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Discussion Starter #1
Hello all,
I'm trying to diagnose a lack of fuel on my 1998 748. I thought Sunday I'd finally get her running again and go for a ride, but it was not to be. I verified I was getting a good spark. Additionally, dripping fuel into the throttle bodies made it run for a second. Key and ignition switch on causes the fuel pump to prime. Fuel recirculates back into the tank, so I'm pretty sure my disconnects and fuel lines are good (it's not spraying inside the tank like I think a split hose in the tank would). I hooked up 5V to both of the injectors just now while I was home for lunch and each clicks. So I think I'm left with either two clogged injectors or that I'm not getting any voltage at the injectors. I'd guess an electrical issue since neither of them are working and both worked fine about two months ago. Also, I think it's easier to test this at the moment... I'm guessing I didn't reconnect something, but I haven't found it yet, hence the trouble shooting.

So my question is: if I have the round connector for the injectors and the throttle position sensor disconnected so that I can check for voltage to the injectors, is it safe to turn over the bike or will I damage the ECU? I definitely want to avoid that. Or should I take the time to make up a little dummy load with resistors?

Thanks,
John
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I think having a local shop diagnose this type of issue is going to be a lot less painful than trying to building your own Mathesis tester.
 

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Discussion Starter #3
Thanks for the opinion, but that doesn't help me. I will likely never take my bike to a dealer. Since no one replied, I've already spent the 30 minutes to build a dummy load and am about to go test now.
 

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Why not just get the Technoresearch software for future issues? I know it allows injector testing on 5.9 ECUs and you could always call them before purchasing to verify the desired functionality with your ECU.
 

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Discussion Starter #6
I have a Haynes manual as well as the factory service manual. It doesn't have that bit of information, hence my question.

I also never said I know everything as you seem to imply. Actually I said the exact opposite by asking my question. If someone had replied that no, it wouldn't hurt anything, I would have saved time. Since no one replied, I spent the time to make the load for the ECU.

To anyone who is inclined to help me out, I tested the signal going to the injectors and it's fine, so it's not an electrical problem. I'm left with either clogged injectors or a problem with the fuel lines. At this point I suppose I'm just writing to myself though as I'm about to go tear into it some more. I can take my pick between testing pressure in the fuel lines or replacing the injectors. I was just trying to avoid that since I just put it all back together...
 

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Can you look down the throttle bores? It's not the safest thing in the world probably, but it should work. If you can see down the throttle bores, you could unhook the coils and crank it over and see if you see the injectors spraying. I don't know how much that saves you from pulling it all apart.
 

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Discussion Starter #9
I can't really see anything spraying. Additionally I stuck my finger in front of one of the injectors (with a glove on) and it didn't get wet. So I think it's either the injectors are clogged or something's blocking the fuel line. I really don't think the fuel line is blocked though (as it recirculates back into the tank and I can get some gas out of the line after undoing the QD's), so I'm going to try swapping in some spare injectors I have.

Thanks,
John
 

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Discussion Starter #10
It turned out to be a fuel line inside the tank that had popped off. My guess is it hadn't fully popped off when I first looked in there but was leaking, but after doing a bunch of other thing I looked again and it was spraying fuel up in the air inside the tank. So I opened it up, replaced the fuel filter, splashed myself on the head with gas, and reattached the hose. Then it started right up.

Thanks for the help,
John
 
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