Help with M20 Engine and Electrical!!

[1989E30325i]

I have an 89 325i with 179k and I have started experiencing some really weird problems with the coolant temp gauge and the engine losing power at the same time.

Problem 1: The car starts fine and usually drives fine until it is fully warmed up. Then all hell breaks loose.... At normal cruising speeds, regardless of what gear or where the tach is in the rpm range, the engine will suddenly lose power and nearly shut down. I have to downshift to second and sometimes to first and smash the accelerator to get the engine to respond and recover from its sputtering and loss of power. Sometimes I get a slight backfire and then it will rev up and run great. Idle is also somewhat rough following each of these "exciting" experiences.

Problem 2: My coolant temp gauge in the instrument cluster consistently reads slightly above the center mark on the gauge. Sometimes when the headlights are on the gauge will read very near and sometimes into the red area of the gauge and then the CHECK ENGINE light will illuminate. If I turn the headlights off the gauge will return to normal and the CHECK ENGINE light will go off.

Both problems are usually concurrent. I have recently replaced the timing belt, tensioner, water pump, thermostat-80 deg, oil pan gasket, and drive belts. I have owned BMW's for years: 95 M3, 95 325is, 93 325i, 90 535i, 88 735i, 88 635csi, and 86 528e, but this is my first E30 and I have never had any experiences like this. Other than replacing the ignition parts, wires, distributor, plugs, etc., I am not really sure to begin with these problems. Any help or advice is greatly appreciated.

[porsche gt1]

for problem one if you are getting a backfire it means one of your cylinders is probably not working properly. I would first check you plugs to see if they have signs of plug failure. If they are fine then your ignition system is probably not the cause. Then I would check you crank position sensor as it has been known to cause issues like this. I would then check your main relay followed by fuel delivery issues (fuel pump, FPR, filter) I am pretty sure you will find that it is a ignition problem.

For problem 2 first off (NEVER LET YOUR TEMP GO IN THE RED) even if it is a malfunction it is not worth the chance of blowing seals and killing your engine.

I believe you have a short somewhere that is connecting your guage with your headlights. you will probably have to follow some wires to see where they are connecting, won't be fun.


*********Afterthought. you said you did your timing belt. if you put in on one tooth less retarding the timing so when the car is warm and at speed it will retard the timing even more and case it to fire improperly and backfire.***** I would start here.

[1989E30325i]

Thanks for your help, I actually was finally able to correct the problem this afternoon. I had a damaged ground cable from the engine to the frame. The hidden side of the cable was totally bare with no insulation and the wire had severely corroded from the inside out. I replaced the ground and all is well again. I am glad that it was a simple fix and not something that required crazy time and money. Thanks again to all that helped and suggested solutions to this tedious problem.