Hi folks,

Yes, I know the 10 valve 850 was apparently not sold in the US. However I am hoping someone can offer me some insights on the following.

Fortunately I have a 1998 V70, the 93 850 and a replacement 850 engine all sitting outside so visual comparisons are easy.

a. My B5252S engine in the 1993 auto, non turbo 2.5L 850 needs replacing. This engine uses the integrated Fenix 5.2 fuel/ignition ECU.

b. I have bought a lower mileage 1994 B5254S (ie 20 valve). I have the ECUs, which appear to be Bosch 4.2 Jetronic and matching Ignition ECU. I do not have a matching engine wiring harness.

c. I could take the head off my old 10 valve engine, recondition it and put it on the newer block. Pluses, minimum modifications to the rest of the car. Minuses, same old lower powered engine & re-doing the head and quite a bit of labour.

d. The Fenix 5.2 ECU combines fuel and ignition. This uses the manifold pressure sensor and air inlet temperature rather than the MAF sensor used in most 20 valve engines. I COULD buy another harness [except that I am findingthat very difficult so far], plus the MAF sensor plus various new hoses and mounts and also make some wiring changes to the car. Pluses are getting a 20 valve engine. Minuses are quite a bit more cost.

e. What about running the 20 valve engine with the Fenix? Here are what I think are the "talking points":

1. I can utilise my existing MAP and temperature sensors and the associated plumbing and wiring and easily connect them up to the new engine. O2 sensors will clearly be compatible with the Fenix.

2. As the Fenix works on a feedback principle, using the O2 sensors to adjust mixture, it would seem that the fuel control should work just fine with the new engine despite the fact that the ECU maps might differ a bit. The MAP and temperature method should have no problems with the different airflow of the 20V engine. I have yet to check the injectors but think they are the same resistance & will check before proceeding.

3. The only real issue I can think of and for which I can find no data, relates to camshaft position sensing. I have been able to find no curves for any of the camshafts. All I know is that the ECU adjusts the spark timing based on all the parameters, including the camshaft position. If the 10V and 20V camshafts are relatively similar in terms of valve timing, I would imagine everything should work reasonably okay. If there are big differencs, I might have problems. It appears from my initial research that the ignition timing at idle will be fine with the Fenix & 20V engine.

Any thoughts on the above, particularly #3? I COULD try #3, see how it goes, maybe put the car on an EGA and dyno to check. I can't imagine I would hurt it as I do not think the ECU can vary the spark timing very far. If scheme #3 did not work out, I could do an in-car swap to the 10 valve head or mod the wiring harness, ECU box and the other bits and pieces to use the MAF rather than the MAP/Temp sensors plus the Bosch 4.2 ECUs.

Does anyone have any web references to the Bosch 4.2? How common was it in 850s?

Regards,

Dave
(Australia)

PS- I'm particularly interested to find if anyone has camshaft or at least ignition timing info.