850 petrol to diesel!

[klunk]

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.

[Martin Cox]

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.

Martin

1998 V70 Tdi auto, 229,000 miles

[andrewc1267]

Originally Posted by klunk

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

[brickman]

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.

[PNuT]

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

[Baffler]

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.

[klunk]

Cheers for getting back guys! Sorry not to respond earlier but i have had a hectic last 2 weeks! Some cracking info you lot provided me, I have the space to do the swap so i will think about tackling it early next year as a bit of a project! I really am an 850 enthusiast and the TDI's are pretty frugal on fuel so it can replace my T5 wagon as a daily! Cheers.

[klunk]

Originally Posted by Baffler

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.

That thread is a massive help Baffler, Cheers for the heads up mate, It would be great if you could do a thread update, I would be stoked to see it! Cheers.

[brickman]

Originally Posted by Baffler

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.

Excellent project! Very few s70 and 854 now, looks like you made the best of those two and saved them for the future! Just rebuilt engine in the v70 tdi, so that much is solid for the next decade, need to get ontop of some minor rust before it gets worse.
After a 1k of running in, oil and filter change is next week, just got 55 mpg out of it, obviously from pottering about and not labouring it helps a lot, but certainly sounds stronger /more consistent sounds and move clean exhaust for the first time ever.
These cars make ideal mid to long distance cruiser thats also capable of good economy and good power (with some mods), and can just about handle a corner.

[JOHN 850]

I've got a 1999 C70 T5 that's converted to a TDI by it's previous owner. It's one of 3 he did as each time he converted one a customer (he's a motorsport mechanic in Wales) wanted to by it off him lol !!

An involved job but having a complete donor car is the way to go. One thing to think about is getting it registered correctly with the dvla and then dealing with the insurance side...

Mine's been laid up for 5 years but I'm wanting to get it back on the road at somepoint as Volvo never did a mk1 C70 tdi and will be something different 😉👍

Best of luck

John