VFR800 6gen MAP voltage

[sba]

Hi,

Can't find information, what MAP voltage should be on idle when engine is worm. Manual says that MAP should measure about 2.7V when engine is not running. So, mine shows 2.85 - this is normal. When I start engine it shows 2.05V and lowers down to 1.95V when hot. I don't think this is normal. Manuals for other MAP sensors say that on idle it should be about 0.5V. Is it true for VFR? I found another (same part number) MAP sensor and connected it to bike - same result. Should I check/replace vacuum hoses?

Thanks.

[Grum]

Do you have an active MAP sensor fault code? What symptoms are you having with the bike?

 

And.... Yes if you have a MAP Fault? Check the MAP vacuum hose to the 5 way junction and make sure the other four hoses from the junction are properly connected at the junction and throttle body, make sure they have no cracks, kinks or damage!

[sba]

There is no fault codes, because sensor works properly (from computer's point of view). Fault appears only when I disconnect sensor. Symptoms I feel - low power on low rpm. When moving on 3k rpm on 3rd and higher gears and opening throttle it feels like it doesn't want to accelerate. But when it reach 6k rpm or higher - it becomes a rocket :) According to PGM-FI description, this bike uses MAP+TPS on low rpm and TPS only on high rpm. So, looks like MAP provides wrong information to computer and it operates inefficiently.

I visually inspected all hoses and haven't found any issues. All seems to be in place and no visible cracks or damage. Also, I connected some gauge (used to sync carbs on zzr) to MAP port (see attached pic - mine was similar) and it showed 10 on outer scale. Not sure if this is normal.

Now I ordered silicone vacuum hoses (found only 3mm internal/7mm external) and will try to replace all vacuum hoses.

But still, would be great if someone can tell, what voltage should be on MAP when engine is idle. Just to be able to check if replaced hoses fixed this issue. 

[sba]

Also, I found a file somewhere, named "Honda Programmable FI - How it works.pdf"

It says that MAP operates in range from 0.5V to 4.5V. Also in quick reference it says that when "Key on Engine Off" it should be 2.2-2.95V and "Normal voltage when hot" should be "Lower voltage". Not sure what they meant, probably 0.5V but I may be wrong. That's why I'm asking.

 

 

Another strange thing: VFR800 service manual says on page 5-17:

Turn ignition on, check voltage - should be 2.7-3.1. Then it says start engine and check at idle - should be 2.7V minimum. How this can be?

Edited September 7, 2023 by sba
screenshot from manual

[Grum]

On 9/7/2023 at 6:55 AM, sba said:

On 9/7/2023 at 6:55 AM, sba said:

When I start engine it shows 2.05V and lowers down to 1.95V when hot. I don't think this is normal. Manuals for other MAP sensors say that on idle it should be about 0.5V. Is it true for VFR? I found another (same part number) MAP sensor and connected it to bike - same result.

Seems normal to me and per the Service Manual. Depends on atmospheric pressure, your altitude, and engine vacuum, so with engine running at idle you would expect the voltage to be slightly lower than engine off voltage. As vacuum increases voltage decreases. My Service Manual states on 5-17 that Idle voltage is 2.7v Maximum not Minimum.!!! Has to be a typo error compared to yours above, but Maximum makes sense to me. See Attached.

Note - The 5gen Service Manual also states that engine Idle MAP voltage of 2.7v Maximum!

- You have replaced the MAP Sensor and ended up with with the same results and have No Fi fault code - Seems to me you Don't have a MAP Sensor issue!

- Perhaps Starter Valve Synch might help with the lower throttle range problem you have. Have you done this? Also injectors might need cleaning and flow balancing.

- Make sure Grounds for MAP, TPS, ECT and IAT are solid back to the battery Negative terminal.

- Definitely replace the Spark Plugs unless they were done very recently.

 

On 9/7/2023 at 10:57 PM, sba said:

Also, I connected some gauge (used to sync carbs on zzr) to MAP port (see attached pic - mine was similar) and it showed 10 on outer scale. Not sure if this is normal

10 inches Hg = 254 mm Hg. Manual states at Idle 150 to 250 mm Hg. Slightly high, but what is the accuracy of your gauge?

 

On 9/7/2023 at 10:57 PM, sba said:

But when it reach 6k rpm or higher - it becomes a rocket :) 

6 and 8gens all do that.  2 Valve operation changes to 4 Valve operation.

 

 

[sba]

11 hours ago, Grum said:

Seems normal to me and per the Service Manual. Depends on atmospheric pressure, your altitude, and engine vacuum, so with engine running at idle you would expect the voltage to be slightly lower than engine off voltage. As vacuum increases voltage decreases.

I'm at 192m above sea level, so should be no big difference from manual. I was sure, that on idle, when throttle is closed, there should maximum vacuum. Seems I was wrong. I haven't found this information for VFR, but for cars MAP idle voltage usually about 0.5V. That's why I thought I may be having problem with MAP. 

 

11 hours ago, Grum said:

My Service Manual states on 5-17 that Idle voltage is 2.7v Maximum not Minimum.!!! Has to be a typo error compared to yours above, but Maximum makes sense to me. See Attached.

Note - The 5gen Service Manual also states that engine Idle MAP voltage of 2.7v Maximum!

Ugh.. So many errors in these manuals. They should add a version, so people can understand which one is latest. Ok, maximum makes sense in context of code 2.

 

11 hours ago, Grum said:

- You have replaced the MAP Sensor and ended up with with the same results and have No Fi fault code - Seems to me you Don't have a MAP Sensor issue!

Yes, I had no faults before and no faults with replaced sensor as well. If 1.95V is correct voltage at idle - seems there is no issue with MAP and vacuum hoses.

 

12 hours ago, Grum said:

- Perhaps Starter Valve Synch might help with the lower throttle range problem you have. Have you done this? Also injectors might need cleaning and flow balancing.

- Make sure Grounds for MAP, TPS, ECT and IAT are solid back to the battery Negative terminal.

- Definitely replace the Spark Plugs unless they were done very recently.

Hmm.. Starter valve sync was made long time ago. Probably it's good reason to do it now. I didn't bother with it because bike starts as usual and idle is smooth. VAX operates properly - 2k rpm on cold, lowering to about 1k after 52C.

How often injectors needs to be cleaned? Is there best practice? I'm asking, because somebody told me that he never seen problems with injectors on VFR and there is no need for cleaning. 

Spark plugs was replaced about 30k km ago I think. May be less. I have iridium spark plugs, they usually work up to 100k km. So, I'll take a look at them. 

 

12 hours ago, Grum said:

10 inches Hg = 254 mm Hg. Manual states at Idle 150 to 250 mm Hg. Slightly high, but what is the accuracy of your gauge?

Not sure it is very accurate, probably ordered on aliexpress. So, this means all vacuum hoses is ok.

 

12 hours ago, Grum said:

6 and 8gens all do that.  2 Valve operation changes to 4 Valve operation.

You mean VTEC ? Yes, it turns on at 6800 rpm and bike goes supersonic 🙂  My personal feeling is that it goes better after 5k rpm, closer to 6k, so no VTEC yet. Very often I ride in traffic, usually on 2nd gear at 2-3k rpm and I have feeling that it don't have enough power, similar to when I had ZZR400 and tried to open throttle on 5th gear - it accelerates, but it feels like it doesn't want to go faster 🙂 It's hard to explain. Everything looks normal, I even checked fuel pressure - also normal. But still have feeling that something doesn't work right.

 

So, anyway, thank You very much for all information - now I have a list of what to check.