Thread: e34 lost power
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Old 11-17-2012, 10:03 PM
robertobaggio20 robertobaggio20 is offline
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Join Date: Oct 2009
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Mein Auto: car
Don't worry. This is probably an easy problem to solve.

1. Please read through the maintenance sticky and download and read through the bentley manual's engine troubleshooting page, located at the end of the relevant chapter.

2. Perform the stomp test if it works on your car. Details in the sticky and demos on youtube, and code descriptions on google.

3. As a quick test (chances of it working are poor), delete all the error codes on your car by unclamping your ecu. Sometimes old codes will hold a system back until they are deleted, or they go through 60 startups without incident (self-deletion). The ecu is in the black box behind the right shock absorber tower. Leave it unclamped for a few minutes, and key2 the car meanwhile to discharge all internal capacitors (Key0=insertion, key1=first click, key2=second click plus lights, key3=ignition). Then key0 and reclamp the ecu. Start the car and let it idle for 10 minutes (5 if you have an o2 sensor).

4. If the stomp test works, use the stomp test to extract and note all error codes on your car, before using it to delete all stored codes and performing the test outlined in #4. After one week of regular driving, pull the codes again and decide if you need to take action on those which are repeated.

5. You might have an o2 sensor issue. You can disable the o2 sensor temporarily by removing the appropriate relay in the ecu box's compartment. Please check bentley for exact position, can't remember offhand. Then start and test drive the car. If it works, you'll probably just need to replace the o2 sensor.

6. Did the workshop you went to previously scan your car's computer ?If they did, what did they find ?

7. The sudden loss of power that you describe is not consistent with vcg (valve cover gasket) failure, which leaks oil into your spark plug wells and affects charge delivery. However, if its not difficult, pull a few leads out and look down the wells. If you can't crane your neck down properly, use your phone's video camera with the flash activated. Make sure the leads are tightly affixed when you replace them.

8. You might as well double check to see if your spark plugs themselves are tight in the cylinder head.

9. You might have a bad ect (engine coolant temp sensor). It can lead to funny engine problems. I'm only suggesting it here because its so easy to test again. Just disconnect the blue coolant temperature sensor fitting on your engine, located right next to the fuel pressure regulator. Then test drive the car. If the problem goes away, this is it. $25 to replace and a diy as well.

10. There might also be an air flow meter issue. If your engine runs with the afm disconnected, then disconnect it and go for a test drive as well.

11. Driving with the o2 sensor, afm, and ect disabled is not dangerous to the car. It is not optimal in terms of power and fuel economy, but this can only be seen when driving for half a tanks' worth and when the engine is pushed. Since the process of disabling them and reactivating them is effortless, I would suggest that you try this.

12. Only try this after you've read (if possible) and deleted the error codes from your ecu and that does not fix the problem. If it does, keep driving the car and if the problem recurs a few weeks later, then start disabling components in turn to isolate the culprit.

13. As mentioned, I'm going to bet that this is a simple problem to fix. I'm going to wager that you sort it out within 90 minutes max.



rgds,
Roberto

p.s. Disabling components generates error codes, so at the end of your test cycle, read and clear the error codes once again.

Last edited by robertobaggio20; 11-17-2012 at 10:14 PM.
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