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Discussion Starter · #1 ·
I have a 2001 Sprint RS 955i. A few years ago I had the dealer trouble shoot and fix a problem with the #2 injector, it kept giving me a check engine light but it still ran fine. Several hundred dollars later they fixed it and it went away, but it does come back every now and then.

But on to the issue. After they "fixed" it, the bike has been slow to start. I mean it turns over fine but you have to give it gas like an old carbureted bike. Now I do know that fuel injection eliminates this. You should never touch the gas when cranking. And if it sits for a bit it will just about drain the battery before it cranks over. Once it starts it is fine with no issues.

You do not hear the fuel pump turn on when turning on the switch. The local dealer is in the process of moving to a new shop and will not be taking appointments for at least a month. By then the summer might be over. I will take any suggestions please.

Chad
 

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1. Check the injector o rings that sit in the head. If the o rings are split, or damaged in any way the injectors will be loose and that will affect starting as you will have a huge vacuum leak right next to the injectors. That is a cheap check.

2. Check the fuel pump is delivering the correct fuel pressure. If I remember correctly it should be in the 42-45 PSI range.

3. Make sure all seals,.o.rings, vacuum pipes are in good order right from the airbox, to the idle air control valve. Pay attention to the vac line that goes to the ecu.

3. Once that is all checked then you can look at checking the throttle body balance them etc.
 

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Vacuum leaks usually creates high idle. But anyway worth a check.
The fuel pressure is 3 bars.


Questions that comes to my mind:
1-What is the fault code when the mil goes on?
2-Was the valves service done ?
3-Was the CO done?
4-Was the throttle body balanced?
5-Was the new injector of the right reference?

The strange thing is the fuel pump not priming.
 

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That is what I don't understand. You don't hear the fuel pump kick in when you turn the switch on
That's probably your issue then. Don't guess though, attach a fuel pressure gauge to the fuel line.

Like I said the fuel pressure should be between 42-45 PSI (+ - 10%) take the measurement in PSI as it's more accurate than BAR. 3 bar is dead on 43.5 psi but it will always be slightly over or under depending on the duty cycle of the injectors at the time, which will change constantly when the engine is running.

Attach the fuel pressure gauge in line with the fuel line, and observe the pressure if at any point it falls below 40 PSI (I think from the service manual) then you have a weak pump/fuel pressure regulator/both should be changed.

Good luck
 

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Vacuum leaks usually creates high idle..
Yes but he isn't taking about the idle, he is saying that the engine is slow to start. I can tell you now that loose fuel injectors will cause the engine to be reluctant to start I have seen it with more engines than I can remember.

With regards to the pump not priming..if the pump is weak and worn out it won't have the ability to prime the fuel system as the closed injectors will offer up more flow resistance than the worn pump can pime against.

You might find that when you crank the bike, as the fuel injectors open up through their duty cycles, it will reduce the resistance needed for the fuel to flow, and the pump will then prime only when turning over which is why its taking ages to start.

Like I said. Don't guess. Attached a fuel pressure gauge to it. If pressure won't build when you turn on the ignition before starting (due to worn out pump) and then starts to build only when cranking (duty cycle starts on the injectors allowing less flow resistance) then yeah...the pump is toast. You will likely find the pressure way down too, in have seen fuel pumps operating at only 20 psi and tne engine still jusy about runs, but is down on power and always hard to start.

Good luck
 

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You might find that when you crank the bike, as the fuel injectors open up through their duty cycles, it will reduce the resistance needed for the fuel to flow, and the pump will then prime only when turning over which is why its taking ages to start.
I don't follow you here. On the 955 there's a return line. I.e. the fuel is flowing continuously through the fuel rail whatever the state of the injectors.
 

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That is what I don't understand. You don't hear the fuel pump kick in when you turn the switch on
Once it finally starts up, after running for say 1 or two mn, if you stop and start it, does it start up normally or is it still slow?
 

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I don't follow you here. On the 955 there's a return line. I.e. the fuel is flowing continuously through the fuel rail whatever the state of the injectors.
It's quite simple really. The fuel line is a pressurised loop, the system primes the loop to a set pressure, the fuel will continue to circulate at that pressure with the fuel injectors closed as the fuel line has a restricted flow at one end so as to build pressure but still allow flow, it's not an open flow or it won't build pressure.

When the injectors start through their duty cycles, the pressure in the rail will drop this can be observed with a fuel pressure gauge attached to the fuel line and shouldn't drop be low 40 psi.

If the fuel pump is at the end of its life, it won't have the ability to prime the fuel system rail to the desired pressure, as it's worn out.

Ok so the problem seems to be the lack of priming.
Can you try to reload the map? Read it first to keep the current one.
Yes that's correct...Low pressure means that when the fuel injectors do open, the fuel won't burst through as efficiently using the built up pressure in the flowing rail, say for example the fuel pump quits at 18psi and stops flowing due to it being worn out, when that injector does open the fuel won't burst through and atomisie immediately for a start scenario, but the opening injectors will drop the resistance enough for the weak pump to start flowing again, and then it will start as the injectors are opening through their duty cycles putting less pressure on the rail.

Where as in a correctly functioning fuel system, the fuel pump starts the flow and maintains the flow at 42 psi in the fuel loop, and when it comes to start the injectors open and fuel can burst through at the RIGHT pressure for a 1st time start.

