jkrueger

Engine: LM7 with stock heads w/2.00/1.59 valves, 227/235 .614/.621 cam, LS1 intake and TB, LS6 MAF, Shorty headers. It is controlled by a F-body computer and standalone harness. The engine is in a Factory Five kit car (Daytona coupe)

When the engine is warmed up but heat soaked yet if you do a WOT pull is stutters and misses so bad it will barely accelerate starting at about 4000 rpm. After driving for about 20mins or a few laps on the track you do the same pull and it is just fine.

The first picture is a screen shot from my HPtuners scan. This is when the engine is warm (ECT is 190) but not heat soaked yet. Starting at about 4400 rpm the injector duty cycle gets very eractic and actually hits 100%. the injector PW matches this. The AFR also drops (richer) slightly about 200ms after the 100% peak.

The second picture is about 10 mins into a track session and looks very normal.

So for some reason the computer is commanding a lot of fuel in the first example. It is like some sensor is working better when it gets heat soaked and giving the PCM bad info when it is not hot.

Any ideas would be helpful.

subeone

iTrader: (5)

get a wideband.

jkrueger

I have one. It is the green trace in the second graph.

JC

2xLS1

iTrader: (25)

Post the tune and the data log files. The dips in the narrow band graphs where you have the cursor are indicative of misfires. IDC is just a function of rpm and IPW. IDC=IPW*RPM/1200. Your TPS is not 100% in the first pic, it is in the second pic. That makes it harder to do a direct comparison between the two.

jkrueger

Here is the log and the file. I know the tune might have a few problems even though it was tuned by an experienced tuner, but I'm not sure that this problem is caused by the tune because it goes away once the engine heat soaks.

At WOT the pcm uses the main VE table and the PE table to calculate the injector pw correct? So the only sensors involved are the map sensor and the crank sensor right?

thanks for looking

subeone

iTrader: (5)

seems like you have a MAF tune

IDC will be inaccurate if injector data is inaccurate

as your rpm's climb, your MAF indicates there is less going in. Do you have an intake that collapses (suctions) under 5k+ rpm?

2xLS1

iTrader: (25)

This value determines when you are using a combination of MAF and VE Table for air flow calculations and when it uses 100% MAF. Anything above this value is using 100% MAF. This value in most stock calibrations is set at 4000 rpm. some are set at 3200 or 3400. Yours is set at 75 rpm so whoever tuned your car has it running on 100% MAF all the time.

jkrueger

It is a short intake. Cone airfilter - Aluminum 45 bend - MAF - Throttle body. All connections with silicone couplers.

Apparently I do have a MAF tune according to the last post. What the heck was the tuner thinking.

jkrueger

Well I guess I will change that. Any pros or cons on why you would have the MAF doing all the work. Seems like you would want a combo of both.

JC

2xLS1

iTrader: (25)

Well the GM Engineers seemed to want WOT to be 100% MAF. There is nothing wrong with that unless the MAF becomes a restriction. U usually lower it in my tunes to about 3200 RPM. I don't really buy into your heat soak theory. I never really saw any problems in the log when the TPS was at 100%. I did notice that your fuel trims are high and unbalanced between the banks.

subeone

iTrader: (5)

when you are WOT, there is a constant amount of airflow being read to the point where the MAF can keep up. But when you suddenly stab the throttle at say 2000 rpm then let off, that sudden airflow change (delta) can't be read that quickly by the MAF so that is where speed density becomes handy because it speed density is not dependent on airflow, but on air TPV (temp,press,volume)

jkrueger

Here is a log from some other scanning I did. I didn't have my Wide Band hooked up, but you can see (starting at frame 138) a pull I did at WOT (TPS 100%) with the same crazy duty cycles.

I will try setting my High RPM disable to 4000 and see if that helps the transition. Reading through that Dynamic section in the Airflow tab is an education in itself.

Is the "MAF airmass filter" a multiplier or an add on number to g/sec number the MAF gives you?

Thanks for all the help, this has given me a bunch of things to look into to try and fix this problem.

JC

Russ K

iTrader: (1)

Log the current misfires on cyl 1-8. Then you will know which cylinder is misfiring.

Russ Kemp

jkrueger

I did think of that and did log that data in some runs on the road (WOT and different loads) and did not see any misfire events. I attached the log below.

JC

2xLS1

iTrader: (25)

Your misfire tables are all maxed at 32767 effectively disabling misfire detection. Probably done for a cam.

jkrueger

Yes it does have a cam in it.

I'll go in and clear the counts and see if they pile up more in cylinder compared to the others.

I'm so far down the learning curve with HPTuners that I wonder if I'm even on the curve. The only other tuning software I have experience with is megasquirt and that was many years ago. These GM computer are like 100 times the complexity of the MS software.

Russ K

iTrader: (1)

Just max the idle misfire tables and return the others to stock.

Russ Kemp