Vtec issues

scottyp19

New Member
Hi, I have a problem when my car is suppose to go into vtec. at about 4500rpms it starts to sputter and lose power and shake the whole car like crazy. wont even let you go past that rpm. and some other times but very rare it wont even try to kick in and it will just drive normal like there is even no vtec in there. i have replaced the CAT, all 02 sensors, plugs (NGK). Have NOT done an oil change yet.
 

imcnblu

Resident G2 Guru of C-I
any check engine lights?

more specs of the car would be helpful. I'm assuming your car is a GS-R, correct?

A few causes could be the following:

Not enough oil in crank case.
Low oil pressure (see note about the VTEC oil pressure switch below)
Knock Sensor failed/failing (if it's OBD2. OBD1 knock sensor does NOT effect VTEC engagement)
VTEC oil pressure switch bad (or could be that the car doesn't have enough oil pressure to engage VTEC)
VTEC solenoid is bad or needs cleaning (this is really easy to do if you need to)
Throttle position sensor is faulty or not calibrated correctly (if the TPS isn't calibrated correctly, you won't have VTEC)

Now, if you're lacking oil pressure, there could be several reasons. Here are the most common causes.

Again, not enough oil in the crank case. Check how much oil you have, first. This should be the first thing you do, always.
Oil may be old, and not have the viscosity needed to provide consistent pressure.
The oil pump may be going out and in need of replacement.
Oil pickup in the crankcase (that pulls oils from the pan through the rest of the system) may be damaged. This could have happened if perhaps the oil pan took an impact and dented it. It MAY have damaged the oil pickup. If the previous owner, or perhaps you did it (not pointing fingers, or anything. just pointing out possible scenarios for you that might help you find out the problem), replacing JUST the oil pan won't fix the problem. If the pickup was damaged, it needs to be replaced. this is one thing a LOT of people overlook when they have VTEC problems. It has been the culprit of a lot oil pressure related VTEC problems, and a lot of times, people did everything else BEFORE checking out the oil pickup.

Here are the things I'd do, in this order to diagnose.
1. Check oil level and condition. if it's really black and grimy, it's gotta go. or if extremely runny.
2. Pull the VTEC solenoid (shouldn't need to pull the whole thing, just the top half above the oil pressure switch) see if the screen is clogged up with anything. if it is, clean it up)
3. Check the calibration of the Throttle Position Sensor (google the process, it isn't hard to check. Calibrating it can be a pain, but simply checking the specs of it is really easy)
4. Check oil pan condition. If there are any noticeable dents, this is a big red flag. PULL the pan off (follow obvious oil draining process first, otherwise you're in for a MESSY treat) lol
5. If the pan is dented, get it replaced. It'll only be in the way. At the barest of minimums, try to straighten it back out (as long as the baffle isn't messed up, which it probably is if the pan has a significant dent)
6. Check to see if there is anything wrong with the oil pickup. If it's dented, bent, or otherwise flawed, replace it. Even if this isn't the immediate cause, it's really easy to replace and will only help. can't hurt.
7. If those are all in good shape, then it's time to get into the nitty gritty. Time to start disassembling a little bit. Remove all your belts, pulleys etc. to get access to the oil pump. (you'll be removing all your accessory belts, all your timing covers, so yes, a timing belt/tensioner/water pump replacement makes sense if it hasn't been done in a while) as well as removing the pulleys, and main the crank gear that drives your timing belt. once all that is out, you'll be removing your oil pump. check to see if it's working correctly. a reputable service manual will come in handy to tell you everything to look for. but, since you've already gone as far as taking it off, you might as well just put a new one on.

hope that helps. feel free to hit me up if you need any help.
 

scottyp19

New Member
that deff is alot of info to help me look for the problem. but yes its a 2000 gsr. no CEL. and on my vtec solenoid there is no screen. could that be a big problem?
 

imcnblu

Resident G2 Guru of C-I
did you remove the 2 or 3 bolts that hold solenoid onto the head? That screen is mainly to filter any contaminants from getting into the mechanism that locks the rockers into place. It's not terribly important, but what I would do is, if you can, remove the whole solenoid from the head (a little oil will spill, so have a rag ready to catch the drips)

one thing you can do, is test the vtec solenoid itself. take it off the head (you only need the top half of the assembly), unplug the connector for the vtec solenoid. now, take a piece of wire and run the wire from the hot side of the battery, and then touch the solenoid to a solid ground. pressing it against the head should do the job. if you hear it clicking, then the solenoid itself is working.

it sounds like there is an issue with the oil pressure switch, though...

I want to see if a previous owner messed with the CEL bulb at all. Because, considering the issues you're having, you SHOULD be throwing some kind of CEL. With the car running, disconnect the MAP sensor (on top of your throttle body). That should throw a CEL instantly, but the car will run fine otherwise (just don't try to drive it hard, just let the car idle).

If the CEL doesn't come on, then it sounds like someone who owned the car before you took out the bulb for the CEL to hide an issue of some kind. Best case scenario, then, if the light doesn't come on, is to take your car to a local auto store that does a free CEL scan and see if they come up with anything.

If they find codes, tell us what they are and I can help out a lot more in terms of letting you know things to replace ;)

If you need to, I might be able to help over the phone. If you're interested, PM me, and i'll send you my #, you can call me then.
 

NemesisCBR

Boredest Member
Thoroughly covered regarding vtec. Not much else to add but i will say that on a bone stock gsr, a lot of people cant tell whether vtec is on or not but if the ecu detects a problem it may not engage vtec and not throw a code. Ignoring whether vtec is on or not the description you gave might be the icm. Had a similar problem at a lower rpm range. No vtec would not cause the car to sputter. You simply wouldnt have the additional power. Have the dizzy parts tested or swap a dizzy out with a known working one and see where that gets you. Its possible you have two problems.
 


scottyp19

New Member
okay, so before i did an oil change my maint rec light was flashing. so i did an oil change new oil and filter. no luck. still have the issues. and going back to NO CEL.. i had the CEL on b4 i did the 02 sensors and CAT. then i had it erased and went away. so now i know it wasn't bad oil.
 

NemesisCBR

Boredest Member
Report back when you try either what he said with testing the solenoid or what i said about the dizzy.

The engine might sputter during vtec if your oil level is too low or its having trouble with oil pressure and wont necessarily throw a cel for it. If it does it enough times eventually the cel will go on and the ecu just wont run vtec. Dont get hung up on vtec. This might have nothing to do with vtec. Start checking other things.
 

scottyp19

New Member
okay, here is what the problem was.... i swapped out dizzy, didnt do anything. my timing belt needs changing and water pump too.. but awhile back i replaced the CAT & 02 sensors.. and this is this problem. new CAT isn't allowing enough flow and causing the engine to bog down at 4500 rpms. drive it with new cat on, bogs down. drive it with out cat connected just headers on.. runs like a champ!! a lil loud lol but runs perfect. so now i don't know what to do.
 
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