E36 320 Runs badly When Cold

[lesyoungman]

The car has a serious which started a few weeks ago.

The first symptoms were the car battled to start when it was cold and would run very roughly once it had started, until it got hot, then once hot it ran and started without problems.

I used it like this for a week or so (approx 130km a day) then I filled up with fuel and the problem went away completely for two days. Then the problem came back worse than before to the point that it would not start when it was cold without running it down a hill. When warmed up though it still went ok. It seemed a lot heavier on fuel as well.

When this tank of fuel got down to about half the car started running badly even when hot, it would miss badly (basically die when trying to accelerate) and battle to start, hot or cold.

This got so bad that I could no longer drive it, the motor runs extremely badly now and will most times not rev above 3000 rpm.

It is now un-drivable… Any help appreciated...

[Dudesky]

Common culprits for this condition are vacuum leaks or a failing oxygen sensor, but there can be a number of other causes. If your Check Engine Light is on, have the fault codes read.

[c1apton]

As "Dsky" mentioned vac leaks are the most likely suspects - as you mentioned about fuel level making a change in the symptoms you might try looking at the fuel canister hoses located in engine compartment. Other possibilities: fuel filter, air filter housing & bellows tube, & cold start valve.

[theSMELSINATOR]

you didn't take it into the dealer when this problem first appeared?

[lesyoungman]

Originally Posted by theSMELSINATOR

you didn't take it into the dealer when this problem first appeared?

The car has since been to a dealer who replaced the crankshaft sensor and claimed to have solved the problem. It was sort of ok for about a week, had one or two bad mornings only but it is now back to the initial symptoms where it will not start easily on cold mornings and needs to be warmed up before it can be driven. We are moving right into our winter here so the mornings are getting colder so this may be why it happens more. Cant recall what the temperatures were like in when it originally started but we have had very mild weather so far this year, no real cold days yet.

Anyway I expect it won't be drivable again within a few weeks if it follows the same pattern as before. The check engine light has never come on that I can remember.

I am thinking O2 sensor because, when I warm it up, the point where it starts running ok is not linked to the engine temperature. Basically on very cold (below 7deg C) mornings the engine can reach full temp but the car is still hesitating and jerking, on other mornings the engine temp is just above blue and it already goes fine. My thinking is that on the colder mornings the exhaust, together with the O2 sensor, is taking longer to warm up. Going to climb under it tonight to try locate the O2 sensor and check what I need to change it.

[Dudesky]

The O2 sensor has a heater circuit for quick starts, and is not reliant on the exhaust gases getting hot. If you suspect the heater circuit is not working properly, then try replacing the O2 sensor heater relay.

[lesyoungman]

Did the OBD1 cars also have the sensor heater...? This is a 1995 320 with the M50TU motor which i think is a OBD1. Where would I find the relay?

[Dudesky]

^^Yes. Look here:

[lesyoungman]

Thanks for that info... get this, I jacked the car up last night and climbed under to check out the O2 sensors and there are none!!! There were no requirements for cat converters back then in SA and I think the local cars were built to a pretty low spec to keep them cost effective... question, if there are no sensors how does the engine and fuel management system actually work???

[Dudesky]

Well I guess that solves that problem I'd be interested to know as well, there must be another way the engine maintains stoichiometric balance??