O2 control problems - need help

[clockwork]

k thats my sneaky suspicion too & thats good to hear as I have two newly rebuilt MAF's coming from Taylor.

[clockwork]

Just installed the two new aftermarket MAFs from Taylor and when car started up, boy was it horrible sounding. Thought it was gonna die. What a rollercoaster of revs.

edit.
even after a DK motor resync these MAF's are still not playing well with the engine.
I changed out O2 sensors and code 70 went away, but still code 201 on cyl 7-12.
Swapped MAF's and no change in Code 201,
Swapped DK motors and no change in code 201.

Will switch DME's next to see if its a potential problem there...

[clockwork]

Still have this code 201 (O2 sensor controls) error on cyl 7-12.
"Mix at the O2 sensor is too rich. O2 sensor control cannot make mixture any leaner because control limit has already been reached". its so rich in fact that the chrome tips are covered in black soot from a sputtering liquid and smell is repugnant.

red Check Engine light shows up after a few mins of idling OR after a minute of driving but usually if I take my foot off the gas pedal the CEL goes away instantly. assume is acceleration/vacuum related. and this only happend when car is started for first time of the day. on a warm engine I never get the CEL upon start-up.

I replaced
both O2 sensors yet still error shows up,
Purchased two new aftermarket MAF's from Taylor P and they didn't solve anything (disconnected batts for 30 mins to reset but I think this step is unnecessary in MAF replacement/swapping). These in fact made the car run HORRIBLE.
rubber boots from MAF's to DK Motors are new,
DK motors have been swapped (internally cleaned recently) and re-sync procedure done many times,
VCV's have been replaced,
FPR's replaced (2 summers ago),
both Coolant temp sensors at back coolant crossing member at back of engine have been replaced,
intake manifold air temp sensors swapped,
paper gaskets made and installed,
Tested for engine revving with flammable brake cleaner sprayed on IMGs and even valve cover gaskets (both are new within last 30k kms/5 years).

if the O2 sensors is still saying the same cyl 7-12 air/fuel mix is wrong, I'm starting to think it has to be a wiring issue in harness not allowing proper signal to get back to DME.
If it was too lean I'd understand a potential air invasion but this is too RICH of fuel.
So what regulates the flow of fuel into the mix? FPR only (still have not checked)?

the CEL doesnt bother me as much as it diappears, but my fuel economy is atrocious and needs to be solved. Especially at $4-5/gallon.

[Timm]

This sounds like you have a blockage in the fuel return line which is creating high fuel pressure in the rail for the affected side. Might be a good plan to actually measure the fuel-rail pressure. The fuel/air mixture is controlled by the injector duration - and that is set by the DME which gets its primary information from the MAF's, but this is modified by a bunch of other stuff such as the manifold temperature, coolant temperature, RPM and throttle position.

[wokke]

Disconnect both O2 sensors. This forces the electronics to run on a pre set value. Check what happens then.

[clockwork]

Wokke. Will do.
I guess another test too would be If I disconnect both MAF harnesses, that also makes the car run on default values and I can see how my car is affected.

since I know cyl 7-12 has the rich fuel ratio, I will attempt to see if I can find a blockage in the tubing from that bank. this fuel return line is hiding where? rear of engine, near firewall? I've never had to work on it before, but I do know of a rubber hose which extends from engine's right rear corner to firewall and down underneath.

So all the fuel sent through the fuel rails doesnt get used up and what doesnt get used gets sent back to the fuel tank via the valve in the rear wheelwell near the fuel door (which I replaced with a known working valve 2 summers ago).
Where do the 2 breather valves come into play?

[clockwork]

So I learned last night that if you pull both MAF harnesses off before starting car, the car will not stay started. It will turn over and catch but after about 1 second the car just dies instantly.

[clockwork]

So, an update.after years it seems I accidentally found my problem and solved it easily. Apparently one of the wires in the purge valve connection of cyl 7-12 broke off and by splicing the wires back together I'm not getting the error anymore. All I had to do was idle my car and after 10 seconds the red check engine light would appear till I pressed the gas pedal. I have tested a few times today since and never a check engine light. I will keep checking car and even connect to DIS 4.4 or 5.7 to check for errors. I was able to activate both purge valves using INPA after the fix so I'm sure that's fixed so let's hope the error was caused by that but the error is related to fuel air ratio mix problems, so fixing purge valve makes me think this was problem and not O2 sensor or DK or MAFs or engine coolant temp sensors or... If I do not update this post again, consider it solved. Cheers

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