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Just put a 2003 VVT motor in my 99 using the stock ecu. Starts and idles fine but is a real dog up until 6000 RPM when it comes on like a bat out of hell. I did do a timing belt but I checked and double checked that. (still could be the issue).
Ihave not yet hooked up the VVT so I know it's either going to lose bottom end or top end but I wasn't sure which. Based on seat of the pants, feels like I'm losing a lot of bottom end but at this point it has less power than a non vvt 1.8l for sure until almost 6k.
The more I type, the more I think one of the cams is off a tooth.
You might want to give a bit more info. Are you running an aftermarket ecu or the stock ecu? What intake manifold are you using? If using the VVT manifold, did you get rid of the butterflies? Did you mess with the timing belt? Etc.
From what little data I've seen, a bp4w and bp6d make about the same power without the vvt working, with the bp4w holding torque/power up later in the rev range due to intake manifold design. Changing intake manifolds and having a working vvt gives the bp6d more peak and midrange torque and matches the bp4w up top. YMMV.
Cleared the code and it was P1141 downstream o2 sensor but the code stayed gone once cleared. I thought for sure I'd have some more emissions codes pop up but I'll take it!
However, while in there clearing the code,I noticed the the throttle position sensor reading through OBD2 is very erratic. It often does not register opening of the throttle.
I will dig through my parts tomorrow and find a spare throttle position sensor to try out. I am pretty sure this could cause the issues I am experiencing. We'll see.
Swapped the throttle position sensor. No change...
Downstream O2 sensor is definitely faulty. Now I get a P0140 - no activity error. This should not affect much but I will grab a replacement today anyway.
I did so some more testing and it is still very under powered until around 5500 rpm when it's like a switch is flipped and it gains 20-30 hp and revs freely. It also revs freely when not in gear so this is definitely a load related problem.
Should I just remove vtcs to eliminate it as the issue? From what I understand there is no performance gain from it and if anything it's only a detriment to performance.
You can wire it open to test it, its just a linkage. Iirc, you can reach it without disassembling much. I dont know off the top of my head if the stock ecu will throw a code if the solenoid is unplugged. It just restricts intake flow at low loads until the engine is up to temp, then opens completely.
Which intake are you running? If you are running VTCS(what comes on the VVT) and have it connected that may be your issue as the the VICS on the NB1 is activated at that RPM range you are seeing the change over. If you are running the VICS you may have an issue as mentioned above, maybe sticking but I run mine without it being wired up at the moment and dont have this issue.
FYI I ran mine with VVT and VICS disconnected and it really wakes up over 5k alot like you described and now Ive since got VVT hooked up and it made a world of difference between 2-4.5k
I am running the VTCS intake (and the solenoid is connected) so that may be the problem. I'll disconnect it and give it a try. Looks like 99 intake manifolds are under $100. If those are better, I'll go ahead and pick one up.
I ordered a VVTuner as well so can't wait to try it all together.
Last edited by rlogan; 04-17-2019 at 10:10 AM.
Reason: spelling
04-13-2019, 07:13 PM
VVT swap - post swap performance
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