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Bike shutsdown when wet


Snork

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Not a good thing when you live in a wet state, but twice now my '96 RT has stopped running while on the Hawaii freeways. It's almost as if I reached up and hit the kill switch. Nothing. Lights but no action. After the first time it happened, the one and only local BMer shop was couteous enough to come get the bike and then proceed to charge me 350 big ones to "clean a corroded fuel pump relay". This time I had the bike towed home to let it dry out, but to no avail. It's dry but still won's start.

Any ideas on what could be causing this wet shutdown and subsequent no start? Any ideas would be welcomed. Thanks.

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Not a good thing when you live in a wet state, but twice now my '96 RT has stopped running while on the Hawaii freeways. It's almost as if I reached up and hit the kill switch. Nothing. Lights but no action. After the first time it happened, the one and only local BMer shop was couteous enough to come get the bike and then proceed to charge me 350 big ones to "clean a corroded fuel pump relay". This time I had the bike towed home to let it dry out, but to no avail. It's dry but still won's start.

Any ideas on what could be causing this wet shutdown and subsequent no start? Any ideas would be welcomed. Thanks.

 

One candidate has to be the Hall Effect Sensor. When you switch on do you hear the fuel pump run for a short time?

Also, pull a plug lead and using a well grounded (to the engine) spark plug check for a spark when you crank the bike.

 

Andy

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Hey Andy,

Thanks for the reply. Yes, I can hear the fuel pump come on when I turn the switch on.

 

What is the purpose of the Hall sensor? Steve.

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The Hall sensors (there are two of them) trigger the ECU to fire the fuel injectors and the spark plugs. They are mounted at the front of the engine and have been known to fail after getting wet. Triggering of the fuel pump is another event driven by the HES, so failure of the pump is an idicator of a problem. Non-failure of the pump however, does not mean the HES have not failed.

If you do a search over say the last year for +HES +failure you should find lots of information on diagnosing for HES issues.

 

Andy

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95% probability of a bad HES (Hall Effect Sensor) harness. The wire insulation in the stock harness isn't up to the temperatures encountered where the harness is clamped to the HES plate and eventually it fails (this will undoubtedly happen on all oilheads of this vintage, the only question is when.) You won't be able to see the damaged insulation as it will be inside the heat shrink tubing where the harness terminates at the HES assembly. After the insulation fails and moisture migrates into the harness then you will see exactly the symptoms you describe. The bike may run OK, or poorly, or not at all after things dry out but the only permanent cure is to replace the HES harness with wire using a high-temp insulation such as Teflon. Some replace the HES pickups themselves while it is apart but odds are they are OK and the harness insulation is the culprit. Another symptom might be a stuttering tach needle but that doesn't always occur.

 

Luckily the necessary repairs aren't difficult or expensive, this document describes the whole affair. Note that often the insulation at the connector end of the cable will look fine and the unit will test good off of the bike... In my case I even submerged the entire HES plate in water and it still tested fine! But as soon as I opened up the harness I was greeted by insulation that had literally turned to dust.

 

You can also just buy a replacement HES assembly but it is expensive, and unless Bosch (the OEM) has changed the insulation material it will eventually just fail again. The harness was apparently designed for underhood temperatures but not to be clamped directly to the engine block as it is with the oilheads.

 

(Kudos to Mick for helping me to see the light, BTW...)

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Thanks Smiller,

Looks like I need to focus on the HES. Thanks in advance for anything you have on troubleshooting or repairing the harness.

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The document above probably explains it all better than I can. Removing/replacing the HES plate is pretty straightforward but please feel free to ask us any questions if they come up. Remember to mark the position of the plate (since moving it adjusts ignition timing.) If you don't end up disturbing the sensors then you can just line up the marks when you reinstall and proper timing should be restored.

 

My suggestion would be to first inspect the wiring under the shrink tubing where the HES cable clamps down to the HES plate (the location I'm referring to will be obvious when you have it in your hand.) The insulation there will either be cracked and damaged (likely) or it won't. If the insulation is damaged then you probably have found your problem and do not need to replace the HES pickup units themselves, just the wiring, which makes the entire job a rather easy one.

