Street Tune w/ check engine light

[Restless]

So I'm thinking about getting my car street tuned this week, basically just lower the vtec a little and add 2step, but wanted to know if this check engine light would interfere with the tune at all? I haven't checked the code yet to see what it is yet, but it fluctuates on when it comes on. Sometimes once every 2 weeks, once week, or maybe 2-3 times a week.

[ugafan001]

fix the issue first. could be just a loose wire or bad o2 sensor ect. If u got a bad o2 or spark plug it will affect a tune. My o2 sensor went out an car started running real rich. The ecu just compensates for bad readings wich will give u a bad tune if this happens in my opinion. Fix ck engine light an then tune.

[Restless]

Well I have new spark plug wires & spark plugs & changed my O2 sensor a few months ago, but you never know it could be. I thought it had something to do with my oil pressure but then vtec wouldn't kick in, I think , because it does.

[rexload]

You shouldn't even drive your car hard when there is an unknown problem... especially a blinking CEL.
Technically you CAN ignore it and tune the car and hope that you don't damage anything, but why would you want to?
Do it right, figure out the code, fix the problem, and then tune the car.
No tuner in the right state of mind would tune a car that isn't 100% problem-free.

EDIT: also instead of replacing parts randomly and hoping that it fixes the problem. Figure out what is causing the problem first and only then replace the parts. It will save you time and money in the long run.

[jdmwannabee]

don't lower your vtec engagement please. it's not going to work the way you think it will.

[Restless]

Thanks for the advice, I'm all for saving $. I was just waiting on some tax return money to come in soon and I was going to fix it before the month is over. Also, the vtec was only going to be lowered to like 4800. Have you lowered your vtec before and didn't like it or what?

[EJX_Michael]

If you are getting your car tuned, the tuner will know where to set the vtec engagement. (If they don't, you are at the wrong tuner!)

How far away are you from your car? Is it really THAT hard to go jump the service connector and read a blinking light? The ECU stores the code, you don't have to wait until the CEL is on. Seriously, you need to think about getting the motor to "normal" running condition before even worrying about getting a tune.

What ECU are you using?

[jdmwannabee]

Thanks for the advice, I'm all for saving $. I was just waiting on some tax return money to come in soon and I was going to fix it before the month is over. Also, the vtec was only going to be lowered to like 4800. Have you lowered your vtec before and didn't like it or what?

if you lower vtec arbitrarily, you often lose power and get terrible gas mileage.

[Restless]

I'm using a stock ecu right now, P13, but yeah I was going to check to Cel code in a few hours. I haven't had a check engine light come on in a week so far, but the ecu should have stored the cel code right so I shouldn't have a problem when I jump the connector to get it to come up? Thanks for the input though as far as your reasons not to lower vtec, but that's kind of why I wasn't going to lower it that much or now just leave it as is.

[deevergote]

If the light goes on and off, it's very likely a Code 43 (often comes on when you reach highway speeds...) That would be your o2 sensor. Pull the code to be certain.

Fix ALL known problems with your car before attempting to modify anything! That is the most important rule for enthusiasts, and the one that the majority of irresponsible, impatient kids ignore.

Tuning it will do no good if there is something wrong.


As for lowering the VTEC point to 4800, you won't hurt anything by doing that (aside from not feeling it anymore.) Honda actually set the VTEC point rather high, because that kick in the pants you get at 5200 was fantastic for selling Preludes! 4800 is the general "optimal" rule of thumb RPM... but jdmwannabee is right, unless you do it on a dyno, you won't guarantee that you're not losing power. Every engine is different, especially old ones.

[Restless]

Always appreciate your advice deev. So I did find out the cel codes and I have 2 (12 & 17). I found out, but correct me if I'm wrong, that 12 is the EGR lift sensor and 17 is VSS(Vehicle Speed Sensor). When I did the auto to manual H22 conversion last summer there were some extra wires that didn't need to be plugged in so some are kind of hanging. Could some of these unplugged wires be throwing these codes?

[deevergote]

If those wires go to the vss or egr, sure. If not, then check those components, and make sure the wiring is in good shape. Identify the wires you didn't use and make sure they're supposed to be unused. Be sire they are properly capped and secured. If everything checks out, try another ecu to see if the ecu itself is faulty.

[Restless]

The ECU may have been the problem, because when my tuner changed my ECU out to a p28 he said the p13 wasn't OEM it was some kind of aftermarket ECU and surprisingly my speedometer is working good and no check engine lights. Hopefully it stays this way.

[deevergote]

There are no aftermarket P13s... but some people attempt to chip and tune them, so that may have been the case. That, or it was a JUN P13, which would be the only one that is truly modified properly.