ABS Pump Joy - 1993 RRC

[richardthestag]

Hi All

I have a problem with my ABS pump that I would like your advise on.

Car is a hard dash RRC 3.9 1993, it is my daily driver, not had ABS problems before.

Friday night in torrential rain, the abs light came on and then shortly after the brake warning light. two reds. Stopped ok, checked fluid level ok and that brakes worked. switched off ignition and back on again and noticed that the abs pump did not kick in. Brake pedal was hard but stopped the car fine.

Today been diagnosing, no voltage to the abs pump on the red wire when tested on the back of the pump.

Checked the following with ignition on or engine running;

- two 5a fuses under seat and B1 in dash fuse good 12v.

- 30a fuse - 0volts hmmmm

- for some reason i pulled ABS relay and checked pin30 - 12v ... strange, checked 30a again and 12v

- pushed relay back in and it clicked. checked pin 30 and it was 0v

- pulled abs relay and bridged pins 30 and 87 - 0 volts plus no ABS pump noise.

- Disconnect abs pump from loom and I get 13.8v (with engine running) up to the abs pump connector under the bonnet.

- Maybe pump is fubar. So I connect pump red wire to 12v battery and it works.

Just in case I am going mad!! ECU Connector;

- pin 9 - 12v

- pin 10 and 25 - 12v when brake pedal pushed

- white wire from pin30 on ecu to abs pressure switch has 11.86v

- Two black wire from pressure switch and black/brown from pump all have good earth.

I have tried to no avail, different pump, was working when put on the shelf 5 years ago, different abs pressure switch and different ecu. The circuit works find until the abs pump is connected.

Any ideas?

[duncmc]

I suspect that you may well have a pressure switch that has failed or is sticking. I had two fail or stick on my Blue RRC I used to have.

If the switch has stuck at pressure the pump will not run which happened to my last switch. I, however had very low pressure in the system and had to press the brake pedal very hard to stop. However, to confirm I would first do another check. If you have a spare pump with a known working pressure switch, just simply unplug the suspect pressure switch and try the "replacement". Hopefully the pump will then run. If you haven't a spare, you can jump the pins for the main pressure switch. Right now I can't remember which of the five they are, I am trying to find it for you. Here we go found it....if you pull the connector, there will be 5 pins as you look at it. Two on the top row and three at the bottom. Jump the top left with the bottom left and the pump should run.

If you look at this link about half way down (post 332) you will find my last problem with the pressure switch. http://forums.lr4x4.com/index.php?showtopic=69483&page=17

Failing a bad pressure switch I wouldconsider for ecu problems or wiring problems. Good luck, and hope this helps.

[richardthestag]

Hello

thanks for your reply

bridging top left and bottom left on the pressure switch connector, pin 3 is white from ecu and pin1 is black to ground, did nothing to the pump :-( running 12v to the pump connector red made the pump fire straight up.

I have a spare ecu, abs relay, pump and switch which worked on the last car made no difference here though

I have a spare switch, the plunger moves, but only if I pull it with pliers. I have tried to bench test it without much success.

Looking at the switch

top row left #2 White Orange from Relay

top row right #1 white from ecu

bottom left #5 black ground

bottom middle #4 black yellow ?!? to something

Bottom right #3 black ground

I am doing a simple continuity test.

Testing from pin #2 white/orange from relay to

#1 ground did not have any continuity regardless of where the plunger was.

#5 ground and #4 Black-yellow were open regardless of where the plunger was.

Testing from pin #3 White from ECU

no continuity any pins regardless of plunger position

Next step is to strip the spare switch as per your post and see if I can get it to behave.

[richardthestag]

stripped spare pressure switch, great instructions btw

Free the plunger up but it only moves maybe 1mm .... how far should it move?

The torx switch was stuck, leaned on it a little and found the click Now testing continuity between

- #2 (relay) and #5(ground) / #4(Black yellow) I get continuity on both until the torx is pushed and clicks. :-)

- #3 white (ecu) I get continuity to #1 when the microswitch is depressed

to the car now......

edited to add

made no difference, pump not run when test switch rigged up

Disconnected pump and tested voltage to red feed, 12v until torx screw pressed. tested continuity from black to battery and it was continuous but not absolute. i.e. if I connect the two terminals of my multimeter together in connectivity test mode it reads zero. testing from black to earth it was reading 0.08.

