Oil Pressure Warning light not ON

[pfield69]

Hi, I have just purchased a 1.9 twin slider with a few annoying problems (so expect to see lots of new topics by me).

This Problem is the oil pressure warning light which does not stay on with the ignition on and engine not running.

A quick check showed that niether sensor was connected (it looked like the wires had ripped).

I have connected the blue/black wire to the 0.3 bar sensor (left side of enginge/top of cylinder).

I can not see the 0.9 sensor anywhere. I under stand it should be near the water pump.

When the ignition is switched on the warning light blinks on momenarily. I am unable to create a fault by shorting either sensor or leaving them open circuit. I guess the system doesn't work when it fails a system on check.

Would I be right in saying that below 2000rpm the 0.9b sensor is open circuit and the 0.3b sensor is closed, then at +2000rpm the 0.9b opens.

Does any one have any ideas on the fault and anyone have a good pic the the 0.9bar sensor location.

[Aidan]

re the position of the high pressure sender - only in late engines, it's possible the engine has been swapped for an earlier one, or a rebuilt one using an early core and it doesn't have the high pressure sender at all, but to find it just run your left hand down the pulley belt from the water pump and you should find the flag connector or the spade end just in front of the belt nearly at the bottom.
It's possible that the bod circuit itself has been removed from the dash or that the wiring into the multiplug has been messed with just to shut up bod if it was going off because the new engine doesn't have a high sender.
the high pressure switch closes with sufficient oil p and the low pressure switch opens at correct oil p so the bod can be kept shut up by wiring the connection to earth, which is what may have been done, at the dash rather than at the engine end
you'll have to pull the dash to investigate but once you've done that you can continuity test the wiring front to back as well

[AngeloEvs]

The oil pressure led is controlled by the BOD PCB in the speedo but Im curious when you decribe the oil pressure switch on 'left/top of cylinder'. The 0.3 oil pressure switch on a post 86 DG is accessed by removing the push rod tube cover plate which is underneath and not on top.

[pfield69]

I thought this is where it went?

I can't see one otherwise.

I have had the dash out and all looks as it should (I think). The flxiboard main contact is slightly corrodid but all conducts ok (now). There are now visible jumpers added and the circuit looks like its never been desturbed.

[Aidan]

high pressure switch it's an inch or two above that (that's the bottom of the pressure release valve) pretty much in line with it facing backwards in the block, if it's there at all; the low pressure one comes out from between no 3 and 4 pushrod tubes a couple of inches off the bottom l of your picture, the two cables should end up together in a two pin staggered plug that mates with a mirror image plug in the engine bay loom above no. 3

[pfield69]

Thanks Aidan

I can't get under it yet but will look.

It does however look like abum steer.
Based onthe fact the hi pressure is normally open and lo pressure normally closed (which isn't the case with mine ) I shorted the lo pressure line (blk/bl) to earth and the hi pressure was effectively open (not connected). I checked continuity from earth to the corresponding connections od the instrument panel and all was as it should be. When the ignition is turned on I still get the momentary flick of the oil pressure switch.

I have checked the circuit as best as I can with no obvious damage to the the flexi pcb not the logic pcb built into the speedo housing.

As I have a problem with the temperature gauge should I be looking elsewhere?

Any idea what the voltage on the voltage regulator should be?

[pfield69]

btw voltage is 9.46v

[Aidan]

there's a 6 page test process for the bod system in bentley manual, i think you need to go through that, i believe there's a bentley pdf on the web somewhere, if not i have it on cd, it's too big to email the whole thing and I can't send the individual pages cos the scanner is on the pc with no spare hd space which won't do anything.

[AngeloEvs]

Fitted in the speedo is the pcb that checks the condition of the low oil pressure switch. When this switch is closed the pcb operates the LED (unlike pre 86 vans in which the oil pressure led is directly connected to the switch). The low oil pressure switch is normally located near the push rod tubes and the high oil pressure switch has nothing to do with the operation of the LED so you can ignore this unless the buzzer is sounding. The oil pressure LED should go on and stay on with just the ignition on and engine off. Since the LED is switching on briefly you can eliminate the LED as being faulty or lack of a 12V supply to the PCB circuit. You are left with a possible faulty PCB or a faulty/incorrect oil pressure switch or a wiring error. You know the condition of the switches as you have mentioned them in your thread so:

1. Remove the wires to both the oil pressure switches and connect the wire to the low oil pressure switch (Blue with Black stripe)to a known earth point (such as the engine block) and see if the led remains on. If the led still lights briefly then you need to check

a) the condition of the connector terminal on the blue/black wire and that the connector and wire are OK.

b) the condition of the edge connectors under the dash (on the membrane pcb and in the edge connector itself).

c) the DOPs pcb in the speedo (I will detail that later if necessary).

2. If the led does stay on permanently then measure the resistance of the switch to chassis (engine off) and check that the switch is connected to chassis. If not then the switch is faulty or the incorrect one is fitted.

[Aidan]

I have a couple of petrol bod circuits here if required once you've isolated the fault

[pfield69]

Thanks that may come in very handy.

Is that the flexicircuit at the back of the clocks or the pcb inside the speedo housing?

[AngeloEvs]

PCB that controls LED and sounds buzzer is in the speedo housing and Aiden has those available. The membrane circuit that runs across the rear of the dash and connects all your dash electrical system has a 6 pin socket which clips into the rear of the speedo. This connects to the oil pressure warning pcb inside and has to be gently pulled out. Removing the rear speedo panel (secured by 4 screws) gives you access to the oil pressure pcb which can then be removed by unclipping it. Just take care when lifting the membrane from behind the speedo.

[pfield69]

Thanks AngeloEvs

I kind of cut out the middle man and checked continuity between test point on flexi circuit to engine terminal. All appears fine.

I have checked the edge connector which has lifted (I will repair later) but still make excellent connection.

The PCB in the speedo housing has not seated correctly but does not appeared damaged (ie dry joint, cracked tracks) or modified.

Aiden; I can't find the Bently manual online for free. I have downloaded another manual but that doesn't help.

How much would you want for one of your boards as it looks likey to be this?

I could lend you some software to extract pages from a pdf (and much more) if would be willing to send me the section I need.

can you confirm that the voltage stabaliser is producing the right voltage as I have a temp gauge problem that may all be linked

[Aidan]

output of voltage reg should be 9.5-10.5 V
issue there would also effect fuel guage
pm your address and I'll send out a cd, but I'm away for the weekend from 4 today Thursday, give me a call if possible

[AngeloEvs]

Shown below is the connector that pushes onto the oil pressure pcb. You can determine if the oil pressure pcb is faulty by inserting a 470 ohm resistor across the vacant connection points shown below. If you have a Maplin store these resistors cost a few pence and any value between 330 and 2000 ohms will do the trick, alternatively buy a 5mm 12V Red led which requires no resistor , fit that in place of the current LED and just wire link across the vacant connections. Your oil pressure LED is now connected directly to the 0.3 bar oil pressure switch as on pre 86 vans and should illuminate with the ignition on. If it illuminates then the pcb is definitely the likely problem and get one from Aiden.