Matt, if you do have a burnt valve or other potential mechanical issues then you should at the very least do a compression check on all the cylinders (do all of them to give yourself a baseline for comparing to the cylinder giving you problems). If you do have a valve that is leaking then it will likely show up in slightly lower compression in the leaky cylinder. Then I would try a leakdown test on the cylinders to see if it they can hold compression (again I would do the others just to get a baseline for comparison purposes). This diagnosis should be done before you go tearing down the motor to have a look see.


Mark, did you do a compression test when you burnt the valve on yours? Leakdown too? If you did, I am just curious what kind of psi you were seeing? I agree that I don't think the SMT is likely the cause of a consistent single cylinder misfire since it is only a sensor output modifier, not an engine management system.

 

Sage advice, and something I should have mentioned before I dropped a diagnosis. I blame having been at work for 16 hours when I wrote the above... Thanks Jamie.

Matt... Here's a quickie on a leakdown test:

http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm


Something else you can do fairly quickly is the "tissue test". Hold a tissue or paper towel up to the exhaust pipe while the engine's running at idle. You should only see the towel flutter _away_ from the pipe. If you see it trying to be sucked into the pipe, that's a bad sign. It comes from an exhaust valve being open (or burned open) and the piston creating a vacuum on the downstroke.



Yeup and yeup. All cylinders 'cept #2 were sitting around 160; #2 was a big goose egg. Leakdown was cool - (well, not really), you could hear and _feel_ the air coming out of the tail pipe.


Matt, like I said in the rebuild thread, a local buddy is doing most of the work,. not a dealer. As such, anything that he's quoting me in terms of pricing is ballpark and will vary from place to place, person to person, or even one person between jobs. As well, I'm taking the opportunity to build up a couple of spots in the engine to get even more power out of it... Those parts are more $$$ than stock, and I'm replacing some things that don't "need" replacing.

I can say that doing it yourself, or having a buddy do it will be substantially cheaper than having the dealer do the work. Call the local dealer, ask for the service manager and ask what their time charge is for replacing a burnt valve. That should get you close to their labor charge. Then figure about $15/valve for stock valves, $60/ea for pistons, $300/engine gasket set, $180 for rings. Those are discounted parts cost, so they're pretty static.


Good luck man. And, umm "Welcome to YotaTech".

Out of curiosity, you mentioned that you had been to other forums and they couldn't figure out what was going on. Which forums?


Yeah, I know. I think I may ask one of the mods to split the thread into pieces or, I'll start a new one and copy the relevant pieces to it.

 

LMFAO!!!! Or dating a bi-polar chick...If I ever do that again, please I beg you, or anyone, SHOOT ME!



PS - subscribed!

 

So is this a potential problem with an OBD I equipped boosted system as well? And you are correcting below the open loop threshold for what pourpose, to gain power there and prevent lean out?

 

Umm, it doesn't really have anything to do with OBD I/II, it's more of a ECU issue. Actually, it's probably an issue with any vehicle that uses an O2 sensor. There will be some sort of ECU that is looking at the O2 sensor to help make decisions on what to do with fuel.


Basically we're looking to do away with the concept of closed loop while under boost. If we can get the ECU to sit in open loop, then it will take itself out of the picture in terms of managing fuel. That lets us have absolute control over fuel flow through the SMT or That Other Product.

In closed loop, the ECU will work to run it's world at 14.7:1. If we can get more fuel into the engine while under boost, we can make more power and get better acceleration. But we can't get control if the ECU's in closed loop, so we keep looking for a way to force open loop.

Lean out really isn't an issue at the boost/vacuum threshold, that becomes an issue for us at WOT.

 

Ain't no expert on this, as you know, but it does occur to me that the response time in a closed loop is fast relative to what you can do manually. And that may be important in anomolous nonlinear cases.

Could be dead wrong about the importance, but it did occur to me. Modifying a closed loop (if possible), would seem safer.

 

Ummm, I think I understand what you're saying...

Forcing open loop isn't for the purpose of manual control ("manual" in the sense that you have a knob mounted on the console so you can tweak on the fly) it's for getting the ECU out of the way so that something more "user programmable" (e.g., SMT6, FTC1) can get in there and do it's thing.

And yes, it's most certainly "unsafe" in the sense that if you do this, and you don't have a piggyback fuel controller (or choose to not program the one you do have) then you can easily get into a VERY lean condition and torch a piston or valve.

It's also a huge PITA for those folks that drive between altitudes or where the weather can change drastically overnight. If thee ECU is out of the way, then it's _out of the way_ - it's not going to compensate for air density, humidity or temp.

But... for those folks that want to play, the ECU's gotta be shut down and shut out.

 

^ Mark if you are using a MAF sensor you will always have temp compensation Its a hot wire it will read the temp variations in the air and move to a different load cell on the smt6 thus changing your fuel value

 

Oh now Johnny... You dern notherners come in hear and think ya' own da' place, settin' all us southerners straight and what knot.


(rough translation: tanks, I shudda' knern dat)

 

^^ .....yes.....

 

weasy you ever get around to installing that SMT6 on a 3vze with your cams yet?

 

Na man i have been so backed up with other things right now that i put it off till the new year....only matter of time