When testing the old FPR it was hammering like an old toilet ballcock valve by my gauge flutter, I used paint thinner as a test liquid.
I then mixed up some ATF with thinner app 30% ATF ratio then retested.
After almost a quart passed through with many vacuum signal cycles from the beginning or approaching initial bypass to 85 psi with a high flow bypass.
Retested it became smoother almost normal operation.
Flushed again with thinner it started to stick and hammer more again but not as much.
No way i'll ever reinstall it, add to my Rover wall art.

On my test drive with the replacement FPR I have a safe local industrial park road allowing full throttle passes hard to 5,400 rpm's 3rd into 4th until 4,000 rpm's up and back then a instant hot shutdown like when reading plugs.
Parked hot 3 minutes with a clean quick restart, repeated but let it heat soak 10 minutes again the same good hot restart.
Both times the booster fans kicked in from this hot shutdown without letting it idle or easy drive cool down.
Yesterday from cold start to warm I let it idle for 11 minutes, exhaust started smelling lean hot as well the temp went up to 3/4 scale which it never has as normal is 40% of scale and solid.
The radiator is custom built of four row. Stat is also rather new so not the problem either. Original stat failed with 1/16" max open, above 30 mph the temp would climb. I drive by the gauges Rovers can be destoyed quickly with temp climbs off the scale within 45 seconds at 60 mph.
I went for a drive around the block to cool it down it acted lean stumbling but cooled down.
Today with a 4-5 hr dry weather window the FPR swap happened. Hell took 10 minutes max.

I would have to say hands down the FPR was the problem, I must add the coolant temp gauge sensor I installed has a wider range of resistance cold to hot than the original allowing me more gauge needle swing than ever before.
Call it a win win plus all the other sensors have already been changed out.
Even the spare 3.9 mass air meter I installed to test.
BTW I have a 4.6 mass meter this another upgrade with airflow vs the 3.9 but didn't reinstall after the last smog test. Runs stronger with the 4.6 meter being this is a 4.6 sucking more air.

I'll be staying active on this forum, oh and thanks Savannah Buzz and others, fun to chew the fat with gearheads.
Yes i've given up on factory trained Rover Tech people, anything beyond text book flow chart yes/ no replace they haven't a clue.
Talking, thinking outside the box or thinking common basic mechanical sense.
BTW did my injector cleaning unit photos open up? It was also used with FPR testing.

Carl.....~~=o&o>.....

 

Might wat to look this site over for tuning ideas and other things - people have wrung more out of the 3.9 that you might imagine.... Tuning

 

Savannah,
thanks for your last posting and sticking it out with replies.
Lots of great ideas all thinking outside the box vs those R & R by the book of dealership thinking "techs".

BTW, toying with a 3.9 is a waste in my book with it's problems vs a stronger 4.0 and 4.6 block, plus why have another 3.9 B&S from a 4.0 when the 4.6 can be had?

I'm not into pumping up a lazy engine into a bomb, just wanted a clean running 4.6 with low end practical torque vs bragging rights of maximum hp.
A clean running engine that's not a totally dead slug and fun to drive.
For all out there are the 350 chebbie transplants (yuck).

On the heads posted by "tuner" they pointed out the childish looking quality control Rover used with production engines with vast amount of gains to be had just by applying standard common sense that any gearhead with the basics can apply.
Like I mentioned before, gasket port matching alone is worth more than a bigger cam. Adding mild port cleanup and shaping vs production castings, a little here little there adds up in clean free power.

BTW I've already done all the head work, port matching the intake and exhaust manifolds besides the added plenum top spacer for more trumpet clearance.
With my additions I increased plenum chamber volume plus intake runner length vs cutting down trumpets and reducing low end torque rpm's vs raising them. Cam change, lifter preload, dialing in the cam to crank as well double row roller timing chain.
I must mention the original 3.9 and ECU on the 5-speed had that "normal" by dealerships nasty 2,500 rpm "flat spot zone" or leanout condition, a large PITA especially with town driving 90% of my travels. Slotting the TPS increasing voltage to the ECU helped a little at best. This is something an auto trans can hide due to fluid drive (convertor slip) vs direct power transfer of a manual box.
With the 4.6 install plus the RPI Tornado chip this surge zone was reduced by a vast amount but I still had a slight trace of it even after the injector upgrade.
With this last hot restart problem coming about with the old FPR going randomly bonkers readings below minimum of pressures and specs.
Hell after pressure checking three spare Rover FPR (one new two used) they all measured below minimum spec this was why I installed a 3 Bar FPR vs 2.5 Bar OEM. Now for the first time ever the 2,500 rpm transition lean zone surge is finally 100% gone.
This is the best it has ever run, like a new toy you have to keep playing with it or driving in my case enjoying my added progressive efforts all in the right direction.
The dizzy mechanical advance is recurved to match this 4.6 as well the best vacuum advance unit i've found from Oz.
I still wish I had a later "Q" series manual transmission transfer box the forever whine is not that cool in my book.

Prost,

Carl.....~~=o&o>.....