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Discussion Starter #1 (Edited)
Hello everyone. I have an issue with a ’91 Bentley Turbo R. When the car is warmed up and I’m braking for a stoplight, the oil pressure drops to the first notch on the oil pressure gage (not zero all the way left, but the first notch to the right), the revs drop to 350-400rpm, check engine light comes on and the computer starts beeping at me, the oil pressure light comes on in the info window at the very bottom of the center display, and if the a/c is on, the car will stall pretty quickly, without the ac on, it’ll run terribly for as long as I’m at idle and it’ll stall if I don't nurse it with a little accelerator pedal. If I put the car in park, turn it off and then turn it back on, I’m ok for the next few lights sometimes. Other times, once this issue starts it’s every time I get down to idle and I’ve got to go to someplace where I can let the car sit for a while. Turning it off and back on always works to correct the idle at a stoplight, but after driving along again, it will come back unless the car sits for hours. The oil pressure has been consistently to the low side from what it was since this began (low by about half a notch difference of what it was according to the oil pressure gage). I cannot think of any correlations which coincide with this issue aside from using a smaller oil filter. Does anyone have any leads? I'm going to change the filter back to a Crewe Bentley filter and check the engine codes this week, after which, I'll report back here.

So far, I've read it could be the oil sender. I have not been able to verify a connection between the oil sender and the computer. The car has the Bosch fuel injection, constant injection system (CIS) known as a KE-Motronic. Does the sender have any connection to the computer or could it be a sensor causing the revs to drop? The other thing I've read is carbon build-up can cause the throttle body to stick and cause similar issues. Lastly, it could be a fuel delivery issue. Has anyone encountered something similar and what was the solution?
Thanks, Rich

EDIT - SOLVED
Turned out the oil filter was too small. It caused a bottleneck, this setting off ECU sensors putting the car into damage control. Upon using the OEM oil filter, everything was back to normal. What I learned, always use the correct size oil filter.
 

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It appears when you just breaking a little (just push pedal) while driving or fully stopped the car with brake pedal and hold it in the "D" mode of gearbox?

The oil pressure IMHO dropped because engine rev dropped to 1/2 of nominal value. "Check engine" error and other symptoms appeared due the same reason. Probably with those revs there are not too much power to drive A/C compressor and even alternator has too low revs for work.

Maybe a problem with idle valve or switch? However, check first all electrical connections... (see other posts about cleaning connectors, fuses, relays etc.).

EDIT: Anyway you could perform on-board fault diagnosis when symptoms will appear.
 

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The oil pressure IMHO dropped because engine rev dropped to 1/2 of nominal value.
A big, Seconded!, on that opinion. I'd say that all of the issues are secondary to idle speed dropping grossly below normal limits to keep everything running correctly.

My guess is that if this issue is addressed, all else will fall away.
 

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have had same issues with my 90 Turbo R. Apparently the idle drop/charging light coming on/check engine light coming on, is a known issue with this era of cars, even when newer.

Once the check engine light flashes on, you have to turn the ignition off and restart the car to reset the ECU. Also, use the diagnostic button to check engine fault codes through your dash. Sounds easy, but it took me some research and reading of the manual to figure out how, and what the number of short and long flashes all mean.

On my car I did a major "tune up". All spark plugs, new high quality Magnecor spark plug wires, air filter, oil change, cleaned all electrical contacts (several times), checked and sealed all hose connections to try and ensure no vacuum leaks anywhere, etc., etc. Didn't make a bit of difference, idle kept dropping and car stalling at rest. Car was fine for longer drives, ran "fine" on the highway, other than a lower than expected top speed.

Then, I removed and cleaned the "idle control valve", when that did not work to sort the idle issue, I replaced it with new. Then I replaced the alternator, with a new aftermarket AC Delco. Improved charging, but same idle dropping issues. Then I pulled all eight fuel injectors, found the rubber insulator/sealing sleeves were all age hardened and shrunken, allowing injection air leaks and resulting in weakened fuel mixture. While I had them out, for good measure, I replaced all eight fuel injectors with new Bosch injectors.

on the subject of fuel injectors, whether you replace them or not, at least replace all the rubber injector sleeves to seal the air leaks. I was told I did not need to replace the injectors, and could just clean them. After being told that, I did go through the cleaning process on the old injectors, I did get 5 of the 8 old injectors spraying a relatively decent pattern after cleaning them out with "Diesel Purge" and compressed air. That said, I do not regret replacing them with new, especially given the amount of work required to get them out and then back in with new sleeves.

