Continuing Oil Pressure Problem - still need help...

[Jeff C]

Hi all - been absent a while but my problem remains the same

First some history. I had the Engine oil pressure warning with my M30 engine - and a flickering oil sensor light when the engine was idling when hot (ie at a stoplight). I replaced the sensor and also the canister - Solved the engine oil pressure warning in the mornings, BUT my warning light continued to flicker when the engine was hot. Suggestion was made to replace oil pump (PITA) but my local mechanic replaced the pump for me. The flickering although a little better remains. If I just feather the gas slightly the light goes out so I have been feathering the gas while braking at stop lights- not a lot of fun

Two other items of note - Am running a early JC chip, when I swapped the OE chip back in the problem actually got worse - the light did not flicker - it was ON immediately bright red.

Secondly after a really hot run - half hour of driving at speed and coming to a idle - the light is not on, it takes a little while about 3-5 min before it flickers. Whereas in the city after driving 10 minutes and coming to a stop the light will flicker immediately. Could this be a result of O2 sensor feedback somehow that with a hotter engine, the car is not running as rich, so the RPM's are up slightly????

I would adjust my idle up slightly BUT I have a car with ASC so no ICV

I tried to test for vacuum leaks with carb cleaner but not sure if I did it properly - did not find any leaks

Any thoughts would be much appreciated.

Jeff

91 535ia (with ASC)

[George M]

you have done all the right things...replacing the oil cannister and oil pump.
A couple of comments. A chip shouldn't matter at all...as to oil pressure...likely coincidence more than cause and effect as to any influence by changing the chip...aside from slight engine temp difference normally compensated by the thermostat. What happens with any aging motor is as the bottom end wears...oil pressure reduces to to increased operating clearances...likely your issue at idle. I would first try a different viscosity oil...perhaps even a synthetic. You didn't mention what climate you live in. If a warm climate try a slightly heavier viscosity oil. Make sure the engine isn't operating hot at idle as in stop and go traffic. Could run a slightly cooler thermostat...say around 75C or so...will run one needle width to left of center. Also, be sure to pull the valve cover and check the timing chain piston tensioner to make sure the little reservoir is filling properly, you are getting oil to the top end and that your banjo bolts are nice and snug holding down the oil bar for adequate oil penetration to the cam and rockers which diminishes somewhat at low RPM.
While you are at it inspect the cam...in particular the forward section to see if there are any signs of oil deprivation. Lastly, after trying the above you can put a oil pressure gauge in line to physically measure oil pressure at lower engine speed to see what the pressure reduces to. Make sure your oil pressure sensor connector is nice and clean. You didn't post mileage but if up around or over 200K you may have some big journal clearances causing your issue. Generally however low oil pressure at idle is solved with a new cannister and oil pump...was in my case with 140k miles on my M-30.
HTH,
George

[Jake]

I hate to say it but I'd suspect excessive internal oil clearances. What does it idle at? On a engine who's internals are good, idle would have to be annoyingly low before you'd get an oil pressure light to flicker (assuming the oil pressure indicating system is correct).

You could take a look at the rocker arm shafts. They're hollow and carry oil pressure out to the rocker arms. Have a look at the plugs on both ends to make sure they're not loose and bleeding oil pressure off. I've personally seen this once before on an M20 (very similar to the M30).

After a quick check of the rocker arm shafts, if you don't find anything obvious I'd check oil pressure with an external pressure guage and confirm you do in fact have low oil pressure.

If it is in fact low, you may be able to restore some lost pressure by simply replacing your rod and crank bearings. Rod bearings are fairly easy to replace with the engine still in the car. Crank bearings are a bit more difficult but still possible.

HTH,
Jake Larsen

[Jeff C]

Hi George - as to your questions - I am in Northern Ontario (on the other side oft the 'U.P.') - I have run Mobil since 50000, this winter started at 5w30 light went on really easy - switched to 10W30 less light - will switch to 15-50 soon (have the jug in the basement) - I have a feeling that when I do that the light may not flicker as easily (I was running 15-50 in the fall before the canister and pump were replaced). If the different viscoscity oil solves the light problem do I still need to worry?

Secondly - I had replaced both banjo bolts first, 1 was loose. Had replaced the water pump and T-stat at the same time as the oil pump (car never ran hot - always at the center markl) - How would I check to see if the resevoir by the timing chain piston tensioner is filling up ????

Mileage wise is about 150 000 miles - was going to put in a VDO kit similiar to Gordon to monitor, but thought I would see if the minds on this board had anything else to say befor e I went through with that.

JAKE - My idle is at about 750-800 RPM - pretty solid - might dip to 700 when I come to a stop sometimes. I had the banjo bolts replaced but I don't think I checked to see if the oil bar caps were still in place. I did have my machanic check the pressure but I don't recall what it was, he seemed to think it was a little low though. Maybe I wil have to install the VDO gauge. How tough a job is it to replace the rod and crank bearings - what is involved (as briefly as possible for now)

What would you guys consider as 'normal operating oil pressure' - should I rev the engine to check pressure at speed or do I need to worry about catastrophic failure from the auto tranny

Thanks again

jeff

91535ia with ASC

[George M]

Jeff...try the "get dirty test". Did you remove the valve cover yet to check the stuff I mentioned? The oil reservoir is a little pocket on the front of the engine within the upper timing cover that fills with oil due to bleed off of the head that is the oil supply for your timing chain tensioner piston. Check the chain tension with a long screwdriver while you are at it...it should be pretty taut to make sure the piston is pumping up properly. The get dirty test/second data point test includes firing your motor up when hot without the valve cover or at least the valve cover wiped down on the inside to see if oil is being flung all over the top end and everything is getting lubricated properly even with low oil pressure. Try the stuff mentioned in this thread and report back what you learn before you even consider changing bottom end bearings which is a big tear up.
George

[Jeff C]

Thanks, George I'll Get dirty in the coming weeks and let you know

regards

Jeff