Duty Cycle too high? misfire :/

[maxo-tt1]

hello guys, i still could't tune my car. last time i logged, noticed that duty cycle is about 70% at 2rd hear 7000rpm 19psi boost. (sometimes till 80%)

that's too high yes? i think thats why i get misfire after ~6500-7000 rpm.

i use 800cc siemens deka injectors, 450 walbro, -8an feed line, -8an filter, Aeromotive regulator. base pressure at idle about 45psi

engine: bmw m52 3.0(8.5:1 pistons. garrett gtx35 turbo). IGN 1a coils + bkr7e plugs

ecu: ms3x pre-1.4 alpha

i already start think its megasquirt issue

any ideas please?


p.s if i dont boost more than ~17 psi, car runs ok, if i increase boost, i get misfire.

5.msl run log with 1.1 bar wategate spring
11.msl and 13.msl much more. cant remember

here is all logs i logged yesterday. low boost run till 6.msl
http://arqivi.net/all.zip

[dontz125]

70-80% is a good range; you can start running into issues over 85%, although some people have successfully run past 90%. The problem is that the changes become non-linear, so it's harder to tune.

That said, with a good amount of duty left on the injectors and encountering misfires as you go past 17psi boost, I have to wonder if you aren't losing spark.

[elaw]

70% duty definitely is not too much! I think most people consider 85% a good upper limit, although I've gone to 100% and lived to tell about it.

In the "11.msl" log file, I assume the problem is occurring around the 23694-second point when you hit high boost? It seems like as you go into boost, PW rises and AFR gets richer to a point, then AFR suddenly goes very lean even though PW continues to rise.

I'm thinking this could be one of 3 things:
1) Fuel pressure regulator not referenced to manifold pressure - so fuel pressure doesn't rise as you hit boost and eventually there's just not enough pressure.

2) Something else limiting fuel pressure or flow in the system. A relief valve in the pump maybe? Clogged fuel filter?

3) An ignition problem. Perhaps enough fuel actually is getting delivered, but the spark plugs are not firing for whatever reason - coil output too low, gap too large, bad wires?

[dontz125]

A situation where PW is increasing and AFR is increasing that suddenly flips to very lean (while PWs continue to climb, no less!) is indicative of a misfire - the fuel isn't burned, so all that unused oxygen goes by the O2 sensor, which suddenly reads dead lean and confuses people. This sudden lean reading does not in and of itself indicate a malfunction in the fuel system.

I'm not a turbo guy, but I keep seeing comments about problems with "the spark blowing out" as boost rises past a certain point. Sure sounds like what you're experiencing.

[elaw]

I agree... I probably should have put a spark problem as #1 on my list.

What are your spark plugs gapped at? If it's more than about 0.025", try reducing the gap a little. I think some folks running high boost go as low as 0.020".

Also do you have good heavy wiring for the power and ground to the coils? Those coils require a lot of current... I'm wondering if a voltage drop somewhere could be causing a weak spark.

[maxo-tt1]

thanks for replay guys.

as for spark, in past i had blowout problem with its stock coils, at that time i was getting rich afr. thats why we thought it was coil problem and bought new 1a. after that no more rich afr. i'm quite sure i have good power and ground to coils. did custom spark wires. with msd 8.5 wire and msd terminals and boots. i really cant think its spark issue again

now when afr getting lean, how it can be spark symptoms? if spark plugs cans fire ok, then it should show rich afr yes?

gap 0.02"

[dontz125]

If the plugs are firing and the mixture is burning, it should show rich. If the plugs STOP firing and the fuel is unburned, it will show VERY lean.

Another possibility is rich misfire. I'm on my phone and can't see the logs - what are your AFRs like, just before they drop?

[elaw]

The AFR I'm seeing in 11.msl is rich, but not ridiculously so. It's around 14.7 at low load, and drops to 12.3 just before the problem happens.

[dontz125]

*scratching head* On a turbo? That' doesn't strike me as much rich at all.

[maxo-tt1]

in 13.msl for example last good point 12.1 and than suddenly 17 and than 18.

i thought lean afr only because of fuel delivery issue. now i have to recheck ignition again. but for now no idea what to check

sometimes i get 1 of my spark plug wet too much that 1 cylinder cant work. maybe just because sometimes afr goes rich about 10:1? is 10:1 rich that much to make spark plug wet? (it mostly happens when engine is cold. so i think its just tune issue.)

after that i dry my spark plug and using again. sparks are getting damaged when they get wet? can't i reuse it?


i've checked fuel pressure. installed camera under hood. bad quality but we can see that arrow goes up @ boost
https://www.youtube.com/watch?v=9yzbjlR ... e=youtu.be (after 50 sec)

[nismoautoxr]

this sounds very familiar. i think you need to be monitoring fuel pressure at the point where it goes dead lean. Too much fuel pressure can be as bad as not enough on certain injectors . I once tuned a GMC with a turbo charged 4.3 v6 . It used a ball and seat injector . The engine would run strong untill it got to about 15 PSI and then the rising rate regulator would send fuel pressure from 40 to 90 PSI and the engine would fall on its face and the AFR would go full lean. Preventing the rise of fuel pressure cured this problem.

