LS1 Injector/Fueling Question on WOT

[Brootus]

I have a 1998 Camaro with an NA LS1 that I am having issues with intermittently popping/misfiring under WOT in the high RPMs, and it seems to get worse the hotter the car gets. I have been baffled on what this issue is and have been trying to figure it out but haven't had any luck. First I replaced all the spark plugs and wires with no luck. Its hard to datalog because its intermittent, sometimes the cars pulls smooth with no issues. But I was able to datalog it when the issue occured recently, I will post a picture below. I will upload the entire tune file tonight when I get home. But you can see in the pictures my injectors B1 & B2 & the duty cycle fall off under WOT before I let off the gas. Has anyone seen this before? I've had the same tune in the car for several years with no issues, and I've checked all my previous datalogs of the car and never seen this before. I appreciate any help or insight on this, I have been going crazy trying to figure it out.



log picture 1.jpglog picture 2.jpglog picture 1.jpglog picture 2.jpgcurrent tune 5-19-24.hpt7-7-24 misfire datalog.hpl

[Markolc81]

If it's worked fine for many years until now, and you haven't made any software changes, then it's something mechanical. First thing I would suspect is fuel pressure falling off in the high RPMs.

[Brootus]

Thanks for the reply Mark. That?s what I was wondering, like a weak fuel pump? I didn?t know if the logged injector pulse width per bank is what the ECU is commanding it to be, or what is actually being read. I know my tune is basically an open loop tune also never goes closed loop, and relies primarily on RPM and the MAP.

[bk2life]

I know my tune is basically an open loop tune also never goes closed loop

Why?
Is it that radical you need this?

[Brootus]

Absolutely not, it?s just how my tuner tuned it. It has a large cam and he was having trouble tuning it so he went that way with the tune I guess. But I?ve never been completely happy with the tune, but never had any major issues with it.

[gtstorey]

If the car is in open loop, it doesn't have a way to self-adjust to changing conditions. If something mechanically changes, even just a little from age, it's not going to run well, especially if it wasn't spot on to start with.

I would check fuel pressure and give it a good visual inspection. If no problems are found, I would get it retuned by one of the pro's on here.

[Brootus]

If the car is in open loop, it doesn't have a way to self-adjust to changing conditions. If something mechanically changes, even just a little from age, it's not going to run well, especially if it wasn't spot on to start with.

I would check fuel pressure and give it a good visual inspection. If no problems are found, I would get it retuned by one of the pro's on here.

That makes total sense actually, it would have no feedback to correct anything in my case then. In my head I was thinking if I had reduced fuel pressure it would pulse width the injectors longer to try and keep up with the fuel demand, but I guess that isn't true if you have no feedback right? I can install a fuel pressure gauge on my fuel rails and see if notice any issues to start, but I guess I can only tell that at idle or if I rev the engine up from under the hood.

[gtstorey]

Tape the gauge to the windshield so can see it while driving. Of course, if it's not correct while idling or snapping the throttle while parked, it isn't going to get better while driving.

[Brootus]

Tape the gauge to the windshield so can see it while driving. Of course, if it's not correct while idling or snapping the throttle while parked, it isn't going to get better while driving.

Excellent idea! I will test it at the rails first and then I can try and tape it to the windshield while driving and see how it reacts.

Does my graph in my picture of the injectors and duty cycle I posted make sense to you now? I kept thinking what I was seeing in my data log was what the car was commanding, but I was wondering why it would be commanding less fuel at high RPM's.

[gtstorey]

Injector/Duty cycle is still climbing with map/maf so I assume it's doing whatever it's set up to do based upon those parameters.

[Brootus]

Injector/Duty cycle is still climbing with map/maf so I assume it's doing whatever it's set up to do based upon those parameters.

If you see in my picture here, I circled the area where fuel starts to fall off and I am still under 100% throttle at this point and for a little bit after that. Up until that point it does look like its climbing with the map/maf.

DATALOG.JPG

[gtstorey]

That may just be PID reading frequency not lining up. If this is truly in open loop, it pretty much has to be following whatever values are set in the tune for injectors to whatever is controlling them. But I have never set anything up to do open loop.

But you need to look at your injector pulse width, not duty cycle since that is based upon rpm and your rpm is moving around in that section. B2 injector is holding out a little longer, maybe, than B1. But again may be polling rate.

And you are at 100% throttle, not under.

[Brootus]

That may just be PID reading frequency not lining up. If this is truly in open loop, it pretty much has to be following whatever values are set in the tune for injectors to whatever is controlling them. But I have never set anything up to do open loop.

But you need to look at your injector pulse width, not duty cycle since that is based upon rpm and your rpm is moving around in that section. B2 injector is holding out a little longer, maybe, than B1. But again may be polling rate.

And you are at 100% throttle, not under.

Sorry that was a terminology mistake on my end, I meant I am still at 100% throttle.

I did notice that with injector B2 is holding a little longer too. On this data log below injector B1 is holding just a little bit longer. Very strange to me. I don't know why the injectors would fall off like that while still at 100% throttle.

I thought maybe it was frequency not lining up at first too, but I looked at all my previous data logs of the car before I starting having these issues and the frequencies all line up near perfectly.


DATALOG 2.JPG

[gtstorey]

Injectors are not set to run on throttle, they are set to run map/maf or some combination. I think you are worrying to much about minor details when you likely have a bigger problem.

But have you looked at your tune to see how/what is controlling fueling and does that match the data log?

[Alvin]

It would be far better if you posted the log and not snap shots.

[Brootus]

Injectors are not set to run on throttle, they are set to run map/maf or some combination. I think you are worrying to much about minor details when you likely have a bigger problem.

But have you looked at your tune to see how/what is controlling fueling and does that match the data log?

Yeah you're probably right, I just have been struggling with this and this graph was the first clue I could find of a potential problem. To me it's definitely felt like a lean condition with the popping at high rpms but I haven't had any proof,

I have been looking at the tune quite a bit, it seems like it's primarily based off of the MAP and RPM for the fueling. It looks like ECT and IAT could play a factor too, but those all looked good and normal readings during the data log. I can send the tune file in a couple hours when I go home for lunch if you want to take a look?

[gtstorey]

I won't have the ability to download a tune until this weekend at the earliest and even then, I don't know enough about these ecm's to be able to review efficiently. Add in open loop, and I wouldn't be much use. But you might get others to weigh in if you post tune and log.

But go back to post #2. However, in open loop, the mechanical/electrical problem could be a small one.

[Brootus]

It would be far better if you posted the log and not snap shots.

Okay understood. I am going to upload my tune and log file in about an hour when I got home. Thanks!

[Brootus]

I won't have the ability to download a tune until this weekend at the earliest and even then, I don't know enough about these ecm's to be able to review efficiently. Add in open loop, and I wouldn't be much use. But you might get others to weigh in if you post tune and log.

But go back to post #2. However, in open loop, the mechanical/electrical problem could be a small one.

Yeah I feel you are right, since nothing else changed on the car I feel like it has to be a mechanical problem of some sort. I will test the fuel pressure just to see what its reading.

[bk2life]

I have a 1998 Camaro with an NA LS1

what is done to the engine?
CAI?
headers?
no cats?
large exhaust system?
cam?
cam specs?
Without this info and a tune and a datalog, we all area just guessing.

I have seen a few 'completed' tunes where the shop forgot to turn things back on since they were in a rush or lunchtime or whatever.
It is possible this is the case for yours.
On a street car, like under 1200 hp, there is no reason not to be using o2 sensors to help with fueling and overall drivability.

I'd like to see the tune, and I bet from a few comments in here, we can make it run much better for you.