C5 Engine bay fuse/relay block

[Andy1B]

Anyone know how to separate the layers in a C5 engine bay fuse/relay block. I've seen this done on a C6 and thought it would be similar but I can't work it out. The cables are too tight to be able to pull it up far enough to turn it over and see how the multi plugs are fixed in. I can see there are 3 captive nots in the fuse board. I've tried putting bolts in these and tightening to see if they push the multi plugs out but there was too much resistance for me to feel that this would work.
I've had problems with the fuel pump relay and want to check the connections that the relay goes into, to see if they are corroded or have widened, making the connection loose.
Any help gratefully received.

 

[oelarse]

What have you measured regarding continuity in this system ?

If you use a multimeter and measure resistance (ohm) between PCM term 9 and ground G105 you should be able to locate and bad continuity in the control circuit .

If you remove fuse 13 you can measure continuity on the relay power side from relay 35 ( J12 ) to positive side of pumpmotor and from negative side of pumpmotor to
ground G401 .

G105 , G401 and splicepoint SP122 are places where the bad continuity is likely to appear .

 

[Andy1B]

Thanks for this. As a definite NON-electrician I've been learning and feeling my way around this issue. I've cleaned SP122, G401 and G105 (although the way the car is up on blocks at the moment I can't reach the block end of that one yet) . All were in good condition but I cleaned them anyway. I also took the front right wheelarch cover off and disconnected the large multi-plugs on the PCM. I didn't do any checking but they looked in good condition, no sign of the corrosion I've seen in some pics.
As background, the reason for doing all this was because the fuel pump wasn't working. I'd been advised it was probably the pump so took the tank out (this C5 has the later FFS fuel system so pump is mounted on top of the tank - not an easy job!). I connected the pump directly to the battery and it worked. I then re-connected it to the loom, took the relay out and bridged terminals 87 and 30 and the pump ran. I then went through cleaning all the grounds as above, tested the control side of the relay (T85 and 86), had a test light come on for the 2 seconds but when I reconnected the relay it still didn't work.
I had already tried swapping the relay for the horn relay and thought it had worked, but only temporarily. I tried it twice and the pump ran for 2 seconds, came in, washed my hands, went out and tried it again but it wasn't working. Stumped, I then read up on testing the relay itself. I activated the switch and the resistance was very low so I thought it was OK. That was when I thought maybe the terminals that the relay fits in may have opened up so I tried to separate the fuse/relay board and posted the question.
Today I put everything back together, bridged T87 and 30 to confirm the pump ran, tried the relay again but still no go. This time I heard the relay click so I knew it was switching, but it clearly wasn't putting the power out. This time I tried the relay from the a/c and it worked!!! I've now tried this more than a dozen times and the pump runs for 2 seconds every time.
So, it appears to be the relay but I'm not sure if there is something that's causing the relay to fail. The horn relay now doesn't operate the horn. It clicks and if I tap it the horn works but only temporarily. I had also used the fog-light relays but they didn't activate the pump and if I put them in the horn position they don't operate the horn either. Seems I need 4 new relays and that's probably more than a coincidence. (I can't vouch for the fog-light relays to have been in working condition as I can't remember the last time I used them).
I would still like to take the fuse/relay board apart if possible, just for peace of mind, so if you can help with this, or have any other ideas, I'd be grateful.

Hope all is well with you and yours in this lockdown. How are things in Norway?

 

[oelarse]

I am glad to be of any assitanse Things are getting better in Norway due to early lockdown of our country but a lot of businesses are still shut down . But primary school (youngest grades ) are opening later in April .
The fuel pump always runs only approx 2 seconds building pressure before it stops when when you switch ignition key on .

 

[Custom exotics]

Regardless of weather or not your fuel pump is working have you actually checked for other things like do the leads/plugs spark as you crank as said pump will only prime for couple of secs when you turn ign on then wont reengage till engine turns over you may find you have an ECU fault we just had exactly that prob on a c7 02 sensor extension loom got to hot and melted causing a short even after they were replaced car would not fire primed briefly but that was it somehow short had corrupted ecu all was good when replaced so check for spark on cranking and again if when using a probe to power feulpump DO NOT run a direct feed from battery as this can melt a pump in seconds if pump runs then in theroy car should start feel free to give us a call if you want to chat through bits in more detail call us on custom exotics 01279441233 we are in on tues from 9.30

 

[Rich]

Nice offer from Custom Exotics - thanks guys.

 

[Andy1B]

Regardless of weather or not your fuel pump is working have you actually checked for other things like do the leads/plugs spark as you crank as said pump will only prime for couple of secs when you turn ign on then wont reengage till engine turns over you may find you have an ECU fault we just had exactly that prob on a c7 02 sensor extension loom got to hot and melted causing a short even after they were replaced car would not fire primed briefly but that was it somehow short had corrupted ecu all was good when replaced so check for spark on cranking and again if when using a probe to power feulpump DO NOT run a direct feed from battery as this can melt a pump in seconds if pump runs then in theroy car should start feel free to give us a call if you want to chat through bits in more detail call us on custom exotics 01279441233 we are in on tues from 9.30

Thanks for this. After a lot of research and self-learning it turned out to be a 'simple' case of a relay fault. Putting a jump link into where terminals 87 and 30 sit got the pump running. Swapping the fuel relay for the horn relay worked temporarily (twice!) then stopped again. Swapping the foglight relays didn't work but I swapped the a/c relay and it now fires first time every time. I had also tested the relays individually and they appeared to work, but not in the car. Ordered 5 new relays from Rock Auto (£29 delivered) for 4 replacements and a spare and all is now good. See this link for more info on the pitfalls of (unnecessarily) removing the fuel tank to change the pump. C5 fuel pump replacement (FFS code like C6)

I'd still like to know how to dismantle and clean the fuse/relay block as I still suspect dirty or loose terminal connections may have been at the heart of this problem..