is baffling, im thinking the carbon is your issue though, especially if you run ~89 octane or less on a regular basis.

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Hi,ArmyofOne

I bought the car at 186,000 kms and since that time I used Esso at 92 octane, but this year they dropped it to 91 octane. Which I still use. So this car has been getting the proper fuel for a long time now. It's never seen less since I owned it.

Daffy

[ArmyofOne]

this is baffling, im thinking the carbon is your issue though, especially if you run ~89 octane or less on a regular basis.

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Hi,ArmyofOne

I bought the car at 186,000 kms and since that time I used Esso at 92 octane, but this year they dropped it to 91 octane. Which I still use. So this car has been getting the proper fuel for a long time now. It's never seen less since I owned it.

Daffy

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then the damage was probably done long before you got it...

there is little doubt that TOP engine decarbonizer will cure your issue, but i was merely givving you a cheaper alternative to try.

i think i need to run that engine decarbonizer through mine as i havea slight knock too, but does anyone know where i can find it? i dont want to pay $100 either! LOL

[SRK]

Octane has nothing to do with carbon deposition. Carbon is a function of fuel air ratio, and the engine maintains fuel trim by the O2 sensor so closely that modern engines produce very little carbon. Adding powerful solvents and other gunky chemicals to an engine to "clean" it internally do more harm than good.

Use Chevron Techron fuel additive if you must - it is approved by Bosch of Germany, and then drive the hell out of the engine for a bit. That will clean it more safely and more reliably.

[92Lex]

I agree.

Excessive carbon build up is usually because of an engine that has been running too rich for an extended period of time. Another cause would be worn piston rings or leaky valve seals.

[daffy]

I agree.

Excessive carbon build up is usually because of an engine that has been running too rich for an extended period of time. Another cause would be worn piston rings or leaky valve seals.

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Hi 92Lex,

I just finished putting my engine back together. I changed out the waterpump, timing belt and two idlers, fan support housing, spark plug wires, rotors and distributor caps. I also cleaned out the throttle body. To my surprise the engine fire right up and got no airbag light on the dashboard (because the battery was out for a few days). I took it down the road and the car worked perfectly!! I guess the scope doesn't always work. I and very happy now and will probably work more on my car myself rather than leave it to the "experts". I was so close to taking the heads out, I have to thank my one mechanic friend for convincing me to do my own compression test. I would like to thank this forum for giving me some insight to my problem. I will be back next problem I get. Thank-you

Daffy :D

[92Lex]

Everyone's here to help. I'm glad you tackled the job yourself and saved yourself hundreds of dollars. Nothings more satisfying then doing it yourself huh? I love that feeling.

[daffy]

Everyone's here to help. I'm glad you tackled the job yourself and saved yourself hundreds of dollars. Nothings more satisfying then doing it yourself huh? I love that feeling.

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Hi, 92Lex

I agree, so why does Lexus here have a scope? They should have picked up my problem really easy, fixed the car properly and kept a satisfied customer. Now it's likely I will never go back. I didn't feel to good to hear from them that it may need a valve job at about $5,000+ when it really would have taken less than $150 for parts to fix it. Well I sure learned a valuable lesson here. Thanks, Daffy :)

[92Lex]

Probally just human error, I'm sure they wanted to give you an accurate diagnosis. Maybe the tech was just a little tired?