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.

[RobertK]

So make 2 threads about it.


Seriously.. If I had to take a guess..

Problem 1 = Fuel Pump on it's way out or the fuel pump relay. (Edit - A Bad temp sensor could also cause bad throttle problems.)

Problem 2 = Bad ground on the temp gauge or a failing temp sender (seperate from the temp sensor).

Have you tried pulling you CEL codes yet to see what's being thrown by the ECU?

[1989E30325i]

Thanks a lot. I will definitely check out those systems and also take the car to my mechanic to have the fault code read. Thanks again.

[PiercedE30]

just put the key into the second position and then hit the gas (all the way to the floor) 5 times and the engine light will blink and give you the codes, no need for a reader.

[1989E30325i]

I will go do that right now. I will post the code ASAP, thanks.

[1989E30325i]

how many digits are the codes? edit- i found the code - 1221 (o2 sensor 1). I wouldn't think that the o2 sensor could be creating all the other problems that I am experiencing. I am thinking more along the lines of the fuel pump, as mentioned by Ritalin Kid, and the bad ground.

[NC325iC]

poor mixture caused by a bad fuel pump could throw an o2 code couldnt it?

[ivo316]

I don't know if the M20 has the same systems as the M10, but mine played the same idling tricks on me, the culprit was a hose that goes from the (in my case carb) to a temp sensor that recieves two vacuum hoses, one comes from the carb/manifold into this sensor, right beside the warer hose that goes to the radiator, and from there the hose goes back to a "throttle control thingy", it seems this temp thing cuts the vacuum when hot, and the broken hose left the vac thing open all the time, replaced the hose and works great. ;)

[92 mtechnic cabrio]

do you have a factory AFM? If so, just check the plug connection on the AFM, it could be loose, I had almost teh same problem as described in #1

[92 mtechnic cabrio]

also, unplug hte O2 sensor from the harness side and see if the problem happens the same exact way

[1989E30325i]

Thanks for the info guys. I will definitely check everything suggested tomorrow. I am also considering possible issues with the various grounds throughout the car. When I turn my headlights off when the problems are happening the problems go away instantly. I do have a stock AFM and I think the failing o2 is pushing the issue even further. Thanks for all of your help.

[PeaveyBassist]

Also check the injector harness plug. The signal for the temp senders for the gauge and the ecu go through the same plug and can make the engine run extremely rich (if the ecu thinks the coolant is WAYYYYYYY cold). Check for corossion in all the pins.

Will

[1989E30325i]

Thanks peaveybassist I didn't know that. The temp sender issue sounds like it could quite possibly be the culprit.

[porsche gt1]

Sorry didn't realise you posted twice. For problem one, you said you did your timing belt and tensioner. If you were of by a tooth or two it could have retarded your timing. When you are running at cold temp your timing is different then when you are warm. When you are warm and cruising (not giving it gas) the ecu retards the timing. If your timing is already retarded by quite a bit it could cause a stalling as the engine would not compress in the right order (suck squeeze bang blow) then when you gave it gas it corrects the timing and boom you get a backfire and it runs fine again.

[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.