NicD

iTrader: (7)

That's not how it works, it cuts fuel entirely to the cylinder so there is no such thing as a half pulse that causes a lean condition on the limiter... as long as the injector is the only fuel source, ie no meth injection, etc. You had other problems that caused that.

truckdoug

iTrader: (25)

so you're saying that a cylinder with no fuel in it will not go lean?

explain this to me like I'm 5

Black89Z51

iTrader: (2)

If there's no fuel in the cylinder to cause detonation, all it does is act like an air compressor. There's nothing there to cause damage other than compressed air.

kingtal0n

iTrader: (1)

A fuel cut is exactly that- a fuel cut. The cylinder will compress air and "nothing else" will be in the cylinder when the spark occurs, so nothing will happen. Its like cranking a motor over with a starter and no fuel system (at 7000rpm or whatever). This is the primary choice of OEM manufacturers for rev-limiting, and is considered far safer than spark limiting.



There are still a couple ways you can have a failure in this scenario, though.
1. leaking injector. A leaking injector will obviously leak fuel into the cylinder even when the injector doesn't fire. This situation should be somewhat rare because it takes a fairly precise amount of fuel (air fuel ratios between 19:1 and 15:1 might burn, where 20:1 -> 30:1 will not burn) to spread the fuel molecules enough through the air in the cylinder to get a enough reaction (burn), and furthermore, it has to go for several cycles (chances are, the first combustion event at 18:1 isn't going to rise temperature and pressure enough to damage the cylinder, it is subsequent cycles at high temperature provided by the first few that cause premature pressure spiking and piston damage with poor fuels).


2. Fuel sharing between cylinder is an issue on some engines. Some fuel cuts are "staged" or "intermittent" to reduce the stress on the engine, I am not sure I used the right word there but you get the point, it will cut fuel to one but the next will receive and then cut fuel to the next, and so forth, to gently limit the engine. AEM has this technology, for example. If you have an engine with that kind of fuel cut, and the manifold has been modified for short runners (custom intake design) then a cylinder might pull fuel from a neighbor. This is possible because fuel is supposed to sit on the intake valve before the valve opens, depending on injector phasing.


notes:
Fuel injector phasing is a controversial tuning subject. The OEM manufacturers typically time the fuel injection to END before the intake valve opens. Sometimes this is skewed due to high duration camshafts with long open valve times on engines which require long injector pulses using original injector timing. Some engines seem to have much better throttle response when spraying directly into an open intake valve from off-idle, but I believe that has more to do with the style of injector than the design of the engine.


"nothing else" is in quotes because there is always something else in the air. For example, oil residue from the cylinder walls is always present, or should be. Pollen and fungus is in the air and almost impossible to completely filter out. A single pollen grain contains innumerable objects, including at least eight variety of metals (sodium, potassium, magnesium, molybdenum, etc) and perhaps hundred thousand compounds (containing chlorine, sulfur, nitrogenous/ring structures, ribonucleic acids etc) these unfiltered atrocities react in the heat of combustion to form a sticky conglomerate that will stay somewhere for the life of the engine, and as more get inside, gradually gums an engine to it's death, and should be taken seriously for engines which you intend to drive hundred thousand miles or more.

kingtal0n

iTrader: (1)

Couple more things worth mentioning,

You can generally check for leaking injectors by inducing a fuel cut, coast, engine brake (you probably downshift to stoplights like this all the time) and listening for backfires on a hot engine (hot exhaust). A true fuel cut will engine break without any engine "cough" or "sputter/backfire". When you hear "pop adee poppdoo oopo ppoopop" as you are engine braking up to a light that is how you know there is a leaking injector, or the ECU doesn't have the fuel cut configured properly.

The wideband should also read blank "-.-" during the fuel cut/engine brake


The fact it was cylinder number 7, the infamous, is a very powerful clue to the mystery of failure. Something about that cylinder is weaker, or weakened in some way. There can be many theories (steam port, manifold design, piston materials, bore shape) so I wish you will provide as much detail as possible, i.e. what manifold is on the engine, what kind of fuel rail/fuel system, what steam port config, did you dissemble the engine ever, did you add fuel to number 7 using the ECU (extra fuel for it), are you running a single wideband in the downpipe or duals, and anything else you can think of.

Here is an example of the details I am looking for:
LS1 or LS6 manifold, 4-corner steam port solution, 3% extra fuel to number 7, single wideband in downpipe, never dissembled the engine, OEM single feed/no return "dead head" fuel rail

truckdoug

iTrader: (25)

yeah it pops like an anti-lag on the rev limiter. here is a clip from when it had the 5.3/gt45 combo...you can hear it right before it goes slow motion in this video

this engine did have pretty excessive blowby as the rings were really sludgy.

heck the ringlands could have been busted before I even got the motor. it was a work truck that was rode hard and put away wet

but for details here goes:

it's a NNBS intake with an adapter to the typical 75mm 3 bolt truck TB

the steam port is the older ls1 I think, goes to all 4 corners of the heads.

the fuel system is a wally 450 with -8 feed to an aeromotive fpr set for 4 bar at anything under 100kPa (it is referenced roughly 1:1) the return is -6 and the feed from the fpr is -6 deadheaded to the rail. i run 91 pump e10 as that is most common in my area.

I pulled two pistons when I had the pan off with the intention of gapping the rings...but they were already at .028-.030 top and similar 2nd ring gaps.

