Cars, even the ones as old as the legendary E30, are complex machines. Every time you turn the ignition, a number of processes and systems have to come online and work together to start the engine and keep it running. What happens when you turn the ignition in your E30 3-series, and the engine refuses to start? How do you diagnose the problem? Let’s find out.
The Trifecta of Gasoline Engines
A no-start condition in any gasoline engine means that you’re missing one or more of the following:
That being said, we’ll only deal with the first two problems as compression is rarely the cause of the no-start condition. If you still want to check for compression, you’ll need a compression test kit and a good one at that.
No-start shouldn’t be confused with no-crank. If your engine isn’t cranking when you turn the ignition on, that means you’re dealing with a bad battery or a bad starter motor in most cases. You can check the battery by taking it to a shop that has a battery testing tool.
You’re looking for consistent voltage and cold cranking amps in the green. A no-crank condition could also be caused by a bad alternator that isn’t powering the battery, which in turn goes flat. For the purposes of this troubleshooting guide, we’ll assume that your engine is cranking but isn’t starting.
The first and easiest thing to check is whether there’s a spark.
To check for spark, you’ll want to either use an inline spark tester tool or do it the old school way using a spark plug or a screwdriver.
If you have a spare spark plug, you can use it, remove an ignition coil wire from one of the cylinders, insert the spark plug into the connector, and set the whole thing on an intake manifold or other neutral chunk of metal. Have someone crank the engine, and you should see the spark at the plug if there’s any.
The screwdriver trick works pretty much the same way. Instead of a spark plug, you take the screwdriver and stick it into the spark plug wire, and then you place the metal shaft of the now live screwdriver next to a metal surface (the intake manifold works great) about as close as a spark plug gap would be.
Have someone crank the engine and watch for the spark between the screwdriver and the intake manifold. A word of caution — ignition coils produce high voltage power. Use a screwdriver with an insulated handle, or you will get zapped.
If there’s no spark, we need to check the following:
- The ECU (or DME as BMW likes to call it)
- Ignition coil
- Spark plugs
- Crankshaft Position Sensor
Spark plugs are the easiest to check. Simply remove each spark plug and check them for a gap as well as any damage. A damaged spark plug won’t be able to create a spark.
The next thing to check is the CPS. The BMW E30 isn’t an overly complicated car by today’s standards. Whereas modern 3-series are literally packed with all kinds of sensors and electronics, the BMW E30 used only one sensor to give the ECU all the timing data.
That sensor is the CPS. To locate the CPS, look for the cold side coolant hose. The CPS is right near that hose on the front of the engine.
Removing the CPS
To remove the CPS, you’ll need a 5 mm Allen key. Undo one bolt that’s holding it in place and remove the wire. Testing the CPS is slightly trickier and requires the use of a multi-meter. Set the meter to measure resistance (Ohm setting), and place the probes of the meter on the two pins of the CPS.
You’re looking for around 500 Ohms of resistance between the two. Generally speaking, any value from 470 to 550 should be good. Anything outside these values is a solid indicator that you’ll need to get a new one.
Checking the Ignition Coil
Older cars like the BMW E30 were built using simpler technologies. Unlike modern cars, the E30 has only one ignition coil. That one coil is providing the spark for all six cylinders. One of the reasons why no-start conditions are more frequent on older engines is using a single-coil. If it goes bad, you won’t be getting any spark in any of the cylinders.
The coil on BMW E30 has two input points (as pictured above) that should show voltage if you use your multi-meter to check them. If there’s power on these two points, remove the plug on top and check for spark using the same screwdriver trick.
Check the Distributor
The distributor is a device that takes power from that single ignition coil and spreads it to the cylinders following a specific timing pattern. It is also the next thing you need to check. Remove the distributor cap, remove all spark plug wires and inspect the rotor inside the distributor for any signs of wear.
Next, inspect the wires leading to the distributor cap. Check and make sure that each wire is making solid contact with the distributor cap. If all is good here, we’re moving on to relays and fuses.
Check Relays and Fuses
Checking the fuses is relatively easy. Simply inspect each fuse and check to see if it’s broken or not. Relays are slightly more challenging to check. Start with the two unloader relays as pictured above. If bad, these two can cause a no-start condition.
If those are good, focus on the main relay and the fuel pump relay, as pictured below. The main relay is, well, important. If it’s dead, the engine won’t be getting any spark.
The fuel pump relay is also important as it provides the fuel pump with power once you turn the key to the accessory position before cranking the engine.
If you’ve established that spark isn’t the problem, it’s time to check whether the engine is getting any fuel. There are several things you’ll want to check:
- Fuel pumps (yep, there are sometimes two)
- Fuel rail
- Fuel pressure
The E30, at least the early versions, came with two fuel pumps — the one submerged inside the fuel tank and a high-pressure fuel pump sitting in front of the rear driver’s side wheel. There are two ways you can check whether these pumps are working.
The easiest way is to simply listen for them engaging when you turn the key to accessory mode. You should hear the pump priming the fuel system. It will hum for a few seconds and then shut off. If you can’t hear the pumps, it’s time to inspect each individually.
The other method is much more rudimentary and involves removing the fuel line from the fuel rail and then cranking the engine. If there’s any fuel coming out of the fuel line, there’s a decent chance it’s not the fuel that is causing the problem.
But wait, there’s a catch — simply having fuel pushed through the fuel line isn’t enough. It has to be pressurized. Unfortunately, the only way to check if your fuel pressure is good is to get a fuel pressure gauge and install it between the pumps and the fuel rail.
Testing the DME requires you to roll up your sleeves, get your multimeter and follow the diagram below. We’ve outlined what each pin is and how to check every single one. Keep in mind that this diagram is from the M20 fitted with 1.1 Motronic system. Your particular version of the BMW E30 could be running a different setup.
Be Patient and Methodical
The BMW E30 is an easy car to work on. That being said, troubleshooting a no-start condition will require you to be methodical and, most importantly, have enough patience. There are many things to check and double-check. The good thing is that finding the culprit behind a no-start condition usually leads to some of the parts that are easy to check.