1988 XJ6 VDP - ABS Fault

Hi. Im having fun getting to know and fix on the car during my vacation - and taking advantage of having the car in front of the house where we are - not possible in NYC.

I have had an intermittent ABS fault since I had the car. Read all the posts and checked the relay in the trunk - no signs of dry contacts but resoldered them all anyway.

The issue is odd - the fault only occurs when i put the ignition on but dont start the car straight away. If it start the car immediately i almost never get it. Often it clears after starting.

The car does like to turnover a lot (need to check the crank shaft sensor) particularly when hot but not only. The battery voltage takes a hammering and it seems if i rev the car to get the battery voltage up after starting i rarely get the alarm

I charged the battery over night and i also left the charger on - and turned the ignition on - and the fault still occurs. I measured the voltage at the relay and its 12.4volts. The relay is making contact and passing the 12.4volts through it

Any ideas what this could be would be appreciated

Ian regarding the long cranking, before you try to start the engine try priming the fuel rail by turning the ignition on and off a few times and then crank to start. What it sounds like is the fuel rail is losing pressure. Cycling the key a few times give the pump the 1/2 second prime.

Thanks Robin. I have tried stopping the cranking and restarting and it seems to start quicker. Sometimes it cranks for a long time. I will look into the fuel regulator issue in this case. Thanks again.

Its generally the non return valve in the pump/return line. Not the FPR.

ok thanks - ill search that then to see whats ahead for me

This is where I fitted a NRV on my ‘40

Thanks Robin. Neat install
Well i tried today the multi key turn. I can hear the pump coming on for a second or less each time. The car turned over before starting -no improvement. Is it worth taking the crank sensor out and cleaning it?

Any thoughts on the ABS fault - it now only seems to do it if i turn to second stage ignition without cranking.

Ian …

As far as your ABS fault problem goes have you checked the archives? Scheeese … nobody checks the archives … a ton of information there.

But just as a quick review, the cause of the warning is almost always the over voltage relay in the trunk.
Pull the relay and first make sure the internal fuse hasn’t blown and the relay is actually closing. Then check that even if the relay is closing you may not be getting continuity through the power side because of a bad solder joint. I’ve had both of those items fail on my '89 model.

Also years ago I actually had to replaced the ABS control module in the trunk to solve the problem. As I understand it it"s extremely rare for that to fail, but it did in my case. But hey, after owning my car for almost 30 years I’ve pretty much seen it all.

1 Like

Ian, not sure if cleaning the CPS is going to achieve anything but it shouldn’t hurt, and by doing it now you will know how to do it later on if it does decide to quit permanently.
I had a problem with my ‘92 ‘40 where there was a bare patch of insulation on the shielded wire from the CPS that would occasionally short to earth and cause the engine to stall, invariably when I was at the head of the queue at a set of lights :frowning:
So that is something that you could check while you have the CPS out.

Thanks Grooveman

I most certainly am not one that doesnt read the old posts as i stated in my first paragraph “I have had an intermittent ABS fault since I had the car. Read all the posts and checked the relay in the trunk - no signs of dry contacts but resoldered them all anyway”

The over voltage i have tested and measured the voltages on the feed to the relay and the outlet. It operates properly and there is 12.4 on the outlet. I re-soldered anyway and no change. If i start the car up straight away there is no fault - abs does the dynamic test and ive tested it in earnest a few times in the wet/gravel and it works perfectly.

I will go over the wiring diagram again and see where the output from the overvoltage sensor goes.


Thanks Robin - i am away at the moment 400 miles from home so decided to leave the CPS alone for now. Ill check the plug/type and order a new one as a spare before disturbing it i think.

I have to say i am really enjoying the car. I replaced all the plugs, distributor arm, and leads and the improvement in performance is noticeable. I measured the resistance of all the leads and plugs and the difference was shocking.

Got a reversing camera installed and working yesterday - a really nice quality one built into the license plate frame. After 3 weeks i think ive done most of the bits i needed to :slight_smile: