Hello Guys,

I have 1999 c5 corvette, i have imported in 2015 to PL. Since last year im struggling with lambda ratio readings, which i have actually 4.97 on idle. When reving 2500 rpm it drops to 2.69 and stops. I have recently updated exhaust from catalitic converters TIER1 to EURO4, i have replaced both front o2 sensors to bosch, and rear ones to delphi. its readings are proper, no DTC popping up. Absolutely no problem with the fuel - oxygen mixture, car accelerating fine, there no smoke. During the test CO=0, HC=0. this car is california NB6 emission standard. So i suspect the A.I.R check valves. Those are last parts i can replace, whole system piping and hoses are tight. I dont understand where is the problem with this lambda ratio? Or maybe this is a problem with a measuring method? They using one probe installing it in one exhaust exit of 4 existing. Anyone had such problem, or can suggest me what can be done to resolve this problem? The cause of doing that is a need to obtain an equivalency certificate for this car to EURO4. Thank you.

 

1. Lambda = 1.0: Represents the stoichiometric point.
2. Lambda < 1.0: Indicates a rich mixture.
3. Lambda > 1.0: Indicates a lean mixture.

You mightt have bad 02 sensors
My bad

 

Stoic is 1.00 so if you are at 4.97 that is lean and if it drops at 2500 RPM you have a vacuum leak…what are your long and short term fuel trims at idle and at 2500 RPM ??

 

That may be an idea with those trims. I will check tomorrow. But I have checked AFR that is 14.8 on idle. I post also photos of this measurement with 4.97 lambda ratio and the earlier with slightly elevated lambda. THe o2 sensors have 1000 miles on them. So they are barely new. I bought also a faulty sensor (it was replaced to the good one same day), then ECU give an error immeiately and the engine idle roughly. I have tightened conecctions on the passenger side of the throttle body. On this piping i have found rubber elbows that were leaky. I have replaced both of them using a regular oil resistant pipe pieces. I dont have any idea where is more vacuum lines. Prior to do this i have checked lambda and it was 1.15 so slightly elevated (i have felt an odour coming from the tail pipe after startin cold engine) After tightening those connections lambda value was raised. After replacing cats the smell was gone. I dont see other vacuum connections on the back of the engine near a firewall. Those vacuum are located only on the top of the engine (LS1)? Do you have some vacuum lines diagram ?


After tightening vacuum lines conected to the throttle body, replacing cats to EURO4 and all lambda sensors.

one year ago. Lambda was elevated. Proper value should be 0.97 to 1.04. After this i have started to search started

 

 

Hello i have checked today the fuel trims and there are:

Engine load 2.35% (Idle)
Coolant temperature 84 Celsius (183,20 F)
Short term fuel trim - Bank1: 0%
Long term fuel trim - Bank1: -0,78%
Short term fuel trim - Bank2: -1.56%
Long term fuel trim - Bank2: -0,78%
Manifold pressure 41 kPa (0,41mbar)

Engine load 11.37% (c.a.2500) car is standing with trnasmission in N position
Coolant temperature 90 Celsius (194 F)
Short term fuel trim - Bank1: 2,34%%
Long term fuel trim - Bank1: 9,38%
Short term fuel trim - Bank2: -0.78%
Long term fuel trim - Bank2: 9,38%
Manifold pressure 52 kPa (0,52mbar)

Engine load 29,02% (Car is running 3rd gear) c.a. 2000 rpm, c.a. 40-50mph (accelerating)
Coolant temperature 89 Celsius (192,20 F)
Short term fuel trim - Bank1: -0,78%
Long term fuel trim - Bank1: 25%
Short term fuel trim - Bank2: 4.69%
Long term fuel trim - Bank2: 25%
Manifold pressure 96 kPa (0,96mbar)

Those numbers looks fine, i have found leak in the rubber case of PCV valve - i have repaired theat using rubber hoses - On the back of the engine are also some rubber connectors between the vacuum lines, maybe those are faulty, but i dont know how to get this place. Better i will order those vacuum lines on ebay or amazon and replace during the winter in the heated garage. Can also i suspect the AIR valves? I have read that those are immortal...?

 

Those numbers are not fine…your long terms went from -.78% at idle to 25% under load…that is either a bad or dirty MAF Sensor or a fuel delivery issue (clogged injectors, clogged fuel filter, weak fuel pump)…under load your O2 sensors should go full rich…over 800-900 mv’s signifying proper fuel delivery…what is your MAF reading under load in grams/second ??…AIR valves would not cause a vacuum leak…2 part video..you should watch it !!

 

Hello, today i will dismantle vacuum lines to check their tightness especially on the back of the engine. Every year i clean the conical filters and the MAF sensor using egr cleaner based on isopropyl alcohol. Injectors were not checked until i have bought this car. Fuel pump was replaced from the original Walbro to Deatschwerks DW300 3 years ago(Cause of the noisy work). Filter was replaced but...for a filter - no name. It is possible i must buy a quality one. That's true the filtration element inside can be damaged. I have replaced 3 years ago. Also in US you use RON 92 fuel? Any additives of alcohol? In EU the weakest fuel is E10 RON95 (10% ethanol). Maybe the software must be updated/tuned to handle properely this octane rating? The MAF values i will check today also and let you know what they are. Thank you for the tips.

 

I have founf next problem with vacuum lines:


And have replaced with SMC Y connesctor 3x10 mm tube slot. (white means clean so for food industry etc) - it laso possible to use it from Festo etc black ones.



After this repair i have measured manifold pressure that was on cold engine 0,36 mbar 36 kPa and with 176F coolant temp.
And also MAF 7,04 g/sec - throttle was 2,35%,

When 82,4F -> 9,26g/sec
when 192,2F ->95,02g/sec and engine load 33,7%
Short term fuel trim bank 1 +14.06%
Long term fuel trim bank 1 +13,28%
Short term fuel trim bank 2 +4.69%
Long term fuel trim bank 2 +13,28%
MAP 91kPa
V=77kmh -> c.a. 50mph

the engine idling very smooth after sealing all punctures in vacuum lines. above conditions was measures relatively short time 1-3 sec. - we have slippery today, its rainy and relatively cold outside 0 (32F )to -1 deg. C (31F). So i cannot measure it right way.

On saturday we will have better wather so i go to the emission tests to check result of tightening those punctures