Heads

[daffy]

Hi

Well I am, today, going to rip apart my engine to get the heads off for regrind. The car has been acting up for a while now and at 390,000 kilometers probably due anyway. It's a 1991 LS400 and I really like this car. I just wonder how long the bottom end is going to last? I have been using Amsoil since about 190,000 kilometers. Hoping by using this oil, it would extend the engine life... So far it doesn't seem to burn oil.

This is the first time I've worked on an engine with overhead cam. I once rebuilt a 1980 351 V8 Ford half ton and still drive it today. But this Lexus engine Is probably different. Am I doing the right thing?

Daffy

[SRK]

I don't think you are doing the right thing. Just because the car is "acting up" and "its probably due" is not diagnosis, and insufficient reason to tear the heads off. If you have access to a manual, read up on the procedure. You will find it is unlike any other car I know of in terms of camshaft drive system.

Diagnose the thing - figure out what is truly wrong with it, rather than the shotgun approach. That method is expensive on any car, but especially so on these cars.

[UCF3]

well I have to agree with SRK, but if you think you want to tackle such a job be prepared to complete the job throughly. Our great Toyota Blocks require you to bring the block back to factory specs, otherwise you may experience problems.

Perhaps you could describe some of the problems you're experiencing right now, and we'll try to answer some of them.

[daffy]

Hi,

Well the reason I was going to take the heads off was because at a Lexus dealer they had done a compression test with these results: 1-170, 2-200, 3-210, 4-210, 5-220, 6-210, 7-215, 8-200. They stated that #1 cylinder was too low and causing my jerking(like it's missing). It is most pronounced at about 70 to 80 kilometers when I am coasting. It also idles a little rougher than it did when I got the car. This jerking was barely noticeable when I got the car, and now is so annoying. The Lexus mechanics thought that the heads needed to come off for a regrind.

I then talked to a retired mechanic and he came over and said to me "do your own compression test". I thought he was nuts! Why would I repeat this procedure?

Anyway I looked in the manual under compression test and did exactly what they said. My results are, with two different compression testers (both Mac made) : 1-190, 2-190, 3-190, 4-190, 5-200, 6-190, 7-210, 8-190. My mechanic friend was tickled pink! He said this engine is perfect mechnically. If I were to add oil to the cylinders, this would only make the readings higher, so I could see no point in doing this. The high readings are probably due to carbon build-up. Further reading the manual, says that compression should be 178psi or higher with a min. 142 psi allowed. The range between cylinders- 14 lbs.

So the only concern I have is one cylinder reading high. But this shouldn't cause my engine to run like it does. Anybody know?

Daffy

[lexus400]

I'm not sure what the "cause" of the problem your having is but those compression readings are fine. I would not be pulling off the heads.. anything within 10% between cylinders is more than acceptable. I have had good luck spraying throttle body cleaner into the throttle body while someone else keeps the engine running. The Gen I's are carbon prone and this would certainly help. I assume that Lexus did all the obvious checks (plug, plug wire, etc.) on this cylinder right ?

Bob

[92Lex]

I agree with lexusl400, a 10% difference is acceptable.

[daffy]

Hi,

I am not taken these heads out with compression like I have. I believe this engine mechanically is perfect! I have been using Amsoil oil since 186,000 kilometers and it now has 390,000. I just recently had new plugs and spark plug wires replaced. So my problem must be electrical elsewhere, corrosion of some connector, bad sensor or something else. Lexus had it on their scope and found nothing wrong with anything. I guess the only thing left is to put it on a dyno and scope at the same time to see if anything shows up. What do you think?

Is it possible that the cylinder with the highest compression has too much carbon and when the engine warms up it begins to glow and starts to act like a diesel?

Is it safe to run some kind of cleaner through the throttle body? I would be concerned about a large piece of carbon flaking off inside the engine and damaging the valves. Thanks

Daffy

[92Lex]

It sure can. Take a look at the cylinder you suspect is carbon fouled... if it is then use a top engine decarbonizer. If you have access to a dyno then throw it on the dyno and see if the NOx is high.

Oh hang on...so your car feels normal when it's cold but jerks once it warms up to normal operating temperature? Are you sure it's not fuel related?

