ok, under non WOT acceleration (and in 3rd 4th & 5th in WOT), when VTEC engages the power weakens or goes 'flat'...

i have a DIY A/F meter set up and this shows that the mixture goes lean almost as soon as VTEC engages.

it takes a little time (200-500rpms) for the mixture to go to rich again, and the power comes back as soon as this happens.

also on my dyno graph, there is a noticable dip when VTEC engages.

i know that this may be sorta common, but it is really noticable right now...

why is this happening?

how can i fix it?

i have a OBD0 B20VTEC with cam gears and B&M regulator...

thanks,

t..

 

need a better ecu program
raise fuel pressure

 

so you think my PR3 ECU is not really capable of handling the B20VTEC set-up?

would a V-AFC help, or would a chip help?

if a chip, any suggestions of which one from where???

thanks Stephen,

t..

 

my FP is set to 51psi (vac removed)

this was set during a dyno tune...

t..

 

also just wondering why tehre is a "micro-lean-out" just as VTEC engages?

is it due to the large amount of air being dumped into the cylinders?

or what?

do ohter people experience this problem?

t..

 

What injectors are you running? B20Vtecs require lots of fuel to run "well." I would raise the fuel pressure if you don't have a fuel controller. Running rich is better than lean.

You are running lean at the VTEC crossover because the motor is switching from the small lobes to the large lobe which draws in a lot more air at that particular time. Your ECU is not dumping enough fuel at this point, especially with 2 liters AND VTEC.... A fuel controller is something you definately need. The reason why it doesn't do it across the rev band is because the ECU dumps more fuel in the upper end, also, it will adjust according to the O2 sensor readings. It can't do this right when VTEC engages because it happens too quickly. Stock MAPS aren't very good for bigger displacement upgrades...

 

i am running the stock 240's - i have been told they will be ok upto about 55psi...

i might be getting some 345cc prelude ones down the track.

but now i guess my priority is to get a V-AF controller...

yeah, i guess you are right- it does happen so quickly at VTEC and the ecu would need to 'catch-up'

that is where a AFC could boost that little bit of the fuel at VTEC cross-over...

thanks!!!

t..

 

i used a p28 with hondata runs like a champ

 

i think that it is a common problem to have the dip at the stock vtec setting...i think the af controller would help or a chipped ecu...correct me if im wrong

 

You know what I'm gonna say dont you T

M-I-C-R-O-T-E-C-H !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

I would invest in a hondata system to cure this problem. With the hondata you will be able to tune the vtec dip out. the changeover point should be a smooth one. good luck.

 

hey guys, thanks for all the responses...

i guess i seemed like i knew what i was doing eh?!?!

well, i really should have started with the basics, such as changing the spark plugs!!!

new Bosch spark plugs and some fresh Mobil 1 and the lean out/flat spot has gone...

strange how it only occured at the VTEC cross-over though isnt it...??

ah well, it is gone now...

t..