Explain AFR/FUEL TRIM Waves? 10% Steady State.

Can anyone explain these waves in my AFR/STFT's? Steady state conditions....... Because the problem is they carry over to PE ..... 5-15% out on PE ...... Crazy.

I've tried setting the car back to stock using MAF/VE.... They are still there. Only really happened after Hi-Flow Cats. Tried everything to tune this out...... I'm stumped.

eg. Highway perfectly stable steady state condition (any tune, maf, mafless, stock transients, multiplied transients -impact factor only-...... stock throttle vs full response same deal)........ See pictures.... the waves are like 7-9% on average, complete steady throttle with no map movement etc.

You can see my VE is smooth, timing is smooth......... trims on a histogram are all within average +-3.... the cells beside the spikes on the photo are perfect virtually +-1 ...... but with the spikes the min maxes are quite massive. I'm wondering if it's like Idle airflow but it has a stock cam....

It has me stumped.... What am I missing here? Where do I need to look? I would have uploaded a scan but there's a file size limit on here.... I'll post my tune if necessary.

If you have O2's enabled, they are narrowband and they control the mixture like using a light switch on and off.
Oops I'm too lean, richen it up...nope, nope, too rich lean it out. Always chasing it's own tail.
Vehicles that use wideband O2's for control do a better job. I have the same issue in steady state from .97 to 1.03 lambda.

How do you get those 3d maps of the ve table for a 6L

Yeh but the problem is it does the exact same thing in open loop on the wideband, it's not just the narrowbands in closed loop.

Fuel pressure steady at cruise?

What are your injectors doing? Have you logged injector pulse width or duty cycle and overlaid it with the WBO2 readings? Also fuel pressure.

Fuel pressure is solid at 399kpa. Flow rates look normal. no misfires on a particular cylinder. Haven't looked at the duty cycle side of things.

I did have 1 injector go about 40,000kms ago which i replaced so im wondering if just one of the injector is playing up . im sure the vcm scanner used to do flow rate on each injector but now its just 1st and 2nd bank.

i have a feeling my issue is mechanical. cant remember if i have replaced the fuel filter. unless im just missing something tune wise....

i did also fit my headers myself but maybe since having hi-flow cats made and fitted at the exhaust shop they maybe caused a leak over tightening the cats to the header or something.

it does feel a bit like a clogged fuel filter.... and ok symptom..... it pulses on the highway under a bit of load in 6th.... not always... but yeh

Alright.... I have no idea about the waving lines except to say maybe my answer will lie in adjusting the switchpoints to help control it.

Basically my car runs fine until like 89'c on the ECT and then after a while one the actual oil heats up it seems to have I guess hotter cylinder temps causing it to lean out too quickly. Now the car has a stock cam and it is mafless. Tried some idle tuning via ECT etc, no go.... pushes the car forward and funny things.

So my question now is...... should I just raise idle to help decrease the temp issue.... The car holds the AFR's much better if I raise the idle somewhat...... I dont feel I need to 'other' then to help control AFR's as I guess it makes it move the air in and out better 'as a whole' keeping the cylinder temps down.

Basically once the oil is hot the whole AFR's goto sh...... and the closed loop tries its best to control it but is causes drivability issues. Its always had this issue but been made worse by the hi flow cats.....

Using the fans to keep the temps down drains power.... not ideal so.

I would look to the ramjet. I don't know that particular model but if it directs much more air than stock directly at the MAF, I have seen many instances where you get that fluctuation in AFR and even surging at steady driving. I would at least try the stock intake, (or restricting any direct flow for a test) before going crazy looking for other stuff.

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Originally Posted by realcanuk

I would look to the ramjet. I don't know that particular model but if it directs much more air than stock directly at the MAF, I have seen many instances where you get that fluctuation in AFR and even surging at steady driving. I would at least try the stock intake, (or restricting any direct flow for a test) before going crazy looking for other stuff.

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Its mafless, no maf. The highway is about the only real spot that has higher flow then normal due to it being a ramjet so air directly flows in...... But i doubt its that.

That said I did move a tranny cooler when I fitted it and the pipes are still sort of somewhat infront of the ramjet, which could probably throw charge temps out somewhat at hotter temps.

I'm having the same problem on my 4cyl E37, but at 40-45mph in 4th with RPM 1500-1700. Nothing I do changes it. Attached is a log and the config I was using to find the problem.(Not my normal config...) This is open loop but problem is magnifyied in closed loop. Most of the surging/afr bounce is in the beginning of the log, starting at around 5 seconds...