View Full Version : tecky help

12-05-2004, 12:02 PM
I was out and about cruising this morning at about 9 am. It was about -14 and I didn't plug the block heater in last night. Anyways, after about 10 minutes of driving, the following symptoms appeared:

1) I let go of the gas pedal and the engine continued reving at its present rate. After a few kicks to the pedal, the revs resumed to normal.

2) 1 minute later, the engine dies at a red light. I pull over, start the car a number of times, and it continues to die. I wait 10 seconds, try again, and it started. Pressing the gas, I found that something sounded like it was chocking. I looked down and noticed that there wasn't a girls head in my lap..j/k, anyways, I had lots of smoke come out the exhaust, and the car is now back to normal. It seemed like something was plugged for a minute, and then got tossed out the exhaust...really weird.

Any ideas of what this may have been caused by...


12-06-2004, 02:48 AM
... thick oil? I dunno.

12-07-2004, 01:10 PM
problem one sounds like maybe a frozen throttle body, got stuck open. Problem 2 maybe a leaky cold start injector...or a bad thermo switch/temp sensor...just a guess, but thats where I would start.

12-07-2004, 07:26 PM
thanks, (knock on wood) it's been fine ever since...hopefully it holds out. *th-up*

12-07-2004, 08:44 PM
#1 does that in my dad's Subaru, usually does it when it's really cold outside and you start it up, even if you wait a bit, and leave. Not sure if it's a problem though.

12-08-2004, 01:11 PM
That just may be the stock choke.

12-08-2004, 11:29 PM
Problem 2 maybe a leaky cold start injector....

the m20b25 doesn't have a cold start injector, i donno if the m20b27 does.

First problem sounds like a either the trottle stuck, or ur gas pedal cable is sticking.

Clean the trottle body up, lube the gas padel cable. See if that helps.

12-09-2004, 01:31 AM
m20b27 does have a cold start injector and that is exactly what happens if it turns on while the car is running. The excess fuel confuses the shit out of the computer, and it takes either 1 minute or so to sort it out (coughing and smoking the whole time, even if you restart it) OR (as I've discovered) unplug the battery for any length of time and restart. Good way to test for 'confused' ECU.

12-09-2004, 02:46 AM
He has a 325is so it does not apply to him

12-09-2004, 04:38 AM
Right, missed that part, my bad. No CSV.. :-o

12-09-2004, 10:01 AM
thats interesting... I guess I just assumed since the m20b27 had one the b25 would have one. I wonder why that is... :confused:

Thanks for clairifying though, learn something new every day :)

12-09-2004, 10:39 AM
Is a cold-start injector a type of choke? When I start my biatch in the winter, it idles at ~ 900 rpms' for a couple of minutes and then drops to ~ 650-700 rpm's (normal).

12-09-2004, 10:53 AM
not really...but it kinda has the same effect. Essentially it adds fuel to the mixture when its cold so that it runs rich until it warms up....where as a choke manages to do the same thing, but instead of adding fuel to richen the mixture, it cuts off the air to do it.

12-09-2004, 11:02 AM
that's awesome. it's like the difference b/w a turbo and a supercharger...sort of but not really.

12-09-2004, 11:03 AM
so would a rich mixture be ~ 12:1...air to gas.

12-09-2004, 11:06 AM
yep, thats pretty rich.

12-09-2004, 11:14 AM
in fact thats much too rich, unless you are running forced induction...the most power is made between 13.1:1 - 12.7:1, where as the most efficent is 14.7:1 (stoich)

12-09-2004, 12:00 PM
wicked, thanx. *th-up*

12-09-2004, 01:59 PM
The cold start valve is not present on the 2.5 litre motor as it has the more advanced engine management. The computer actually tells the injectors to squirt in more fuel when the thermotime switch (or its equivelent) says to do so. It provides the same effect with less parts (so its not subject to a leaking CSV, which can cause poor economy, rough running and burned cats).

12-09-2004, 02:04 PM
cool, thanks for clairifying.

Didn't the earlier 325i's like 87' come with earlier versions of Motronic though? which therefore would have a Cold start injector?...Because I thought Motronic 1.3 wasn't used until 89. :confused:

12-09-2004, 02:08 PM
Good point. Maybe its only the motronic 1.3.. hang on, I'll check my pdf verson of the haynes I have kicking around. :)

12-09-2004, 02:14 PM
Yep, the cold start injector (not valve, oops) was on every L-Jetronic and early Motronic cars. So, when we say "eta" then it has a CSI (not the miami kind) and if we say pre-87, then it likely has a CSI as well.. so ara325's 1990 doesn't have it.

12-09-2004, 02:17 PM
Boy, am I post-whoring here.. haha.. just a though on his car though: do cars without the cold start injector still have a thermotime switch? If so, and it is failing, it could cause the symptoms listed. The Haynes seems to suggest it wouldn't have one, but how does the engine know its cold for fuel purposes then.. the Coolant Temp Sensor? If so, that could also be the problem.

12-09-2004, 02:26 PM
thats a very good possiblility, it would have to know somehow when to dump extra fuel in, so a bad temp sensor I would think would do the same thing.

Alright so its safe to say that all motronic, motronic 1.1, and L-Jetronic. would have a cold start injector. good info. thanks. :)

12-10-2004, 04:06 PM
Could the mass-air sensor control the fuel levels...that's sounds oxy-moronic, but you knever know...it could the math backwards from the air input...wait we're talking temp though, right? Thermostat controls the coolant, so i have no idea...hehehe!

12-10-2004, 04:33 PM
the air flow meter does control fuel. All it does is measure the air comming into the intake, and add's or Subtracts fuel based on the amount of air comming in, and the intake air temperature. :)

12-10-2004, 05:45 PM
so i was on the right track...for once in my life...hehehe.