Euro 550 OBD plug . Yes it is there and I have found it.

The last testdrives I made were with half power most of the time, so I was not comfortable running above 3000 rpm, so maybe my LTFT is now indeed a "good"value , but without meaning...will have to do that over as you decribed Ian.
I think I will wait until I have my extra scanner and the extra OBD to OBD2 Fiat connector, so I can watch both banks at the same time, so I can hopefully see some data shifting on one bank compared to the other when the stumbling/low power occurs.

About the resistance, when I place one probe of the meter (set on the lowest possible ohm setting of "200") on pin 6 of the left ECU connector, I get correct low resistance on pin 1 of the Right MAF connector (=00.4 or 00.5 which is the same as the probes touching) .
But when I place the probe on pin 3 of the Maf connector, I get a 35,0 restistance , 70 times higher.
When I check the other bank: Right ECU vs Left MAF, there is no resistance between pin 3 MAF and that ECU connector 6 at all, as you would expect.
So there definitely is a difference.
But: when I test by using the Left ECU connector and the Left MAF connector, I also get a reading, found that out yesterday. No idea what it means other than that the two harnesses are connected, maybe by that plug you point out. I will see if I can find it and clean it a bit with Deoxit D5 (should be the best electronics cleaner I read)

Then about the throttle valves and TPS, I removed both elbows to expose the valves. Engine off.
I looked at the left butterfly, looked ok, gap of 0.05 mm or something like that. Same for the right side butterfly: closed with 0.05 gap.
Then I put a stick between the seat and the pedal, to slightly depress the pedal (1 cm) and thus open the valves a bit.
Instead of the left valve (the side with the low TPS%) , it turned out that the right side was opening less than the left side (or vice versa)
Strange, should have been the other way around?
How about this: with light throttle, say 5mm depressed, the left valve is opening already, disturbing/using up the vacuum on the left side, so the other side loses a bit of vaccuum as they share the plenum, resulting in a lower MAF reading on that side. This could explain the right MAF dip that occurs when you open the throttle.
Does not explain why at higher rpm the car stumbles, but at least it might help some. Or is this just a little detail and am I looking for too much in it?

 

I have read the section in the WSM about the TPS's , but in that description you need a breakout box tool on the ECU. Impossible to find for a 5.2 motronic of course...
Using Ohmmeters sounds a lot easier to do...but when I have my second scanner, hopefully this week, I can also see if the % of angle opening is the same. As I think that percentage is calculated by the ohms or volts, correct?
The right TPS has 2 plugs instead of 1, any idea why? And what the function is of those pins?

About the Left ECU on Left MAF, same pins : pin 6 ECU and pin 1 and 3 on the MAF connector.
And yes, the scanner was connected to the left ECU while testing, will try again today with the scanner disconnected and the plugs connected to the loom as in normal use.
Good thinking! Will report back.

 

Just came back from more garagetesting.
The dip in the MAF value when lightly touching the pedal seems smaller, but the highest value at 2400 rpm I got was still too low at like 12g/s.
Also snap acceleration (fast depresssing of the pedal to the floor and letting go) only gave like 70 g/s, where it should touch twice that number. So the throttle valve is not the cause, the adjusting I did yesterday evening has very little effect.

Ok, engine off, back to the resistance testing. (Scanner disconnected from the loom, plug reconnected)
The strange resistance on pin 3 of the MAF connector was now 42.5 with the engine hot. And already 41 a minute later, probably going back to 35 or thereabouts.
So resistance rises with temperature and it isn't the scanner... Any clues in that?

Then on the resistance measured when connecting Left pin 6 ECU connector to the Left MAF connector: pin 1 gave 0.3 (low value, but should there be a value at all?), and on pin 2 also 0.4 . But pin 2 is a signal value, correct? should not give anything , and certainly not on the left bank...
(I mistakenly said pin 3 of the left MAf in my previous posting , that should be pin 2!)

