Oil pressure problem from Le Mans

[G5FTH]

Hi All,
When driving my Griff to Le Mans it was going great until the last 100k. The engine started running rough as though a misfire had developed. It limped along and all was fine.
Oil pressure/levels, water level and obvious electrical connections were checked at Le Mans when the engine was cool.
Coming back the same misfire was apparent although it sat comfortably when at a steady speed, complaining when under acceleration.
At one point I had to pull over as it was running so rough, 10 mins later it was back to the "mild" misfire.
All the time the engine temp and oil pressure was exactly as it should be.

Then as I pulled into the dock at Zeebrugge the oil pressure light flickered, the oil pressure guage showed low (but some) pressure and the car was not happy. I switched it off and called the AA from Hull and have been on a transporter all day back to Edinburgh.

Its the 5L Serp engine and I am thinking oil pump for the low pressure and possibly for the rough running as it has hydraulic tappets??? I have ordered an oil pump kit which will arrive tomorrow and just wanted some pointers if possible?
Maybe I have an electrical misfire and the oil pressure is a seperate issue?
The Steve Heath book does not go into replacing the oil pump, so is it easy?

Thanks a lot guys,
A slightly deflated Griff owner on his way to the bar!

[ChimpOnGas]

G5FTH said:

Maybe I have an electrical misfire and the oil pressure is a seperate issue?

^^^^^THIS^^^^^

The oil pressure sender is a bellows type and are very unreliable, replace it with one of the cheap ones from Ebay which work well & see what pressure you get.

http://www.pistonheads.com/gassing/topic.asp?t=984...

The misfire is like you say probably something electrical (rotor arm, ignition amp ect),or perhaps fuel starvation caused by a blocked fuel line/filter say.

If you didn't hear horrible clattering from the tappets I doubt you really had low oil pressure.

[neutral 3]

Worth changing the fuel filter as they are tucked up out of the way and don't seem ever to be changed. My one ran much better once changed.

Also check the Air filter, they don't seem to get cleaned or changed regularly as it's a pig of a job to do. Again my one was gradually running worse and well down on power. When I pulled the Air filter it was filthy and starting to disintegrate. It's a foam filter which is oiled. A new one from TVR Power made a huge diference to the rough running and performance and fuel economy.

[Pupp]

If it was misfiring to the point of dropping a cylinder or two, it could be the idle might have been erratic enough to make the pressure lamp illuminate if it nearly got to the point of stalling at low rpm. The lamp and gauge work off different senders. If the misfire turns out to be ignition related, give some thought to changing the oil in case you've got any fuel contamination

[davetherave1970]

I'll go for:-
Misfire = coil
Oil pressure = gauge and/or low idle as Pupp said

I've had both of these issues.

[Vixpy1]

Had the same on my Chim years ago, it was the big fuse

[G5FTH]

Thanks everyone,
Lots of good info as always.
I am going to change the oil, filter etc and also connect up a seperate oil pressure guage to acheive an accurate reading (have ordered a new sender too).
I am also going to replace the coil and check leads/plugs/cap etc.

[MPoxon]

I had a similar oil pressure issue on mine a few years back. The oil pressure gauge and oil pressure light both take their reading from different senders so unless both show low the chances are you are OK.

This was my issue with the gauge, when accelerating the gauge would drop to 0, but no warning from the light.
https://www.youtube.com/watch?v=EpBOHBOTAuw

This was resolved by replacing the sender.

[Bluebottle]

Not wishing to be the voice of doom, but this may also be the symptoms of a failing cam.

[ChimpOnGas]

G5FTH said:

Thanks everyone,
Lots of good info as always.
I am going to change the oil, filter etc and also connect up a seperate oil pressure guage to acheive an accurate reading (have ordered a new sender too).
I am also going to replace the coil and check leads/plugs/cap etc.

Good logical first steps

Just be careful not to fall into the trap of diagnosis by component replacement!

I understand how tempting it is to take this approach, but it's not the method adopted by professionals.... and for good reason.

Personally I'm trying to understand Bluebottle's comments about a worn cam causing low oil pressure, only the followers are under oil pressure and they'll pump up to a completely flattened cam lobe with no discernible loss in oil pressure or increase in noise

If the oil pressure is genuinely low the followers rattle like hell, hard for even a deaf person to miss.

Like others have said a cylinder down can mean the idle drops below 600rpm where there becomes every chance you'll begin to see the oil warning light glow momentarily.

The fact it's losing power, dropping a cylinder then recovering does point towards an ignition fault (plug, plug extender, HT lead failure ect ect), or potentially fuel starvation (fuel blockage, injector failure ect).

My money is still on an ignition fault, if the car starts to suffer when it gets hot but recovers when allowed to cool, it does indeed point towards the ignition coil (or possibly the amp).

The truth is no matter how well meaning contributors are it's virtually impossible to diagnose this type of problem over an internet forum, you need to complete some basic diagnostic checks rather than blindly replacing parts hoping you'll stumble on a solution.

