1991 525i with about 115k on motor. With the drive belt off, I started the motor to try and flush the cooling system. It didn't start at first then started very sluggishly. I didn't run it long then put it all back together. Now it idle's very rough and doesn't run worth crap.

I really hope I didn't roach the motor, but I can't imagine what was damaged as the drive belt only pushes the water pump and the alternator?

Help...not my daily driver but I love this car.

Quick question. How were you going to flush the cooling system without running the water pump?

Force water into the intake system with a hose. The engine was cold so there wasn't any issue with temperature changes so I put the hose on the intake side of the opening and had water quickly run the system. When I tried to start it though, it ran so badly that I didn't get a chance to move any water through the system. I just put it back together.

Why would you run the car without the water pump running anyway?

Is the 91 a M20 or M50? If it is a M20, could someone chime in as to if the timing belt also operates the alt and water pump?

If it does, you could have indeed croaked the motor, since the M20 is, if I recall right, an interference engine.

Force water into the intake system with a hose. The engine was cold so there wasn't any issue with temperature changes so I put the hose on the intake side of the opening and had water quickly run the system. When I tried to start it though, it ran so badly that I didn't get a chance to move any water through the system. I just put it back together.
if this was the case then running with the pump off wasn't an issue but it sounds like you forgot to remove your thermostat! by having not removed that, you basically had blocked off the water inside the motor from escaping and none of the coolant in the motor was circulated.

how long did you have the motor running for?

Is the 91 a M20 or M50? If it is a M20, could someone chime in as to if the timing belt also operates the alt and water pump?

If it does, you could have indeed croaked the motor, since the M20 is, if I recall right, an interference engine.
if the timing belt was off, the motor would not have run at all.

By "run", I wasn't sure if it actually did a sustained run, or if he just used the starter to push the old coolant out, hence my question.

Is the 91 a M20 or M50? If it is a M20, could someone chime in as to if the timing belt also operates the alt and water pump?

If it does, you could have indeed croaked the motor, since the M20 is, if I recall right, an interference engine.

Timing belt operates the intermediate shaft (which drives the oil pump) and it drives the camshaft. Nothing else. And yes, if it's busted you're going to bend some valves/break the casting around th rocker shafts -- f up your cylinder head.

By 'drive belt', do you mean the accessory-belt or the timing belt? I am assuming you meant the accessory-belt.

I can't see any way that this would have goobered anything up other than having the cold water keep the thermostat shut. In any case, the cold water from the hose would keep the car from overheating. The timing belt is a completely different system than the drive belt - so that isn't anything you should worry about.

Just thinking outside the box here - you were running the car off the battery since the alternator was not turning. That may have screwed up the computer so try disconnecting the battery and doing a static-discharge. Join the disconnected battery cables together for about 10 minutes or so. That will wipe the memory and force the car to re-learn everything. Also - if the car has an air-pump (smog - I don't know these engines so I can't say for sure...) it may have forced the car to think it wasn't getting the correct air and messed up the air/fuel mix.

Regardless - do the static discharge and try again.

It's the M50 so the timing is off the chain. I also had the thermostat out when I tried to flush the system. The reason I tried to flush the entire system is when I pulled the old water pump some large items came out with the coolant. Something may have broken off the pump or got into the system and was flowing around the motor. They were too big to get into the radiator. I noticed there is a coolant line to and from the throttle body area any idea if running with out coolant to that would cause a problem. I'll try the battery discharge because you are correct, the engine was running without alternator for about 3 min. as I ran the water through the block.

By working around the water pump area, you might have broken or disturbed some old sensor wire (shaft position, coolant temp). Spark plug cables also run around that area. Water hoses below the throttle are going to the heater inside the dash.

Hahaha.... not that I can be that helpful, I don't really know what you may or may not have done to your car...

I just think it's hilarious that your name is "hindsight".... oh the irony.

Good luck getting it back in action, that sucks

I believe I have found the problem, and it has nothing to do with the cooling system. When the engine cap is removed it's pretty easy to see that one of the ignition coils is cracked and isn't functioning. I imagine what happened is when I had the thermostat housing off, the ground wire for the DME was also off and when I tried to start the car having the DME not being properly grounded fried one of the igintion coils.

I'm working on getting a replacement coil and spark plug and when it' s installed, I'll let you all know if that's the issue. Thanks for all the insight. I named my boat Hindsight and it really is an appropriate name for most of the stuff I do.

Has nothing to do with the DME not being grounded. The DME grounds through your harness, the coils ground through the block. You just have a failed coil - its coincidence, nothing more.

Replaced the cracked iginition coil and all new plugs and nothing happened. I tested the coils one at a time by removing the connector to each coil as the motor was running and found that the number 2 and 5 cylinders were not running. I then changed the coils from cylinders that were running to the 2 & 5 cylinders but there was no change. Both of those cylinders still were not running.

Next I'm doing a compression test to rule out physical damage then ...... I don't know. The onboard diagnostic doesn't show a problem. Can you believe the check engine light is not on? It sounds like a diesel pickup but the computer doesn't think there is a problem.

There is also a strong smell of gas as it's running so the fuel is getting to the cylinder, just not being burned. I'm losing patience but I remember how much fun it is to drive so I know I'll end up fixing it in the end.