Back to stock boost?

Just a thought to see if you are indeed chasing unmetered air.

 

Use your Cobb and log

 

Af sense 1 (afr)

Af correction 1 (short term fuel trim)

Af correction 3 (long term fuel trim)

maf (metered air)

Rpm

 

Start with the car at operating temp and at idle

Slowly increase the rpms to about 3k

 

If the af correction is big at idle, and then gets smaller as you increase rpm, you are chasing a classic intake leak.

 

Note at idle the Maf should read something very near 2.5 g/s

 

 

I’ll add these to the log and get the info.

 

 

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On other cars I have read about owners with exhaust or transmission lines picking up false knock. Knock sensors can fail as well. I haven’t read about many 4th gen GT with this issue. (I am assuming the Knock sensors are similar)

If it were the knock sensor or something loose under the hood, I wouldn't think the octane booster would have made any difference. If i read your posts right it started to learn to 1.0 after you added it with good gas. It would read false knock regardless if it were the sensor Edited August 4, 2020 by poconoracing

If it were the knock sensor or something loose under the hood, I wouldn't think the octane booster would have made any difference. If i read your posts right it started to learn to 1.0 after you added it with good gas. It would read false knock regardless if it were the sensor

 

That is a good point.

Just a thought to see if you are indeed chasing unmetered air.

 

Use your Cobb and log

 

Af sense 1 (afr)

Af correction 1 (short term fuel trim)

Af correction 3 (long term fuel trim)

maf (metered air)

Rpm

 

Start with the car at operating temp and at idle

Slowly increase the rpms to about 3k

 

If the af correction is big at idle, and then gets smaller as you increase rpm, you are chasing a classic intake leak.

 

Note at idle the Maf should read something very near 2.5 g/s

 

Log below:

 

https://docs.google.com/spreadsheets/d/1iLBCRYbk2oJ6nQgKX9RDFkQqoEWlLWOxU3lIbUgh0FU/edit?usp=sharing

Looking at you log its a little tough to compare because it looks like you were snapping the throttle vrs a steady climb to 3000 rpm.

 

Its interesting, your car idles ~100rpm lower than mine, and i had the ac off. I also learned our cars don't follow the standard g/s rule for the MAF - normally it should be right around the engine displacement. Must be a turbo thing.

 

Add the MAP sensor to your log. It's listed as Man Abs Press in the Cobb. That would definitely affect your boost levels and play a big role in the Fuel metering

 

And warm up the car

start the log and take it from idle to 3000 rpm in the driveway.slowly and steadily.

 

I attached mine so we can compare.

datalog1.csv

Edited August 6, 2020 by poconoracing

I'll add the MAP sensor...for some reason I thought you said MAF.

Here you go:

 

https://docs.google.com/spreadsheets/d/1-rVVv578_hox41iKgGfbs-T5vnNbuci5hhIwjiREHeI/edit?usp=sharing

look at your line 86, and my line 229

 

same rpm - your MAF is showing more air (13.6 g/s vrs 11.4) and less vacuum (4.43 psi vrs 3.98) - the MAP is showing relative air pressure - lower is more vacuum. And Boost psi (your -9.78 and my -10.18) again my car has more vacuum at the same rpm

 

I'm at about 1200ft above sea level and kansas city is bout 910ft so there would be a little difference (about .2psi if my googling is accurate)

 

So first, check to see if the MAP sensor is correct. Add it as a gauge on your accessport and key on, engine off see what it's reading. It should be barometric pressure, same as your weather app. You'll have to convert inhg to psi.

 

Assuming it reads correctly, you have to have some sort of intake/vacuum leak or the MAF is over reporting the airflow.

 

One thought is plug the hose to the PCV valve temporarily where it eneters the intake and see if it's stuck open. You wouldn't see it, but it would be a leak.

 

I assume you dont have a smoke machine - Check every connection and hose from the airbox where the MAF is and the intake plenum. Pull the milkjug from the right fender out and check it for cracks, anything. Lastly do a vacuum test on the motor. Maybe you have a leak between the manifold and the head, I doubt that but it's possible. This screams something was disturbed by your body shop. Maybe cap the vaccum port for the evap system and see if that solves it. Youll get a CEL, but it may narrow it down the EVAP system. Much of the evap system is in the rear of the car. I think if this were the issue you would have a CEL for an Evap leak.

 

I attached the service manual info to vacuum test the motor. You'll need a vacuum gauge but its pretty simple.

