Cold Start Gremlin!

[High.miles.big.smiles]

Replaced maf with a used until. No changes. I'm beginning to think it's a cam position sensor. In going to clean the crank pos sensor and order a cheapo Rock Auto cam sensor to troubleshoot, then invest in a BMW unit if it fixes it. I hate throwing parts at the car but at this point I don't have any more leads.

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[bigjae46]

I was going to say probably an issue with your idle air or the SAP on the pass side.

Idle air is a more likely cause. The valve gets filled up with crud. I’d pull it out and check to see if the valve moves freely.


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[eacmen]

You can't see MAF readings? That sounds like a problem. But not likely to affect cold start.

Have you checked ignition coils?


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[High.miles.big.smiles]

Smoke tested the car, no luck at finding a leak. Convinced it's a sensor at this point.. all sensors look fine on inpa but cannot see maf readings. It doesnt seem to make a difference when it's unplugged so I'm not sure. Have a fourth injector code and misfires but I think those are derivatives of a bigger issue

[Icecream]

My ancient copy was taken from old M3F.

In any case, I Googled it for you 😁; here it is:

http://www.unofficialbmw.com/images/...lectronic1.pdf

I have been looking all over for definitive information on the ICV, it’s function and how much it really affects power response at low rpm. This answered it. Up to 15% load (which sounds significant), the icv is in control. Thanks for posting!

[Speed Monkey]

My ancient copy was taken from old M3F.

In any case, I Googled it for you 😁; here it is:

http://www.unofficialbmw.com/images/m3engineelectronic1.pdf

[eacmen]

Dude, that’s a whole lot of questions, but there are many answers. You made me geek-out 🙄 and look through my PDFs; here is the info you seek. I hope it helps you.

What PDF is that from? link?


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[Speed Monkey]

Dude, that’s a whole lot of questions, but there are many answers. You made me geek-out 🙄 and look through my PDFs; here is the info you seek. I hope it helps you.

[High.miles.big.smiles]

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.

That was an awesome response and exactly what I like to read when I'm trying to find an issue. Thanks for the info.

Does the ECU soley rely on the coolant temp sensor, mad, and airtemp then for open loop operation? What other sensors are heavily leaned on in open loop that differs from closed? I'd change my coolant temp but the dash reading is fine.

[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.

[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?

[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?

[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!

[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.

[High.miles.big.smiles]

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