OT- Hard starting BMW, Fuel injectors? Options

[jnp914]

A friend just asked for help in diagnosing his BMW:

-starts fine when cold

-starts fine immediately after turning it off

-impossible to start after 15 or 20 minutes

-starts fine when you wait until the engine is cold


To me, sounds like something in the enrichening circuit, blah blah. Any ideas?

[DuckRyder]

Your 535 is L-Jet (or motronic?) right?

320i is K-jet or actually KE-Jet on an 83. There are very limited electronics and the computer (if it even qualifies as one) alters mixture based upon the 02 sensor by way of the frequency valve which basically pulses the fuel supply. Unplug the valve and it is back to standard K-Jet.

The Thermo Time switch activates the cold start injector. There are varying values of them, but they usually activate the cold start injector for X time under X temperature. However, you still will not get much spray out of the cold start injector if the check valve or accumulator has bled all the residual pressure off. The recall I mentioned alters the warm start mixture using the cold start and the aux air valve. It was for a hard warm start.

Based on his somewhat limited description, my guess would be one of the injectors leaking, and flooding it. Restarting it warm does not give it any time to flood and waiting later allows the fuel time to leak around the rings and into the pan. However, it is just a guess. People some times bend the injectors trying to remove them and cause these sorts of problems. Remember CIS/K-Jet injectors are completely mechanical, and if one fails to seal it will dump fuel. Could also be the aux air valve hanging, a vac leak, bad control pressure regulator.......

It also could be the check valve, either fuel pump, or accumulator that has been mentioned, but if it truly starts fine cold they certainly would not be the first thing I went for. Typically, they cause very extended crank times. They are however very common issues.

The nice thing about K-Jet is that about all you need to diagnose it is a fuel pressure gauge and a D-VOM.

If he would like to join the Digest, I can approve him immediately. There are some folks there that know 15 times what I do about K-Jet. If he will post up an introduction and detailed description of what he has done and any recent repairs, I bet he will have it fixed before the night week is over.

The Digest URL:

http://groups.yahoo.com/group/BMW_E21_Digest

Brandon also has a very nice FAQ - tech page at:

http://www.e21bmw.net/tech/index.php