The early 955i had a continuous pressure fuel loop that was always on. Some of the latter ones didn't have a fuel loop, my Daytona only has one output to the rail and no return line, so the pump brings the rail to pressure and then shuts off flow until starting, the early ones are a continuous flow, but still need certain line pressure, and if the pump is worn it will stop flowing once it gets to a point where it can't push the pressure through.

Hope that helps.

Get a fuel pressure gauge on it and check is the only way

If you start it right after it is fine, wait a couple of hours and it is slow
This makes perfect sense, if the engine has been running it's hot so it won't need to run as rich on its starting scenario, resulting in the ecu injector duty cycle being much less, so on a fuel system with low pressure it won't affect it so much and it starts easier.

However after a couple of hours left off, when you go to start the bike the ecu will send much longer duty cycles to those injectors as it needs a richer mixture to start, a low fuel pressure will limit the ability for the injectors to deliver a richer mixture on cold start scenarios giving you your hard starting issue.

Hope that helps
 

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Discussion Starter · #12 ·
Two things.

How do you use a normal fuel pressure tester? The book says you can only use the Triumph specific tester because of the connectors.

And the book says that the Sprint RS does not have a fuel pressure relay. Is this correct? or did I miss something?
 

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Two things.

How do you use a normal fuel pressure tester? The book says you can only use the Triumph specific tester because of the connectors.

And the book says that the Sprint RS does not have a fuel pressure relay. Is this correct? or did I miss something?
You may need to make up your own connectors and pipe.

Its fairly straightforward. You simply connect it inline with the fuel rail.

You can get universal pressure testers on eBay.
 

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On the 955 you have to open the loop and introduce a T. The cleaner way is to use a male and a femal fuel fitting connected to each side of a T (by mean of pieces of hoses and clamps). The third end of the T connected to a pressure gauge.
The less clean way is to remove one of the fuel fitting clamp and introduce your T in the circuit.

This kind of stuff may provide all what you need.
 

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Discussion Starter · #15 ·
An update here and I know my means and methods will pick up some criticism but at times you just gotta go with what feels right.

So I wasn't able to get what was needed to test the fuel pressure, due to time, availability, and just because. My gut told me that it was a fuel pump because of everything above, really the only thing that made sense. So based on that I went ahead and ordered a fuel pump from Quantum Fuel Systems Quantum Fuel Systems It came in fairly quick and when I had a free moment installed it and then looked for another free moment to put the tank back on the bike which I did last night.

Immediately when turning on the switch you knew there was a difference, you could hear the pump. Started, it started just like it should and it ran perfect. Couldn't have been happier with the results. Trusted my gut which has been doing automotive stuff all of its life and it worked. Yeah I should have tested but I just had the feeling that was the problem. Either way it worked.

But of course the fuel connections are leaking since I didn't have the O rings to replace on them. After much internal debate I went ahead and ordered metal fittings to replace the OEM factory ones. Yeah they cost a pretty penny but I think in the long run it is worth it.

I should be back on the road mid next week which is perfect timing for when the Dr released me from my hernia surgery.
 

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Told you it was the fuel pump! 😂

With regards to the pump not priming..if the pump is weak and worn out it won't have the ability to prime the fuel system as the closed injectors will offer up more flow resistance than the worn pump can pime against. ........
If pressure won't build when you turn on the ignition before starting (due to worn out pump) and then starts to build only when cranking (duty cycle starts on the injectors allowing less flow resistance) then yeah...the pump is toast. You will likely find the pressure way down too, in have seen fuel pumps operating at only 20 psi and tne engine still jusy about runs, but is down on power and always hard to start.

Good luck

Don't forget to replace the o-ring s with fuel resistant ones.

Personally it's exactly what I would have done, just replaced then pump. But i thought I'd let you know the correct procedure. It would have been interesting to see what pressure it was achieving, my guess would be less than 20 psi...😁👍🤪
 

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Well, good job. The goal is achieved.
If I was picky I would ask whether the pump throughput is fitting the need. But as they seem to have a model fitting guide all is well.
70$ is not bad as compared to the ridiculously expensive Triumph one (423$ on bikebandit).
 

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I wonder whether the fitting guide is so accurate. They propose the same pump for the sprint GT... We know it's not fitting 1050.
 

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Well, good job. The goal is achieved.
If I was picky I would ask whether the pump throughput is fitting the need. But as they seem to have a model fitting guide all is well.
70$ is not bad as compared to the ridiculously expensive Triumph one (423$ on bikebandit).
It's funny but I ordered a genuine denso pump from fowlers here in the UK and that was only £120.
 

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Discussion Starter · #20 ·
The pump was a dead on match. It came with multiple filter socks and like I said it matched up perfectly.

The fuel fittings I bought have Viton O-Rings and I probably over paid for them but it was late and I wanted coming in so I bit the bullet and bought them.

New Brass/Chrome Fuel Line Quick Disconnect Set with VITON O-Rings (Seals) Installed.
Both Male and Female Fittings have Shut Off Valves.
Both Male and Female Fittings have VITON O-Rings.
Made in the USA.
Auction is for a complete set of 4 Fittings - 2 Male Fittings and 2 Female Fittings.
Male Fitting has 3/8" ID, 1.28" Length, Insert 1/4" Flow.
Female Fitting is 1/4 BSPT, 1.15" Length.
Chad
 
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