Cold Start Gremlin!

[High.miles.big.smiles]

Chasing a Gremlin with my 2002 s54...
On cold start the car acts like it is not receiving enough fuel. It will misfire, and when given throttle, it will choke and drop to 250-500 rpms. If you stay in the throttle it will eventually rise.

The car will do this until it is warmed up. You then must cycle the key on and off once, then the car will idle and drive as well as ever.

No codes save for misfire code.

The car runs PERFECT once it is warm, and will stay running well the rest of the day. Just on initial start up until water temp is around 160, it has these issues.

Vanos has been gone through, Fuel pump is new, no leaks that i can see, unplugging MAF does not seem to help.


At this point I am trying to track down which sensors could cause this issue, and then be unred during hot operation. Any ideas?

[Mspir3d]

Did you reset the adaptations and drive it for a while? Sounds like a vacuum leak to me if you did.

[eacmen]

Was this something that just started happening or did it come on gradually and got worse?

Some first thoughts:

Check codes.
Reset Throttle Adaptations.
Check for vacuum leaks.
Clean ICV & replace TPS


Sent from my iPhone using Tapatalk

[Icecream]

What cylinder is misfiring? All of then or one? Check the condition of the plugs first. Before first start of the day, take them out. Are they dry and healthy? Any mysterious coolant loss?
How old are plugs, coils? Have the injectors been cleaned/replaced? I had a significant misfire when cold when my injector started failing until it warmed up. Then it failed completely.

[Speed Monkey]

Time for the peanut gallery 😁 to chime in - cars in general (gasoline ones that is...) when they are stone cold, they run in an open loop, meaning without the use of O2 sensors to govern the air-fuel mixture. The ECU relies on a temperature sensor to default to closed or open loop. Old 911s use a sensor in the block, as with the family of VW/Audi/Porsche products that use early Bosch Jetronic CIS systems, which include K, KE, etc. Our modern M’s use the water temp sensor, or this below:

Take this as information rather than a diagnosis or an instruction/suggestion to spend $50 bucks on a sensor. Like others stated, do some testing to determine your faulty part(s), then proceed to buy. Good luck squashing your gremlin.

PS, Every bit as important as the sensor is, it is only good enough based on the connector’s or wiring’s condition. On a car that’s now 15 to 20 years old, the connector might have oxidized a bit which degrades the signal, or if the wiring is moving around, this may lead to slightly damaged conductors that lead to an intermittent connection. Moisture, being that this sensor is very near a water/coolant source, that wicks and works its way under the insulative casing will have a corrosive effect and degrade the conductor’s ability to carry a signal.

Monday fun-day where I chime in again, from ECS’s site, temp sensors can be had for the cost of an In N Out double-double combo meal Including animal fries w/extra grilled onions. That seems fairly inexpensive. The original image got deleted somehow, so I am just re-posting the same info.

Let’s talk about cold start some more as I think it might help the discussion. First, some definition of terms: Open Loop engine operation means the engine is running without O2 sensors engaged, hence “open loop”; fueling is predetermined by a set parameter by the ECU. Closed Loop means the engine is warm and the ECU now engages the O2 sensors to govern the AF mixture.

Cold Start - When the engine is stone cold, the ECU knows this from the temp sensor, because it is cold. When one turns the key, a cold start (open loop) program is used, which separate and not related to warm engine operation (closed loop). This cold start consists of injecting more fuel in the bore, because when it’s cold, the very finely atomized fuel droplets are attracted to the cold cylinder wall where some fuel droplets condense while others remain suspended just long enough to touch-off from the spark plug, leaving sufficient fuel for cold start combustion. Next, more fuel requires more air, which means the ISV opens up resulting in increased idle. Engine timing as part of the cold start is retarded to compensate for the condition of cold start - remember this, as this is key.

With that background, let’s run through a scenario of insufficient fuel at cold start. Like that stated, very finely atomized fuel will condense on a cold cylinder wall, hence the term “washing of the bore,” which means condensed fuel washes off the thin oil film on the bore, which leads to ring wear that everyone is familiar with. Anyways, insufficient fueling when it’s cold will lead to a hard start because much of that fuel is condensing on the bore wall, and a rich mixture is mandatory.

Next for this discussion, let’s say the injectors are still providing insufficient fueling for cold start - at some point when the engine is cranked continuously and long enough, enough fuel will be available for cold start but it’s a rough idle. What causes the rough idle, a combo of a lean mixture and retarded engine timing. Next, you’re late to work as usual so it’s damn the torpedoes and full speed ahead. You hit the gas, the mixture is lean, engine timing is advanced on an engine with retarded timing and bingo, the engine stumbles hard, and the car bucks like your girlfriend when... - well, you know.

Fueling is key to a cold start. Without enough fuel, some of you may like the feeling of your M3 bucking like your girlfriend, but it’s bad for the sled. Tackle your fueling problem, the hard cold starting, stumbling in cold operation and a bucking ride’m cowboy M3 will likely be resolved.

