Lean Misfires at 2700-2800 rpm

[DoctorDex]

Noticed something peculiar today. On initial startup (first ~ 30 seconds) the car doesn't miss if I rev it through the 2600 - 3000 rpm range. Normally it'll pause for a sec. when it gets to 2600, but on cold start up it doesn't do this, whereas on hot start up it will.

This brings me to the next question, what is causing the misfire to fix itself on cold startup?

It could be the extra fuel dumped in by the FPR solenoid, but I doubt it. I'm more inclined to think it is a result of the simultaneous fuel injection (all injectors fire simultaneously with the CAS signal from each cylinder, ie. 3 times per crankshaft revolution). Simultaneous injection also occurs with acceleration enrichment. This would explain why the problem is less noticeable with hard acceleration.

This leads me to believe it is a problem with injector timing. Possible causes could be CAS (leaning away from this one) or trouble with injector valve opening time (? faulty fuel injector resistors or maybe even a weak battery).

Personally, myself I have a _very_ weak battery. I've run it dead one too many times. I think I'm going to finally get around to replacing it. I'm also going to check my fuel injector resistor pack and I'll let you guys know if it makes a difference.

[badass3000]

Originally Posted by DoctorDex

Simultaneous injection also occurs with acceleration enrichment

does it really?
not sure about that, sounds weird.

I am switching back to stock coils/wires now.
I tried a known good resistor pack last month.
have you lately ran the car w/o a logger hooked up?
that would be weird if the logger was somehow doing this. Ill give anything a try.
mabey unhook the BC too, I am just looking at all the mods that WE have that are similar. and we do have lots of the same stuff.

would you be opposed to putting your car back stock?
I just simply cant do it, no stock mass, inj, intake.
I dont mean the turbos, exhaust, clutch, crap like that, mainly the electronics.


CAS, still nobody has tried a known good yet!

Battery, mine is a newish optima blue top, in pretty good condition

[DoctorDex]

Originally Posted by badass3000

does it really?
not sure about that, sounds weird.

Found the info on stealth316.com. For the injector activation time info see here: http://www.stealth316.com/2-fuelinjection.htm#j2

For the info re: battery voltage affecting activation time see here: http://www.stealth316.com/2-fuelinjection.htm#j3a

Originally Posted by badass3000

would you be opposed to putting your car back stock?

I would do it, if I thought it would fix the problem. However, I don't think it'll fix the problem. I'm pretty sure I've had this problem since I bought the car with the stock MAF in place, just it was less noticeable with the stock flywheel. I don't have stock injectors either.

Originally Posted by badass3000

CAS, still nobody has tried a known good yet!

Do you have access to a known good CAS? I'd have to buy a new one and I can't see them allowing me to return an "electronic" part.

Originally Posted by badass3000

Battery, mine is a newish optima blue top, in pretty good condition

Are the blues marine batteries? Are they pretty much the same as the yellows?

[keithmac]

I`ll just clear up my earlier contribution, I`ve been re-tuning the e-manage and couldn`t get rid of the stutter at 3000 rpms no matter how much fuel I added.

Just bowsing through my settings and found I`ve left a line of 5degrees ignition advance at 0 psi (atmosphere) in the Timing Table. So if the timings advanced 5 degrees on my car the engine doesn`t like it and missfires at the common point (1/4 throttle, 0 boost/vac), aprrox 3000rpm).

If you`ve got hugh injectors with the correction set up then it`s possible the timing could be pushed into this position and a missfire will result?. I wouldn`t of thought 5 degrees would make any difference but it does!.

[DoctorDex]

Originally Posted by keithmac

If you`ve got hugh injectors with the correction set up then it`s possible the timing could be pushed into this position and a missfire will result?. I wouldn`t of thought 5 degrees would make any difference but it does!.

When I get the chance, I'll drop my base timing to 5*, then 3*, then 0* to see if it makes any difference.

Edit:Setting the timing to 5*, 7.5* and 10* makes no difference to the miss. Its still there, only it "feels" less noticeable, but it shows up on the logs just the same.

[badass3000]

that will make you car run like crap

[DoctorDex]

Originally Posted by badass3000

that will make you car run like crap

If I was to lower the timing, I'd only do it for a few minutes just to see the effect. IMHO, I don't think it'll help the miss.

[keithmac]

Just thought I`d mention it, I`m running approx 13.5:1 afr in the "miss zone" and it`s completely gone. If you can adjust the ignition advance via a map/table it` be worth pulling timing there to see if it makes any difference.

2000 2500 3000 3500 4000 4500 RPM
-20 -10% -5% -5% -10% -20% AIRFLOW CORRECTION (0psi)

That`s what my corrections look like at the moment, gradually leading in and then out of the enrichment at atmo.

Rich missfires can log as lean on the Wideband but I`m sure this has been mentioned on here before.

[DoctorDex]

Here's what "fine tuning" looks like on the SAFC-2 (it doesn't fix the miss even if I richen it up even more):

2400 2600 2800 3000 3200
+3% +14% +14% +3% 0%

My baseline compensation is done with the MAFT, which is why my compensation numbers are much lower than they should be with 550cc injectors.

Like I said before, the only time the miss is fixed is on cold start up (simultaneous injection). The miss is always present during cruise, it is less noticeable on acceleration and I think I get a miss on decel. Every time I decel through the 2800-2600 rpm range, I get a pop from my exhaust. No popping anywhere else in the rpm range on decel.

[DoctorDex]

What brand of injectors is everyone using?

At the moment, I'm of the belief this is a problem with injector timing. I doubt it is a problem with the CAS because as soon as sequential injection starts (when the car is warm), the car starts to misfire in the 2700 +/- 200 rpm range. During cold startup during simultaneous injection it is _smooth_ through this range, both revving in neutral and if I jump in my car and drive immediately.

Any ideas? What are all the components involved in controlling sequential injector timing? From the top of my head, all I can think of is ECU, CAS, fuel injector resistor pack and the injectors themselves. Anybody have anything to add to the list?