E90 320i - Erratic Idling, 3 Cylinders

[DarrylvanNiekerk]

Please can someone help shed some light on an issue that has been plaguing my car for the last few years.

I had the standard exhaust removed including manifold and a sports exhaust installed. Directly thereafter, and not related to the current issue, the car started smoking. Catalytic converters were masking a valve stem guide issue that the previous owner caused by meddling where they shouldn't have. That was solved.

Then I started to notice the car cutting power or hesitating around a right hand corner every now and then. This grew to cutting power sporadically and eventually being completely retarded at low engine revs, sometimes up to 6500.

I sent my car to a mechanic I trust who consulted various BMW specialists and had it on many launches. We went through changing VANOS, coil packs, injectors and various other items - thankfully he never got brand new but swapped from vehicles that worked to confirm whether this made a difference to no avail.

There have been a variety of fault codes from Valvetronic eccentric shaft sensor (which was replaced, this time at cost), O2 sensors ageing, heating, mixed up, misfire on various cylinders and plausibilization exhaust gas oxygen sensor.

Spark plugs have been replaced many times, injectors cleaned, valvetronic motors cleaned, engine flushed, timing checked and rechecked. Every time we think the problem is sorted it flares up again after a few days. Ever so slightly at first but then to a point where it becomes undriveable.

There are very few options now except to try and reinstall an exhaust manifold with O2 sensors and hope that solves the problem. I used to love the car so much but it has become such a frustration, I haven't been able to drive it for the last 3 months as it is currently on firing on 3 cylinders.

Thank you.

 

[Bmwed]

Swap your exhaust sensors. Did you reinstall the exhaust sensors?

 

[momo1]

Have you had it scanned for errors?

Have you had a pressure test on the fuel pump?
mine gave in a around 130000km

 

[iambengiey]

Did you redo your computer box to allow higher intake exhaust? Did you by change change air intake supply as well?

 

[DarrylvanNiekerk]

Thank you very much for the replies and suggestions.

Swap your exhaust sensors. Did you reinstall the exhaust sensors?

The exhaust shop replaced the manifold with a free flow down pipe without any sensors in it. My mechanic fitted cat foolers but this does not seem to have made a difference.

This is the first I have heard of exhaust sensors. I was under the impression there were only catalytic converters and O2 sensors. I have been under the impression the only thing left is to install a factory manifold with the sensors in place so that the management system has something to work with.

---

Have you had it scanned for errors?

Have you had a pressure test on the fuel pump?
mine gave in a around 130000km

The last scan I did not show anything amazing apart from misfires.

I have had the pressure on both the fuel pump and oil pump tested and both were perfect.

---

Did you redo your computer box to allow higher intake exhaust? Did you by change change air intake supply as well?

The computer software was updated to a later version which changed a few things and allowed the revs to go up to 7000 but apart from that not much else.

There was no specific mapping to allow for increased flow and we debated whether this should be done but without concrete evidence that this would solve the problem it might be another couple of grand wasted.

Would this need a piggy back system or can the stock ECU be modified to allow for these changes?

We also discussed the change in temperature of the gasses because of the change in flow and whether different spark plugs needed to used.

 

[Bmwed]

The sensors that are on the cats needs to be refitted to the branches. I had my previous bmw de-catted and they swoped the sensors around. Car was running bad an missing... Swoped them around and all sorted

 

[iambengiey]

Thank you very much for the replies and suggestions.

Swap your exhaust sensors. Did you reinstall the exhaust sensors?

The exhaust shop replaced the manifold with a free flow down pipe without any sensors in it. My mechanic fitted cat foolers but this does not seem to have made a difference.

This is the first I have heard of exhaust sensors. I was under the impression there were only catalytic converters and O2 sensors. I have been under the impression the only thing left is to install a factory manifold with the sensors in place so that the management system has something to work with.

---

Have you had it scanned for errors?

Have you had a pressure test on the fuel pump?
mine gave in a around 130000km

The last scan I did not show anything amazing apart from misfires.

I have had the pressure on both the fuel pump and oil pump tested and both were perfect.

---

Did you redo your computer box to allow higher intake exhaust? Did you by change change air intake supply as well?

The computer software was updated to a later version which changed a few things and allowed the revs to go up to 7000 but apart from that not much else.

There was no specific mapping to allow for increased flow and we debated whether this should be done but without concrete evidence that this would solve the problem it might be another couple of grand wasted.

Would this need a piggy back system or can the stock ECU be modified to allow for these changes?

We also discussed the change in temperature of the gasses because of the change in flow and whether different spark plugs needed to used.

---

---

Usually on an e90 for example O2 sensors need changing every 100 000k's. It's risky doing changes without going through every checklist. My recommendation is test your car output kilowatts, test each electrical component before doing anything else on the car. I suspect you might have damaged some other electric components in the midst. Revs over 7000 don't damage exhaust system but your pistons, if you hadn't changed to stronger ones it could have an impact on the engine as a whole

Sent from my VIE-L09 using Tapatalk

 

[DarrylvanNiekerk]

The sensors that are on the cats needs to be refitted to the branches. I had my previous bmw de-catted and they swoped the sensors around. Car was running bad an missing... Swoped them around and all sorted

I discussed this with my mechanic and the concern is that the air flow through the downpipe is different now from when it was using an original manifold. Will this not change the readings supplied even if we reinstall cats? Would someone then need to update the software to account for a different flow and thus air temperature or is this not necessary?

---

Usually on an e90 for example O2 sensors need changing every 100 000k's. It's risky doing changes without going through every checklist. My recommendation is test your car output kilowatts, test each electrical component before doing anything else on the car. I suspect you might have damaged some other electric components in the midst. Revs over 7000 don't damage exhaust system but your pistons, if you hadn't changed to stronger ones it could have an impact on the engine as a whole

Sent from my VIE-L09 using Tapatalk

I will try to get it onto a dyno with a launch attached, something we did a while ago to try and replicate the hesitation and find out what was causing it without any success. Everything on the actual engine appears perfect so it must be an electrical or sensor fault, the trick is finding out exactly what though.

I did some research online and came across a few potential faults:

1. Crankcase Vent Valve
2. MAF Sensor
3. Vacuum Leak
4. Vanos Solenoids
5. Camshaft Ledge Bearing

The red line limiter used to be at 6500rpm and as I mentioned during a software update this was lifted to 7000rpm. It is pointless pushing the car to that point because it has no power up there but I did find it useful in 1st every now and then because the drop in revs to second was so large that it often was below the power band. So only on a few occasions has it been taken up to 6900rpm or so, and then only for a split second. I doubt this has damaged any internals?

 

[DarrylvanNiekerk]

So. I went past my mechanic today, finally found some time. We put the launch on and it came up with:

2A70 Valvetronic, servomotor
2F08 Intake-air temperature sensor, signal
2D00 Throttle actuator

All of the above were Historic so not really showing up any faults. After looking around for a while we came across the knock sensors on cylinder 1 and 4 which were throwing up quite a bit of voltage. My mechanic asked me to push and hold the revs a bit so I sat with the revs at about 6 350 rpm for about 30 seconds.

There was a slight smell of burnt oil and a few pops and then it began to run pretty smoothly. The idle was smooth with a slight hesitation on initial acceleration but all in all the car ran on all 4 cylinders and is pretty much normal again. During a test drive I noticed it is a bit lethargic and under powered but is back to being smooth again.

Seems that maybe we are not running the best spark plugs for the setup in the car and they must be fouling, something we have noticed far too regularly in the past. So now to research the best plugs to use in the car and hopefully that is all.

Thank you to everyone who posted and assisted in giving advice.