I am not adding any extra fuel to 7, I'm unaware if the stock pcm has that capability. I had planned on putting a "fat" injector on that hole, but when they were flowed that were within 1% or less of each other.

single wideband about 18" after the turbine

here's whats odd...the plug looked good on that hole. I cut it apart and checked it out with a loupe...no obvious signs of detonation on the plug or the piston.

i'm not salty about it happening, I just wanna avoid doing it again if possible.
I chalk the it up to the cost of learning

kingtal0n

iTrader: (1)

I am surprised when you pulled the piston to check the gap you didn't go right for number 7 and 8 first, just to see. It sounds like somebody had it apart in the past, the it sounds like somebody gapped the rings for boost, does this add up? So maybe it was already broken. I bet you never did a compression test on the engine either? They will often seem to run fine even with a half broken piston as long as it doesn't affect the oiling character of the engine.


Thanks for the details, I am assured from the massive number of #7 failures (I imagine in my head, I haven't actually been keeping track or anything) that the most common components have been rules out, i.e. fuel rail, manifold, port design. That leaves piston material (has anybody tried switching number 7 for number 1 and seeing if number 1 breaks too soon? lol) and the block itself, I suppose. In my mind, it almost has to be a fuel distribution issue, that is being overlooked because the wideband is averaging the values and so nobody is catching it, or a timing issue (perhaps the crank or cam sensor is going "early" in that region). In short, I think I will pull a bit of timing and add a bit of fuel to the rear cylinders if possible.

truckdoug

iTrader: (25)

i doubt it was apart before, likely just really worn out.

it was a real sludge pig. like crude oil, bunker fuel looking insides lol

why didnt i pull 7? well I had planned to pull them all. looked at 2 or 3 with bigass gaps and said **** it

cosbysweater

I have a Volvo 244 running microsquirt for ecu and tcu, gen4 lq4/80e vs s366, loaded his Fairmont microsquirt tune in it and haven't touched it. Car rips, could use a little cleanup, but mostly due to minor differences.

jay_rich

iTrader: (8)

I also went through and copied some settings for setting up my MS3-pro. I found it was easier just to build my own tune, stole the timing and fueling tables then altered from there. Car runs pretty good. Just cold start issues

thatoneguybriz

iTrader: (2)

^^This.

Even Matt says in the youtube Q/A videos to use the tunes as base files to get stuff fired then modify from there.

brandon6.0

iTrader: (32)

I don't think any tune file is actually supposed to be used as a direct swap and done. Tune files posted rather hptuners or ms3 etc. are for setting up a base file for starters. Like injector data, timing tables etc. all fueling should be tuned via fuel trims or wideband for a complete tune for max power and drivability by u or your tuner personally!! Now, don't get me wrong u can upload a tune and run it as is. But they are not intended for that.

kingtal0n

iTrader: (1)

In a map car, especially an OEM ecu map car, you can't ever finish a tune. I can spend 9999 hours tuning a map car and still not be happy. There are too many variables. No matter what you load, you are never finished, it always needs play time.

Now I am not saying you can't get close. Lots of stuff is really close. You can load or tune a car yourself in a couple hours really close and be happy about it. It depends on the individual tuning the car, and the kind of car it is. Typically, daily drivers take way longer than race cars. Race cars are all about the bottom (final) line- last row fuel and timing. It won't ever use the cruise portion of the map, for example. A daily driver need to be able to start cold, hot, in a variety of climates and altitudes, and atmospheric conditions, and also drive nice in all of those, and you will never hit anywhere close to the entire map unless you personally own the car and tune it every single day yourself everywhere you go for years.

maf cars are able to compensate for a variety of conditions all by themselves- its a little shortcut. I always recommend a maf for daily drivers because they make it easy. Still could use some effort, but it often takes wayyyy less time to get it "close" and even less to be happy with.

truckdoug

iTrader: (25)

yeah no kidding. I figured at week of driving my NA truck around in OLSD and I'd be dialed and ready to put it back on the MAF....nope "I CAN GET IT CLOSER!"

dburt86

iTrader: (2)

Base tunes are not all created equally. Just because a base tune runs decent, does not mean its setup well. A tune can have alot of poor data in the base settings that at first glance may seem irrelivant, until you start having issues.

Things like 1st tooth angle, injector data, over compensating accel enrichemnts, very loose EGO correction are to name a few.

In my eyes, a base tune is a good tune from one car that is a starting point for another car. That doesnt mean you can over look doing the very basic/essential things. (like syncing timing and verifying injector data)

My point is, dont be an idiot.

dburt86

iTrader: (2)

This is more important to the stand alone users.

The jabronis using stock ECU's have a little more wiggle room to copy and paste.

stevieturbo

True, but regardless. All aspects should be checked to ensure everything is correct for the vehicle it is being used on.

denmah

iTrader: (2)

most of it is total junk

coltboostin

Its just a different way to adjust the base correction. Its not a huge deal either way, he probably just didn't change it after swapping motors.



This is correct. If there was an issue with GMs fuel cut everyone would blow their motor up on their first drive LOL. Not one person with a turbo LS is not buried in the limiter at some point during their day.

truckdoug

iTrader: (25)

what is your rev limiter set at? do you pull spark at the high end to soften it up?
are you spraying water/meth? how do you keep it from spraying while on the limiter?

the more I learn, the more questions I have.

In my case i'm beginning to think the problem was something else. maybe it was cracked before I ever got the motor. it did have both exhaust manifolds cracked which I had never seen before