First a little background, friend and I were on the 500 km trip last weekend and everything was fine until we came back and stopped for a snack at the end of the day. After an hour later we headed home and his bike refused to start. Took the trailer and towed bike to his garage. Luckily this happened 2 km from his house.
Problem: fuel pump won't prime
This past week we checked the following:
Kill switch - works
Battery - loaded
Relay engine cut works and 12.8 V on the exit clicking when key is turned
Relay fuel pump works and 12,8 V on the exit clicking when key is turned then switches off
Fuel pump works when connected straight to the battery
Measured voltage 12.8 on the terminals for second and then goes off (when relay clicks off)
When cranking starter, it turns and on fuel pump terminals voltage jumps to 12.8 V
Zener diode was missing for come reason from it place when we stripped ignition key.
We replaced fuel pump and zener diode and still nothing, no priming.
It looks weird to me that with 12.8 V on the terminals, the pump won't turn.

Any help is appreciated.

 

have you tried bypassing the BAS?

Does this bike have HISS?

 

If it has a zener diode I wouldn't have thought it has HISS?
What country are you in plamenh?

Are you sure you have oriented the zener diode correctly? Check the voltage drop after the zener diode, it should be in the order of around 9V or so. I think the zener Honda uses is 3.3V or 3.7V, any less or anymore may not have the correct voltage at the ECM to allow the fuel pump to prime.

Checking the BAS as 74demon has said is also a good idea.

 

Yes, we did bypass BAS, by shorting it. I did forgot to mention it.

 

The bike has HISS, but also has zener diode "plug". My friend is sure that zener was never there, so I decided to try it anyway and that is why I've got one and plug it in. We tested it both directions as I wasn't sure what is proper orientation. All the trials we did was with ignition key clipped by the HISS.

Again I can not understand why would show voltage on the pump terminals and not prime???

By the way I'm in located South Africa - Johannesburg

Thank you 74demon and RRfoever for your help. It has been a second day we battle with this bike and I started getting this feeling that we are chasing our tails.
I downloaded service manual, did some reading, but could not find any proper description of the problem and testing procedures, that is why I rely on you people with more experience with these bikes.

 

I didn't think the HISS bikes use a zener diode as well, I have never checked to see if mine has a zener so I'm not a 100% certain.

1) I am not too sure what you mean by "ignition key clipped by HISS"?

2) Is your HISS light on the cluster blinking or lit up by any chance when you go to Ignition ON?

3) When you get 12.8V at the pump's terminals do you mean this is the voltage you see when you go from Ignition OFF -> Ignition ON, or is this the voltage when you directly connect to the battery?

4) What service manual are you using, the original Honda one?

Let me check my Haynes Manual & Honda Workshop Manual to see what it says. I am thinking...could it be the HISS ring? If that has failed or the wiring is damaged then it won't recognise the key. Let me see what the manual says.

 

Well it goes like this:
1. When we stripped bike apart and do testing original key we clipped to immobilizer ring to be able receiver in it to read chip in the key. It needs to be close as otherwise it will not read it.
2.HISS light is not blinking on the panel when ignition is on everything looks normal
3. Yes that is what I read on the cables going to the pump when I switch ignition on, 12.8 V lasts for a second or two (priming voltage I assume) and it goes to 0 as pump relay clicks second time. If I crank then again voltage goes to 12.8 V
4. I use original honda manual 460 pages it is in electronic format from the net.

I will also try to download Haynes if I came across.

 

Hmm, that is very strange indeed. I'm wondering if your ground is a floating ground and that's why you're reading 12.8V anyway.

Have you checked if there is continuity from the fuel pump negative to the battery negative?

If you need me to look up specific pages on the Haynes manual let me know. There is also a good wiring diagram in colour, I can try to upload some pictures for you.

 

Yes there was a first think I did check the cables and negative from the pump to battery.
I did check all the connectors, cleaned them and used contact cleaner on them.
Color diagram would be great if you can upload it. I did not found Haynes manual in PDF yet on the net to download, I'll keep on looking though.
I'm determined to get to the bottom of this problem.

Thank you RRforever for your help

 

Have you checked for spark and injector pulse?

That will tell you if the issue is a pump only circuit or not.