 

As far as the MAF goes all you can do is replace it. If you can't find any leak, and the MAP is ok. Go OEM or denso. Aftermarket MAF's are a crap shoot.

 

If I can think of anything else I'll post it

5. Intake Manifold Vacuum.pdf

Edited August 6, 2020 by poconoracing

There is still a good amount knock reading on cyl4. Air leak can still be a factor, however upon my experience.. it be all cylinders showing counts then.

 

If you’re up to the task.. swap cyl 2 and 4 injectors and see if it’ll change the count.

 

 

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On every car I've ever worked on what you just said is 100% true. You would get lean misfires on all cylinders.

 

I don't know if its the knock sensor placement, or the design of the cooling passages with the hotter cylinder #4, but for whatever reason a slightly lean mixture = knock in cylinder 4.

 

You do raise a definite possibility - a partially blocked/sticking fuel injector issue could do it.

 

fueling would be the next logical place to look.

I have worked on injectors before on my old Cherokee. Ended up having to replace all of them. Got pretty good at removing the rail in like 10 min with all the troubleshooting.

 

I’ll check the procedure on the GT.

 

Edit: just checked, the intake manifold has to come off?

 

 

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Edited August 7, 2020 by Falcor

I have worked on injectors before on my old Cherokee. Ended up having to replace all of them. Got pretty good at removing the rail in like 10 min with all the troubleshooting.

 

I’ll check the procedure on the GT.

 

Edit: just checked, the intake manifold has to come off?

 

 

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Negative

You should be able to do everything while the intake is installed.

Remove the “death” shield from the tgv housing. About four 12mm bolts. Believe also a ground point is connected on the rear of the shield.

Once that’s removed, you can access the two 12mm holding the rail down.

After that, disconnect the injectors connecter and swap them. Make sure to oil up the orings and inspect them.

 

 

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I just thought of something else you could easily check that would affect fueling.

 

Your Intake air temp sensor and coolant temp sensor could throw off your ecms fuel strategy.

 

Pretty easy to check with the Cobb. With the car cold, select them as gauges and turn the key on but don’t start it. The should both be reading ambient air temperature.

 

The IAT is part of the MAF sensor.

I just thought of something else you could easily check that would affect fueling.

 

Your Intake air temp sensor and coolant temp sensor could throw off your ecms fuel strategy.

 

Pretty easy to check with the Cobb. With the car cold, select them as gauges and turn the key on but don’t start it. The should both be reading ambient air temperature.

 

The IAT is part of the MAF sensor.

 

 

He unplugged the maf once and drove it with the same issue still. Therefore maf is fine.

 

Unplugging maf causes the car to run off the factory specs on ecu and map sensor.

 

 

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You know, looking at that last log again I just realized you need to log AF3 learning, not correction.

 

Learning is the fuel trim

He unplugged the maf once and drove it with the same issue still. Therefore maf is fine.

 

Unplugging maf causes the car to run off the factory specs on ecu and map sensor.

 

 

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Just considering things that can be easily checked that would effect the fuel strategy.

I have worked on injectors before on my old Cherokee. Ended up having to replace all of them. Got pretty good at removing the rail in like 10 min with all the troubleshooting.

 

Negative

You should be able to do everything while the intake is installed.

Remove the “death” shield from the tgv housing. About four 12mm bolts. Believe also a ground point is connected on the rear of the shield.

Once that’s removed, you can access the two 12mm holding the rail down.

After that, disconnect the injectors connecter and swap them. Make sure to oil up the orings and inspect them.

 

The death shield is a PIA to R & R, I think it is only 3 bolts. The middle bolt is will need a swivel socket and you will be doing it almost blind. I would replace the o-ring and 2 injector gaskets. You don't need to create any additional issues due to fuel leak or intake manifold leak.

 

I would probably check for intake track for leaks 1st. Trust me, the fuel rail won't a 10 minute job like your Jeep. I had to do it twice on the driverside, because I ran the injector wiring wrong when I did the intake.

I'm starting to miss that old Jeep.

 

Hopfully I'll have time to check it out this weekend. It's hard finding time since we are packing and prepping the house for sell. We are getting a temporary rental until we sell our house in KC and then find a house in Pittsburg, KS (company moving).

fwiw, my knock sum always read higher for #4 without issues. The sensor is mounted closer to that cylinder too.

fwiw, my knock sum always read higher for #4 without issues. The sensor is mounted closer to that cylinder too.

 

Does your DAM reset to .812 on each startup like mine?

I have the Cobb ots stage 2 tune, and it resets at 1. Every few months I catch it at drop at .90