Could my problem be bad ground distribution, wiring diagram says e100, where is that?

tested other components on that ground distribution horn, headlamp etc and they were all good, except the air con compressor clutch... hmmmm

[duncmc]

I am afraid that I am as puzzled as you are.

The pressure switch plunger can move quite a lot. It is very hard to get to move I found, but it is more than 1mm. Mine was stuck all the way in.

The Torx screw operates the ABS light and ETC light when you switch on as pressure builds up it turns them off.

It is the other microswitch that the main plunger presses on and turns the pump on/off.

If changing the ecu and relay haven't made any difference, and you have 12V at the pressure switch but the pump still doesn't run when you operate the microswitch then you must have either a wiring fault or faulty replacement parts I think?

[richardthestag]

found the cause yay

Thanks Duncmc your posts helped me with my diagnosis.

If relay, switch, ecu and everything else in place provide 12v to the red connector for the pump, YET it drops to zero when the pump is connected it must be the feed. My brain just wasn't working on current not being high enough to run the pump.

Ran 12v from battery to the fused side of the 30a fuse. ignition on and pump fires up and cuts out at right pressure hoo 'kin ray

now.... Orange pink heavy wire feeds that fuse. It is not ignition controlled. It must loop somewhere into the loom you got any idea where? Don't really want to rip the dash apart but am going to pull the section out under the steering column.

This is the bit from the manual

P119 fuseable link.

[David Sparkes]

Recalling previous threads, from long ago, about fusible links, ISTR they are something of a fault liability in themselves. So much so that LR started selling a kit of replacement links that entailed cutting the old ones out and soldering the new ones in (the links being provided with wire tails to facilitate this).

Whether these repair kits are still available, and what the part number is, I couldn't say at the moment.

Do you know where these links are located, or is that what you are asking?

IIRC they are bundled in the wiring loom, perhaps on the inner wing. I think they were easy to get at, once they had been exposed by removing the wrapping from around the loom. look for a 'fat' bit of the loom.

A word of caution; if you start disturbing these expect the other links to fail as well.

If you can find the originals, then fine, use them, you may well get another 20 years from them. However, also look at more modern solutions, perhaps in terms of 'Maxi-fuses', which area larger version of the now standard blade fuses.

You would have to check you manual to establish what rating you need.

ETA, Well glory be, I actually managed to find the TSB!! AMR3928 is your magic number.

Personally I'd treat this Britcar quote as a target price, especially as you have to add VAT.

HTH

861694.PDF

[duncmc]

I have an original Land Rover paper workshop manual as well as RAVE. It covers the 1990 model year when the ABS first came in. In that section there is a specific wiring diagram for the ABS. For the model years after there was not a separate new diagram so I can only assume things didn't change. That is the 1991,1992 and 1993 model years.

The 1990 diagram shows the wires to the 30A Maxi fuse to be Brown/Orange from the fuse to the pump relay, and just brown the other side which is linked to a terminal post/battery positive and the ignition switch.

An orange/pink wire isn't in the diagram I don't think. So you are on your own tracing I am afraid.

I have tried to scan the pages in, but they haven't scanned very well. Its too big to fit on the scanner bed properly!

[richardthestag]

Hi David, duncmc

First class advise, found the bundle of fuses between the battery and the cooling header tank. Might need yo lift the header out of the way to get access.

Cold and dark here by the time i got the dash back together so a job for tomorrow night.

Wish me luck

[richardthestag]

for completeness in this thread.

Feed for the circuit (power distribution) on my 93 rrc runs back to the battery on an orange with pink tracer wire. it goes via the fusible link that had gone high resistance I guess. I found them all wrapped up in a sock like mess that sits between the battery and the cooling header tank.

Wary of the notorious fragility of this area of the loom, I unclipped the main loom from the inner wing. pulled back some of the protective wrapping, found a bundle of orange wires one of which had the pink tracer. after disconnecting the battery I snipped the wire, insulated the old but still live dead end and extended the loom end directly to the battery positive. 12v feed to abs circuit is restored. 10 minute fix for nearly 2 days of diagnosis

Temp fix will be properly done at the weekend with a new single fusible link to protect the circuit.

thanks for your help chaps

[duncmc]

Excellent work, well done!