Announcement

Collapse
No announcement yet.

Doesn't Start—Fried O2 Sensor and Main Relay

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Doesn't Start—Fried O2 Sensor and Main Relay

    My '91 vert died on the freeway a few weeks ago, and my mechanic just gave up. Here's everything I know:

    It died smoothly, dropping in RPMs without any noises etc. From then on, it cranks but doesn't start. According to my mechanic, the O2 sensor and main relay were both fried. He also says that it fried the DME, but I don't think he's removed it, and when I took it out it the circuit board looks totally clean.

    Mechanic says it's not the fuel pump or crankshaft sensor, so I've ruled those out. He says it's a short in the engine wiring, as you can hear a brief click when you plug in a good main relay. The click comes from the alternator/alternator wires—is a click normal, or evidence of the problem?

    I figure if the alternator area isn't supposed to click on connection then that's my problem, and I need to figure out how to get the engine wiring harness off so I can rewire. But if not, I'm lost. Any advice is very much appreciated, and if pics or more details would help let me know!

    Thanks,
    Alec

    #2
    Update: I removed the harness, found a bit of exposed wire near the alternator, wrapped the wire, and replaced the harness. Still no change: She cranks but doesn't start. I'm at a loss.

    Comment


      #3
      First of all, I’m sorry you’re having trouble. Our cars are somewhat complicated and these kinds of problems can be very frustrating.

      Two thoughts:
      1. I’m sure there are other mechanics nearby who might be able to help you more. If budget is a problem, you might want to go to a local meet and see if you can get help from someone in your local E30 Community to dig in with you.
      2. If you want to fix this yourself, the Bentley manual has good troubleshooting advice in it. Beyond that, I did a little web search and found this comprehensive diagnostic flowchart on e30zone.net. It’s a real gem. http://www.e30zone.net/e30zonewiki/i...s_Troubleshoot


      Good luck! I feel your pain.
      Jon (OO=[][]=OO)
      1992 325ic white, stock with a 5-speed swap
      Palm Beach County

      Comment


        #4
        Thank you for that diagram! When I started working on it this morning, it cranked non-stop as usual. I tested for spark, but then when I started it it stopped cranking altogether. When I started it again, it would heave like it was trying to crank and then completely die. Now, it doesn't even try to crank, but just clicks and then starts to whine. Any idea what's up? Battery tests at 12v, and I haven't changed anything since it worked earlier this morning.

        Also, my mechanic removed a belt, probably the alternator belt (if there is one). I figured I wouldn't worry about reinstalling it until after I got it running, but could this be a source of the problem?

        Comment


          #5
          Im going to assume its not the alternator belt since thats ran off of the water pump and crank pulley. Theres another belt that powers the AC condenser, which can be removed.

          Is your car in time?

          Comment


            #6
            Originally posted by AlecB View Post
            Thank you for that diagram! When I started working on it this morning, it cranked non-stop as usual. I tested for spark, but then when I started it it stopped cranking altogether. When I started it again, it would heave like it was trying to crank and then completely die. Now, it doesn't even try to crank, but just clicks and then starts to whine. Any idea what's up? Battery tests at 12v, and I haven't changed anything since it worked earlier this morning.

            Also, my mechanic removed a belt, probably the alternator belt (if there is one). I figured I wouldn't worry about reinstalling it until after I got it running, but could this be a source of the problem?
            Missing belt will not affect ability to run, but without the water pump the engine will overheat once you are able to start it.

            I suspect that the battery is now weak due to all of the attempts at starting. Put a charger on it.

            You can fix this. Follow the diagnostic flowchart and check each item in the proper order. Given air, fuel, and spark she will run. You just need to figure out which one(s) is missing.

            Most people fail at diagnosis because they don’t attack the problem logically.
            Jon (OO=[][]=OO)
            1992 325ic white, stock with a 5-speed swap
            Palm Beach County

            Comment


              #7
              Did you pull the valve cover off to check the cams and check timing?

              Comment


                #8
                Just stumbled across this old thread—Sorry I didn't comment earlier. In the end, the mechanic I went to replaced the main relay with the wrong type of relay. The original problem was the CPS.

                Comment

                Working...
                X