[3-Serious]

So I started to feel a slight hesitation when I would floor it in 3rd gear around 4thousand rpms. I figured it had to be spark plugs because they have around 20k on them. At first I canceled out the idea of it being injector related, because all 6 were replaced last year around this same time. I also had the cylinders walnut blasted at the same time. So to me the only reason for this hesitation had to be the spark plugs.

So I today I replaced the spark plugs and the car felt better. Than slowly as the day went on I noticed it slightly happening again. So I logged the car on the way home, everything looks perfect the timing, AFR, boost all looked spot on. Then I took a look at my STFT and they were going all the way up to 30-34% by midrange and then brought down to negatives by the meth. On my old logs from about 2-3 months ago my STFT's wouldnt go above 12-15% then would come down by because of the meth. So I believe its injector related, and I'm scheduled for a tune tomorrow. So the question is, is it still safe to get tuned? I would post the logs but I use Virtual Dyno to veiw them and they are impossible to read with a screen shot. If someone would like to take a look at the logs I will send you the file if you PM me your email.

thank you and sorry for the long rant.

[Jeff@TopGearSolutions]

It's possible. But in defense, it is much colder then it was 3 months ago, so it would require more fuel as the air is more dense, theoretically.

[BMJ]

Originally Posted by Jeff@topgearsolutions

It's possible. But in defense, it is much colder then it was 3 months ago, so it would require more fuel as the air is more dense, theoretically.

agree with Jeff, if you notice that stock i would think it will feel much worse with a tune going.

[3-Serious]

Originally Posted by Jeff@topgearsolutions

It's possible. But in defense, it is much colder then it was 3 months ago, so it would require more fuel as the air is more dense, theoretically.

I was actually just thinking that too, the last log I did was in early October weather was no where near what it was like today. For example my Inlet temps in October were 60 at its lowest, today's my inlet temps were reaching 37 degrees. The car feels strong it only feels hesitant once an a while only from a 3rd gear roll maybe its in my head because I drive my car less in the winter.

[Fun w/N54]

Assuming it wasn't your TCS kicking in maybe time for blasting...how many miles?

[3-Serious]

Originally Posted by Fun w/N54

Assuming it wasn't your TCS kicking in maybe time for blasting...how many miles?

Had it blasted last January I don't think it'd be due this soon. Like I said I also changed the spark plugs today too and the Injectors were done last January as well. Also when I log or get on it I always turn TCS completely off. So I don't know, and it only happens from a 3rd gear roll. I guess either way I'm going to go in for my tune appointment and hope nothing bad happens

[sickem]

Where are you getting tuned?

[benzy89]

Try pouring in some strong fuel injection cleaner or 100 octane (best option) -- It's possible the injectors might be dirty/clogged up

[GeorgiaTech335coupe]

I just replaced an injector yesterday that was only 3 months old. It was 100% bad and caused my car to have slightly hiccups mid pull, usually misfire up top, and cause my STFT of that bank to act funny in comparison to the other and cause AFR to act funny as well.

These injectors can go bad very quickly....take it from someone who has had over 20 injectors in his car.

[3-Serious]

Originally Posted by GeorgiaTech335coupe

I just replaced an injector yesterday that was only 3 months old. It was 100% bad and caused my car to have slightly hiccups mid pull, usually misfire up top, and cause my STFT of that bank to act funny in comparison to the other and cause AFR to act funny as well.

These injectors can go bad very quickly....take it from someone who has had over 20 injectors in his car.

See my car isn't hiccuping or back firing just slight hesitating then it flys like usual. and in my logs the AFR looks solid still and so does everything else.

[3-Serious]

Originally Posted by benzy89

Try puring in some strong fuel injection cleaner or 100 octane (best option) -- It's possible the injectors might be dirty/clogged up

ill give that a shot , do you recommend any good ones?

[Joshboody]

Originally Posted by Jeff@topgearsolutions

It's possible. But in defense, it is much colder then it was 3 months ago, so it would require more fuel as the air is more dense, theoretically.

with flash your trims shouldn't change with weather... it's something else either in hardware or tune adaption. If the banks follow each other likely not an injector.

OP, post a log... if you can catch the hesitation, it should show in the log. Can you hear a change in exhaust note when it happens?

[Jeff@TopGearSolutions]

Originally Posted by Joshboody

with flash your trims shouldn't change with weather... it's something else either in hardware or tune adaption. If the banks follow each other likely not an injector.

OP, post a log... if you can catch the hesitation, it should show in the log. Can you hear a change in exhaust note when it happens?

Is that because it is load based? Therefore in more "efficient" colder weather where the air is more dense it will simply lower boost but power will remain similar and therefore require similar fueling?

