'77 320i Stutters & Sputters - NEWBIE NEEDS HELP!

[gfulcher]

Greetings! I'm not new to vintage german cars - but I am to ones with a radiators and fore-mounted powerplants! Actually, my friend just purchased a near-cherry '77 320i (E21) with 85k or so original miles, driven by the wife of a Bimmer mechanic. Anyhow, the original owner sold the car to my coworker, who sold it to my friend - basically, just passed the car along. We brought the car to my garage where it sits until the following problem is solved.

The only thing apprarently wrong mechanically is in regards to a stutter/sputter/bog/lack of power - but only after the engine reaches operating temperature. Runs GREAT up until this point - it happens every time without fail. (which I think is a good thing as it can be replicated).

Once the stuttering starts, all we have to do is turn the car off momentarily, fire it back up and viola! no problems - runs like it did while cold - but only for a minute or less and then it all starts over again.

Also, the engine has trouble getting much past 4800 RPM when the problem occurs - when 'cold', it goes to redline rapidly. Fuel consumption seems excessive, too - yet there is no smoke in the exhaust.

Engine has new points/condensor: Dwell is adjusted to factory specs. Timing is adjusted to spec at 2400rpm. Car has a new cap/rotor/wires & plugs. Fuel pump is pushing out the proper pressure and the vacuum readings average 15 - 18. Haven't yet performed a compression check.

My logic is that this is a temp-related problem, perhaps with a sensor, sending unit or valve being controlled by the aforementioned. Could it be as simple as a relay?

We're awaiting arrival of a Haynes manual tomorrow, but I"m eager to hear any suggestions! I'm not yet up to speed with all the parts' names and locations - but hope to be after a few more hours under the hood.

Thanks in advance!

Greg Fulcher
'41 Oldsmobile Model 78 Sedan
'67 VW Squareback
'68 Deserter Dune Buggy
'72 Porsche 914 (2.6L Big Four)
'73 VW THING
'98 New Beetle (winter beater)

[Jared at Pelican Parts]

Is it carbureted or CIS?

[gfulcher]

Hi Jared.. Sorry - it's got the K-Jetronic F.I.

Thanks!

-greg

[Jared at Pelican Parts]

I would first check that the air boot going from the sensor plate to the throttle body is in good shape. Accessing it is a pain in the ass, however..

After that, check all the vacuum hoses around the engine as well as the valve cover gasket and the oil filler cap. If I remeber correctly, I believe the ealier M10 engines had a two piece intake manifold with upper and lower runners. The gasket between is also a souce of possible leaks.

If those are in good shape, I'd check the ignition timing. (on my 320i, I usually ran it a few degrees advanced with a larger plug gap)

After that, I would check the warm-up regulator. that might be the problem, however you may want to first check that you are getting power at the regulator first.

[malak]

Congrats on your new purchase. That was My first BMW, and they are fun cars to drive.
With the bosch CIS system, one of the best things you can do for yourself is to purchase a fuel pressure gauge designed for the system. You can pick one up at most internet tool suppliers for around 75$ or so, and trust me, it is well worth it. It will save you $$$$ in treating problems.

1)Just off your symptoms it could very well be the system pressure regulator, also called warm up regulator. it is a small rectangular shaped box on the side of the eingine that has two fuel lines. One from the very top of the fuel distributor to the regulator, and the other connects to the reserve line going back to the tank. It is realy hard to Dx without a pressure gauge.

2)The fact that it runs cold and also runs when you first start the car it sounds like the cold start injector is working like it should, firing a short burst of fuel for about 8 seconds or so when you first turn it over, the after that.... It almost sounds like a lean fuel condition with the sputtering and lack of acceleration. an easy way to check is to take a 3mm allen wrench ( a long one) and insert it in the idle mixture screw hole, in between the fuel distributor and the air boot on the air housing box. turn it to the right in 1/4 turn increments to richen the fuel mixture . If the sputtering smooths out even a little, Your running lean.

3) I also suggest you pick up the book "tuning and modifying bosch F.I" by Ben watson. It will take you through the Dx process with the pressure gauge. Trust me, the gauge will pay for itself,