Oil pressure dropping

[Trip]

I've got a very strange problem with oil pressure.

Since i fitted an Oil cooler, Pressure when cold has dropped slightly from 8 to 7.5bar. When warm it drops down to around 2bar.

I took the car on the strip for a better workout but did not rev it past 6k rpm. Pressure holds good to 8bar but as soon as soon as i finish the run and remove my foot from the gas pedal to start applying brakes, the pressure drops to a barely 0.5bar. If i rev it at that stage it does go up but goes back down. On 2 occassions the car stalled too.

My setup is as follows
OE oil cooler removed and replaced with mocal sandwich plate (without thermostat)
5/8 rubber high pressure rubber pipe
11 row front mount oil cooler
Oil pressure sender and 1bar oil pressure switch remotely fitted next to rocker cover.

 

[Smo]

Firstly mate did you top up your oil after fitting the cooler? It seems obvious but a lot of people forget that fitting the cooler increases the amount of space your oil has to occupy and don't add more to make up for it.

 

[Trip]

Oil levels are fine.

 

[Smo]

Could it be time for a new oil pump as the current one struggles to cope with the increased volume perhaps?

 

[Trip]

Oil pump is brand new and should be uprated (or at least that what i was told from the reputable seller/ uk tuner)

 

[stumo]

Cambellju had a similar problem, i can't remember what the outcome was.

Pressure holds good to 8bar but as soon as soon as i finish the run and remove my foot from the gas pedal to start applying brakes, the pressure drops to a barely 0.5bar. If i rev it at that stage it does go up but goes back down. On 2 occassions the car stalled too.

so you are pressing the clutch at the same time as coming off the gas? If the tickover is low (you said it's almost stalling) then the oil pressure will be very low.

 

[Trip]

Cambellju had a similar problem, i can't remember what the outcome was.



so you are pressing the clutch at the same time as coming off the gas? If the tickover is low (you said it's almost stalling) then the oil pressure will be very low.

it wasn't almost stalling.. it stalled :roll: but the low oil pressure happens before engine stalls.

thanks

 

[PobodY]

My revs drop really low when I brake hard too, but mine doesn't stall. There is a diagnostic procedure for it in the manual, and I think it's to do with vacuum lines on the back of the manifold. - Mine has only started doing it after I removed the PCV... but my oil pressure is fine.

EDIT: Diagnostic procedure 14 - Engine stalls after decelerating.
The short version is: disconnect the AAC - do the revs drop; if no check the AAC valve and circuit; if yes check the idle screw for clogging by disconnecting the TPS (it just says "throttle sensor harness") and see if you can set the revs to 850rpm (+/- 50) using the idle screw; if no check the IAS and throttle chamber for clogging; if yes then check each injector (and then check the plugs are ok) - disconnecting each injector should cause a momentary drop in the revs (and obviously if one doesn't you need to check it; after that go to the fuel pressure (which is a bit hard to check if you don't have a gauge, but essentially what you're doing is checking that the diaphragm is still working); then check the lambda sensor (ECU diagnostic mode II); after that you're on to replacing the ECU.

Was Jim's solution to disconnect his lambda sensor?

 

[Fast Guy]

Could it be oil surge? What sort of speed are you slowing down from?
Can't you use the gears when slowing down to keep the revs up?

 

[PobodY]

Mine is fine until I put the clutch in to come to a full stop; then it bounces a bit and settles at ~900rpm.

 

[Trip]

Could it be oil surge? What sort of speed are you slowing down from?
Can't you use the gears when slowing down to keep the revs up?

What i was doing was moving starts, WOT and rev to 6krpm until i reach around 70Mph and press the clutch and realeasing the throttle. To say the least i was holding with a 300 bhp cosworth and i was only boosting 7psi and not reving past 6K rpm.

It could well be oil surge. I will remove the oil cooler and see if it makes any difference.

 

[Trip]

My revs drop really low when I brake hard too, but mine doesn't stall. There is a diagnostic procedure for it in the manual, and I think it's to do with vacuum lines on the back of the manifold. - Mine has only started doing it after I removed the PCV... but my oil pressure is fine.

