Feedback Disabled on Clamp Error and also maybe Fuel Pump issue?

Hi, looking for some advice. 1998 Abingdon VVC (MEMS 2J), 32k miles now in California / Nevada. On a long club run in the foothills, it ran great for 3+ hours ambient temps 25C. On the way home, it stalled at traffic lights and struggled to restart. When it did start, it idled high (1100-1200 vs. 900 normally) and didn't want to rev. Once underway it was fine and started behaving normally after about 30 miles. Got home to find pScan telling me "feedback disabled on clamp" (O2 sensor fault I think).

I cleared that, it hasn't recurred in two 25 mile drives with pScan hooked up. pScan showed O2sensor #1 active. When cold, voltage went 0.5V. When warm, at cruise (40+mph) or at traffic lights it went to 0.0V. At low speeds (traffic) it's about 0.3 to 0.5V. Taking foot off the throttle at speed, jump quickly from 0.0V to about 0.4V, 0.44V, 0.5V and then decayed to 0.0V in about 10 seconds. Car seems to behave normally, no stalling & no restart issues. pScan doesn't have a waveform display, these are averaged readings.

I thought the O2 sensor is supposed to read 0.1V to 0.2V (lean) to 0.8V or 0.9V (rich) -- I've seen a number of voltage ranges on the Internet. Is my O2 sensor definitely or probably bad?  

Wondering if the initial stalling is more likely a fuel pump (check valve not sealing) or somehow related to O2 sensor. Have a spare pump, but don't want to just throw parts at a problem w/o understanding the cause (condition, cause, correction, check).

Could an intermittent fuel pump issue have triggered the feedback disabled on clamp error message?

Changed ECU coolant temp sensor a few months ago after a previous hot restart issue when pScan confirmed erroneous readings on the sensor when restarting and engine hot.

What you described regarding erratic idle and erractic errors and behaviour is turning my suspicions on VVC HCU control valves - solenoids.

Have you done any work on the car which had as consequence that you needed to disconnect solenodis connectors? If yes are you sure you put them back in correct position?

Welcome aboard I see your new here, You may want to have a look at this checklist: https://www.the-t-bar.com/forum/54-how-tos/99326-a-check-list-for-new-owners
It won't help with your current problem but it may point you in the right direction for some other stuff.

When the fuel pump on mine failed it didn't show anything on Pscan. That's not a fault with the Pscan it's that MG/Rover obviously didn't make provision for fuel pump failure to register as a fault in their original OBD software. I suspect you may have 2 unrelated problems......one being the pump and the other O2 sensor fault being the other.

The first time I had fuel pump failure it was intermittent so that made it very difficult to diagnose as the damned thing would work fine whenever I had the means handy to test it!
The car would die in the arse and wouldn't restart for 10 minutes to 1/2 an hour and then come good and be fine for the rest of the day. the problem might be back sometime during the next dat or not rear it's ugly head again for a week......completely random!
So if you have the same problem I had you may have to wait until it shits itself properly for it to show its true colours!

The second time the pump failed was due to filthy fuel it just stayed dead!

Hello, thanks for your response.

No, I have not had to do any work around the VVC solenoids and haven't disconnected the leads.

The last thing I did (a few months ago) was replace the ECU's coolant sensor. I could take the solenoid leads off (one at a time!) and spray contact cleaner on them in case they are dirty. I've heard that solenoid issues can be diagnosed by disconnecting and running the car in fixed mode (up to 5000 RPM). 

I've got a new fuel filter, a replacement fuel pump and new sock filter, and am ordering an O2 sensor.  My flexi was starting to leak at the last MOT so I will replace that when I do the O2 sensor.

Hello Cobber, thanks for this. I have done most of those things:  coolant alarm, new timing/aux belts, understand the bleed procedure (used a vacuum method), have workshop & electrical manual, have new cap & a spare, have pScan, have the taillight covers.  Only thing is I haven't done the clutch arm -- waiting until the clutch needs doing for that. Had to replace the rotary coupler and coolant temp sensor for ECU.  I search the site pretty regularly when I have questions which is why I haven't posted much.  I've got 3 other MGs (2 MGB and RV8) and on the MGF I fitted Mike Satur FCCKit, servo brace, etc.  Got some MGF friends in the US and UK and talk to them when I have issues.

Sounds like your pretty well organised, don't be a stranger and please keep us in the loop about your results.

ajlincoln1965 wrote:

I've heard that solenoid issues can be diagnosed by disconnecting and running the car in fixed mode (up to 5000 RPM). 
 

Yes, that is correct. I would disconnect them and see how car behaves regarding your issues.