Car ran much better with new rubber injector sleeves sealing the injection air leaks, and with all 8 injectors spraying properly. The final step was to have the fuel injection mixture properly set up, using an air fuel ratio "sniffer" at a shop. Simple adjustment, there is a mixture adjustment "screw" on the fuel injection distribution head. It may have a tamper proof plug on it or it may not.

Turning the air/fuel ratio adjuster with an allan key adjusts the air fuel mixture. Adjusting the air/fuel mixture to correct after dealing with the injection air leaks and with all eight fuel injectors working properly solved my cars issue completely. Idle no longer drops, car starts perfectly first turn of the key, battery warning and check engine warning no longer come on. Also, previously the car topped at at roughly 160-170 kph no matter how long throttle held to the floor, now the car is much stronger all through the rev range and no longer runs out of breath at 170, now runs to its design maximum if given enough room.

As for the oil pressure, when rpm drops, oil pressure drops, simple mechanical result. The gauge is likely not all that accurate anyway, and looking at a wiring diagram I do not see any connection to engine management systems, it is just a simple warning from a basic mechanical oil pressure sender, could just a well be an idiot light as a gauge. Replace the oil pressure sender if you want, but I doubt it will have any effect on your dropping idle issue.

Anyway, the above is what worked for my car, with the same mechanical fuel injection system your car has. I did all the work myself, other than the final set up of the injection mixture adjusting screw as I did not have the required test equipment to read the air/fuel ratio from a sensor up the exhaust pipe to adjust it properly.

My car now runs much better than it ever has previously during my ownership, or for that matter during the previous owners ownership. I suspect some previous shops or owners may have been compensating for the injection air leaks by fiddling with the fuel injection adjuster screw to try and compensate for the air leaks, with poor results. Seems very obvious, after the fact and now knowing conclusively from direct examination of the hardened shrunken rubber injector sleeves and comparing them to new sleeves. Removing the old injectors was easy, they were loose and wiggled around in their respective holes. Installing the new injectors, with new rubber sleeves, took lubrication and force and the new sleeves very clearly are an air tight seal.

Final comment, when my car was stalling at stop lights (for years) I could not trust the car for my wife or other family members to drive it, and it ran like such crap it was not even saleable. Now that it finally runs properly, all thoughts of sale have vanished, but bloody hell it took me most of three years of frustration to sort the running issues.....My thanks, again, to all the forum members here who offered advice along the way!

Paul LeClair
 

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Nice results Paul. It's amazing how hard the injector seals can get. I sprayed a bit of silicone on the new sleeves to massage them into the intake manifold along with new injectors. I do not like to cut corners and prefer new whenever possible. I also sent out the fuel distributor head for cleaning/calibration. The motor runs like a watch for 2 yrs now.
 

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Hi Wraithman. Goos suggestion about the fuel distributor head. I may still send the fuel distributor head out for cleaning and calibration this coming winter, but there is no one I know of local to me who does that sort of thing, so will have to be sent away somewhere. The western Canadian driving season for nice cars and motorcycles is short, roughly mid April/early May to mid October each year, and I do not want the car off the road for the rest of this driving season, it runs well enough now to finish this driving season. Really enjoyable to drive now, I am using it as my "daily driver" now for the rest of this season, if my wife has not beat me to the car. Anyway, the car is getting daily use, and my 28 year old son has been taking it out in the evenings on hot dates, not sure how dating works these days in the time of CoVid19 but seems to still be going on... The car seems much happier being used daily, it just runs better and better.

To get the new fuel injectors and new injector seals in I wound up using a light skim of rubber friendly synthetic brake grease, did try silicone spray but it just was not slippery enough in my case for how tight it was to force the new injectors/seals into place. They are very definitely air tight now. Wonder how long before the new injector sleeves start to shrink and leak air?

The new Sanden air conditioning compressor just installed has a bit of a belt whine, going to look at the tension set by the shop that recharged the system with the new compressor etc., other than that all is good with the car at the moment, even have all the hydraulic mineral oil leaks fixed all at the same time, took a third re sealing on one of the brake pumps to finally get the car "dry" underneath. Will see how long the dry condition lasts....😉

Paul LeClair
 

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Check with Jim Walters about the FI dist. I did mine in the dead of winter when the car was used less. They are easy to remove and ship in a small box. Some rebuilders may have your head part number in stock for exchange, therefore limiting your down time.
 
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