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Honda 90hp VTEC - loses power, won't rev above 3,000 rpm ADVICE PLEASE

C

cmgrant

New member
HELP - Advice sought for engine that starts well, but loses power after 30 secs..:-(

https://youtu.be/JTUXMp_Fuys


Outboard starts well every time, hot or cold! From initial cold start will rev easily to full power - but only for 30-60 seconds....then starts to misfire/pulsate like in video, and won't rev beyond 3000 rpm.

Local Honda dealer has attended twice and changed the complete fuel system (pipes, filter, bulb), but no improvement.
My next closest dealer is 200 miles away, a long haul...!

I suspect fault is electronic sensor, as engine CAN rev fullpower short periods, and will run sweetly below 3000rpm, but the fault always appears at exactly 3100 rpm.

which sensor could do this?... Pulsar? (£250!) CDI? (£600!) all suggestions appreciated! :)
Many Thanks
 
It is hard to say what could be causing your problem. Did this problem start all of a sudden or did it get increasing bad over time?

I would hope that the dealer found an issue with fuel pressure......and that is why they changed all the fuel related parts.

If it fails so fast, why didn't the dealer take the boat out with Dr. H and see what parameters were out of range?

They could have done a cylinder drop test to see what cylinder was causing the problem. Then zero'd in from there.

Before investing in new CDI etc, have you changed the spark plugs. It could just be a spark plug or two misfiring after it gets a little warm.

Bottom line, this could get expensive if you are just guessing on what parts to change without some direction from Dr. H or HDS tool.

Besides....did the dealer just give up? Have they contacted Honda for help? I am not sure if they have that type of support in your country (but I hope so).

I am not sure when the VTEC is supposed to kick in on the 90, but it might be related to that and possibly oil pressure.

Also, if the neutral safety switch in not opening up when the motor is put into gear, then the motor thinks it is still in neutral and will try to limit the rpm. The only thing....it would try to limit it all the time and not run ok for a short time.

So you see, it is nothing but guessing without more data to limit the number of directions to explore.

Wish I had the magic answer....

Mike
 
Thank you so much for your kind reply Mike Hondadude

The engine actually belongs to by lil' bro' - I'll share your reply with him so he can take up your suggestions with the dealer.
btw, what is the Dr. H / HDS tool? Is it an electronic engine analyser that all dealers should have that would diagnose a faulty sensor/CDI?
- actually - just found out ..https://www.youtube.com/watch?v=aqOQcK5uuH8 - which mentions the VTEC has a 'Guardian Mode' ... could my bro's engine actually be going into guardian mode (but without buzzer sounding for some reason?)

I believe the dealer only tested the engine with the boat still on the trailer and reversed into the water - but this problem does not seem to occur until the engine has been under full load for 30-60 secs.
Thanks, Mike - you may have saved lil' bro' whats left of his summer fishing!
 
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Dr. H or the HDS are two computer diagnostic systems that all dealers "should" have.

Have your dealer check the horn and warning light operation with the above mentioned systems to be sure that the warning system works.

If the shift switch is not working properly, the motor will run like it is in guardian mode, but there would be no audible or visual alerts.

Never had an issue with a Honda that way, but I have had a couple of Suzuki motors that acted just like yours and one turned out to be the shift switch and the other turned out to be the ECM (no recognizing the switch). The diagnostic system will tell you what the ECM thinks it sees from the switch.

Mike
 
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