320i Running Rich/Poor Acceleration once Warmed Up

[B320i]

Now it's my turn for this infuriating problem, which began after the car had been parked up for a couple of months, battery disconnected for about half the time, then reconnected by housemate and the car taken for a run to charge the battery before being parked for a few weeks. The battery was a bit low when I first restarted it.

Car starts up easily when cool, and runs fine during the warm-up phase, it accelerates well and smoothly. After about 10-15mins (about the length of my commute to work), dependent on the outdoor temperature, the car will suddenly run very rich, with poor acceleration and batch-firing injectors. The car will immediately restart if shutdown. Prior to this issue, the vehicle didn't have any misfires, or acceleration issues when warmed up - it performed as you would expect the small 2L 6cyl engine to.

About 6 months ago, the fuel filter & oxygen sensors were replaced and there were no issues from that, perhaps a slight performance & economy improvement.
Knock sensors are about one year old, which were replaced in search of a cure to pinging (which settled down for a while but never really went away, even on 98RON/93AKI petrol).

Tried disconnecting the MAF to see if there was any change in the running both with the engine on and after a restart. No change.

Am waiting on a Peake Research code reader to come in the post, in the hopes it will want to communicate with the Siemens MS40.1 DME fitted to this vehicle and shed some light on the situation before I go splurging on Genuine parts, which for the vehicles equipped with a Siemens DME are eye-wateringly expensive.

My thoughts lie with the following:
- Coolant Temperature Sensor (ECT?)
- Intake Air Temperature Sensor (IAT)
- Camshaft Position Sensor (CPS)
- Old battery (now 5.5yrs old)

A combination of the first two would likely explain why I haven't been able to completely eradicate the pinging issue for any significant period of time. Not really sure on the symptoms of a failing CPS; but batch-firing injectors would seem to put weight in this theory. I had thought a CPS fault would cause trouble with starting and/or random stalling.
A failing battery could also be an issue - the fault developed after the car was started with the battery being quite weak. Need to try disconnecting the battery to see if that could be the culprit.

Regarding the CPS, the OEM Part # for my 1993 320i is 12141730028. RealOEM lists the part 12141703221 (found on later E36s) as having superseded the other, with the note "nonexchangeable retrospectively." Can this later part be used, or is it likely to be a waste of time & money if I need to replace the CPS?

Thanks to anyone that can weigh in with some ideas.

[Tapanui]

Clean the connectors on the coolant temp sensor and inlet temp sensor. Also check your viscus unit. My 320 did the same and turns out it was over heating from a clapped out viscus and a faulty temp sensor.

[B320i]

Clean the connectors on the coolant temp sensor and inlet temp sensor. Also check your viscus unit. My 320 did the same and turns out it was over heating from a clapped out viscus and a faulty temp sensor.

Viscous coupling on mine is good, but will definitely try cleaning the connections for the two sensors. Was the trouble on yours only once the engine had warmed up?

[Tapanui]

Yeah crook coolant sensor was the culprit for mine. when started up ran fine, but when it heated up started to run real rich and started pinging. There are a few things that make a car run rich with EFI. Such a crook Coolant temp sensor, a faulty Mass Airflow Sensor, or a Throttle position Sensor. Before I would go changing parts it would pay to check your earths, clean the connectors and use a MAF cleaner.

[B320i]

Did some testing today to figure out where the problem could lie. Connections for the Cam sensor and coolant temperature sensor are clean.

When at operating temperature (where the car is running rich, injectors batch-firing, poor acceleration), the coolant temperature sensor (Part number 13621730034 for the 1993 320i with MS40.1 DME) tests to about 158 ohms. For the Bosch Motronic equipped vehicles, a reading of 0.27-0.40 k ohms should be expected at 176ºF (80ºC). After the car has sat for 1.5hrs, the reading was in the ~180 area (this would equate to .158 and .180 k ohms, presumably). Anyone with an E34 520i or E36 320i that could confirm the correct readings for this sensor?
Unplugging this sensor didn't really change the engine behaviour much, perhaps a smoother idle.

Cam sensor was also unplugged with and without the coolant temperature sensor unplugged, too. No change in engine startability (it started straight up), and still the bogging/batch-firing injectors/running rich as before, so I presume the engine is in Limited Operating Strategy / Limp mode given two sensors necessary for properly fine-tuning the engine were missing.

Hoping a readout of the codes will confirm where the issue lies.