[Andy2424]

Time for the peanut gallery 😁 to chime in - cars in general (gasoline ones that is...) when they are stone cold, they run in an open loop, meaning without the use of O2 sensors to govern the air-fuel mixture. The ECU relies on a temperature sensor to default to closed or open loop. Old 911s use a sensor in the block, as with the family of VW/Audi/Porsche products that use early Bosch Jetronic CIS systems, which include K, KE, etc. Our modern M’s use the water temp sensor, or this below:

Take this as information rather than a diagnosis or an instruction/suggestion to spend $50 bucks on a sensor. Like others stated, do some testing to determine your faulty part(s), then proceed to buy. Good luck squashing your gremlin.

PS, Every bit as important as the sensor is, it is only good enough based on the connector’s or wiring’s condition. On a car that’s now 15 to 20 years old, the connector might have oxidized a bit which degrades the signal, or if the wiring is moving around, this may lead to slightly damaged conductors that lead to an intermittent connection. Moisture, being that this sensor is very near a water/coolant source, that wicks and works its way under the insulative casing will have a corrosive effect and degrade the conductor’s ability to carry a signal.

Thanks for the plausible explanation :-) What does yellow mean? Thanks

[Pnick]

That yellow looks like an image that didn't load. If you put your cursor on it and right click...

[Andy2424]

That yellow looks like an image that didn't load. If you put your cursor on it and right click...

I tried that, it doesn't work!

[High.miles.big.smiles]

Have not reset the adaptations, what does this do exactly? I agree, I need to figure out which sensors the car is relying on in open loop that differs from closed loop since I dont have any specific codes. I also agree that it could be a potential vacuum leak, I have yet to find anything but these things can be pesky..

[High.miles.big.smiles]

Also, the misfire codes started as cylinder/injector 4, and have now worked their way into a multiple misfire code

[Icecream]

Also, the misfire codes started as cylinder/injector 4, and have now worked their way into a multiple misfire code

The way i understand it is if the car goes limp, it will misfire all cylinders. Everytime a coil has gone bad for me, this is the case. Misfire logs on bad cylinder first then quickly logs all cylinders. Point is, even though one cylinder is bad, the car eventually goes limp mode and misfires on all and logs them as such . Start at cylinder 4.

[Andy2424]

In the old forum I reported about this solution, which I installed in my car. It makes things better, but it still happens from time to time. I will change the sensor as suggested ...



https://www.probsten-tech.de/z4mm3-s...ruckelloesung/


The right solution would of course be a software update, unfortunately, I don't have the options!

[High.miles.big.smiles]

Doesn't the gauge temperature in the dash cluster come from the sensor that is in the block? So if it is functioning incorrectly would that not be apparent on my cluster gauge?

Also why does cycling the key initiate it to function correctly? Wouldn't the move from open to close loop take place during a singular ignition cycle?

[High.miles.big.smiles]

Noticed I have a code for an EGT sensor. Inpa code 79. Does this sensor feed the DME useful info during cold starts?

[Speed Monkey]

EGT (Exhaust Gas Temperature) sensor, the way I understand it, is it does what its name implies; it monitors exhaust gas temperature, which is particularly important on a high performance engine, and back in he day, 100 hp per liter of engine displacement was the domain of cars with a prancing horse on its placard (Ferrari). The following is background on the EGT and function. Excessively hot exhaust gas is damaging to the catalytic converters, and on the M3, those are positioned right tight against the cylinder head’s exhaust port. Let’s take a plausible “what if” scenario on how the EGT comes into action; let’s say a driver is working the engine very hard on a twisty track. At high engine revs, the time for complete air + fuel combustion decreases, so some unburnt fuel (hydrocarbons) evacuates the head quickly and is routed into the catalytic converter.

A catalytic converter is where unburnt hydrocarbons go to get processed into water, carbon monoxide/dioxide and other gases. Remember, hydrocarbons are fuel, and if one dumps fuel on anything, it will get very hot quickly. Catalytic converters can only withstand so much heat, before it breaks down the converter’s structure, or in other words, melt. On a super high revving engine like a S54, let’s face it, it’s an efficient air pump, which allows it to make 100 hp per liter; this means an abundance of fuel Is required, and unspent fuel in hydrocarbons will stress the converters; to prevent catastrophic engine damage such as burnt exhaust valves and the myriad of things excessive heat can do to an aluminum head, an EGT is inserted into the system as a safeguard, so the converter’s core won’t become overheated, and melt.

The EGT is a thermocouple that sends a signal to the ECU. When the signal (voltage) falls out of the specified range the ECU expects to receive, a DTC code is triggered, and the ECU will make some adjustments (like slightly reduced engine power) because one of the engine safeguards is not operational.

The short answer is that the EGT does not affect open loop cold engine starting. Sorry for being verbose 😐, but some background is essential to describe the EGT’s function.