Vtec Spec1 not engaging Vtec. Suggestions?

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4-cyl
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Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Wed Apr 20, 2011 5:07 pm

This is my first post here, but I have owned my CB400SF V-tec Spec 1 for almost two years now. The bike ended up in a mild crash a couple months ago, and I replaced the right-side engine cover. Since that time, I’ve had a problem with the engine refusing to engage the V-tec. Here are the current symptoms:

1. Engine CDI unit was replaced when the original unit wouldn’t function. It was replaced with a used unit that was stated to be MY2000.
2. The engine runs great, but it limits itself at 8,500rpms. The V-tec does not activate.
3. I had access to a brand new (direct from the local Honda parts dept.) MY2000 CDI at the time, and the bike wouldn’t even turn over with it installed. It ONLY runs on the used unit I have.

Some things I have learned:
a. The MY1999 CDI unit is no longer available from the factory.
b. The MY2000 CDI unit is a different part-code (, but that shouldn’t matter, right? 1999-2001 are all Spec1 computers).
c. Someone over at vfrdiscussion.com was having a similar problem with their bike, but the V-tec on that bike was working fine after the bike warmed up. They traced it back to the temperature sensor which doesn’t allow the bike to operate above 8,500rpms when it’s cold.

I’m not positive, but I don’t remember not being able to blast into the higher rpms if I really needed to when the bike was cold. Also, my bike NEVER goes past 8,500 anymore--cold or not.

Is there something I’m missing here? Is there some other electrical component, connector, or internal mechanism that would be limiting my rpms? I want to say that the used CDI I obtained is not a V-tec CDI. If that is so, what then is my actual problem?

Thanks in advance for any help. I can’t seem to find a manual for this thing (I live in Korea, by the way), so diagnosing this on my own is proving hard.

:rocks:

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by Cammo » Thu Apr 21, 2011 5:31 am

4-cyl wrote:my bike NEVER goes past 8,500 anymore--cold or not.

I want to say that the used CDI I obtained is not a V-tec CDI. If that is so, what then is my actual problem?
You need a vtec cdi!!

The proper (vtec) cdi sends a signal to the engine to switch it from the low lift cam lobes (low rpm running) to the high lift (high rpm running).

Basically, your engine is only running on the first of the 2 sets of cam lobes! Only the vtec cdi will work on this model.
"It's just a ride" Bill Hicks

4-cyl
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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Thu Apr 21, 2011 9:47 am

Thanks for the reply.

Yes, I know that a V-tec CDI is required. As previously stated, I was able to plug in a MY2000 Spec1 V-tec CDI, and the bike wouldn't even kick over. That's why I'm here looking for other suggestions.

I mis-wrote the part you quoted. I was meaning that even if my current CDI isn't a V-tec CDI, there is still a problem since the other, known V-tec CDI units wouldn't work.

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by Cammo » Thu Apr 21, 2011 2:28 pm

Ah, ok.

Do you mean the bike wouldn't crank over with the other vtec cdi fitted? Or it would turn over but not fire?

If it didn't crank over at all I don't think it would be related to the cdi, just a coincidence or other problems perhaps. The cdi is separate to the entire power/cranking circuit, it shouldn't stop the bike from cranking over on the starter.

If it turns over but doesn't fire, it could just be the incorrect model of cdi, there may have been several cdi models for vtec bikes. Honda has been known to change/move contact points on different model cdi's so they're not compatible without rearranging some of the pins in the plug.

What are the top row of letters/numbers on your original (broken) cdi? This is what you need to find in a compatible cdi.
"It's just a ride" Bill Hicks

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Fri Apr 22, 2011 10:52 am

Ah ha. You make be onto something here. The bike would turn over when I fitted the MY2000 V-tec CDI, but it would not fire. The next question seems to be, how do I get my hands on multiple year wiring diagrams since the MY1999 CDI is no longer available for sale?

If this really is the problem, it is ridiculous. Why would Honda change the connectors around for no reason? IS there a reason? Are there other components that have changed along the way besides the CDI?

