Recently replaced D16B on my 98 Civic with a JDM, which runs perfectly normally, EXCEPT that VTEC (apparently) engages at 5500 RPM. In my previous experience with stock 1.6 VTECs, the switch seemed to occur about 4000 RPM, and was pretty smooth.

This engine pulls very slowly from 4000 to 5500, and then has a dramatic horsepower gain at 5500. Below 4000 and above 5500 its behavior is completely normal.

Am I right in thinking that this is late VTEC engagement? Is there anything else that would explain the dead zone and abrupt kick-in?

And most importantly, how can it be fixed?

Any help deeply appreciated!

 

D16B doesn't exist... do you mean D15B?

Anyway, i'm pretty sure VTEC engagement is 4800 RPM or so.

 

Yes, D15B, my memory bad.

What would explain normal power below 4000, and above 5500, but a big deficit in between? If VTEC is coming at the wrong RPM, what could cause that, and how can it be fixed?

 

BUMP

Any ideas? Suggestions?

I did some reading on the D15B, there seems to be a version with 2 VTEC solenoids, I only see one on mine.

Thanks for any help!

 

There's two different D15B's. One is the JDM d15b, the one almost always swapped into civics in the US; it's a single-stage vtec like most other honda engines. The other is the EDM d15b, with the 3-stage vtec. I'd be willing to put money on you having the JDM d15b.

As far as vtec engagement, I don't know exactly when it should engage, but I know the d16z6 and d16y8 both engage at 4800rpm, while B18c's and b16's engage at 5500 rpm. Given the slightly higher rev limit of the d15b, I'd say it would be in the 4800-5000rpm range.

As far as the dead zone in the powerband, what mods do you have? Is it a stock engine? My guess would be something with either timing or the ignition system, but that's just a guess at this point (assuming there actually is a dip in the powerband and it's not just a placebo).


Welcome to the forums btw

 

reaper, thanks for the reply, and your message of welcome!

Yes, it's a JDM D15B from jdmenginesinc.com, installed bone stock as a short block.

No, it's not a placebo effect: I've driven more than 200,000 miles on 3 other stock Civic VTEC engines. The other 3 were all very similar to each other, with a relatively smooth torque curve, except for the noticeable (but not really jarring) upward inflection between 4000-5000 RPM.

Compared to my previous experience, this motor is definitely slower approaching 5500 RPM (the tach needle seems to drag), and at 5500 there is a very abrupt and dramatic change in torque and engine sound: it feels like an instant 20 to 30 percent power jump. It's like a exaggerated version of how suddenly power can increase on some turbo installations.

I don't know why this installation is behaving so differently, or how to cure it. The deficiency below 5500 RPM can be a real nuisance in traffic situations (merging on the highway, for example).

 

No problem.

As far as your vtec concern, if it's the vtec system that's actually causing the problem I'd think it would be vtec coming on too early, since it would cause a dip in the powerband and then pick back up. Honestly, I can't think of a reason for vtec to engage at the wrong rpm.

 

There's 3 D15B's. There's also one that in Japan is dual carbeurated, but when they ship it to the US they put a block off plate on the 2nd fuel pump or whatever and people then just use it fuel injected. It's non-VTEC and resembles a D15B7.

 

'88 CRX 1.5X and Ferio MX. Forgot about that one. I'd assume the OP has the d15b that came in the EG4/EG8 though.