An external oil pressure gauge will tell you a lot, a fuel pressure gauge connected to the rail will help too, an old school Sun tuner machine and someone who understands how to use it will tell you the rest.

If you go to your doctor complaining of a heart murmur he won't immediately refer you for a pacemaker in the hope it MAY just solve the problem.

He'll refer you for a barrage of tests so when the confirmed diagnosis is finally made and supported by the results of the tests, he'll be confident he's addressing the problem correctly first time round.

Sticking with my medical analogy so-called ‘innocent’ heart murmurs are extremely common and need not be associated with medical or heart conditions so do not require treatment or lifestyle changes.

That pacemaker would have been an expensive & traumatic mistake.

Keep calm, take a deep breath and do your tests before immediately thinking the worst and buying any more parts it's highly likely you simply don't need.

Good luck with it & keep us all posted on the results

Edited by ChimpOnGas on Wednesday 18th June 17:24

[Pete Mac]

I'm with Dave on this, you need to logically run through the system, however if it was me I would get the oil pressure sorted before I worried about the misfire and I am assuming they are unrelated.

Does the oil light come off the same sender as the oil gauge? If the enswer is no then you probably have a low oil pressure problem as both your gauge and your oil light indicated a problem. If the answer is yes then changing the sender is a quick and cheap first indicator of whether you have a problem or not. Pete

[ChimpOnGas]

Pete Mac said:

Does the oil light come off the same sender as the oil gauge? If the answer is no then you probably have a low oil pressure problem as both your gauge and your oil light indicated a problem.

The answer is no Peter.

The sender for the gauge is a bellows type that allows a variable output, the sensor for the oil warning light is a separate unit and known as an oil pressure switch because its more or less either on or off.

What you need to know know is as long as the engine is spinning over 600rpm if the oil warning light comes on it's usually too late as the switch is set to bring the light on at around just 3-5psi.

However if the idle speed is allowed to drop to 600rpm (perhaps due to an ignition fault) the oil pump may be turning so slowly and so producing so little pressure that the oil light starts to glow or flicker.

While your synopsis is totally logical, on this occasion and because of the "low rpm = low oil pressure" condition I would be inclined to investigate the reason for the low rpm first.

It's also important to know the oil pressure switch is extremely reliable, conversely the bellows type oil pressure sender is extremely unreliable & inaccurate so your oil pressure gauge readings should not be trusted.

A proper external oil pressure gauge plumbed into the oil gallery is always the most reliable way to confirm true oil pressure, which is why any decent mechanic will have one in his armory of diagnostic equipment.

I know I've already warned against diagnosis by component replacement but in the absence of expensive oil pressure testing equipment a cost effective alternative is just to replace that bellows sender.

While unreliable after a period of use the bellows senders do usually work pretty well when brand new, but it has to be said it is very much a second best cheap option to a quality external oil pressure gauge.

As I've already said it's impossible to diagnose the OP's problems over an internet forum, to return to my medical analogy its like the difference between calling NHS Direct and actually going to see your doctor.

Indeed if you've ever been unlucky enough to call NHS Direct you'll know they are clearly trained to immediately refer you to your GP if your symptoms indicate the possibility of anything potentially more serious than a common cold.

As the doctor must see the patient, the mechanic must see the car to diagnose the problem.

Wishing the OP the very best of British in finding his problem

[ChimpOnGas]

Vixpy1 said:

Had the same on my Chim years ago, it was the big fuse

OP, don't ignore this one from Vixpy1.

If you've suffered a flat battery or flickering charge light along with your other symptoms do check your 100 amp fuse under the car.

[ChimpOnGas]

Finally and not wishing to scare the OP, this is something that can happen to the serpentine Rover V8 oil pump.

http://www.youtube.com/watch?v=nh5DnOjpNpY

But it wont give a loss of power just low oil pressure.

So with the symptoms you've described, you must complete your logical process of diagnosis before assuming the worst.

[G5FTH]

Hi All,
When I was on the AA truck getting a lift home I spoke to Ray at V8 Developments and he advised that this was a straight forward case of the camshaft shell bearing coming off. The lack of oil pressure is caused by the oil squirting out with no resistance. This also causes the tappety noise.

Once the car was home and after posting on here I looked into it further. The oil pressure is very low and does not rise with a few revs, and the engine is tappety. Initially I was not sure whether the low oil pressure was causing the rough running (hydraulic tappets not lifting correctly) or whether I had two issues.
I decided to look at the low oil pressure first. I connected a new gauge directly onto the engine and it confirmed low pressure.
I drained the oil which looked fine with no bits in it.
I then removed the sump and found a silvery paste at the bottom. No debris that you could feel, but it glitters when you rub it between your fingers. My first thought was Bks! and
I am now going to remove the engine and send it off to be fixed. If I do have an electrical fault causing a missfire (which I doubt) its the least of my worries.

I also talked to TVR Power who said the same as Ray from V8 with no prompting.

Thanks again for your help everyone.