Stock AFR ratio

Z_ealot · 03-17-2020, 01:52 PM

Quote:

Originally Posted by ByThaBay

To confirm you’re tuned correctly plot the afr target against the actual afr for each bank and the lines should follow each other relatively close. As far as the targets themselves, that becomes tuning preference based and each tuner can have his own targets that he wants your car to hit.

Already done and they follow each other exactly like they're supposed to, only reason this came up is because I've been burning oil and did a compression test to check the piston rings, all cylinders were good with the exception of 3 and 5 which were leaking, both tested at 210psi hot and 260psi hot/wet but lost about 20psi over the course of 1 minute with the leak becoming slower as pressure went down, tech suggested that afr was to rich and was fouling the oil and causing it to burn but the readings and targets refute that so I'm trying to get a leak down test scheduled at the dealership to see exactly what's going on

SonicVQ · 04-09-2020, 07:43 AM

Quote:

Originally Posted by Z_ealot

... I've been burning oil and did a compression test to check the piston rings, all cylinders were good with the exception of 3 and 5 which were leaking, both tested at 210psi hot and 260psi hot/wet but lost about 20psi over the course of 1 minute with the leak becoming slower as pressure went down, tech suggested that afr was to rich and was fouling the oil and causing it to burn but the readings and targets refute that so I'm trying to get a leak down test scheduled at the dealership to see exactly what's going on

What was the compression pressure for each cylinder?
For reference, the factory spec is:
•*Standard: 242-341 PSI
• Minimum: 178 PSI
•*Maximum cylinder to cylinder difference of 14 psi

How much oil does it burn?

Z_ealot · 04-12-2020, 09:50 AM

Quote:

Originally Posted by SonicVQ

What was the compression pressure for each cylinder?
For reference, the factory spec is:
•*Standard: 242-341 PSI
• Minimum: 178 PSI
•*Maximum cylinder to cylinder difference of 14 psi

How much oil does it burn?

210 across all cylinders hot and dry, between about 250-260 hot and wet across all cylinders. The only exception is cylinder 3 and 5 which start out at the same psi as all other cylinders but then lose about 20 psi over the course of a minute. As for how much oil is burning, keeping track of it since this last oil change i did it had burned a half quart in just under 1500 miles. Also threw a vacuum gauge on it just to test out and vacuum gauge reads a steady 16 in/Hg which seems like something's up there but talked to my tuner and he insisted it's fine. Also checked cylinders 3 and 5 with a borescope and they show no obvious signs of head gasket failure, still have a nice thin coat of carbon on each of the piston tops so not sure what's going on. Only thing i don't have available to me and I'm not capable of doing where i live is a leak down test which I'm trying to get scheduled at the dealership

SonicVQ · 04-12-2020, 01:02 PM

Quote:

Originally Posted by Z_ealot

210 across all cylinders hot and dry, between about 250-260 hot and wet across all cylinders.

Was the accelerator pedal pushed to the floor?

Quote:

Originally Posted by Z_ealot

The only exception is cylinder 3 and 5 which start out at the same psi as all other cylinders but then lose about 20 psi over the course of a minute.

Compression gauges have a check valve so the pressure doesn't drop to zero after cranking has stopped (where a intake/exhaust valve may be open)
IF after your test, the pressure dropped, that is a gauge issue, not a cylinder issue.

Quote:

Originally Posted by Z_ealot

As for how much oil is burning, keeping track of it since this last oil change i did it had burned a half quart in just under 1500 miles.

1 quart in 3,000 miles is in the normal range and you don't need to worry.
Start to worry when it burns a quart in 1,000 miles.

Quote:

Originally Posted by Z_ealot

Also threw a vacuum gauge on it just to test out and vacuum gauge reads a steady 16 in/Hg which seems like something's up there but talked to my tuner and he insisted it's fine.

Assuming the gauge is accurate, my stock VQ37 has an intake vacuum at hot idle of around 22 in/Hg.
You might be on to something here...

Quote:

Originally Posted by Z_ealot

Also checked cylinders 3 and 5 with a borescope and they show no obvious signs of head gasket failure, still have a nice thin coat of carbon on each of the piston tops so not sure what's going on. Only thing i don't have available to me and I'm not capable of doing where i live is a leak down test which I'm trying to get scheduled at the dealership

If this was my car, I would not worry about anything and just drive it.
However, for your peace of mind, I hope you can get a leak down test done.
Good luck!

Z_ealot · 04-12-2020, 01:27 PM

Quote:

Originally Posted by SonicVQ

Was the accelerator pedal pushed to the floor?

Compression test was done after heating up the engine a good amount and then taking everything apart to do the compression test and fuel pump fuse pulled, i did floor the accelerator pedal before and during engine cranking though just to make sure injectors weren't firing.

Compression gauges have a check valve so the pressure doesn't drop to zero after cranking has stopped (where a intake/exhaust valve may be open)
IF after your test, the pressure dropped, that is a gauge issue, not a cylinder issue.

I thought that might be the case, but in the case of all the other cylinders they did not leak compression like cylinders 3 and 5 did and i left the gauge on each cylinder for a good minute after cranking had stopped.

1 quart in 3,000 miles is in the normal range and you don't need to worry.
Start to worry when it burns a quart in 1,000 miles.

Good to know, I'll keep an eye on it.

Assuming the gauge is accurate, my stock VQ37 has an intake vacuum at hot idle of around 22 in/Hg.
You might be on to something here...

Tested with the same gauge before i had it tuned and it was at the same 22 in/Hg as your stock VQ.

If this was my car, I would not worry about anything and just drive it.
However, for your pease of mind, I hope you can get a leak down test done.
Good luck!

Thanks!

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