Lol... I know it.

"Mop-mop-mop, all day long. Mop-mop-mop, while I sing this song. Gonna Wax this floor gonna make it shine.....gonna clean off the spray paint with Tuprentine!" -Adam Sandler "They're all going to Laugh at you"

Locker 'er up.

 

Do you see much carbon on the pistons? I have seen the tops of pistons that are black. Something that cannot be avoided unless you have virgin pistons. Unless the guy was running it into the ground with little to no maintenance, I have yet to see much carbon build up on modern motors that are FI. Last few I have seen were relatively clean.

 

Bump it a little. 2 deg increments. See what happens.
Confirm if there are real KC's being recorded or is there something bangin around in the engine compartment confusing the knock sensor.

Not to worry, the wheels won't fall off nor will the engine explode!

 

How often are you tearing into engines?

I figure if it was running rich enough to foul plugs out because of 24# injectors instead of the stock 22#. Then I'd guess it could leave carbon in there that could cause what they call carbon knock.

I've looked around, and see alot of mention that you can get knock from carbon build up. I figure people wouldn't be talking about it if it was a problem that ended 30 years ago.

I had found what looks like a TSB from Ford with regards to carbon knock. So, there is a modern motor that has a possible carbon knock problem according to Ford. Looks like their fix is to decarbon the engine by injesting carburator cleaner into a hot engine. Looks like Ford is telling people to do something similar like Seafoam to clean carbon inside the engine.

http://www.explorerforum.com/forums/...ad.php?t=57953

 

Me personally, no. Friend with whom I hang around a machine shop, does. Usually it is one of the motors they wheel in thru the backdoor.

I do agree that carbon buildup is possible no matter what. My point was that don't know if it is that likely if the engine is properly maintained. Every engine I watched him tear apart has black pistons. Whether it is so much that it becomes a problem, I don't think so. Last time I took my motor apart I had one dirty piston. It was the one where the spring had broke and the piston hit the valve and removed a chunk. It held about the same compression as the rest and you wouldn't know till you tore it down. It was letting more oil in.

 

And the same goes for 2 stokes, carb'ed engines and so on. A small amount of carbon builds up on the piston crown and combustion chamber right away...and then is created and burned off at a constant rate. It gets no worse, it gets no better. Pour some water down the TB and boil the carbon off, and it'll come right back in short order. Unless there is something wrong w/the engine (burning oil, etc.) a small amount of carbon will always be present, and shouldn't be an issue. (Which I why I question the pouring of a $10 a bottle product down the intake. What's the goal??)

I don't anymore very often, but I used to tear motors down a lot; probably a couple a week, for my job. Mostly two strokes as we have nearly zero 4 stroke failures, but still, some head gasket jobs, etc. Like aklim, I never saw more than a thin coating of carbon on the piston crown and combustion chamber.

P.S.; did you know that the detergent in gasoline actually "washes" the valve, piston, and combustion chamber? If you run the engine richer, you actually end up w/a cleaner chamber, etc. In fact we use "piston wash" as a gauge for jetting on our snowmobile engines; we look for thumb nail sized wash marks by the transfer ports on the piston crown, which is "safe" jetting for us. Pinky nail sized wash marks would be appropriate for someone looking for power and willing to take a little risk. A fully carbon covered piston is too lean, hands down. Motor will not last. When we have a carb problem and it runs way rich (stuck needle and seat), the piston is so washed, that it literally looks like it just came out of the box.

 

On second thoughts, maybe the better example was my buddy who broke a head gasket on his Ford 302 and my Turbocoupe 2.3 motor. We would break head gaskets at least 1 time every summer and since I drove my Merkur every day, at least 3 times a year. You could use gasket remover and it would take the carbon off but it would come back. The amount wasn't very thick. It was reasonably constant. When you rebuild an engine, you usually get a moron that has run it into the ground so that could mean that excessive blowby and oil was burning which might make the carbon level thicker. When we tore down our functioning engines, we never had carbon spikes in it.

 

Why would you increase your timing to get rid of knock? I thought people had problems with knock when they increased their timing?

I seem to recall some guys setting their timing by increasing it till it knocked. Then they backed it off some. If it is already knocking, I don't understand why you'd increase your timing?

How do you confirm knock counts? The only thing I can think of is I replaced the tensioner with a Dayco as the PO had the wrong one on there even though it worked fine. I noticed the tensioner makes a rattle sound that you can hear and also hear with your scope. I replaced it as a warranty return and it too rattled. That is the only thing I could think of with regards to a false knock.

I called Dayco and let them listen to the tensioner through my scope. And they said it shouldn't be making that noise. So, I guess I'll replace it again and hopefully the tensioner won't rattle. The tensioner the PO put on didn't rattle.

 

Josh, JrRifleCoach may have meant retard the timing. Maybe not, but that is what *I* would do; I'd retard it a bunch. It'll run like a dog, but you know there's no way it can be pinging. If you still get knock counts, you have a mechanical issue.


^exactly.

 

I'm wondering if the tensioner making a rattle could be causing the knock sensor to count knocks? Though, the knocks only happen at throttle with engine load. I'm gonna replace the tensioner, so I hope the new one doesn't rattle like the last two so I can rule the tensioner out or not.

 

One simple way. Get the engine good and hot and into closed loop. Remove the serpentine belt and see. My buddy would drive up to the staging line, unhook the belt and push the car to the burnout point, do his burnout, run the quarter mile and drive back easy. Hook up the belt and drive for a bit. He was in extremely low 12 and wanted to break into the 11s. He did.