-- EDIT --
A fairly involved Google search found me this .PDF document from the Russians: https://forum.bmwland.ru/index.php?a...=post&id=42165 which has resistance figures for the MS40/MS40.1 DME. It seems the readouts for the Coolant Sensor are definitely questionable, the lower Ohm figures also explain why I've never been able to cure the pinging issue despite new O2 sensor, fuel filter & knock sensors.

Another thread on BF here has some more useful insights: https://forums.bimmerforums.com/foru...-wizardly-help - and also note the Cam & Crank sensors are "hall effect," or "pulse generators" on RealOEM, so I think they're completely different to those found on the Bosch Motronic. Trying to test these with a multimeter is apparently a fool's errand.

[B320i]

Many months later - here is an update.

The second Peake Code Reader I've sourced produces E10/E11 errors and refuses to communicate much like the first. Tried disconnecting the ABS fuses & relays to no avail. I suppose the other solution might be to try finding the power source(s) for the body electrics and disconnect that; early E36s supposedly had a ground issue that would hang up the diagnostics. It could also be the Siemens DME... Was able to reset the oil service indicator.

A replacement coolant temperature sensor did not solve the problem. However, up until the point the car decided to go into limp mode, it was performing much better. So that was a nice bonus.

Finally a new Camshaft Position Sensor was installed. There was a break in the wiring insulation thanks to the strain of the way this wire had been routed. Perhaps heat-soak would cause signal degradation. The sensor was 26 years old, too. A lot of research about the CPS revealed the following:
- Both the OE 12141730028 and newer 12141703221 (e.g. from the E36 328i) are hall effect sensors and are wired the same way, and seemingly use the same reference voltage
- The OE part has a metal body and uses an o-ring. The newer part has a plastic body and a 'ledge' at the end where an o-ring would sit. On the older M50 engine, the part WILL NOT fit if you use the o-ring. Without it, it fits perfectly. Contacting FCPEuro and a couple of other parts outlets (in addition to the RealOEM information) says the newer is considered an acceptable drop-in-replacement for the M50 with Siemens MS40.1 DME
- The OE part has a right-angled connector; (as the harness has the connector facing backwards) whereas the newer part does not.
- The CPS I removed (with damaged wiring) was tested with a multimeter. Resistance tests over-read by about 2-3ohms when cool. Obviously Euro-spec E36s have no CEL, and my unfortunate results with diagnostic equipment mean I cannot saying if a CEL was lit. Judging on the limp mode described (very poor, hesitant acceleration, running very rich, batch-firing injectors), the CEL, if fitted, would have illuminated.

The newer style CPS works and the engine has far more pep than I've ever known it to (the past three years it seems to had it's good and bad days) in six years of ownership! Will report back in relation to any pinging. Suffice it to say, I suspect an ageing sensor has contributed to this issue, too.

[Eric93se]

Leaking injectors, run cleaner over the next 3 tanks of gas. Try Royal Purple, use a different brand each tank.

[m17aka7]

OP, from what I understand you are now with the 12141703221 CPS on a M50 vanos head, correct? As I'm currently running the same combination, I have oil leaking around the sensor. It appears that it does not seal good (as the newer one doesn't have the o-ring), resulting in a malfunctioning CPS. Did you encounter such an issue and if so how did you fix it? Also from the research you did it appears that the two can be interchangable, so worst case scenario, I would have to get a new 12141730028 CPS? Any help would be appreciated, as there is so little written on this topic.

[B320i]

Apologies for the thread resurrection, but I feel it's worth answering this query for the benefit of people searching online in future.

I investigated the use of the newer part 12141703221 from the OBD-II cars (328i with MS41.1 DME) given the scarcity, and extremely high cost, of the original Siemens component used on this generation, 12141730028. The cars it was used on (base model 6cyl 320i/520i with Siemens MS40 or MS40.1 DME) were only available in the "EU spec" markets, which explains the cost/availability conundrum. Reply 6 details how I determined the newer part was a suitable fit.

Unfortunately the car only ran for another month or two after this fix before head gasket failure (more precisely, the cylinder head corroded into nothing around the back by the heater hose flange) sidelined it. There were no oil leaks during this time, except from the oil filter housing which was on the to-do list. All I could suggest is ensuring the surfaces are clean, and finding some sort of small gasket (maybe even RTV?) that might help with seepage.

A reminder for everyone else: for goodness sake, change your coolant on time! I finally got a hold of the service history months after the failure, and the car had very low utilisation and servicing for a period of 5-10yrs. I presume a lack of coolant changes in that timeframe were major contributors to the deterioration of the cylinder head in my car.