[daffy]

92lex,

I don't think it is fuel related for a couple of reasons. (1) the spark plugs are a chocolate brown, all 8 of them (2) I can cruise down the highway at 120 kms/hr all day and this car seems to run just fine. and good gas mileage. An easy 30mpg + (canadian gallon). So I conclude that the fuel system is working fine. But can anyone tell me how long the fuel pump last in a Lexus? Maybe I should be thinking of changing it before it gives me trouble?(390,000 kms.)

Back to my problem, it is most annoying when I let off the gas a little when at about 70-80 kms/hr and it starts to jerk. step on it, it seems to go away. Let right off the gas, no problem. When I cruise around town, I have to shut the overdrive off to get the rpm up to prevent this jerking motion. I thought maybe fuel mixture isn't quite right, but the plugs indicate that it is. Thanks

Daffy

[daffy]

I'm not sure what the "cause" of the problem your having is but those compression readings are fine. I would not be pulling off the heads.. anything within 10% between cylinders is more than acceptable. I have had good luck spraying throttle body cleaner into the throttle body while someone else keeps the engine running. The Gen I's are carbon prone and this would certainly help. I assume that Lexus did all the obvious checks (plug, plug wire, etc.) on this cylinder right ?

Bob

←

Hi Bob,

Yes Lexus checked everything and come up empty. Their solution was to take the heads off. I don't think so...

Daffy

[92Lex]

Does it jerk when your foot in on the pedal or off?

[monarch]

Have the plug wires, distributor caps and rotors ever been changed? With OEM replacements? If not, they are long overdue. Also, have the valve clearances ever been checked and adjusted if necessary? If not, they are long overdue.

[daffy]

Does it jerk when your foot in on the pedal or off?

←

Hi 92Lex.

It jerks with my foot on the pedal(holding it still). It does it with cruise control on as well. Again this is most pronounced between 70-80 kms. Only when coasting.

Daffy

[daffy]

Have the plug wires, distributor caps and rotors ever been changed? With OEM replacements? If not, they are long overdue.  Also, have the valve clearances ever been checked and adjusted if necessary? If not, they are long overdue.

←

Hi Monarch,

The wires have been changed and I just finished checking the resistance and they appear ok. The distributor and rotors may not have been but wouldn't that show up on the scope? I don't think excessive clearance on the valves would cause a problem like that, again would that not show up on the scope?

Daffy

[92Lex]

If it had something to do with the ignition you would be able to see it on the scope. Does your rpm change when it jerks? If it had something to do with the clearance of the valves it would of showed up when you did the compression test.

Try what lexus400 said....clean your throttle body. Try that first and if the problem is still present then just repost.

Torque converter, intermittent maf sensor, low fuel pressure, malfuntioning fuel pump?

[daffy]

If it had something to do with the ignition you would be able to see it on the scope. Does your rpm change when it jerks? If it had something to do with the clearance of the valves it would of showed up when you did the compression test.

Try what lexus400 said....clean your throttle body. Try that first and if the problem is still present then just repost.

Torque converter, intermittent maf sensor, low fuel pressure, malfuntioning fuel pump?

←

Hi 92Lex,

The more I get into this, the more I am thinking... that one cylinder with high compression (because of carbon build up) is probably what is doing it. Carbon glows when hot and when I let up on the gas a little, it must sort of diesel at this time only on that one cylinder. When I step on it, it seems ok, so the extra fuel must prevent this dieseling action on acceleration. If I let my foot right off the gas, there's not enough fuel for it to diesel. and so it doesn't jerk. Am I on to something here?

I have notice my temperature guage is reading lower than it used to and so could make the engine carbon up easier? I have told Lexus to check into this for me awhile back, but they though it wasn't necessary. I think I will install a new thermostat anyway. Opinions?

And the throttle body to my knowledge has never been cleaned in 390,000 kms. I notice a little rough idle, so I will clean up the throttle body by taking it right off and do a real good cleaning.

Any safe way to remove carbon from my cylinders?

I feel I might be onto something here! Thanks, Daffy :)

[92Lex]

If you feel strong about your theory then pull out a spark plug...use a scope to look at the top of your piston(s). If you see excessive carbon build up then use a top engine decarbonizer.

