Lambda voltage not oscillating 3SGTE

[Lee H]

Still in pursuit of my continuing issues.

Quick recap. Wideband lambda reading really rich on cold start <10:1 and rich on hot idle 13.5ish. Hard to start when warm. Lots of black smoke if started, turned off and started again.

Raced it at York the other week and was holding back on boost over 5k rpm. Sometimes showing mega rich, sometimes mega lean.

Decided to start fault finding today, tested the voltage on the lambda and it just rises from 0.2 to 0.9 then stays there and doesn't oscillate whatsoever. I am led to believe it should oscillate quickly between 0.1 and 0.9. Read this might not be a lambda fault as a dead lambda would read low voltage and something else is causing the rich running?

Also remembered I'm running a Walbro 255 on an otherwise stock setup so that might be overfuelling it due to higher flow through the rail? Is this a known problem?

Any advice much appreciated. Got no fault codes.

Lee

[C35Rob]

I'm no expert, but surely the Lambda sensor isn't taken into account when on boost, as it'll be running open loop.. i.e not fuelling based on lambda feedback.

my car is mega rich when started, then gradually walks back to 14.3-14.7 on idle (running a power FC), the fuel pump shouldn't matter as the fuel pressure regulator will, erm, regulate the fuel pressure, unless it's boobs, then that could be a contributing factor.

however if AFR's are off on idle then o2 sensor is a likely culprit.

[Lee H]

I initially thought that about the fuel pump but a few people have said more fuel will enter the engine as the injectors open due to more fuel being there at that split second. Aftermarket ecu will allegedly eliminate that with correct tuning.

Will try another lambda tomorrow and see if its any different. It is mega rich, gauge only goes down to 10 so no idea how low the afr is going.

[C35Rob]

I initially thought that about the fuel pump but a few people have said more fuel will enter the engine as the injectors open due to more fuel being there at that split second. Aftermarket ecu will allegedly eliminate that with correct tuning.

Will try another lambda tomorrow and see if its any different. It is mega rich, gauge only goes down to 10 so no idea how low the afr is going.

That split second thing sounds like total balls to me! It wouldn't matter if you had 1 or 100 walbro pumps, as long as the regulator can return the fuel (I.e it's functioning correctly) you're not going to be "forcing" extra fuel in. Have you checked fuel pressure? (Although if that was the issue it'd be running rich all the time, unless the fpr was sticky....)

[Lee H]

Just found a few instances online (albeit varying brands of car) where changing the fuel pump on a stock car led to issues.

I have bought a used fuel rail, regulator and injectors so might swap that in as well.

[thomp1983]

If you've been running rich for a while the lambda is likely dead, you can test it off the car. Have you checked the wiring from the lambda to the ecu?

I assume you've checked for air leaks?

[Lee H]

If you've been running rich for a while the lambda is likely dead, you can test it off the car. Have you checked the wiring from the lambda to the ecu?

I assume you've checked for air leaks?

Swapped the lambda today for another I had lying around and now its sticking at 0.12v with this one. Still really rich.

If I unplug the lambda I don't get an ecu light however if I then flash the codes out its registering a fault code which I find odd.

Can't hear any air leaks. Running a ST205 chargecooler so not many boost pipes etc.

[PW@Woodsport]

Lee, can i ask how you are returning fuel to the tank please mate?

[Lee H]

Lee, can i ask how you are returning fuel to the tank please mate?

Drilled the evap line out to 6mm and gutted that one way valve thing in the fuel pump holder. That's now my return.

[PW@Woodsport]

Ok, it's not that then.

Have you checked for air leaks between the AFM (presuming rev1/2) and throttle body?

[Lee H]

Ok, it's not that then.

Have you checked for air leaks between the AFM (presuming rev1/2) and throttle body?

I'm running a rev 3 engine. What fuel pumps do the v6 roadsters tend to run on?

[PW@Woodsport]

I use V6 pumps, they plug straight in to the Mk3 carrier assembly.

[Lee H]

I use V6 pumps, they plug straight in to the Mk3 carrier assembly.

Right. Had a look at my spare mk2 turbo pump and it's miles too big to go into the mk3 carrier but not convinced that's the problem anyway.

[PW@Woodsport]

Agreed, the regulator would take care of the excess fuel in any case.

Make sure your vac line to the MAP sensor is good, not split or loose.