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Discussion Starter #21
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That was my thought, when I cut that wire it came up with c41 and no fuel pump noise. I guess I’m best off cutting the wire that goes to the ecm then? So it doesn’t back feed?
If the FP relay is connected properly, there is no danger of "back feed" into the ECM.

While I have not opened an ECM to determine the root cause failure. My guess, based on similar circuits, is that the output drive transistor for the fuel control line has failed in the ECM. if so, having an external voltage connected to the Yell/Blu wire (somehow) will not damage the circuit any further.

Still, you may want to confirm that the Yell/Blu wire has continuity back to the ECM. If it is open, that could be the problem.

There is another potential problem that would cause the OEM circuit to fail. To test it, verify that the Org/Blu wire has 12V all the time - even with a load on it. If not, it may have a poor connection at the large white gang connector, or an open fuel fuse. It can be loaded by connecting jumper from the Org/Blu wire to the Yell/Red wire (disconnect the existing jumper before doing this test). This will cause the fuel pump to run, and the voltage on the Org/Blu wire should remain high (at least 11V) while the pump is running.
That’s a great bit of info thank you, I will try that test and see what it does.
 

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Discussion Starter #22
... Proper idle and smooth low rpm running are greatly affected by TB and TPS adjustments, in my experience. ...
Correction on my previous comment. I was partially crossing the TOS with the TPS as the TOS was fresh on my mind from a current project. Sorry about that. Six5 is correct regarding its affects on high/low RPMs. I didn't correct myself earlier because it wouldn't cause your stuttering at half throttle, and so focusing on it won't solve your primary issue. Not sure if syncing the throttle bodies will either (unless theyre seriously out of whack), but certainly worth trying. I still think the issue lies in a restriction, possibly caused by the bad pump wiring.

Also note that the R has two additional injectors, which kick in at higher RPMs.




NOTE: Years ago I did the TPS and TB sync and so no changes in RPMs or throttle response, so that's the experience I'm going off. In short, my experience there is limited.
What is TOS? I pulled the plugs to check as you’d suggested, the rear one was black and dry and the front one looked normal. They were however 2 completely different types of plugs and can’t imagine that will help. When I had it running with the air box off I could see when the secondary injectors fired too 👌🏻
 

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TOS = Tip Over Sensor. I was working on a tank the day I answered you, so I had the TOS on the brain.

I suspected one of the plugs would be black on one of the cylinders. Weak spark or rich mixture. I was expecting it to be wet though. Guess it depends on how long it sat before you pulled it. First things first... see if the different plugs was causing the issue. Maybe that one was causing the weak spark. May be as simple as that (I hope).
 

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Discussion Starter #24
Still waiting on new plugs to turn up. Fitted the new fuel pump and the old one wasn’t working right, the new one filled the filter instantly and now I can hear the fuel flowing through the system. When I took the old one out I pulled the return line and no fuel came out with the pump running 😝
While it was apart I stripped the pistons from the front callipers as they were sticking, what a pain of a job that was! All done now though and it rolls and stops lovely.
 

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Can you take some images of the pump? Not a lot of info out there are what makes the pump fail, and honestly, this would be the first confirmed pump failure I've heard of, so I'm curious as to where it failed. Corroded wires? Clogged fuel screen? Clogged fuel pickup line? Worn Pump motor?
 

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....Not a lot of info out there are what makes the pump fail, and honestly, this would be the first confirmed pump failure I've heard of, so I'm curious as to where it failed.
Really Josh? You haven't heard of a pump failure before?

Typically, they just get old and weak, or clogged up from old varnished fuel or rust.



Corroded wires? Clogged fuel screen? Clogged fuel pickup line? Worn Pump motor?
The pump in my R went out due to age/wear & tear. It was used regularly and sounded fine, but it eventually became so weak it only created a dribble through the pressure regulator.

The pump in my '98 TLS was technically still functional (after 20 years), but since I had to open it up to repair a gasket leak, I also replaced the pump, because I didn't want to go back in there anytime soon.
 

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...Really Josh? You haven't heard of a pump failure before? ...
Sure I hear folks saying "bad fuel pump" every other day (for cars and bikes), but not once has it ever resulted in the pump actually being the culprit in the end. This is the first for me.

But... you actually satisfied my curiosity in your reply. Your pump never actually "died", it simply lost pressure over time. So a pump may sound fine even though pressure is weak. Thus the only way to know for sure is to test flow and pressure. That's what I was looking for... potential signs and or dead giveaways.
 

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Discussion Starter #28
So yeah the pump sounded like it was running normal, but obviously wasn’t making enough pressure to come through the fpr. It looked fine when I took it out the first time to do the filter mod which is why I didn’t give it much thought at the time, it only seemed odd how long it took to fill the new clear filter. The pre filter looked fine, wiring was good and it’s still there on the new pump pre filter. There wasn’t any crud in the tank either, I think it was just old age that got it.
 

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Discussion Starter #29
Good news! It now runs perfectly! The only thing wrong now is the oil cap seems to leak 😝 I set up the suspension as that was a mile out and it rides great now. Super happy!
 

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I am having a similar problem as well, similar mods too. The pump is the only thing I haven't swapped yet because it runs very good and smooth until I open the throttle up more than half way, then it bogs down until I release it then it lunges a little and returns to normal. I will be swapping pumps tomorrow based on this thread.
 

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Discussion Starter #32
I am having a similar problem as well, similar mods too. The pump is the only thing I haven't swapped yet because it runs very good and smooth until I open the throttle up more than half way, then it bogs down until I release it then it lunges a little and returns to normal. I will be swapping pumps tomorrow based on this thread.



Hopefully a new pump sorts your issue too 👌🏻 Mines been spot on since.
 
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