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Newly installed used engine refuses to start


I bought a wrecked BMW 325i for its good engine. It ran in the wreck, but now that it is in the other car, it will not start. The engine I replaced ran, but had lots of issues including just being worn out. Both cars are '94s. About the only difference is the one I want to run is an automatic.

When I crank it, the engine turns over for about three seconds, and then quits turning over. Crank again, same result. It does not seem to begin to “catch”. It has fuel and spark. I have looked for missing grounds. What have I missed?

Anytime you replace an engine, you have to make sure all the ground connections are reconnected.


Sounds like a fun project! Assuimg the new engine is mechanically and electrically sound, it’s probably something simple, but what it is may take some time to find. Why the reference to the automatic transmission? Do you mean you not only installed a replacement engine, but a replacement automatic automatic transmission too? Please clarify the engine and xmission config of both cars prior to and after the swap.

And engine should crank for more than 3 seconds, whether it runs or not. Maybe start with that, as it should be easy to diagnose, and may point you in the direction of why it doesn’t catch and run. Have you had the battery load tested? Have you measured the voltages at both starter terminals during attempted cranking? Edit: Measure between the terminal and the starter case.

Other than that, if you are certain the fuel pressure is ok, and it is injecting fuel from the fuel injectors, and you have a good visible spark at the spark plugs, then the problem is likely among

  • Ignition timing
  • Valve timing
  • Compression
  • Fuel/air mixture

Those problems are best addressed using the diagnostic software provided on the car’s ECM. Are you able to read the DTC codes?

I would check for battery voltage at the S terminal of the starter (that’s the little wire) and the main battery cable at the starter while an assistant turns the key. If you keep your 12 volts after the engine quits cranking then the trouble lies in the ground side–poor engine ground, etc. or a bad starter. If you lose 12 volts at the main lug at the starter, battery or cable problem. If you lose the 12 volts at the S terminal, time to trace backwards to see where that comes from. You’ll need a good wiring diagram and probably a scan tool.

Any security or anti-theft system on this car?

The engine originally was in a 5-Speed car. It is now in one with an automatic. Both engines ran in their original cars. I say that in case there is a difference in the two engines for that reason. I don’t think there is. Does anyone know if that might be an issue?

Since the engine ran in the 5-speed car, I don’t think there can be anything wrong with the valve, or ignition timing. The distributor was not removed. Compression must be OK for the same reason. I have no good way to scan anything electronic on an OBD 1 BMW 325i.

Are you using the wiring harness from the good engine, or the bad engine?

Which pcm are you using?

Perhaps the pcm is seeing an unauthorized start

Just for clarity, some people create confusion with the use of the terms “crank” and “turn over.” Both of these mean the same thing. But some use one or the other for when the engine starts running. So clarify. If the engine cranks and then runs for about 3 seconds and stalls then I’d be looking at a security/anti-theft shutting down the spark and/or fuel injectors. If it just cranks for about three seconds, doesn’t start at all and just stops cranking then you’re looking at main power - cables, grounds, battery as suggested. Did you happen to give the battery a full charge? Presumably it is also cranking weakly if it just stops after 3 seconds.

An engine from a vehicle with a manual transmission into a vehicle with an automatic?

The computer must love that?


Did you swap out the sensors? The computer has to read from correctly calibrated sensors to work right. Did you just check fuel pressure, or did you also confirm fuel injector operation? Did you put a timing light on it to confirm proper timing? In this situation, assume nothing.

How are you at wiring schematics? A quick look at the AutoZone website shows that there is a huge difference in the starter wiring when comparing the standard to the automatic transmission cars. Howeer, just a cursory glance doesn’t show anything that an engine swap should alter.

Motors cranks so I assume security is ok. U unplugged X number of sensors from orig motor and all wire harnesses are plugged back in. So u turn key, 3 sec crank and starter disengages even with key turned.

Does anyone know if ... [an engine difference between manual vs automatic equipped vehicle] ... might be an issue?

Engine differences, manual vs automatic transmission? hmmm … well there shouldn’t be much in the way of differences, but almost certainly the ECM will be different, at least the software configuration. And I think the throttle body on my manual xmission Corolla is different if the same car is equipped with an automatic. Why this is, I’m trying to think, but not coming up with anything other than maybe the automatic version of the throttle body supplies a vacuum port which is used by the automatic transmission. Maybe somebody here knows why a throttle body would be different, manual vs automatic.

A manual trans vehicle might not have cruise, whereas an auto trans vehicle probably does

I have cruise on all my manual shift cars, including my '88 Supra. They have a cruise cancel switch on both the brake and clutch pedals. I’ve put engines from manual shift cars in Automatic cars and vice-versa. Usually, there is very little difference in the engine itself, save for swapping a flywheel with a flex plate. But, even tho they are the same displacement from the same model year cars, sometimes they have different sensors and sensor reluctor rings. You really need to pay attention to the crank and cam sensors and sensor rings to make sure the tooth count is the same.

Then all my stick shift cars must have been for losers, because none of them had cruise. And several of them were Toyotas

Doesn’t seem like cruise control would be the issue here. But the wrong placement of the timing pickup on the flexplate/flywheel could make it fail to start. OP, are you able to tell using a timing light where the no. 1 spark plug is firing w/respect to tdc?

"Then all my stick shift cars must have been for losers

Just how wide open did you want to leave that one?


I have no problem admitting that many of my previous rides were loser cars

Nothing to be ashamed of

We don’t all live next to the money tree, but all of my cars did their jobs pretty well

Money tree? I purchased the Supra 8 years ago for about $3000. My 1990 Protege was 7 years old when I bought it for $6000 with a 5-speed, cruise, and working air. It doesn’t take a lottery win, just shopping around.

Cruise control? What the heck is that? Neither of my vehicles have it, hey they don’t even have AC … lol …