Car can't drive when cold. only once warmed up. Misfiring when Warm....

[fiftytakedowns]

So the m42's got a super irritating problem and I have lived with it for nearly 2 years now. and I am pretty much fed up with it. I've been contemplating 24v for this reason.

Anyway:

The car literally can not drive when It has not fully warmed up. it will idle (HARDLY), and will immediately Cut out/ Die / BOG if you tap the gas.

This problem gets increasingly worse the colder it is outside.


I have no clue what It could be as I thought I had replaced most of the parts involved. But I did get multiple parts at the JY to hope that I could systematically eliminate with no luck.

[jlevie]

The most common cause of that is intake leaks. A smoke test of the intake is the best diagnostic for intake leaks.

[gearheadE30]

I'm with jlevie. Colder air is more dense, so you will see a bit more of a change in behavior with colder air, especially when the car needs to be a little richer for cold running. Have you done the mess under the intake and such?

[Kershaw]

pull your intake boot (connects air box to throttle body) off and give a good look.

[fiftytakedowns]

I'm with jlevie. Colder air is more dense, so you will see a bit more of a change in behavior with colder air, especially when the car needs to be a little richer for cold running. Have you done the mess under the intake and such?

THe previous owner did the mess under the intake, and I looked at the thead to verify that it was all done correctly.

pull your intake boot (connects air box to throttle body) off and give a good look.

I have done this quite a few times, but I am open to suggestions and will do it again. Any particular place you think I should look?

[arty818]

i had the same problem when i bought my car. turned out to be like 4 intake leaks. sometimes u cant see the intake leaks by just looking you need to take every piece off and bend them. mine had a duct taped intake boot leaking, the hose that goes from throtle body to valve cover, and the skinny hose that goes from valve cover to fuel presure reg. Also my valve cover was leaking. all of these are really cheap and ez to replace so try it out.

[MR 325]

Another common issue causing hard starts and poor running when cold is a bad DME coolant temp sensor.

[fiftytakedowns]

i had the same problem when i bought my car. turned out to be like 4 intake leaks. sometimes u cant see the intake leaks by just looking you need to take every piece off and bend them. mine had a duct taped intake boot leaking, the hose that goes from throtle body to valve cover, and the skinny hose that goes from valve cover to fuel presure reg. Also my valve cover was leaking. all of these are really cheap and ez to replace so try it out.

you mean the skinny hose that goes from the throttle body to the fuel pressure reg? do you think a smoke test can help find these intake leaks?

I replaced all the gaskets within the intake system: throttle body, lower and upper Intake plenum. But I have a spare intake plenum so ill swap over the gaskets and cross my fingers.

Another common issue causing hard starts and poor running when cold is a bad DME coolant temp sensor.

This is What I thought it might be too. but I replaced it a year ago and had no prevail. luckily I have ANOTHER spare, so ill see if that does anything. Im writing a list down right now so this weekend I can tackle it when I can see the car.

[Eecen]

I'd imagine you've done this, but I don't see it mentioned;

Have you un-plugged the connector on your firewall harness (under the plastic cover), the "M42club Hot/Warm Start Issue"?

[fiftytakedowns]

yes I have. I was hoping it was something that simple as well.

[vpilarrt]

Mkae sure the AFM barn door is moving freely/not gummed up. I've had that on really cold mornings (<20°F). Sprayed the inside of the AFM with Carb/Choke cleaner - problem solved.

[fiftytakedowns]

I tried swapping out with different AFms to no avail.

[xwill112x]

Put a m50 in it, problem solved.

edit: my m42 knocks like crazy when i first start it up...has for years too. I dont really mind, as i have a m50 waiting in my basement :)

[JakeP]

I'm having the EXACT same problem as you on my 91 318i. Thought it might be the ICV so I swapped a junkyard part in and it was even worse.

The most common cause of that is intake leaks. A smoke test of the intake is the best diagnostic for intake leaks.

Doesn't really make sense if it only does the crappy idle when the motor is cold. If it was in intake leak, it would cause a crappy idle all the time.

Another common issue causing hard starts and poor running when cold is a bad DME coolant temp sensor.

I'm really leaning toward this. OP, where does your temp needle sit when the car is fully warmed up and running well? Lowest quarter of the gauge?

[fiftytakedowns]

I'm having the EXACT same problem as you on my 91 318i. Thought it might be the ICV so I swapped a junkyard part in and it was even worse.


Doesn't really make sense if it only does the crappy idle when the motor is cold. If it was in intake leak, it would cause a crappy idle all the time.




I'm really leaning toward this. OP, where does your temp needle sit when the car is fully warmed up and running well? Lowest quarter of the gauge?

when fully warmed up it sits SMACK dab in the middle of the gauge.


IS there any way to isolate whether this is a Fuel issue, a Spark Issue, or an electrical Issue?

Im planning to attack this in a couple ways this weekend:

- I am going to replace the ground strap between the block and the Chassis, because it looks very rough, and the wires are exposed.

-Additional ground between head and block for sensors.

-check all other grounds for contacts specifically the one from the DME to the shock tower or battery tray. (for some reason my hood has a ground strap on it) Any other grounds to check?

For Fuel:
I will jumper the Fuel Pump relay and see if for some reason something is telling the fuel pump to stop working maybe?? causing agressive Bogging, or no running whatsoever.

Check to see if any return fuel lines under the car have been Kinked cuasing fuel pressure against the flow.

I ahve no Idea how to test if it is not getting spark. or anything. Im really confused what would cause such an aggressive failure.


Here are some Videos of how it runs:

http://www.youtube.com/watch?v=Eu5npniUyl4

http://www.youtube.com/watch?v=NF3NEp_dnX4