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?

had the same type of problem with my 87 325is. turned out to be a brittle fuel line. once i replaced it everything was fine. no more check engine lights or difficult hard starting.

BMW's been making cars since the '50's - can you narrow it down just a little?

if it's a CIS car, i'd suspect a fuel accumulator or check valve.

YA! What are you working on. I've owned several and working on most of um. But you need to narrow it down a little.

sorry 'bout that.

'83 320i

Sounds like a leaking cold start injector or injector.

There is also a check valve on the fuel pump that is key.

Send him these places and we will hook him up.

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Also, although it is slower.

http://323i.atinfopop.com/4/OpenTopic

so - CIS, yes ?

accumulator - they fail. check valve - they fail, and when they do, the accumulator won't help you.

also - check for vacuum leaks between the metering box and throttle.

my money's on accumulator/check valve.

Does the oil smell like fuel?

WAG...

Does this thing have a Coolant temp sensor? If so it could be faulty.

Seems to me the engine thinks that it's cold when it's hot. Next time, when it doesn't start, get him to floor the pedal and keep it there and crank. If it starts this way then it's a sign that it's getting too much fuel for the temp of the engine.



Marc-André

It doesn't have a CTS at least not in the sense you speak of.

It has a thermo time switch, but its not consitant with his symptoms.

This is a pretty good page on CIS.

http://www.users.bigpond.com/INTERJECT/KSI...LN.HTM#Why%20is

There was also a recall for this problem. It added a new harness, a dashpot and a relay on the firewall. If his car does not have it, he might be able to add it.

My bet, intank fuel pump....or external fuel pump...

on my '79, I have an external, don't know about internal...lots of info on yahoo groups at 320ibmw_e21.....herb

oops, BMW_e21_digest....

lots of discussion on fuel pumps...search latest archieves...

My 1985 535i is experiencing the same problem. According to the Bently manual this is most likely a fuel related issue. Try checking your fuel pressure regulator or the fuel check valve if you have these (these are the next to check on my list). Let us know how this turns out.

What makes me bet against the fuel pump and/or check valve and/or accumulator is that it is only a warm start problem. Usually those items will cause at the very least extended crank times when cold. They also typically don't cause tempature related problems.

At least thats been my 'speriance

Duckrider-
I would agree with your assesment (and I'm far from an expert on this) however, I know that these FI systems have a cold start injector that provides an extra squirt of fuel during a cold start. This is controled by a temp sensor on the block and won't allow this extra injector to opperate under warm starts. My understanding is that if the static fuel pressure drops (ie overnight) the cold start injector will mask this problem, but it becomes aparent when warm and the injector is disabled.
This is just my $.02 based on where I'm at with trying to solve my own version of this problem.
DR, where would you recommend checking if this isn't a fuel problem? what about the 02 sensor?
Thanks!

When I worked at BMW, we would run into this problem occasionally. Usually the check valve in the fuel pump was the problem. The check valve would stay open , (dirt usually), and allow the residual fuel pressure to bleed off.
The complaint was that '" I went into the store for a gallon of milk , and it wouldnt start when I came out".
The check valve is replaceable by removing the outlet line from the pump, unscrewing the valve from the pump, replacing the valve and crush washer , and reinstalling the line. Again with new washers.
You also should check for vacume leaks , or a lean running condition . this can give the same simptoms.
Good luck
Dave

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