Example 2 was a tuned port corvette with 30 lb/hr ford motorsports injectors . Car had a intermittent no start on cold starts . It was found that the cause was that the fuel pressure regulator had been changed to an adjustable one
and it had 70 PSI during cranking and the injectors would not spray. Dropped the pressure and they sprayed .Tuning this car on 40-48 PSI fuel pressure and it never had another issue .


Just food for thought from the memory banks . As Don and Eric says it could be any of the things they have listed as well .

[maxo-tt1]

this sounds very familiar. i think you need to be monitoring fuel pressure at the point where it goes dead lean. Too much fuel pressure can be as bad as not enough on certain injectors . I once tuned a GMC with a turbo charged 4.3 v6 . It used a ball and seat injector . The engine would run strong untill it got to about 15 PSI and then the rising rate regulator would send fuel pressure from 40 to 90 PSI and the engine would fall on its face and the AFR would go full lean. Preventing the rise of fuel pressure cured this problem.

Example 2 was a tuned port corvette with 30 lb/hr ford motorsports injectors . Car had a intermittent no start on cold starts . It was found that the cause was that the fuel pressure regulator had been changed to an adjustable one
and it had 70 PSI during cranking and the injectors would not spray. Dropped the pressure and they sprayed .Tuning this car on 40-48 PSI fuel pressure and it never had another issue .


Just food for thought from the memory banks . As Don and Eric says it could be any of the things they have listed as well .

nice info. i'll try today without vacuum hose to regulator.



i've just found the second image bellow over the net. its already more than 800cc/min @ 10 PW. my logs says i got 11.9 PW and 322cc/min @ 7000 rpm.

[nismoautoxr]

nice info. i'll try today without vacuum hose to regulator.



Not exactly the advice I was giving but if you do that just be very mindful of the AFRs when you do It. I recommend knowing exactly what your fuel pressure is doing at the point things go south . Its still recommended in a boosted application to have a reference of some sort so that the pressure on the nozzle side of the fuel injector is accounted for but point of post is to tailor that reference and the fuel pressure for what works best on your setup.

[maxo-tt1]

nice info. i'll try today without vacuum hose to regulator.



Not exactly the advice I was giving but if you do that just be very mindful of the AFRs when you do It. I recommend knowing exactly what your fuel pressure is doing at the point things go south . Its still recommended in a boosted application to have a reference of some sort so that the pressure on the nozzle side of the fuel injector is accounted for but point of post is to tailor that reference and the fuel pressure for what works best on your setup.

today i've tried with hose off from regulator. the same issue. good afr(11-11.5) till 6700 and then suddenly 13-17

so pressure is no the problem i think

[nismoautoxr]

nice info. i'll try today without vacuum hose to regulator.



Not exactly the advice I was giving but if you do that just be very mindful of the AFRs when you do It. I recommend knowing exactly what your fuel pressure is doing at the point things go south . Its still recommended in a boosted application to have a reference of some sort so that the pressure on the nozzle side of the fuel injector is accounted for but point of post is to tailor that reference and the fuel pressure for what works best on your setup.

today i've tried with hose off from regulator. the same issue. good afr(11-11.5) till 6700 and then suddenly 13-17

so pressure is no the problem i think

Lets disect what you just said. You said you pulled the reference hose off and you have decided that pressure is not the problem based on that ? Did you put an actual pressure gauge on the fuel rail and checked to see what the fuel pressure is when the problem occurs?

[elaw]

Actually, if you didn't do dramatic retuning, the fact that nothing changed when the hose was removed is a red flag by itself.

In general, disconnecting the vacuum hose from the FPR on an otherwise properly running engine will result in the mixture being very rich at idle and light load, about right when MAP is around atmospheric, and lean when the engine is under boost.

If you did not see the above when you disconnected the hose, something's wrong either with the FPR or the connection to the manifold.

[maxo-tt1]

Lets disect what you just said. You said you pulled the reference hose off and you have decided that pressure is not the problem based on that ? Did you put an actual pressure gauge on the fuel rail and checked to see what the fuel pressure is when the problem occurs?

yes... i decided so..

no, it will not be easy to connect gauge on rail. maybe fpr gauge not shows correctly?

[maxo-tt1]

Actually, if you didn't do dramatic retuning, the fact that nothing changed when the hose was removed is a red flag by itself.

In general, disconnecting the vacuum hose from the FPR on an otherwise properly running engine will result in the mixture being very rich at idle and light load, about right when MAP is around atmospheric, and lean when the engine is under boost.

If you did not see the above when you disconnected the hose, something's wrong either with the FPR or the connection to the manifold.

there was no changes at all at idle with hose connected and disconnected. strange yes?

also no changes when i increase/decrease pressure. just gauge shows that pressure goes high or down.

[nismoautoxr]

Lets disect what you just said. You said you pulled the reference hose off and you have decided that pressure is not the problem based on that ? Did you put an actual pressure gauge on the fuel rail and checked to see what the fuel pressure is when the problem occurs?

yes... i decided so..

no, it will not be easy to connect gauge on rail. maybe fpr gauge not shows correctly?

can you see the gauge on the regulator when the engine starts running badly? If not that is the reason i suggested that you monitor the fuel pressure when the problem occurs which means you will need to put a fuel pressure gauge on it that you can see when the problem occurs .