850 - 2.0 Engine (LH ECU) replaced with 2.5 (B52524FS) - Is ECU replacement necessary as well?

omaralqady · Post by **omaralqady** » 21 Sep 2017, 04:55

I live in Egypt, where mechanics handle things in a not so scientific way, so when my previous engine (2.0 with LH ECU, I don't know the engine model) went bad, the mechanic said the best solution was to replace it. He replaced it with the only engine he could find in 'good' condition. (The new engine is B52524FS which is supposed to work with Motronic 4.4 according to what I saw online)

Ever since the replacement, the car has been giving a lot of black smoke on acceleration (and therefore naturally consumes fuel excessively as well), and doesn't really run smoothly in general.

It gives the following codes:
On Pin 2:
113 (Couldn't find at https://www.matthewsvolvosite.com/read-codes-volvo-850)
121 (MAF sensor signal)
123 (123 ECT signal)
223 (IAC valve opening signal)
232 ( Long term fuel trim, idling)

On Pin 6:
123 Engine Coolant Temperature Sensor (ECT) from Control module missing or faulty

When I reset the codes, the car runs a lot more smoothly, the black smoke decreases significantly (something close to 90-95% improvement), but fuel consumption stays quite high. It does this for about 50 KM, then the lambda light turns on again, and the codes come back, along with the excessive black smoke and the rough-ish running.

My questions:
1. Can the codes above be relied upon even with the potential engine/ECU mismatch?
2. If I can trust the codes, should I just replace my MAF according to them? (would that make the problem go away or is more needed)
3. OR should I actually replace the ECU with a Motronic 4.4 and then see how the engine works with it?

I'm not an expert in this, actually I don't much really, except through online research, so any tips/ideas would be appreciated.

Klausc · Post by **Klausc** » 21 Sep 2017, 12:12

I would first check that the MAF, ECT, IAC are actually plugged in. If I understand correctly, the mechanic installed a 1997-98 engine in your 1995 and did not replace the wiring harness. I don't know if the pins are in the same location between the LH Vs the M4.4.

omaralqady · Post by **omaralqady** » 21 Sep 2017, 17:41

I know the MAF is connected and working (to an extent), because when I disconnect it, the engine starts rumbling, and then dies, unless I connect again.

The IAC is also connected and causes some rumbling when disconnected as well.

As for the ECT, I don't know its location, but I don't think it would cause such problems as those listed above, as far as I understand.

Is there a way that I could verify whether the MAF and IAC are working properly and that they're not merely functional to an extent? (If there is even such a thing)

Klausc · Post by **Klausc** » 21 Sep 2017, 19:58

113 is fuel trim at low or high rpm.

Because the problems go away when you erase the codes and the computer has to relearn the driving habits, I will assume everything is connected and working properly.

With the 'new' 2.5L engine, I would try the M4.4 computer. Just make sure the battery is unplugged before you remove/install the computer.

Post by **misha** » 22 Sep 2017, 08:42

Besides ECU in order to match the engine,you will need a complete wiring harness from a donor if you want it to run decently.
Totaly different engines,different capacity,different power,injection system,emissions system.....it just won't run without it's original ecu and original wiring harness.
Newer engine and it's ecu will need a chipped key and a lots of things from a donor car in order to start...at least.

You chose the worst option.

omaralqady · Post by **omaralqady** » 25 Sep 2017, 02:12

Thank you guys for the information, it seems like this is as complex as I thought it would be then, maybe even more.

I might look into replacing the engine again with one that is more in line with my car with its current set up, if I can't find the appropriate items to handle the modifications you mentioned here.

Thank you very much for the helpful info.

Post by **Clemens** » 25 Sep 2017, 03:16

Well, the question is if the mechanic hacked up your harness badly when fitting the newer motor in there.
Do you still have the original motor? If so, get it fixed mechanically. I guess you should be able to find someone who does that work at an affordable price.