Just started finished engine swap, trying to tune 4.8 (wont run right)

[agentruley]

The engine just doesn't feel right.
When cold it misfires hard then after it warms up a little bit it magicly runs a lot better (that was a month ago)
Finally able to drive it down the street, doesn't seem like its missing anymore when cold.
But still doesn't feel right.
Low RPM, under load it jerks and hesitates like crazy, also on a WOT run, as soon as I gun it, it jerks back and forth real hard. idk why.
I have the run I was running, which was just modified to take out some KR and disable Torque management, because when WOT, I was getting -5 degrees of timing (wtf) and took that away.
I also have two logs, one before I took out TM and one after.
I think I might have a sensor bad? (o2, knock, maf) idk but it jus does not run right.
It doesn't have enough power to spin the tires (t56) with a clutch dump. Something isn't right.

[aldrichg9]

Subscribing.
I looked at your logs and want to learn from what others have to say.

[agentruley]

I keep trying to add timing persay (but really keep disabling things that take away timing) and it keeps running better and better.
So I did a few more runs, here is a log and the change in the tune.
I think i either have a broken/bad injector or vacuum leak based off o2 readings or I have a bad sensor, OR i have them flip flopped or wired incorrectly.

[5FDP]

Per the fuel trims, both are at +16 or above, that means a vacuum leak just about everytime.

I also noticed on the WOT run, your bank 2 sensor 1 drops to under 100mv and never moves untill you drop out of the throttle. It should stay with the bank 1 sensor 1 and be above 800 at WOT. Same thing of the second scan, wither 1 o2 sensor drops to under 100mv or both dropped to below 100 and stayed there.

Part of the issue is there.


On your tune, I would set the hot/cold PE % to something like 40-50% instead of 85% to help get the power on sooner, remove the PE delay or put it at 1500 rpms.

[agentruley]

Ok. I understand. Could the o2 and FT readings also point to an injector that is always lean?
And so know do I need to replace said sensor?
or both?

[agentruley]

Switched sensors on the sides and did another run.
I don't know what to say.
How come both the sensors read differently when the engine isnt even running?
Something is funky.
So here is another log of a WOT go around. two or three times,
and then the other log is one of me putting the engine under load at low rpms. to watch for knock and FT values.
From the values I am looking at. either the sensor is bad, or I have a vacummleak/bad injectors or something wrong with fuel system.
Anyone have any input?

[badbowtie]

Like 5FDP Mentioned about fuel trims you are way off on them it could be running bad since they are so far off you are way lean.

[agentruley]

Ok I understand that. But what I dont understand is whats making it lean. Is it the tune thats making it lean?
Is it an injector or vacumm leak and if so how do I determine the difference in between software lean and hardware lean.

[2xLS1]

Your airflow model is off. You are only flowing .56 g/cyl of air at WOT so the computer is only injecting fuel for that airflow and that is why it is lean. Look for an air leak downstream of the MAF sensor.

[agentruley]

So I did the smoke thing, no leaks?
But I did unplug or 'fail' the MAF and ran it on just the MAP, and for some odd reason, it seemed a bit more peppy. It keeps getting faster and faster.
This is a 4.8 with the NBS truck manifold, you think maybe I have a intake gasket leak?
But now this time ago round, I know have knock?
Knock retard is now showing its ugly face, and I am not even running that much timing.
I am so confused now....

[2xLS1]

I'm not seeing any KR in that log. The WOT A/F is richer in that log going by the narrow bands. It is using the VE table for air flow data with the MAF unplugged. You also lost IAT data when you unplugged it. The airflow data in the histogram is skewed because you still have the MAF in the table display. What is this a transplant in and how and where in the intake tract is it mounted. This could be just needing to calibrate the MAF table for how it is mounted.

[agentruley]

I'm not seeing any KR in that log. The WOT A/F is richer in that log going by the narrow bands. It is using the VE table for air flow data with the MAF unplugged. You also lost IAT data when you unplugged it. The airflow data in the histogram is skewed because you still have the MAF in the table display. What is this a transplant in and how and where in the intake tract is it mounted. This could be just needing to calibrate the MAF table for how it is mounted.

1995 OBS chevrolet truck.
I have the MAF right at the throttle body after a 90 degree elbow.
You say there is no KR but I see on the histogram the red line that is KR and it is quite frequent of a few degrees, like 2-5.
Should I load a 1BAR map tune and run it, seeing if it makes any difference?
for some odd reason I have this itch in my neck saying its a bad injector but I have no idea on how to tell....

[mecanicman]

Can you post a underhood picture of setup? What gear ratio in truck? Tire size and make? What trans?

[agentruley]

4.8/t56 3.42 rear end 255/65/16 tires
I know the vehicle speed thing is off
The reason on why I am just so paranoid about this was because in the winter, I would start it up, and it would missfire and not run at all, barely revving to 3grand and now since it has got hot suring the summer. everything is fine.
Seems sketchy to me....
476133_10201256733766381_1672759918_o.jpg

[mowton]

What is done to the motor? Is it stock? If so why are there so many changes from the stock calibration? Post up info on the setup please. If you are trying to tune in MAF, then you need to set the High RPM Disable to 400 to preclude the VE from influencing your readings. You are in closed loop so I am assuming you are tuning with the LTFT which will take quit some time to change so you need to drive around for several sessions to get right.

Your tune appears dangerously lean so need to get the MAF dialed in first. Slow easy runs, log the STFT using MAF histogram and collect nice steady state data and then move up to the next MAF cell.

Ed M

[agentruley]

Good advice man, but screw the MAF.
Engine is stock, and the changes were made by the last person?
I loaded the stock timing tables and VE tables and then set the computer to never go below 18 degrees of timing and then loaded the 1BAR SD tune
AND WOW!
What a difference!
It runs sooo much better now!
I had no idea what kind of difference that makes and now it revs up alot faster and doesn't feel starved in the higher RPMS
Can someone take a look at this new TUNE and LOG of the SD run I just made?
I think I might be maxing out injectors?
But also since I put in the stock VE tables, the LT and ST FT's are leaning back out, or going back closer and closer to 0.
Thats good right? Because before instead of leaning out, they were dumping fuel to compensate for either badinjector/vacuum leak,or bad MAF-MAFsettings

[agentruley]

And then compare that run to the cold/MAF tune run I did earlier this morning

[mecanicman]

You seem hell bent on not running the maf, so the advice I was going to post is pointless. Get your self an IAT sensor and wire it in. Correct your speed so the pcm knows how fast its going. Put stock data back in the file. And then tune your ve table.

[agentruley]

You seem hell bent on not running the maf, so the advice I was going to post is pointless. Get your self an IAT sensor and wire it in. Correct your speed so the pcm knows how fast its going. Put stock data back in the file. And then tune your ve table.

Nah, I am going to exchange my current MAF for another one but I am still going to keep the 1BAR sd tune for now because it runs so darn good.
I will tune the VE when I figure out how, but now I have to swap rear end gears.
But the advice, i still want to hear it
Just trying to make sure everything that was wrong with the engine was tune stuff, and not like a vacuum leak or a bad injector.

[mowton]

And then compare that run to the cold/MAF tune run I did earlier this morning

Not at a computer now. Will check out the files when I get on one. Not sure why you would want a speed density tune on a stock 4.8 but go the route you feel comfortable with. The maf tune us really a blended operation between idle and 4000 rpm and the maf better adjusts for weather changes.

Ed M