 

It is of course possible that the problem is not in the HES but your symptoms and year/age of bike definitely point in that direction. Even if you find no damage to the insulation I don't think you will have wasted your time because the HES harness should be replaced with some Teflon-insulated wiring as a preventative measure in any event. Even if that doesn't turn out to be the problem now you will have at least ensured that it won't be the problem later. wink.gif

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No_Twilight

After you fix the HES, you might ask the dealer for your $350 back since you never had bad fuel pump relay terminals. --Jerry

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After you fix the HES, you might ask the dealer for your $350 back since you never had bad fuel pump relay terminals. --Jerry
And a dealer with experience should have suspected the HES or coil over the fuel pump for the symptoms you described. When an engine just 'shuts off' instantly as if the key had been turned off it usually points to an ignition problem over fuel.
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Jerry,

The one and only BMW shop on Oahu is a source of continual frustration for all Hawaiian riders. Their mechanical and people skills are not up to par.

I am going to write a letter to BMW corporate after I finish the HES to try to get some resolution.

I currently have the Hall sensor apart and that is definately the problem. The wires inside the heat shrink have lost about 25% of their insulation, and the rest just crumbles off when you touch it. Unfortunately, the one wire that I'm supposed to save and reuse, the shield wire, is in rough shape as well. Does anybody know the purpose of the shield wire?

Jerry, what is OAD?

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The shield on the cable is there to prevent electrical impulse noise radiated from somewhere else on the bike from being picked up in HES harness and confusing the ECU. This is probably not a very likely scenario but perhaps best to retain the shield anyway, just in case. If the original shield is really a goner another option is to get some RG8X or RG59 RF cable (should be able to find it at Radio Shack, or perhaps wherever you order the teflon wire from) and remove the center conductor. This will leave you with an insulated and shielded cable shell that you can run the other four HES wires through.

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No_Twilight
Jerry,

The one and only BMW shop on Oahu is a source of continual frustration for all Hawaiian riders. Their mechanical and people skills are not up to par.

I am going to write a letter to BMW corporate after I finish the HES to try to get some resolution.

I currently have the Hall sensor apart and that is definately the problem. The wires inside the heat shrink have lost about 25% of their insulation, and the rest just crumbles off when you touch it. Unfortunately, the one wire that I'm supposed to save and reuse, the shield wire, is in rough shape as well. Does anybody know the purpose of the shield wire?

Jerry, what is OAD?

 

Your HES sounds just like mine was when I took it apart. I didn't use the instructions that have you pulling new wires through the old sheath. I just replaced the entire cable with some shielded Belden wire rated at 200 deg F. and that is what I would recommend if you can find it. The hard part is getting the pins out of the connector so you can solder the new wires on. I made a push tool out of 1/8" or so diameter brass hobby tubing like the directions suggest. Belden has an online catalog telling you all the specs for various wires so see what is available locally and then look it up online. You don't need to find the right number of conductors either as the belden cable will be smaller diameter than the stock cable. I think I used a 10 conductor cable and it fit fine through the grommet that gets it into the alternator belt compartment. Just snip the extra wires short and abandon them. If all else fails I may have a section left in the garage I could send you.

 

OAD is from a series of Nascar commercials featuring Carl Edwards and the other Rousch drivers. My 5 year old son has been an avid nascar fan since he was 3--he's fascinated with the numbers and can tell you the number and sponsor of every driver. Anyway, OAD is Overactive Adrenaline Syndrome implying that the sufferer needs a shot of adrenaline every day. I find the K12RS is a good prescription, PRN.

 

Good luck and don't hesitate to ask if I can help,

Jerry

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Thanks Smiller,

I grabbed a piece of RF I had laying around but had some difficulties getting the core out. Even tried heating it up with a heat gun. Finally, I cut the casing the long way, removed the shielding and the core, and then rebuilt the whole shebang with the new wires and shielding. Then I opened up the split casing and put everything inside of it. Next, I will heat shrink the rebuilt harness. It's bigger than the original wirng harness but I don't think that will be a problem. Also, I don't know the model number for the RF cable I used, but it looked like quality stuff. I think it should be fine after I heat shrink it.

Thanks again for all of the suggestions. I will keep you apprised of my progress.

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No_Twilight

Not sure what you meant by RF cable, RF is usually coax, notmultistrand. Anyway, I hate to be a fearmonger but if the cable isn't up to the heat you'll get the same problem you had before. Good luck, Jerry

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Just wanted to wrap this posting up... got the bike back together and it runs great. My custom made wiring harness did the job. I am currently in the works of trying to get my money refunded from my local BMW shop for incorrectly diagnosing the problem as a corroded wire on the fuel pump relay. Thanks for everyone's help in solving this problem.

 

Jerry, the coax was degutted and then I reinserted high grade aviation wire inside the shielding. This provides the necessary shielding protection and adds a little more solid casing for abrasion protection. The whole shebang is neatly heatshrinked.

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