Replaced the comp in 535i, what else could be keepin car from starting?

Question

I bought a 1989 535i. previous owner replaced coil pack and fried comp.. I replaced the comp, everything works but the car will still not start. What else could be wrong? What else needs to be checked?

I bought a 1989 535i. previous owner replaced coil pack and fried comp.. I replaced the comp, everything works but the car will still not start. What else could be wrong? What else needs to be checked? If the fuel pump relay is ok, is the black wire with 2 prongs about 6 in from battery the fusesable link? If so could that be the problem?

Answer 1

chech the fuel pump relay on the driver side inner fender ,they had a problem with filling with water and not working,other than that get it scaned for codes

Answer 2

I am assuming that your vehicle cranks but will not start. By the word "comp" I am assuming that you have replaced the ECU? (engine control unit). Also based on what you said above I am assuming that the vehicle has plently of battery power.

That being said, i noticed that you used the word "fried" in reference to the ECU.. did you seriously mean fried as in burnt wired and circuit boards? or just one that wasnt working?

If the unit was FRIED meaning burnt, then I would be looking further into the reasons as to WHY it fried, simply replacing a burned ecu might not do anything but fry the new ecu you just put in.

There is a lot of inputs and outputs to those things, and you may need to be looking for a short circuit in one of the wiring harnesses that go to and come from that unit.

If thats not really the issue, i would first check to see if I had any spark at the plugs. I am assuming that you have done this right? If no spark and you replaced the ecu and coil packs, i would be looking for a bad ground attached to the coil packs.

Is the vehcile getting fuel? Check the main fuel pressure first, then check to see if the injectors are working (they click when activate) place a screwdriver on one while someone cranks the engine, put your ear on the handle of the screwdriver and you will hear inside the injector like a stethoscope. if it clicks its firing. if not its not injecting fuel. check all of them in that manner. if they are all not firing then you need to look heigher up the food chain.. next we need to figure out how they are told when to fire... generally speaking most fuel injectors get their signal from the ecu, which in turn bases its decision on when and how long to fire the fuel injector based on a set of rules that use a Throttle position sensor, crank trigger, and a cam position sensor for input parameters.

Throttle position sensors are located on the throttle shaft and are small plastic parts with a connector on it, consult your shop manual for testing it.

Crank triggers, are located either on the front or rear of the engine, and are one of two types, VRS, (variable reluctance sensors) or Hall effect Sensors, VRS sensors are single ended plastic housings that are mounted near the crankshaft trigger wheel, a metal ring with notches cut in it. Hall sensors have a trigger wheel as weel except the hall sensor has a slit in it that snadwiches the trigger (or shutter) wheel. Both these sensors provide the ECU with valuable information about the position of the crankshaft.

A Cam sensor merely provides the position of the camshaft and determins which cyls are on compression stroke and are not always used depending on the manufacturer.

any one of those could cause a vehicle to not start from a no spark situation.

so you need to ask the following questions..

engine cranks?
Got fuel pressure?
Got spark?
Fuel injectors firing?
if you have fuel and spark but no start.. do you have compression in the cylinder?
No compression??? Could be a Timing belt perhaps

It might help if you get more specific on what you have checked, and describe exactly what you are observing when you try to start the car

BTW just read your update, that could be a fuesable link, check it for continuity.

Answer 3

In your fuse block there are fuses for your Fuel pump, Electronic Ignition and computer. check these. Then check to see if the fuel pump is pumping by listening it should run for a few seconds when you first turn your ignition on. Make sure the computer is getting voltage to it use a test light or meter to check it. It is also possible to get a bad comp or coil pack from the dealer. its happened to me before. If these items don't show the problem then it is to much for a home mechanic.