Low karmen hertz, good vacuum, bad idle and performance

[Fattie92]

well im still tryin to figure out why my car runs like crap, and gets 43 counts of knock at WOT. I was starting to think my MAF was bad, but im not to sure, so ill ask you guys. I cant find to much about Karmen Hertz readings to determine if i need a new MAF or not... Well at idle my Hz are betweem 25-31hz. Iv read that if you have bad vaccum, it can cause a low reading. Well i have good vacuum at -19in. I have one very minor boost leak at the throttle body though... but i do not think this is the problem. My low fuel trim is at 135%, and i had a 14% correction on it to have it to 100%, but now its back up in the 130's. At 5560rpm, im getting 1603.9Hz, injector duty cylce is at 96%, pulse with is at 20.73ms, knock is at 43, and o2 is at .89


any help would be appreciated

 

[psychlow]

Sounds to me like you're either maxing out your fuel pump or maxing your injectors. 96% is pretty high for duty cycle. .89v is pretty low for O2 voltage.

EDIT: Now, I realize you're running 18PSI on stock injectors w/ a 255. What do you have your base fuel pressure set to?

 

[nineD5_GS-T]

What is your base timing set at?

 

[Fattie92]

i turned the boost down as soon as i relized what was goin on. Its at 15psi. I have the 255 walbro pump with NO regulator ....i should really get one i guess... i didnt know i needed one. Base timing is at 5, and with the advance it goes to 8 degrees. I took a look at my SAFC peak tonight after i got on it and my karmen was at 2020hz, 43 knock on the logger at 7023rpm and -1 degrees. i figured i need to get some injectors, regulator, and a 2g mas ... but then again i might be working around the problem and just "throwing parts" at it..

 

[psychlow]

First off, good job at turning down the boost. A lot of kids on here know they have a problem and don't think to do that, and bye-bye engine.

Second, throwing parts at it when you know you need them or are going to need them is not a big deal. It's when you replace parts that don't need to be replaced that it becomes something that's wasteful.

If you want to run more boost later, you'll NEED bigger injectors. End of story. So if you put 650s in now to see if it'll solve your problem and it doesn't, no big deal you need them anyway. Same for an AFPR. You need to be able to set the base fuel pressure with that 255, end of story, unless you are a SAFC tuning god, and even then it probably won't always run right.

To me, it seems like you're maxing out your stock injectors at high RPM. If you get an adjustable fuel pressure regulator, you can set the base fuel pressure high, and this will benefit your situtation two ways:
1) You can run higher pressure to make those 450cc stockers run more like 500 or 510 cc injectors

2) Your fuel pressure curve will be linear, and therefore MUCH easier to tune. If you're trying to tune using any of the SAFC tuning guides online right now, it's not going to work because your fuel pressure will be around 50PSI (when the ECU expects 37PSI) until you hit over 13PSI, and then it'll start increasing pound-for-pound.

So right now, instead of having a linear fuel pressure graph, you have a flat line and then a little bump at the top end when the boost pressure "overcomes the overrun," if that makes sense.

Hope this helps.

 

[Fattie92]

yeah that helps a little bit. Will the AFPR help out at idle?
This problem might be totally different, but every now and then I'll get idle surge. IAC is good, and everything else is good, but then again, I'm more worried about WOT then idle.

How could I be out doing the stock injectors with what little I have done?

 

[nine5raptor]

The 14b doesn't have any trouble maxxing out the stock injectors.

 

[talon1979]

Have you swapped out your old lifter for the new style? This may be your problem. Also, it sounds to me like you should replace your throttle body shaft seals. Those things can hurt you more than you may think. I would first replace the shaft seals, then if you still have the problem I would research getting the new style of lifter.

 

[talon1979]

To my understanding a datalogger can't tell if you have bigger injectors, so your duty cycle won't drop. I put in 680cc injectors on my car w/ the same boost and other mods and my injectors still read 97% duty cycle when I know they are not working that hard.

 

[talon1979]

Same for an AFPR. You need to be able to set the base fuel pressure with that 255, end of story, unless you are a SAFC tuning god, and even then it probably won't always run right.

I agree with what you said except for this part. I know of several 1g's w/ 255lph fuel pumps and the car runs just fine. You can take the logger and the SAFC and lean or richen w/ the SAFC until your low fuel trim is near 100%.

 

[Fattie92]

i have thought about the new lifters, but have yet to do them. Also... the throttle body shaft seals... yeah well both of them were leaking, then i replaced them with the ones from Mach V, and then did a boost leak test... no leak. then a week down the road i heard a leak, did another boost leak test, and it was coming from the TB shaft seal again.....####ing bastard seal

I have also heard of alot of 1g's running fine with the 255 w/out an AFPR ... but then a few didnt run good... mine might be one of them ...

Fuel trims.. Without the SAFC, the low fuel trin on the logger reads 139.9% i gave the lo setting a correction of 14+% to get it down to 101%, a week later they are back up to 130% with the same SAFC corrections.

Emissions... I failed emissions. I blew 420ppm Hc's when the limit is like 226ppm. Everything else checked out ok though

 

[nine5raptor]

Originally posted by talon1979
To my understanding a datalogger can't tell if you have bigger injectors, so your duty cycle won't drop. I put in 680cc injectors on my car w/ the same boost and other mods and my injectors still read 97% duty cycle when I know they are not working that hard.

Whatever the logger reads is what your IDCs are. If it says 97%, then they are at 97%.

