Hello again!

I'm continuing my search for faults on my - 95 XJR. For starters the car never runs perfectly on idle but sometimes it's close.
The latest weird thing I've found is that if I drive about a mile or two at about 70km/h it goes back to open loop on bank one and open loop failure on bank two. Still feels good and powerful but sometimes idle really bad at stops.

I can drive country roads and in the city and the Stft stays within limits, but as soon I go steady above 50km/h it goes to open loop and stays there til i shut it off and on again.

I have also noticed when my idle is really bad the OBD reader tells me the engine is 52c when it's clearly much warmer, and the STFT shows +24,2 on both banks.

It seems like something intermittent or electrical, I don't think it's vacuum related.

It can stall on idle when up to full temp, after driving for a longer time, never when driving short like 10 minutes or so.

It's been running rich and bad for a long time with the previous owner so carbon buildup is a fact I presume.

Things I've done :
Changed Coils (changed place and tested new Lucas brand, back to original for now)

Cleaned the throttle house

Tested the temp sensor (two pin) in boiling water and multimeter

Welded the manifolds

Changed to new O2 sensors

New downpipe

New sparkplugs

Tested the MAF with multimeter (seemes good to me)
​​​​

Any ideas?

 

XJR6,

The only part you haven't addressed is the TPS. Usually the car will stall when this goes bad, but it can keep your car from entering closed loop.

Are you sure the oxygen sensors aren't criss crossed? Sometimes when people switch them out, they unplug both of them and then forget which plug was plugged in to which harness. That shouldn't force the car back into open loop.

I have to say, you've gone through all the usual suspects. The car needs to see good signal from 4 sensors to enter closed loop: 1.TPS 2. MAF 3. CTS and 4. oxygen sensors must get to temperature (the readings are not important at this point)

You say you have codes telling you that one bank is worse than the other? Your oxygen sensor wiring might be bad.

Did you check the catalytic converter. That could be bad too.

I think the big clue here is "goes back to open loop on bank one and open loop failure on bank two". Open loop failure on bank two? What is that? Is the car trying to go to open loop, but no longer can read the preprogrammed values?

Based on that alone, I would suspect that the problem is from the injectors/coils out to the second oxygen sensor.... That means, leaking injectors, bad coils (or plugs), exhaust manifold issues, oxygen sensors, catalytic converters.

Will wait for others.

 

I realized now that the OBD said "open loop fault" not "failure"....

I have checked the TPS with the OBD and it seemes good with a steady rise all the way to 95% I think it was. I might check this again to be sure.

The O2 sensors are in the right place I believe, because it runs worse when I switch them around. And I get good readings when I drive at lower speeds and twistier roads.

I have another crank sensor in the boot, I will change to see if it makes a difference.

I will also check the ground cable to the engine, don't think its the culprit but easy thing to do.

Can the transmission do anything with the fueling? Thinking its related to the way I drive....

And I belive the strange behavior of the engine temperature should lead somewhere, but i can't figure out where. The dial in the car reads fine, but the OBD tells me it's only 53C when its actually 90C, but only sometimes...

 

Checked the ECU connectors for corrosion ?

Opened up the sensor wire splicing as the sensor wiring goes over the fuel rail ?

Your engine coolant temp sensor wires are X and Y

 

Yes I've checked the ECU connectors, looks good.
Can't see anything wrong with the wires either.