Point is that you can run it for a few seconds to a minute before it gets too hot as can be seen by the gauge. Within a minute, you should be able to tell.

I have a bad feeling and I'm going to say "I'm sorry for you" but the last time I chased a knock like that, I found that the engine was on the way out.

 

One more thing you can try. Test before and drain the oil. If you dump the thickets stuff you can, even single weight motor oil, you can check it. If the counts go down, your engine is problematic.

 

I don't think I'm gonna dump heavy weight oil in there to see what happens. Doesn't sound like a good check.

Sounds risky to get the engine to 200 then drive it with the belt/tensioner off. I'm getting a new tensioner, so I hope this one doesn't rattle like the last two Dayco. If it rattles, I'll keep warranty changing them out every day till my warranty is up.

The engine shouldn't be on its way out. It only has 92k miles on it.

Is it possible it could be EGR related? I couldn't pull vacuum on the EGR, which I should be able to. I think when you hit the gas, it commands the EGR to open. I know on my scans when hitting the gas I see it calling for "101.59% EGR Duty Cycle."

 

Why do you say that? The thing about oil is that it will cover up some of the slop and that will stop some of the rattling around. For a few miles, it certainly cannot hurt. Reason you are asked to use light weight oil is your fuel economy will hurt and in winter, it isn't good. But WGAS? It is warm enough where the engine will liquefy the oil enough to let it flow smoothly.

What is closed loop again? I doubt it is 200. Sounds like the shotgun approach. Toss parts till it quits. It will not kill the engine to run it for a min from closed loop time.

What does that have to do with anything? My engine was rattling at 80K.

Not sure about that. I tossed my EGR more than a decade ago so I never look at it.

 

Cause alot of these L98's go over 100k miles easily.

I looked at one of my scans. And it went to closed loop around 145.

Would you have to get the battery charged up after driving it a few miles with no alternator charging?

The other problem is no power steering which would be a pain. I'm guessing the rack wouldn't get messed up with no pump running?

On the knocks. I don't believe it is every time. I just noticed on a few scans getting alot of knocks. Other scans hardly any knocks, but maybe I didn't hit the gas on those scans hard enough or something.

 

Mileage is only an average. You can destroy an engine in 5 miles or if you run highway only, you can drag it out longer. Still, you should do that to rule out the problem. It only takes a few minutes and a few bucks of oil. Or you can keep changing pulleys out day after day.

What is the max temp? that should give you an indication of ROUGHLY how far you can take it. Still, 1 mile, give or take should not fry your engine if you run without the serpentine belt. That is all you need to do. Drive it a quarter mile with, drive it another quarter mile without, reinstall the belt, drive it a bit, do another run and see what happens.

A mile or two is fine. Obviously, if you insist of driving with full headlights, mega stereo blasting, well......

Straight track. A mile is ok. Autocrossing, well, maybe not.

You need to do straight runs. That eliminates a lot of other variables. That way, you have WOT vs WOT and WOT+Cruising vs City+Cruising. Eliminate the mechanical first. Then we can move on to the injectors or spark plugs or whatever. If your block is shot, you can change pulleys till the cows come home and it will still rattle. Like I said, that happened to me under 100K so I wouldn't rule it out.

 

I can see another way to do the knock counts. Run till empty, fill 3 gals of race gas, preferably unleaded and see if the knocks go away or lessen. If it does, you have real knock and we can go on with injectors and what not.

Hopefully you didn't have too hot of a plug installed.

 

By too hot do you mean the wrong spark plug installed? Or that some brands run hotter than others?

I've got the NGK FR4 5155 plugs. I don't know if that is considered a "too hot" plug? The AC Delco plug number for the L98 aluminum heads is FR5LS.

The reason why I'd keep replacing the tensioner is my 1 year warranty will be up soon anyways. And the head tech at Dayco listened to the tensioner rattle via my stethoscope over the phone. And stated that the tensioner shouldn't be doing that. So, might as well replace them to try and get a good one before the warranty is up.

I don't know what the max temp is on an L98. I probably wouldn't go over 200 as that is around the time the stat is starting to open. I say you could get some distance from 150* to 200*.

I had ran 87. But filled half the tank with 93. So, I might try and get the tank down some to half and fill with 93 again just so I know I've got 93.

 

NGK goes in the reverse. The lower the number the hotter the plug. http://www.ngksparkplugs.com/docs/te...tnumberkey.pdf

Those are the correct parts for aluminum heads if that is what you have. Steel heads are different. I think you have Aluminum heads.

What are the odds of several bad units out of the box? I think it is slim since you have replaced a couple already, right?

Thermostat is not relevant. I am only intrested in comparing before and after without the tensioner having load and the engine is in closed loop and all that. After all, you are in closed loop most of the time so I want to eliminate any chance of errant results.

Try race gas if you can. After all, if it has knock readings with both race gas and 93, you have other issues.

 

The NGK are FR4. The AC Delco are FR5LS. I don't know if there is a difference between the NGK "4" and Delco "5" with regards to heat rating.

I was just saying that I would only run the temp to 200 as no coolant is flowing anyways till the stat opens. Rather be safe then sorry trying to run it up to 230 or something.

I've read of several others having problems with replacement tensioners rattling. The tensioner the PO had on there didn't rattle.

I talked to the Dayco tech who mentioned about some spring behind the cover piece. And using my scope, the cover piece is where the rattle is coming from. When I move my scope to the other side of the tensioner arm, I can hardly hear the rattle.

The tensioner arm does wabble up and down some. When I push down on the tensioner arm to help keep it from moving, the rattle goes away.