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850 petrol to diesel!

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Old Oct 11th, 2021, 13:04   #1
klunk
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Default 850 petrol to diesel!

Hi, Ok i have a really tidy 1996 850 GLT 2.0 10v auto wagon which the ex wife has been using the last 5 years, I've sorted her a euro3 V70 D5 manual so the 850 is back in my lap! The old bugger is pretty gutless and drinks fuel but it is really clean with only a few previous owners and i bought it 5 years ago from one of my customers for 100 so it stands me in for nothing really, Now i also have a 1996 850 TDI wagon with a cracking engine and manual box but the body is a mix of flat red paint and pretty much every panel has a dent in it! So i'm chewing over putting the TDI running gear into the petrol 850, Mechanically this will be no problem for me as i was on the spanners for 32 yrs as a vehicle tech, My only concern is the wiring, I am hoping the diesel engine bay loom will some way plug into a main loom on the petrol, I will be swapping dash clusters etc, If anyone has done this conversion or can give me any advice or thought's it would be much appreciated, Cheers.
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Old Oct 12th, 2021, 22:21   #2
Martin Cox
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I'm afraid I can't contribute anything useful but it's an interesting idea and as the owner of a V70 Tdi I can understand the appeal.

Volvo themselves, it could be argued, did more or less just that since I believe the diesel was a late addition to the 850 range. Of course they had the advantage of being able to design the wiring loom to suit.

Hopefully those with more knowledge and experience will contribute.

Good luck and I'll be interested to hear how it goes.

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1998 V70 Tdi auto, 229,000 miles
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Old Oct 13th, 2021, 00:05   #3
andrewc1267
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Quote:
Originally Posted by klunk View Post
Hi, Ok i have a really tidy 1996 850 GLT 2.0 10v auto wagon which the ex wife has been using the last 5 years, I've sorted her a euro3 V70 D5 manual so the 850 is back in my lap! The old bugger is pretty gutless and drinks fuel but it is really clean with only a few previous owners and i bought it 5 years ago from one of my customers for 100 so it stands me in for nothing really, Now i also have a 1996 850 TDI wagon with a cracking engine and manual box but the body is a mix of flat red paint and pretty much every panel has a dent in it! So i'm chewing over putting the TDI running gear into the petrol 850, Mechanically this will be no problem for me as i was on the spanners for 32 yrs as a vehicle tech, My only concern is the wiring, I am hoping the diesel engine bay loom will some way plug into a main loom on the petrol, I will be swapping dash clusters etc, If anyone has done this conversion or can give me any advice or thought's it would be much appreciated, Cheers.
I think you are probably right and the engine bay loom will plug in the the cabin loom you could really do with a wiring diagram for both and just cross which pins on the engine bay loom to the cabin loom and I think that they will be the same
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Old Oct 13th, 2021, 11:02   #4
brickman
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Best of my knowledge and experience....

Drop donor TDI entire front sub frame, move the lot over.
Wiring is quite different, same location and trunking from the dashboard distribution panel through the firewall into the ECU box on the front of the wheel arch. But thats about it, everything else is all over the place. TDI fuse box is very slightly higher than the petrol ones for some reason.

I'm gonna go on a limb and say the connections from the ECU to the main distro panel in the dash under the steering column is the same. So if you take the entire engine side harness from the donor it should plug and play. There are no extra special bolt holes/through holes/mounting locations on a TDI over a petrol one. Rad pack is the same as any turbo P80 car AFAIK so can just stick with that lot.

Just resurrected my diesel, did a pretty much full engine rebuild after experiencing a flattened cam shaft + 2 slightly low on compression cylinders, originally suspected bent rods, but turned out to be gummed up piston rings due to me using veg/WVO during summer for the last 5 years. Also got the fuel pump rebuilt as was doing some weird things. Currently running it in again at 280k miles! MPG is up, but vibrations are up too, suspect my collapsed DMF is not helping the situation and maybe an engine mount has gone, as has been sat on one mount + a jack stand for about 2 years!

Runs clean as though, no smoke unless on it. The diesels never do less than 40 mpg, into the low 50's if you are careful. A handy thing in these times of crazy fuel prices.
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Old Oct 13th, 2021, 20:34   #5
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Probably easier than you think, the ECU plugs split in two so keep the engine loom connected to the engine & swap that over...

The bulkhead side you may need to extract a few wires that head over to the ABS ECU area as they may differ slightly...

& the pin outs of the two ECUs for rpm etc....

Or you could just pull the entire fusebox & loom and plug that in
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Old Oct 13th, 2021, 22:10   #6
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I changed my 2.5 10v petrol to the 2.5 TDI some years ago and, as said, you'll need to drop all the front running gear, exhaust, fuel lines, fuel tank, engine loom, instrument panel, ignition and immobiliser. The cabin wiring harness can stay intact and just feed the TDI engine harness back through the fuse box aperture and connect the multiplugs. Sounds like a lot of work but if you have suitable space and a rattle gun for disassembly in you armour you could achieve most of the heavy work over a long weekend.

Provided the pics are still available to view you can have a look at my Project TDI thread. Admittedly it's been a few years since I updated the thread (lost interest after the PhotoBucket debacle) but if you need any other info or pics must let me know. I keep meaning to start a new thread and embed the photos to this site.
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