Ongoing saga of chugging XMV6 relays sticking??

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Paulxmski
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Ongoing saga of chugging XMV6 relays sticking??

Post by Paulxmski »

After I had put the ECU and relays to bed in their plastic basket. I thought I will just have a listen to the engine now that it's warmed up, and hear if it drops into chugging mode. I started the engine and a blip on the accelerator showed it was revving freely then I heard a couple of clicks like relays switching and another blip on the throttle showed it was back in chugging mode. I repeated this 4 times then I opened the plastic box where all the relays except the purple one are lying on the bottom of the box because the connectors have broken off. The relays were clean and bright like new, however I (having switched the ignition off) disconnected each relay and reconnected it. I re-started the engine and it did not drop into chugging mode. I will have to wait now until the engine is cold and try again. Is it likely that one of these relays could cause this to happen. I'm not sure what they do will have to look it up unless someone can tell me?
Paulxmski
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Post by Paulxmski »

Anyone know what the relays infront of the ecu on the V6 do especially the purple mother??
Stempy
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Post by Stempy »

I think the purple one is aircon, then on mine theres a pink one which is the headlamp washer timer, then a brown one which is the start inhibitor relay for the auto box. The green is ABS and the other brown I haven't got round to finding out what it does, and the ones in the cabin fuse box are lighting I think, but again I haven't tested them to find out. Another one of those jobs to get around to. This is a Xantia V6 BTW, don't know how similar the fuseboxes are[:I]
Paulxmski
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Post by Paulxmski »

Thanks Stempy,
You seem to have some more relays than me. I believe one of these relays is for the fuel pump. Yes I also think the purple one is for the aircon. I changed them all over for the ones in my other V6 and unfortunately it didn't make any difference to the chugging situation. So I will have to continue tracking it down.
It has been suggested that when the a/c cuts in it sends a message to the ECU calling for increased revs and that this may be causing the problem. I believe there may be something in this since the dropping down to chugging seems to coincide with the clack of the a/c compressor clutch cutting in. Every time it is started when not up to temp it will rev freely until that happens.
philhoward

Post by philhoward »

Sounds like a big clue, here!
Nearly every car i've ever driven with aircon has had a slight increase when the aircon has been turned on, so that when the compressor does cut in, the drop in revs takes it back down to normal idle speed (or slightly above). When you hit the aircon button (or auto on the climate control, if so equipped), do the revs increase slightly (1-200rpm) or not? As a test, either don't use the aircon, or take the climate control off auto and try it again for a while...
Just because the relay has been changed doesn't mean that the wiring (or even the relay plug) isn't at fault. XM wiring diagram needed here to tell what happens to that signal from the aircon (goes to ground/12V, etc) in order to simulate/test it to the ECU.
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Post by Paulxmski »

Hi philhoward,
Yes does seem pretty indicative. I did start the car once with the a/c switched off. Thankfully I can switch it off whereas in the SEI it's auto which is a complete pain as it kicks in again at will! It didn't seem to make any difference to the initial chugging, but I hadn't arrived at the state of know I'm in now so I will try again with my ear trained on the relays. When I start the car from cold. I have to put my foot slightly on the accelerator otherwise it starts and dies immediately. Once started doesn't seem keen to keep going revs drop to 750 which is low for these should be 850 according to Russek. After a bit picks-up maybe a slight misfire, but definitely no pickup from the air/con switching in. Come to think of it one of the things that impressed me about the car in relation to my V6si was that as I'm cruising along whether in third or fourth it was doing 10% less revs than the other car. For instance at 50 in 4th foot very lightly on the accelerator revs typically would 1900 whereas in the other with A/C on about 2100.
When I tried switching the a/c off and watching to see if the revs died back they seemed to stay constant. This now all fits into the picture.
Which of the ECU's in the bank is the main ECU looking at the box from the front?
I will have a look at the wiring diagram later as you suggest.
Incidentally the a/c is working a bit peculiarly anyway. I was working on the car with it tcking over and I noticed the pipe going through the bulkhead was white with frost, but when I got in the car it wasn't particularly cool and the rheostsat was set for 18 I turned it up to 22 and it all melted away and warm in the cockpit.
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