Overheating = hard start and hesitation

[525_1990_E34]

Fellow enthusiasts,

Several weeks ago while driving up I24 my 1990 525i E34 sprung a coolant leak. Before I could get it safely off the road it overheated... thoroughly. I replaced the water pump, the thermostat, the coolant level sensor, and a coolant temperature sensor right after the incident. I thought that would cure all my woes but alas... I have been experiencing hard starts and hesitation (intermittent loss of power) ever since that fateful day. Here are my current driving observations:

1. Performance can be influenced by the amount of gas in the tank, steep incline, and how forcefully I stomp the accelerator.

2. It seems to run better when it has been running as opposed to sitting overnight in the garage.

3. It will occasionally throw code 1222 while falling on its face in traffic.

This behavior is similar to what I've experienced before when a fuel pump is dying, but despite my patience just hasn't happened after six weeks of daily driving. After giving it some more thought, a dying fuel pump should be coincidence correct? The overheating was up top and away from the fuel pump. At the risk of spawning a red herring, are there any fuel delivery devices in engine proximity that can be damaged by high heat? Are there any devices (emission, electronic, or otherwise) that could be damaged by high heat and result in the above symptoms?

Any advice would be greatly appreciated!

Sincerely,
Zach in Nashville

[genphreak]

You may have checked already but these you must expect a broken headgasket following a severe overheat. Best practice is to treat your cooling system like gold as the ECU is coupled to temperature very closely and on any long block steel motor with an alloy head the speed of expansion/contraction makes headgaskets fragile after 10 years. Many have done their headgaskets, usually after an overheat, so you may need to do the same.

1222 I think is O2 sensor, which is an indication of this as ethylene glycol (in the coolant) kills it dead on the first (or maybe third!) sniff.

Best thing to do (you want to know for sure), is check the oil for signs of water. Simply Drain some oil to check. If ok, take a sample of the coolant and get a garage with a cololant tester to check for the presence of combusible materials in it. You cna have one and not the other depending on where the gasket is broken. If these are both negative you can change the sensor and see if that works.

Beware; if coolant is flowing into a combustion chamber then you could get hydrolock and crack your block/head starting it up one day.

The sensor that can cause the performance degradations you describe are the cam position sensor and the crank position sensor. They are both cheap. I fixed probs with my M50 recently by cleaning crap off the end of the cam position sensor (and dis/reconnecting the plug). It is easiest to get to, embedded in the front LHS of the head just under the PCV hose outlets, whereas the crank position sensor requires removal of the fan etc.