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Tue May 24, 2011 11:15 am

Well, just to keep the information coming, I shall give an update.

After gathering some information, I have found that the 1999 Vtec Spec1 CDI and wiring harness have a specific pin and plug type. The 2000 and 2001 Spec1s have the same pin and plug type (The 2000 CDI part number supersedes to the 2001).

Not truly knowing which CDI I had in the bike (it's 12 years old), I bit the bullet and bought a new wiring harness and CDI for a 2001 Vtec Spec1.

The first thing I did when I received the new harness was to compare it to the one already on the bike--they're identical. This means that at some point in time the wiring harness (and possibly the engine itself) was replaced with a 2000-2001 unit. Hoping that there was a short somewhere, I went ahead and fitted the new harness as well as the new CDI. No change. The bike turns over, but will not fire. The bike will, however, still run on the other, used, "unknown" CDI that I have, but it still won't rev past 8,500rpms.

So, what's next? Let's look at what I know the problem is NOT.

The problem is definitely NOT:

1. Wiring harness
2. Vtec CDI (well, I don't think so anyway since it came brand spanking new from Honda)
3. Coil packs (they work fine when the "unknown" CDI is connected)
4. Regulator/rectifier (it works fine when the "unknown" CDI is connected)
5. Generator (it works fine when the "unknown" CDI is connected)

I wish I knew what model 400 that "unknown" CDI came from. When I purchased it, I was told it was from a 2000 CB400Vtec, but that is obviously false. So, why the hell does is work in my bike up until 8,500rpms and the "correct CDI will not? I haven't a clue.

Anyway, I read on the VFR800Vtec forums that their bikes won't rev past 7,000 (Vtec engagement point) with a broken thermostat. I'm not sure if this really helps me since my bike won't even kick over with the "correct" CDI installed, but it's worth a shot.

I'm also going to try jumping the Vtec solenoid to the battery to see if I can hear the click of the solenoid pin. Maybe the solenoid is dead and not sending a signal to the CDI?

So much speculation and no hard evidence. Please chime in if anyone has any ideas.

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Thu May 26, 2011 4:22 am

Well, I still don't know what is wrong. I replaced both the temp. switch and thermostat this morning. No change. I also jumped the Vtec solenoid off of the battery. I can hear the solenoid click, so it is obviously in working order.

I am at a loss here. I don't know what to do next.

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by gullarm » Mon Aug 15, 2011 9:51 pm

Oldish post I know but I thought of something.

Have you tried running the bike with a manual switch to engage the VTEC at 8500 revs. You say you have tested the solenoid at stand still.

So ride it in a high gear and when the revs hit 8500 flick the switch and see what happens, the VTEC system should kick in and the bike should keep accelerating? So at least you know that bit is working.

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by 4-cyl » Tue Dec 13, 2011 2:37 am

gullarm wrote:Oldish post I know but I thought of something.

Have you tried running the bike with a manual switch to engage the VTEC at 8500 revs. You say you have tested the solenoid at stand still.

So ride it in a high gear and when the revs hit 8500 flick the switch and see what happens, the VTEC system should kick in and the bike should keep accelerating? So at least you know that bit is working.
Thanks for the response. Sorry I never noticed your post. I have not done that, no. I'm getting ready to dismantle the top end and see what is going on in there. I couldn't take the time this summer to remove the engine since the bike is standard transportation for me.

I like your idea, but I am worried what might happen if there IS something wrong in there (maybe a dropped VTEC valve?) and I rev it while moving.

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Re: Vtec Spec1 not engaging Vtec. Suggestions?

Post by Nickd » Tue Dec 13, 2011 12:22 pm

If it's anything like the cars, you need enough oil pressure as well for vtec to engage. It is sometimes possible to engage it with a switch instead of the ecu/cdi.

AFAIK, Honda have never had a failiure on the mechanical Vtec system on any vehicle, so it would be unlikely to be anything wrong there.


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