EDIT: Diagnostic procedure 14 - Engine stalls after decelerating.
The short version is: disconnect the AAC - do the revs drop; if no check the AAC valve and circuit; if yes check the idle screw for clogging by disconnecting the TPS (it just says "throttle sensor harness") and see if you can set the revs to 850rpm (+/- 50) using the idle screw; if no check the IAS and throttle chamber for clogging; if yes then check each injector (and then check the plugs are ok) - disconnecting each injector should cause a momentary drop in the revs (and obviously if one doesn't you need to check it; after that go to the fuel pressure (which is a bit hard to check if you don't have a gauge, but essentially what you're doing is checking that the diaphragm is still working); then check the lambda sensor (ECU diagnostic mode II); after that you're on to replacing the ECU.

Was Jim's solution to disconnect his lambda sensor?

I will do this procedure and check for any faults. I did check the injectors with Datascan by switching off one by one every injectors to see if engine rpm drops. The labda seems fine too according to datascan. According to datascan the AAC valve remains with a valve of around 32/35 and shoots momentary up to 75 when i release throttle and press the clutch.

 

[PobodY]

Ah - there is a datascan version of the procedure (here's the link to Ed's mirror of the relevant pages)... sounds like it could be the AAC in your case. I think that mine will prove to be something very similar.

 

[Trip]

Ok guys.. this is really getting frustrating.

Tried to do the tests with laptop and monitoring the sensors with datascan, upon waiting for engine to warm up i noticed an intermittent fault in the water temperature sensor. it starts fine but jumps to 80Deg fan switch ON and back to original temperature and back to 80deg.. it even recorded a -2Deg C..

Could it be this is effecting the whole problem ?

What else can go wrong !!!

 

[Trip]

i removed the inlet manifold (the second time this week) to get to the water temp sensor and what do i see... fresh oil sitting on top of the oil filter housing.

 

[Trip]

Could it be this "leak" the cause of the oil pressure drop ? strangly my oil levels remained high, actually they are a little higher then the dipstick mark to compensate for the oil cooler.

while at it, I re soldered new connectors for both the water temp sensors and changed the sensors.

 

[Trip]

I finished off doing some work hoping to solve this problem and other hidden problems i may find.

- Removed oil cooler and replaced the standard cooler .
- Cleaned AAC valve, the valve next to it and the idle screw with carb cleaner,
- Cleaned throttle bodies with carb cleaner
- Replaced the water temp sensors and knock sensor with tested good ones.
- Soldered new plugs for the water temp sensors and knock
- Checked and cleaned brake servo valve/pipe
- Cleaned MAF and soldered a new earth, a dap of loctite to secure the MAF connector.
- Soldered new plugs for Injectors

Once i start the engine, I will check my 02 sensor and perform some tests listed on the manual.

Hopefully all these will cure my problem. If weather permits, I will test it again saturday,

If the problem persists, the only other thing i would have to check would be

- Blocking the vacuum supplying the brake servo
- Remove the crank case blocker and replace with PCV valve connected to intake manifold.
- Install a BOV instead of blocking it.

 

[Trip]

Ok Guys, I have reinstalled everything and started the car and re-calibrated idle.

On performing all the tests mentioned in the manual. I found that when i disconnect the AAC valve the revs only drop around 100rpm. On Datascan the AAC values are between 8 and 18. Using the active test on datascan and changed value to let say 40, the RPM did climb though.

Anyone got datascan and can check for me the values of the AAC at idle of a fully warm engine ?

 

[Trip]

In my understanding, if according to the manual my AAC valve should be open between 20 - 40, and mine is only being open between 8 - 18, does it mean the engine is getting an air supply from somewhere else, I.E Leak ???

But on the other hand if i really have a leak, shouldn't the RPM increase ? I did spray lots of carb cleaner on the Inlet whilst engine is running and monitoring the revs. Revs remained constant.

 

[CanadianR]

not much to add to your datascan problems, but did the work you do fix your low oil pressure problem?