Idle AFR changing whilst Idling

[kur4o]

I don`t want to scare you but if there is no oil cooler in the radiator, the options are very limited.
A cracked block is one option. In the heads there is no pressurised oil. If it was a gasket problem, it will be more likely a coolant in the oil problem.

Did you see the actual afr fluctuating at the wideband.

[Terminal_Crazy]

It's a '95 Z28 LT1 with the KC4 Oil Cooler (Coolant runs around the Oil Filter type).

The Oil is fine apart from it disappearing.
I suspected the Edelbrock LT4 Inlet Manifold but have re machined the port faces.
It is however leaking oil now from the rear wall since i went to synthetic after the rebuild.

I've read a bunch of threads about the '95 KC4 leaking oil into the coolant.
'93 and '94 seem to be better and by '96 it wasn't available.

Not had chance this weekend to pull it off and check yet.

Not sure yet also whether to delete it or to just install a full oil cooler.


Thanks
Mitch

[Terminal_Crazy]

Did you see the actual afr fluctuating at the wideband.

It always fluctuates at idle upto around half a point either side but I'm not to bothered about that.

It was running for a good hour mainly sat around 12.5 but one time i looked it was sat at around 15:1.
It never missed a beat, never changed tone or speed as far as i noticed.
AFR was just up there.
10 mins later it was back at around 12.5.

I'll log it next time i run it just to check.
I just thought it was a bit weird as everything is turned off that can be in tuner pro.

Thanks
Mitch

[kur4o]

Oil cooler is the main suspect. Extrenal leaks can`t get into coolant flow.

You can bypass the oil cooler real easy.
With a hose from radiator to pump and than check for oil leak from the disconnected pipe.

At idle if you see more than +- 0.1, 0.2 afr change, the idle individual cylinder trims need tuning.
They are really hard to tune though. Playing only with these trims you can get afr change from 11 to 15.

You might have a exhaust leak or bad sensor.
Check with the stock o2 sensor readings to confirm which side leans out.

[Terminal_Crazy]

I bypassed the cooler and ran the car.
Oil started weeping out of the cooler pipe so i’ve Deleted it for now.
The coolant recovery tank was also full of oil so it’s all been flushed out and cleaned.

I’ll log the idle next time I play with it and get back.

Cheers
Mitch

[Terminal_Crazy]

Ran and logged the car today.

Still running OLSD with flat AFR at 13:0.
This log was just from cold startup & idle.
2017_11_19-001.jpg
2017_11_19-002.jpg

O2's and plugs only have about 1k miles on them.

In my previous log it showed similar results so in this I've increased the rhs cyl trims from 1.03 to 1.047.
However this could be a wrong assumption on the rhs being lean.

Measured exhaust temps 1" out on header
FRONT
165 163
196 182
183 169
171 153

EEHAck idle cylinder test
cyl 1 28.2
cyl 2 29.2
cyl 3 27.9
cyl 4 28.3
cyl 5 28.2
cyl 6 28.5
cyl 7 29.6
cyl 8 28.5

Where next?
Do i change plugs & O2 Sensors anyway as I'll have to remove them to check them anyway.

Mitch

[kur4o]

There might be some mechanical problem with right side. Cylinder misfiring or injector problem. Number 8 seems a little cold.
Exhaust leak is also a possibility.

Right side o2 goes flat and it also shows lean at same time on the wideband. So sensors should be ok.

[Terminal_Crazy]

I'm running out of ideas.
Since rebuilding the motor I've checked everything multiple times.
Pretty much everything is new except the pan and block.
It's had split BLM's and had O2 differences.
It's on it's 3rd set of injectors, 2nd set of NEW o2's

I'm pretty certain the manifold (Edlebrock LT4 performer was) passing air underneath, the ports were wet when i emoved it.
I've remachined it (bought a mill to do it) but not 100% convinced it's sealing the ports.
If I end up removing it I'll have to re mill it and cut down some of the larger sealing areas.

Exhaust leak is pretty unlikely, been over them many times, including the egr ports. ** Might just recheck the M22? plugs i fitted to the headers 9 years ago ***

Cylinder misfire possibly but Steveo's EEHack disdn't highlight any issue with the cylinder test which was straight after the uploaded datalog where the RHS has pretty much flatlined.

Odd how both sides drop around 300Secs and by 550 the RHS has recovered until 1200 secs when it starts to drop again.

Weird !

Thanks
Mitch