[BlueBimmer]

Originally Posted by GeorgiaTech335coupe

I just replaced an injector yesterday that was only 3 months old. It was 100% bad and caused my car to have slightly hiccups mid pull, usually misfire up top, and cause my STFT of that bank to act funny in comparison to the other and cause AFR to act funny as well.

These injectors can go bad very quickly....take it from someone who has had over 20 injectors in his car.

This is a very interesting thread, ever since I got my car back from the dealer with new plugs, I feel some osscilations mid range when I floor it. It is consistent and it's in the middle of the power band (Cobb Stage 1 Aggressive) - it was very smooth before but isn't anymore. Could this be a bad injector - how can I tell?

[eric@helix]

The bottom line is that you should sort out the problem before tuning the car.

[Joshboody]

Originally Posted by Jeff@topgearsolutions

Is that because it is load based? Therefore in more "efficient" colder weather where the air is more dense it will simply lower boost but power will remain similar and therefore require similar fueling?

Any ECU tuning will be mapped per MAF whether calculated or measured directly. LTFT adaptation can change the STFT but this doesn't seem to happen at WOT. If the OP changed hardware (altering VE) this could change trims.

Anyway log boost channels, at least timing setpoint/correction cyl 1, LT/ST trims. And maybe you pump pressures. I bet its torque reduction by the DME

[GeorgiaTech335coupe]

Originally Posted by nickkg37s

See my car isn't hiccuping or back firing just slight hesitating then it flys like usual. and in my logs the AFR looks solid still and so does everything else.

How much boost are you running? These misfires become much more pronounced with more boost and when spraying meth.

Honestly, it sounds like you do have an injector going bad. I've replaced so many injectors on my car and this is how they all started. Slight hesitation that would turn into a misfire. Hard to reproduce on stock boost, easy when tuned.

The best way to test it is to lug the car (go in 3rd at around 2000 rpm and floor it).

The last one I dealt with was a little different now that I have a single turbo, but my point was that injectors can go bad very quickly. I am extremely well versed in dealing with misfires on stock turbos, which was usually bad injectors. Happens when you have replaced 20 of them.

[benzy89]

Originally Posted by nickkg37s

ill give that a shot , do you recommend any good ones?

Chevron Techron is the mainstream option, I'd personally recommend Lucas Oil (they sell a specific "Fuel Treatment" for Turbo/Performance Engines). Like I said, a gallon or two of 100 octane from a Sunoco station would be the best (try to get it in when you're real low on gas & run only the 100 octane).

[3-Serious]

Originally Posted by Joshboody

with flash your trims shouldn't change with weather... it's something else either in hardware or tune adaption. If the banks follow each other likely not an injector.

OP, post a log... if you can catch the hesitation, it should show in the log. Can you hear a change in exhaust note when it happens?

Well im not going to be home tonight, but the injectors follow eachother and in the same pattern as they always do reaching there peak at 4k then going back down together. ill post logs tomorrow. Also I went to get tuned today and em finally on the new v402 maps. The cars hesitation seem to went away. But will log again tomorrow to be for sure. Also put down 415whp and 448tq

[3-Serious]

Originally Posted by GeorgiaTech335coupe

How much boost are you running? These misfires become much more pronounced with more boost and when spraying meth.

Honestly, it sounds like you do have an injector going bad. I've replaced so many injectors on my car and this is how they all started. Slight hesitation that would turn into a misfire. Hard to reproduce on stock boost, easy when tuned.

The best way to test it is to lug the car (go in 3rd at around 2000 rpm and floor it).

The last one I dealt with was a little different now that I have a single turbo, but my point was that injectors can go bad very quickly. I am extremely well versed in dealing with misfires on stock turbos, which was usually bad injectors. Happens when you have replaced 20 of them.

going to log agsin tomorrow and keep an eye out for misfires. Also the hesitation is only in the beging the rpms before then by mid range its gone and by top end its movingg.

[3-Serious]

so here some logs. Sorry if there hard to read its a pain to read sceen pics of VD logs, but I but the main index line on when the highest points of the STFT's were read and you can also see some of the other stuff I logged.

The first log is from October. (weather was in the 50's)

The second log is from two days ago when I made this thread. (weather was in the 20's)

The Third log was today after I was flashed on to the new v402 maps and had some psi added by my tuner.(weather was mid 30's)

The hesitation is still slightly there but it seems to be temperamental as in sometimes I don't feel it and sometimes worse then others. Also only during the first few hundred- thousand rpms when I floor it, regardless of what gear I'm in.

[Mike@N54Tuning.com]

Originally Posted by eric@helix

The bottom line is that you should sort out the problem before tuning the car.

+1

Mike