I think that if there is excessive carbon build up in your combustion chamber that you'd hear a "pinging". I doubt that you have excessive carbon build up in one of cylinders...when you did your compression test you warmed it up to normal operating temperatures right?

[ArmyofOne]

You may want to spray some Throttle body/Intake Manifold Cleaner into that cylinder, this is not generaly a safe practice on a clean engine, because it is unfiltered, however in this case, it sounds liek the piston is already dirty.

1. Pull the plug wire and plug off the cylinder that is high and look at the piston with a flashlight...see anything?

2. if so, Spray the cleaner SPARINGLY in the cylinder. (1/2 a second ofspray)

3. Replace Spark Plug and Wire.

before you restart the engine, do this. disconnect the main wire from the distributor get in the car and crank for 5 seconds, 3 times. replace main wire, and put gas pedal halfway to floor, start the engine. IMMEDIATELY take your foot off the gas once it is going. let idle for 3 seconds, then floor it for a second (bring it to 5,000 or so RPM's) then bring it back down slowly.

**THIS CAN BE PERFORMED WITH GASOLINE, WHICH IS GENERALLY SAFER, HOWEVER, IT IS HARDER TO REGULATE THE AMOUNT OF FLUID GOING INTO THE CYLINDER THIS WAY, TOO MUCH FLUID AND THAT CYLINDER WILL HYDRO LOCK**

so use the TB/IM cleaner. it burns just the same, but it also cleans.

now do a compression test.

if all is OK, do an oil change (to get whats left ot the TB cleaner out of the oil) and enjoy.

i have done this many times on engines of all kinds, it works like achamp.

the other idea is to stick a toweldown inthe cylinder with a flathead screwdriver to rub offthe carbon, but that only flakes it off into your oil and leaves lint and stiff in the cylinder, this method will DISSOLVE the carbon, so you can burn it.

[daffy]

If you feel strong about your theory then pull out a spark plug...use a scope to look at the top of your piston(s). If you see excessive carbon build up then use a top engine decarbonizer.

I think that if there is excessive carbon build up in your combustion chamber that you'd hear a "pinging". I doubt that you have excessive carbon build up in one of cylinders...when you did your compression test you warmed it up to normal operating temperatures right?

←

Hi 92Lex,

I cannot ever hear pinging because I wear two hearing aids and even with hearing aids, hearing is still below normal. Also the Lexus is so quiet, I would probably not hear it anyway. I would have to assume that it is pinging when it jerks. What about the anti-knock sensors, would they not prevent this pinging? Why else would one cylinder be so high?

Yes, I took the car down the highway to get it to operating temperature before compression testing.

What would you recommend for a top engine decarbonizer? I would prefer some product that does it in a slow way to prevent any damage to the valves. Thanks, Daffy

[daffy]

You may want to spray some Throttle body/Intake Manifold Cleaner into that cylinder, this is not generaly a safe practice on a clean engine, because it is unfiltered, however in this case, it sounds liek the piston is already dirty.

1. Pull the plug wire and plug off the cylinder that is high and look at the piston with a flashlight...see anything?

2. if so, Spray the cleaner SPARINGLY in the cylinder. (1/2 a second ofspray)

3. Replace Spark Plug and Wire.

before you restart the engine, do this.  disconnect the main wire from the distributor get in the car and crank for 5 seconds, 3 times.  replace main wire, and put gas pedal halfway to floor, start the engine.  IMMEDIATELY take your foot off the gas once it is going.  let idle for 3 seconds, then floor it for a second (bring it to 5,000 or so RPM's) then bring it back down slowly.

**THIS CAN BE PERFORMED WITH GASOLINE, WHICH IS GENERALLY SAFER, HOWEVER, IT IS HARDER TO REGULATE THE AMOUNT OF FLUID GOING INTO THE CYLINDER THIS WAY, TOO MUCH FLUID AND THAT CYLINDER WILL HYDRO LOCK**

so use the TB/IM cleaner.  it burns just the same, but it also cleans.

now do a compression test.

if all is OK, do an oil change (to get whats left ot the TB cleaner out of the oil) and enjoy.

i have done this many times on engines of all kinds, it works like achamp.

the other idea is to stick a toweldown inthe cylinder with a flathead screwdriver to rub offthe carbon, but that only flakes it off into your oil and leaves lint and stiff in the cylinder, this method will DISSOLVE the carbon, so you can burn it.

