Why Won't My M52 Swapped E30 Run?? [M52B28 BMW E30 Build First Start Problem Solving] 054

Here's what I used in this video:
Multimeter: https://ebay.us/AL2zds
3.5 Bar Fuel Pressure Regulator: https://ebay.us/tLlDtH
Chinese Test Relay: https://ebay.us/4SQBm7

Following the disappointment that was failing to start and run the E30 in the previous video where we fitted the M50 manifold, I set about figuring out what the problem was.

The old man joined me figuring out why the engine wouldn't start. The first and most obvious symptom was the fuel pump not running.

Missing Fuel Pump Relay
We traced the fuel pump wiring and checked it against E36 wiring diagrams for the M52 engine. It quickly became apparent that we were missing a crucial fuel pump relay. It seems really silly now, but this is the kind of finer detail you miss at this stage in project.

Luckily I've hung onto the M40 wiring harness to continue harvesting parts from it, and fortunately the fuel pump relay was the same type and still in place. With this moved over onto the car we could continue diagnosing. Sadly this was just the beginning.

Fuel Pump Check
With the relay known working, we were at a bit of a loss as to why we were still not getting fuel to appear at the rail. With the noise of the M52 engine turning over on the starter motor, it was pretty difficult to distinguish whether the E30's fuel pump was even running. And it does not prime until the engine is cranking. Or at least it didn't under M40 power.

Using a multimeter we were able to confirm which wire should be sending power to the pump, but the reading was extremely low voltage which was a hint for us. With a spare battery, I applied 12 volts of power to the pump and it audibly burst into life pumping the fuel into the line. The pump was not kaput.

Fuel Pressure Regulator or Fuel lines the wrong way around
From here, our efforts turned to the engine side and the fuel pressure regulator seemed like a dead cert. Although at this stage we did not fully understand how it worked.

We imagined that the fuel had to pass through the regulator, and the regulator effectively limited the pressure of the fuel entering the rail. If that had been correct, we'd have been onto a winner.

We removed the old fuel pressure regulator, creating a big mess of petrol over the engine, and switched it for a new Lucal 3.5bar fuel pressure regulator. We also had a play with the original regulator and could not get it to do anything even with vacuum applied, so we assumed it was dead (it probably wasn't).

With the new regulator on, we were disappointed. It was at this stage we realised how the fuel rail works, and concluded it was likely that we'd connected the fuel feed and the fuel return lines the wrong way around much earlier.

A schoolboy error which was rectified by creating a second explosion of petrol and switching them over from beneath the car.

Unloader Relay and DME Relay Problems
With the fuel lines corrected the car suddenly coughed up into life and started. It was the first time I'd ever heard this engine running so it was a huge relief. But the celebration was short-lived as the car would fire up, but die momentarily no matter what.

The mission then progressed to figuring out why the car starts then dies, and it took us back to relays again. The old man used an aftermarket relay and wired it in place of the unloader relay, which it turns out is fully necessary for the car to run. However this did not solve the engine dying issue.

We then moved on to testing the very scruffy-looking DME relay, which appeared to behave strangely when power was applied to the switch directly. Putting 12v from the battery directly to it a few times got it freed up and clicking like it should, however. We confirmed all 3 M52 relays to be working as prescribed.

Full Wiring and Sensor Check
We still couldn't get the car to stay running, and all that was left to check was each wire and each sensor. Not uncommon to have a faulty sensor at this stage, if the crank sensor had been dead it would have explained it well. However, we completed the tedious job of a full check and concluded no sensor issues.

Starter Solenoid Wiring
A breakthrough was had when checking the wiring. It turns out we'd wired one of the 12v battery power wires to the top terminal on the starter motor solenoid, which is why the car ran when the key was turned to crank but would not continue after the key was released. Triumph, the engine runs brilliantly after all these years dormant!

For more helpful how-to guides and restorations: https://www.spannerrash.com/

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