 

Thanks both for suggesting and thinking.
I did some more testing, this time I backprobed the TPS's (measuring on the disconnected ECU connector pins 71 and 44 did not give values). The single TPS on the left bank gives 0.533 V on the outer pins with all connected, ignition on, immobilizer disarmed, engine off.
The dual TPS on the right side , the blue connector has a 4.97 V difference between the 2 pins. The white connector gave 0.499V on the outer pins.
The WSM states that the difference is not allowed to exceed 0.07V , so at 0.034V the TPS's should be ok, at least in a closed position.
And as the ECU only takes into account on/off when the MAF's are working, this is not a path to dive into further I think.

About the connector 179, I think I have found that in the left footwell, near the ECU. Looks undisturbed and clean, but as it is tiewrapped to the main loom, and the connector sits in a sort of bolted bracket, I did not take it apart, did not want to disturb. Any ideas if I can test something on that, I can try to back probe it with my now set of super sharp paper clips...

I think I am going to bite the bullet today and switch the ECUs . Hopefully it turns out one of the ECU's is not good. Funny how you start out hoping for a broken sensor on the engine, to where you come to the point that you hope for a broken ECU...

If all that does not work out, the next thing is doing a major service on it.
So I ordered new belts, Hill Engineering tension bearings etc. So I can check for, and possibly rule out a jumped belt. It has been 4 years since the last belt service so it is due anyway, as I do not know what quality parts were used .
And as I already bought a Goodyear belt tension meter, I will be able to set the tension to spec (I read that most cars have a tension that is too high).
Done my engine out on the 355 succesfully, so I am confident that I will do this the right way and particularly pay attention to the lessons RD posted on this...

But first that ECU swap...

 

Maybe i misunderstood the TPS / ECU pin 71 and 44 test, I tested for volts, not resistance...so when I measured nothing, I reconnected everything and backprobed the sensors, which gave the correct valve-0-position voltages. And as the scanner already showed that both tps's reacted consequently to the pedal, I assume they are ok on part throttle as well.
Only thing that bothers me a bit is the max value of high 70's, and not 100% . I have checked (and adjusted) that the butterflies are 100% open when the pedal is floored, but still the percentage is not 100%. Maybe not important, but I look for all things that are not 100% correct now...

One thing I did not check is the condition of the cats, maybe one is plugged (or both, who knows). I hope that removing a o2 sensor gives enough room for my glasfibre camera, as removing the cats is a whole adventure on its own...

Tomorrow it is time to swap the ECU's (see how I postpone that with every possibility ) , but tonight I am going to measure the capacity of the fuel pumps directly from the return rail. Should be a litre in 2 minutes I believe, will check the WSM again.

 

Ok, small update, did the first testdrive today after installing new fuel pumps. Bosch this time, the garage previously had used a C-brand rip off it turned out.
Still the pumps do not supply what the WSM says is needed (they supply 650 ml in 30 seconds each through the FPR instead of 1.3 liter each) , but the car ran fine.
Idle is still a bit lumpy and v8 sounding, but the accleration is ok without hesitation.
I had scanner connected to both ECU's , so I could monitor the O2 sensors, and the upstream ones were occilating nicely, and reacting to rich when the gas pedal was touched. The downstream ones I am not sure of, my scanners can't show both the graphs together to see if they mimic the upstreams.
The downstream pattern is more erratic, not a nice smooth line between 0.6 -0.7 unfortunately.
I have read they should have a maximum of 70% of the movements of the upstreams, but that is hard to see in a graph that goes to all sides...I guess the cats are over 20 years old and showing it...
The MAF's I could compare better , left to right, and the left ECU (right MAF) was still showing 10-15% less than the other one, when cruising. But on half throttle, the difference was not that clear anymore. So maybe a combination of a very small vacuum leak with a slightly clogged cat, who knows.
And then the fuel trim, the left ECU was showing 6.3 LT, and the right one 0.0 (strange or not?)

Anyway, the car drives as it probably should, and in the coming months I will take a look at the timing (and replace belts, bearings...) and the cats, and will remove the plenums to replace the gaskets.