←

Hi ArmyofOne,

I would be concerned about getting a big chunk of carbon coming off and damaging the valves. I will try a slow way first over many miles. Thanks, Daffy

[ArmyofOne]

You may want to spray some Throttle body/Intake Manifold Cleaner into that cylinder, this is not generaly a safe practice on a clean engine, because it is unfiltered, however in this case, it sounds liek the piston is already dirty.

1. Pull the plug wire and plug off the cylinder that is high and look at the piston with a flashlight...see anything?

2. if so, Spray the cleaner SPARINGLY in the cylinder. (1/2 a second ofspray)

3. Replace Spark Plug and Wire.

before you restart the engine, do this.  disconnect the main wire from the distributor get in the car and crank for 5 seconds, 3 times.  replace main wire, and put gas pedal halfway to floor, start the engine.  IMMEDIATELY take your foot off the gas once it is going.  let idle for 3 seconds, then floor it for a second (bring it to 5,000 or so RPM's) then bring it back down slowly.

**THIS CAN BE PERFORMED WITH GASOLINE, WHICH IS GENERALLY SAFER, HOWEVER, IT IS HARDER TO REGULATE THE AMOUNT OF FLUID GOING INTO THE CYLINDER THIS WAY, TOO MUCH FLUID AND THAT CYLINDER WILL HYDRO LOCK**

so use the TB/IM cleaner.  it burns just the same, but it also cleans.

now do a compression test.

if all is OK, do an oil change (to get whats left ot the TB cleaner out of the oil) and enjoy.

i have done this many times on engines of all kinds, it works like achamp.

the other idea is to stick a toweldown inthe cylinder with a flathead screwdriver to rub offthe carbon, but that only flakes it off into your oil and leaves lint and stiff in the cylinder, this method will DISSOLVE the carbon, so you can burn it.

←

Hi ArmyofOne,

I would be concerned about getting a big chunk of carbon coming off and damaging the valves. I will try a slow way first over many miles. Thanks, Daffy

←

it wont do that, it will disoolve it into microscopic pieces of carbod, liek black water, and it will burn right out.

[92Lex]

Never assume when it comes to repairing these vechicles because it can get costly very quick. Honestly, I don't think the compression in that cylinder is high at all.

To help remove some of the carbon build up from your combustion chamber go buy a can of SeaFoam.

[daffy]

Never assume when it comes to reparing these vechicles because it can get costly very quick. Honestly, I don't think the compression in that cylinder is high at all.

To help remove some of the carbon build up from your combustion chamber go buy a can of SeaFoam.

←

Hi 92Lex,

I just had another mechanic drop by and inspect what I had done. Looking at the spark plugs and compression, he sees nothing wrong with the engine mechanically. He isn't concerned at all about the cylinder that reads high. He thinks it may be a bad sensor, computer is a possibility. He also pointed out that the water pump needs to be replaced, it's leaking (just what I need more work).

Of course the water pump has nothing to do with the problem, but has to be done anyway.

So he is willing to look at it, but needs to have it running before he can say for sure what it might need. I have to put it back together after I clean the throttle body valve, replace waterpump and might as well replace timing belt even though it has only 60,000 kms on it. I am so close at this point.

It's nice to know that the engine is good! :D

I will let you know what we find... ;)

Daffy

[ArmyofOne]

alwyas start with the cheapest first, plugs/wires (just cause they look ok, doesnt mean they are!) ;)

im sorry if i sound too pushy, i just hate to see people waste a TON of money.

[daffy]

alwyas start with the cheapest first, plugs/wires (just cause they look ok, doesnt mean they are!) ;)

im sorry if i sound too pushy, i just hate to see people waste a TON of money.

←

Hi, ArmyofOne

I have new plugs and wires already installed. I am going to change distributor cap and rotor next. Thanks, Daffy