Runs fine when cold! But dies when getting warm! 735i e32

[Unregistered]

Have being reading in this forum now for some hrs..
My 735i-88 will not work when it gets warm! I have had this prb now for some time and it have only getting worse now I cant even drive the car at all. It started in the winter whith problem to start the car after driving.
The first thing i thinked of was the fuel pump, which i chanced after I found a chep own for 55us$. Nothing same problem, next step I took were to chanced the temp sensor. After doing this the engine sounded perfect and I thougt it was back, but after 5-10min the car dies no matter what and u have to whait 30-60min to get it to start again then the same thing it runs perfect for 5-10min the it chunks chunkily dunks brilimbumb and its dead.
Before I replaced the temp sensor the engine sounded like i sick grandma chunking...
So is there anyone out there that have some ideas?? I replaced the fuel filter just some weeks before the prblms started, and for some mounth ago the air filter.
Best regards from sweden.
Marcus

[George M]

clearly temperature related...sounds like your mixture goes bad when it warms which is generally a sign of a failing DME temp sensor. Since you did replace your fuel pump and suspect it was bad...you can put an in-line fuel pressure gauge in and see if your pressure changes as the car warms...unlikely though. Check the connector to the DME temp sensor...make sure it isn't corroded...sensor can be good but connection maybe bad dramatically increasing resistance. I would recheck your new sensor with a multimeter to determine diff temps versus resistance per Bentley as well. If that all checks, check/clean the AFM...run some simple flap versus output checks per Bentley...to make sure there is an approx. correlation...could be the air temp sensor in the AFM also...though they rarely fail. Lastly, most likely a failing O2 sensor. The O2 sensors on these cars are heated and therefore don't talk to the DME when the engine is just started and running cold. As the engine warms, the DME does glean input from the 02 sensor and may be getting bad info thereby adjusting air/fuel incorrectly. Sounds as though you have an early E-32 with 1.1 Motronic which is not suspectible to the stomp test as with later E-32's.
Motronic 1.1 can still be analyzed with a Bentley manual however. My hunch is it is one of the above engine management sensors that is creating your warm driveability problems.
HTH,
George
90 735iL/149k...also own an E-32

[Unregistered]

thanks for a quick replay. This 02 sensor is this the same as the lambdason? On the exhoust? Or where is this o2 sensor placed?

[George M]

a lambda code and O2 sensor failure, though often mistaken for the same thing aren't necessarily related but they certainly can be. Your 02 sensor can be good and you can still get a lambda code from your DME which is generated due to an incorrect air/ fuel mixture which can be based upon any one of a number of things...somethings spawned by a vacuum leak for example which will lean out the ideal mixture. Motronic 1.1 is more primitive than is successor 1.3 and hence codes generated are not as explicit. If you don't know the history or age of your O2 sensor however, I would replace it....they have an effective life of approx. 60k miles. O2 access however is difficult on a big six car...it is tucked up/threaded into the top side of the CAT and therefore generally necessary to drop the CAT down a bit for access to replace.
George

[Bill R.]

thanks for a quick replay. This 02 sensor is this the same as the lambdason? On the exhoust? Or where is this o2 sensor placed?

[Unregistered]

If I search in the dealers products data base i cant find any o2 sensors but what I can find is a lambdason sensor can this be it?

[Unregistered]

opps thanks for this bill

[George M]

this link shows how later OBD 1 Motronic fault codes are parcelled separately into lambda specific codes and O2 codes:

http://www.pelicanparts.com/bmw/tech...de_Reading.htm

Your early motronic car which was not suspectible to the stomp test will generally lump the two issues. If you suspect your 02 sensor, then refer to Bentley 130-9 which addresses how you can test your 02 sensor with a multimeter. The connector can be dislodged without dropping the CAT and you can add long leads to your mm and drive the car to assess 02 function during different driving conditions to evaluate transient response/min and max output (0-1 VDC) it is providing back to the DME.
HTH,
George

[Unregistered]

But if I just diconnect the sensor of the exahust and keep it from getting warm, and the engine just keeps on going shouldn´t this be one way of locating a failing sensor???

[Bill R.]

volvo and mercedes and not so many bmw's ... There's a good possibility that its cracked connections on the fuel pump relay or dme relay circuit board, most likely the fuel pump relay.. They develop round circular cracks where the relay attaches to the circuit board, poor solder joints.. Usually if you resolder the joint they are fine.. What happens is that the solder joint makes contact when cold but as it heats up from the current flowing through the relay it breaks contact and the fuel pump quits, once it cools down completely the circuit is completed again... I will post a picture as soon as I shrink it down some .. Here's a pic

But if I just diconnect the sensor of the exahust and keep it from getting warm, and the engine just keeps on going shouldn´t this be one way of locating a failing sensor???