 

The garage bought them, I do not know. I think in Italy with Autoepoca, but I can't imagine that this specialist company would sell inadequate pumps.

But last time I checked the sleeves, when replacing the pumps the garage bought, they were fine and not sticky or brittle.

 

Ok, final update ( I hope).
After installing the new new pumps, the car got its performance back, more or less.
But it still sometimes hesitated, as if it was on 6 instead of 12 cyls. But only for a few seconds, before all was well again.
But that stumbling was there, and I decided to do the major first, who knows what problems I would find.\

So the last 3 months I have been busy with the extensive major, and that I finished last week. So no more possible air leaks, as all gaskets were new and torqued to spec etc.
First test drive is always exiting, did I bolt all things back right etc...but all seemed well, except for that same stumbling.
So I did a testdrive again with two OBD scanners on a board, to compare both sides of the engine while driving.
I noticed that one of the upstream O2 sensors flatlined on 0.0 V while there was a stumble.
Aha!
So it is a O2 sensor giving no signal intermittently, or maybe the fuse or relay of the fuel pump intermittently stops one bank for a second or 2 before coming back to life again.
So I replaced all 4 O2 sensors, and both crankshaft sensors (had planned to do those anyway, car has driven 129.000 km/80.000 miles so not wasted money.)
Did a new testdrive, and no more stumbling!
Finally!

Even when the MAF values still are not equal, the car now drives really well. Happy!
So thanks to all who thought with me , and helped suggesting!
Really kept me going.

So it was either a crankshaft sensor, or an O2 sensor. (and the wrong pumps, and a broken variable length manifold actuator, and a jammed manifold valve, and slightly mistimed cams, and old fuel filters and and...)

Next thing is buying new rear tires, as it keeps on spinning/activating the ASR.

And building an X-pipe or H-pipe, have not figured out yet which I want
Yes I know, V12 does not need it, but my car has aftermarket mufflers, I think Fuchs, and these only sound sporty while idling.
Above idle the car is too quiet for my taste.

below a picture of the finished product. I understand the plenum is a matter of taste, but I saw it over here somewhere, and liked the idea.
Image Unavailable, Please Login

 

So that fun was short lived...
I had like 50 km of completely trouble free driving, when the next day, when I wanted to show the missus that the car was repaired, it started to slightly stumble again...
(Same behaviour as before the major.)
From that day on I have made several test drives, and the problem seems to get bigger.
It now stumbles for 2 to even 10 seconds, then is ok for like 20 -30 seconds, before it starts again.

What have I tested and done so far:
I connected 2 scanners for simultaneously watching the O2 sensor outputs of both banks, and the left side showed a drop to the bottom (flatline) during the stumble.
(Which in fact is driving on 6 instead of 12 cyls.)
Left side LTFT is 20, right side LTFT is 3. So definitely something amiss on that left side of the engine.
(As it is a euro car, no CEL as that is only for 2 rare faults, while it is very common on a USA car as on that one it is triggered by a lot of things like LTFT etc)

I have replaced up to yesterday:
- all 4 O2's for new Bosch's ,
- the 2 crankshaft sensors with original Ferrari ones,
- checked the TPS (both are ok and react the same normal way during a stumble) ,
- replaced both MAF sensors (both give normal values during a stumble)
- replaced the fuel pumps(twice!!) and filters.
- Cleaned the injectors.
- Replaced the spark plugs with NGK's.
- Checked the injection harnesses for continuity when I did the major, all ok.
- replaced all gaskets for new, so chances of an vacuum leak are very small.
- replaced the 4 related fuses

What next?
Today I replaced all 3 relays of the left side (Fuel pump, fuel pump signal, injector control), but no effect.

Then I connected a separate 12V source to the left pump directly, to check if the connectors on the fuseboard might be the problem, or the wiring to the pump.
But no effect, keeps on stumling/ o2 bottom flatline. Most of the time on the left , but I think I noticed an occasional stumble on the right side (bank 1-6) as well.

