Vtec Engagement BB4

Fourth Generation Honda Prelude topics

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danny0570
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Vtec Engagement BB4

Post by danny0570 »

Hi

iv got a prelude bb4 93/94 and it wont engage vtec. I know it must have been covered before but at the minute it wont engage vtec. I know its not mechanical because when it has fresh oil in it, it engages fine and revs through to the the redline fine. It will stop engaging vtec after about 1.5-2k miles im using 5w-40w fully synthetic castrol oil not bad stuff but cant surley be trashed already?. has anyone got any thoughts, internal problems oil pump? id like to keep my prelude going so would like to get this sorted.

thanks for any help,

dan

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spiffyguido
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Re: Vtec Engagement BB4

Post by spiffyguido »

Is your speed sensor working correctly?

danny0570
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Re: Vtec Engagement BB4

Post by danny0570 »

speed sensor im not really familiar with where it is etc. Im guessing it is working fine because when it has fresh oil in the engine, vtec works fine then its starts working intermittently and pretty much not at all. any thoughts

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spiffyguido
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Re: Vtec Engagement BB4

Post by spiffyguido »

How much oil does your engine burn/leak? When the oil level is low, VTEC won't work because the engine won't be able to get the oil pressure it needs.

LudacrisH22a95
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Re: Vtec Engagement BB4

Post by LudacrisH22a95 »

Definetly make sure your oil is fully topped up i have problems with mine burning oil wish i knew wat is wrong, but anyway Vtec stops engaging long before the oil light starts burning, in my lude anyways!

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RedRacer
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Prelude Model: 1995 Si w/mods
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Re: Vtec Engagement BB4

Post by RedRacer »

This is such a common question and there are numerous aspects of what could be causing vtec to fail.
You can put this into two categories - electrical and mechanical.

First, do you have any check engine codes being thrown? If you have a CEL showing on your dash, find out what it is and fix it. You'd be surprised at how much of the electronics in your car are impacted by some minor CEL code. Example, I had an O2 sensor code on my G35..... shortly thereafter my VDC and TRACTION control systems failed. Why? Because the bad 02 sensor was causing an erratic RPM (undetectable by humans) and that was just enough to shunt the drive systems that controlled my traction and vehicle dynamic control systems. Who knew? !

So if you have done any wiring swaps, etc. and/or you have CEL's thrown, then look there first.

Also, make sure your check engine light is actually working. It should light up on the dash when you put the car into accessory mode before you crank the engine. If it is not showing up in the test before you start the car, then get the light fixed.... you may indeed have a CEL and not know it because of the light being burned out.

Do you have any speed sensor/speedometer or tachometer issues? Vtec will not work if those aren't working.

Oil - Oil pressure is very critical to vtec functioning. If you have low oil pressure you won't have vtec. Causes could be from low oil levels, oil is too thin, dented oil pan. I knew a guy who had this issue and worked on the problem endlessly. He gave up finally and took it to a very experienced Honda mechanic who removed the car's oil pan, hammered out a huge dent in the oil pan, reinstalled it and filled with new oil and vtec worked great! That's all it was.

Vtec oil pressure switch function is critical. If the OP switch isn't sending the right info to the vtec solenoid, or if it isn't working at all, no vtec.

Engine temperature and coolant temp. If the car is not running cool or hot enough, no vtec. Check the temp sensors, thermostats.

Those are the things I would start with...... of course I haven't covered everything and I don't know all the things that can cause vtec to fail. The list is quite long and varied.

Based on what you have said though, I am thinking that your problem is oil /oil pressure related. Remember, synth is very thin....and in a car with higher mileage, it might be just enough that it's causing your problem. Run it out and then change back to regular dino oil, appropriate weight for your climate of course, and then see if your vtec works again.

alfredo25r
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Re: Vtec Engagement BB4

Post by alfredo25r »

spiffyguido wrote:VTEC won't work because the engine won't be able to get the oil pressure it needs.
I've a little problem with vtec too, Vtec engages at 4800 RPM but I feel like it is not engaging hard enough?, I've a friend and I feel like his prelude engages vtec harder than mine. Can this be a problem with oil pressure?

danny0570
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Re: Vtec Engagement BB4

Post by danny0570 »

Thanks redracer good things to look into, Just find it strange that it works faultless with new oil in it revs cleanly to the redline etc then goes intermittent and then not at all over the course of say 1500 miles. If i keep trying to engage vtec it will throw a CEL how do i read these off on a right hand drive car? the jumper plug is somewhere in the drivers footwell? green in colour? a picture would be awsome

thanks for any help much aprreciated.

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spiffyguido
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Re: Vtec Engagement BB4

Post by spiffyguido »

This may help you read the CEL codes:

viewtopic.php?f=3&t=14



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