85 635csi


Alright here's what happens. It will start when cold fairly good. Then after you start driving everything will seem ok then Hard Jerking will occure, you can shift to clear it up momentarily but then then the 2nd stage kicks in. It bacially cuts the power and your speed drops. If you keep it in a higher gear like 3rd or above with pedal floored the speed will only get so low then it will kick back in like nothing ever happened. But in a few seconds it will just repeat. It will eith start jerking Hard or just cut out like before. Also when it gets hot it will kill and it will not start as easy if at all, but if you let it sit, it will start again but be very ruff.

I went through some of the electrical and stated to check fuel system. Thought it was the Reference Point Sensor. Replaced that but still having the same problem. Checked fuel pump, seems to be operating fine when you turn the key on. Changed fuel filter. Will start to go through and test some more sensors tomorrow. Breifly looked at fuel pressure regulator seemed ok but not sure.

What do you think it could be?



Thanks for help.

Need more details -

When you put the car in neutral and rev the engine - does the engine rev freely ?

Or is this a chassis vibration of some sort?

Many, Many things can cause "hard jerking" A good porn movie being one of them :lol

If I can consolidate your diagnosis:

Starts good cold.
Runs good cold.
After fully warm, the engine is so lean it misfires.
After fully warm starting sometimes fails.

Fuel pressure would be a first test, requires a pressure indicator, suspect is the FPR, Fuel Pressure Regulator.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7938562415&rd=1&sspagename=STRK%3AMESE%3AIT

AFM, Air Flow Meter is next, swapping with a known good unit is the fastest.

http://normgrills.net/bcg/Injection.html#anchor41563757

Next is the ECU temperature sensor on the front coolant inlet, smaller two wire shielded plug.

http://members.roadfly.com/kcroncarter/bmwetm213.jpg

Last is the ECU swap with a known good unit.

http://members.roadfly.com/kcroncarter/bmwetm121.jpg




Later,

After you start it warm in neutral you can give it gas and it is not smooth. It goes up and down keeping the pedal at a steady idle. Letting off the pedal will usually result in the engine killing.



I wouldn't say its so much of a misfire, it jerks hard like if you didn't have enough gas when you realease the clutch and it wants to stall.

I tested the Throtle Valve Sensors and it doesn't seem to be working wide open, but works at idle position. Do you think this could be the problem? Not sure if it is that important that it would cause this problem.

OK, if the issues are idle related the causes can be a little different.

Intake vacuum leaks cause most idle mixture issues.

Use a can of spray starter fluid to locate a leak, remember the crankcase and the intake are joined together for pollution control.

The engine will speed up when you spray near the leak.

The idle air valve can also be clogged with crankcase fumes that condense after the engine is shutoff. Yep that gunk in the intake starts in the crankcase.

Many ways to clean and test, but the big deal is to reconnect the electrical connector and feel for the idle air valve motor causing movement.

If you can feel the vibration then cleaning the valve will help the issue.

Later,

A common problem on these cars due to their age is that the electrical connectors get dirty then don't make good contact, causing all sorts of problems.

It happened to me, and when I took it to the dealership, the tech gave me a long list of potential things that might need replacing. Then I took it to this guy just to get a second opinion. Turned out this guy was a guru and had worked on these cars forever, and he just simply unpluged and pluged a few connectos, and the problem went away. Oh, he also found a loose ground wire (engine to chasis) ..look for that too on your car.

So I would advise to clean the electrical connectors having to do with fuel and air delivery. Try to clean them out with compressed air or an electrical contact cleaner. Plug and unplug them a couple of times so that the connector pins have a good clean surface and make good contact.

Use a can of spray starter fluid to locate a leak, remember the crankcase and the intake are joined together for pollution control.

The engine will speed up when you spray near the leak.

Proceed with caution with this. starter fluid is extremely flammable.

Mine had a similar problem, many times it would start without a problem, other times (especially when I wanted to take off in second gear), big kick!! I would get so bad it would die from time to time. I do have some vacuum problems that cause some hesitation (those to be fixed soon), but this was a definately different, more violent kick, low power if it did keep running. When it did stop running, it seem not to be getting any spark and would flood. I came to the conclusion that the car was actually dying momentarily, then running again. Not a particularly good way to get where your going.

OK, so much for the problem, the solution turned out to be the coil cable. The cable had burned clean through inside the boot connecting it to the coil. Understand, It took me a week to locate the problem, and I do drive this beast daily. The beast is taming, it's a slow process. Check it out, hope this helps.