Then I switched the ECU's, and did a new testdrive.
It now flatlines the O2's on both sides! (not at the same time, at least not yet)
Mostly the left side, but absolutely on the right bank as well.
LTFT left is now 17, and LTFT right is now 11.

Should I conclude it is both ECU's? Or one ECU and one harness? Would be absurd, but possible?

And why was it ok for one whole day after replacing 6 sensors, but is now worse than ever? What could have changed? I added premium 98 fuel, so that should not be a problem. My M3 engined BMW runs great on that same gas.

Only thing that has not been replaced yet, is the camshaft position sensor, but when that one fails, the total engine stops, not just one side.
Or am I mistaken , and can a camshaft position sensor affect mostly one bank?
I really am out of ideas and things to replace...
Any help would greatly be appreciated...

 

Hi Ian,
I did a smoke test before I did the major, and all was well then, so I assume the hoses (all of which I checked and some I replaced) are not the problem.
Only thing I did not check for function was the fuel purge system and the idle control valves.
Should I check those for function? The hoses are ok anyway.

It happens at lower rpm's, but mostly I think because I am afraid to use the rpm's above 4000 now.
Most happens at light throttle, or when slowing down for a roundabout, and then accelerating again I sense that I am on 6 cyl. But sometimes on a steady light pedal on a straight road as well. No real pattern found yet.

It does not take long enough time to set a code. I had a CEL once, for a few secs, but when I got home 5 minutes later, there was no pending or stored code.
I think that is because it is a euro car, and those save the CEL + codes for rare occasions...

About the flatlining of the O2's, it is on the bottom of the graph, but there still is a line visible. No power to the O2's would give no signal I think, so I consider the flatlines as extreme lean, which the high LTFT also confirms.
When I lift the throttle, I get the same flatline by the way, before it starts going up and down again.
Normal I would think. Or not?

Regarding the cam position sensor, I do not fully understand how that signal works.
The sensor is on the right bank, and it sends the signal to the left ECU?
If the signal is used for details of the fuel mixture, then both sides need it, correct?
And the ECU on the right side, that does not receive the signal, does it not register a signal miss then? Both ECU's are the same, isn't it possible that both ECU's use a shared signal through that connection?

Would an SD2 help in this case, without codes? I hate to have it towed to the specialist (too far to drive now), but if all that can be tested or replaced has been done, what else to do...

 

But it certainly helps me in understanding the system of signal transportation, and now I have something new to check. Thanks again for your help and time Ian.
If the S118L splice thingy is bolted on the right ECU, I might have "disturbed" it when I switced the ECU's.
Maybe a connection is intermittently faulty, and touching the housing made it worse.

Any idea if the s118l is easily recognizable? I suppose it does not say S118L on the outside? But it has 3 S colored wires, correct? (forgot what color S was, but the WSM or one of your diagrams you showed earlier will help)

The fact that the car was 100% ok for 1 day after replacing O2's and cranksensors, but has been getting worse every day since then, should point to a bad connection somewhere in my opinion. Coincidence is too big that it is a suddenly failing part like the cam sensor.
And the fact that switching the ECU's did not move the problem from left to right, but divided the problem over both sides should also make sense once I have found the real culprit. But for now it is back to measuring wire resistance!

About the O2 sensors, the have a connection near the bellhousing , on the chassis. These connections were clean. The wires then go up to the area between the bulkhead and the inner wheelwell, for yet another connection. I will check those intermediate wires for steady resistance.

And about the vacuum, the MAF values should be very low when it happens, but I do not see any difference in MAF value: for example, with a steady gas pedal, the one MAF gives 15, the other 18.
Strange, but no problem. Then the car stumbles, and the values stay the same, maybe as a result fall to say 13 and 16, as the car slows down a bit on 6 cyls (lower revs, less air)
And as I removed and checked all hoses, I could not really find faulty ones.
The only suspect hoses (positive pressure?) are the 2 on the valve covers on the front, the edges were tearing in a bit.
But I sort of repaired them with "liquid tape", so should not leak, or perhaps a tiny bit that does not affect mixture.