Did you tune the car after installing the 680s? The only way IDCs would be the same on the same boost/mods is if you did not lean out the car for the larger injectors and were running extremely rich.

 

[talon1979]

I would imagine that your leaks caused your fuel trims to go back up. Since the car is running so much fuel now that is probably why it can't idle well or pass emissions. If you need to do emissions again lean your car way out right before you get the car tested. You may want to reset the ECU as well to put all of your fuel trims back to 100%.

You should be able to get this to work if you fix your leaks, if not, then an afpr would probably help you.

 

[nine5raptor]

Originally posted by Fattie92
Fuel trims.. Without the SAFC, the low fuel trin on the logger reads 139.9% i gave the lo setting a correction of 14+% to get it down to 101%, a week later they are back up to 130% with the same SAFC corrections.

Next time you do this, set you afc, then reset the ecu.

Watch the 02 trim.

This will give you immediate feedback as to whether the afc is set right and where the fuel trims are going to be moving to.

 

[psychlow]

Originally posted by talon1979
I agree with what you said except for this part. I know of several 1g's w/ 255lph fuel pumps and the car runs just fine. You can take the logger and the SAFC and lean or richen w/ the SAFC until your low fuel trim is near 100%.

Yeah, but it still takes forever. And what happens when you get more or less voltage/amperage to the pump depending on alternator load? Because the FPR is being overrun, you're at the mercy of the pump's output.

Not only that, the FPR gives you another way to tune your car. Hitting fuel cut? Raise your base pressure some and dial down the SAFC.

AFPRs aren't cheap, but considering what they let you do, they aren't THAT expensive. I don't see why everyone tries to run without them.

 

[Fattie92]

Ok 2g mass was ordered today, next ill order injectors.. but what to go with?? 550's? or 660's ? 550's are cheap and easy to find, but will it be enough fuel? Im sure it will be for now... but then if i throw a bigger turbo on then ill need the 660's?


also, im gonna fix the TB seal leak tomorrow.... i hope.

 

[Fattie92]

TB shaft seal is fixxed.. Drove it home and my short fuel trim is 107% at idle, med trim is 99% and long trim is 99%.

I didnt log any runs, but after i got on it a few times i did notice the knock reading was still the same as before.

 

[Fattie92]

Ok well, sorry this took so long, but i just got my AFPR today... And i hope someone is still reading this post......

well installed it and set base to 40psi, and boost is still at 14... my idle is little better,,... actualy falls down to 790-800.. well i look at the logger and adjust my low fuel trims a little.

Left the highs alone... drove it and logged 25 counts of knock at 5000 rpm... so i messed with the safc to bump it down, got a 13% correction... got it between 10-14.. if i go higher, it will increase knock

knock now starts at 3700rpm

rpm duty cycle timing knock o2
3700 56 15 9 .93
4500 77 12 12 .93
5000 84 13 13 .93
5500 93 16 11 .93
5900 100 18 10 .91
6000 98.5 17 11 .91
6200 99 11 11 .91



Its pretty clear that the afpr with the safc HELPED ALOT.... but still getting some knock...now can i up my base fuel pressure to help out? It would probably bring my duty cycle down a bit more.... which would be good... but i already got it at 40psi... let me know what you think PLEASE!!

 

[CanadianTSi]

Try bumping up the pressure abit

 

[CYCLONE]

I'm surprised that no one even mentioned anything about the knock
sensor itself being bad. Reach around under the intake manifold
the sensor is bolted on the side of the block, right in the middle.
Feel where the wire goes into the sensor, if you get any gooey
(almost like tar) stuff on your fingers its time to replace the sensor.

Let us know what you find. How many miles are on the motor?
You might also have carbon buildup causing detonation.

 

[Fattie92]

Originally posted by CYCLONE
I'm surprised that no one even mentioned anything about the knock
sensor itself being bad. Reach around under the intake manifold
the sensor is bolted on the side of the block, right in the middle.
Feel where the wire goes into the sensor, if you get any gooey
(almost like tar) stuff on your fingers its time to replace the sensor.

Let us know what you find. How many miles are on the motor?
You might also have carbon buildup causing detonation.

The knock sensor is new from mitsu... bout 4 months old. engine has 89900 miles on it.


what is to much base fuel pressure? It appears that im still maxxing out my injectors.... ill be getting 550's within a few weeks... and i got a 2g mass chillin in my room waiting for the 550's.

 

[nine5raptor]

I would keep the base pressure under 60 psi

 

[Fattie92]

...well i noticed im geting up to 43 counts of knock at part throttle....

and after work i bumped my base fuel pressure to 50... car now feels SUPER slow, and eventualy has a sputter higher up. im gonna go cut it back to around 40-45. With all that happening, i noticed very little to no knock at WOT... but felt so slow!!

 

[Fattie92]

OK well i bumped it down to 45. drove it hard, same thing... slow and sputter... so i figured im dumping fuel now, so ill cut it down on the safc. Well dropped my hi from 13% to 10%... semmed little better.. sputter wasnt as bad. So i bumped it down more to 6%.... no more sputter, feels like its getting faster... so i bumped it down more to 3% across the board for my hi. Runs like a champ there i did a quick 1,2,3 gear log, and got no knock in 1st or 2nd, and 12 and dropping in 3rd. My o2's are now reading .95-.97 with 95% duty cycle.


my MBC is screaming at me to turn it up now.... ahh so tempting!!