My comptech supercharged car has been acting weird lately. About 3/4 of the time I get on it the car is absolutely dead, maybe half the power it normally has up to 8000rpms, then it pulls like normal from 8000 to 9000. The other 1/4 of the time it runs just fine. I've reset the ECU a few times but it doesn't really seem to affect anything. It's completely random when the car will pull and when it's dead. Sometimes it'll pull through 1st gear, shift to 2nd and I've got 100hp. Other times it'll pull hard through the first 3 gears, or it'll have 100hp through the first 3 gears but it always pulls hard from 8000 to 9000.

I've checked most everything I can come up with; air fuel ratios are fine, air filter is clean, oil level is fine, vtec is engauging, sc belt is tight, spark plugs are clean, and I did the map whack. The only remaining thing I can think of is to check the ESM. I'm going to try that tonight, but if the ECU is seeing boost and it's going into limp mode I don't understand why it would pull hard above 8000rpms. Has anyone ever experienced these symptoms before? Any idea what it could be? I'm totally lost, help! My car is falling apart!

 

try checking the vaccum line going to your BOV, it might be leaking through air. Maybe tighten your belt.

Are you seeing boost all the way up the powerband?

 

I don't have a boost gauge installed right now. It has to be boosting though, b/c at the top of the rev range it's definitely pulling harder than it would NA. I can't think of any reason it would boost at high rpms and not low rpms.

 

Some things to check

1. ESM
2. Vtec solenoid
3. Boost leak
4. Belt slippage
5. Air filter
6. Oil level

 

The belt slipping would be the normal cause, and is more likely to happen at higher RPM than lower RPM. It would be good to log your boost, or at a minimum, observe it using a mechanical gauge which you can rig up for $30-40 using vacuum line, a T fitting, and a mechanical gauge.

You could also have the car taken to a dyno facility which should be able to log manifold pressure in addition to torque/horsepower etc.

Cheers,
-- Chris

 

If the vacuum line leaked the valve would stay closed (atmosphere is the same as boost, just not as much). I also can't see a belt slipping at low rpm and not at high rpm.

I would think it's possible the bypass valve could be defective and opening/closing intermittently, like maybe an internal spring broke or something. You might try closing off the bypass hose (not the vacuum line) to see if the problem still occurs but don't run too long or at high boost in that mode, or at least refrain from sudden lifting of the throttle, let it down easy.

You might also want to remove the SC belt for a day or two and see if VTEC shows consistent performance; you'd at least know if it's an SC issue or something else.

If you have a volt meter you can connect it to the MAP sensor wire going INTO the ESM and monitor the voltage (the original MAP voltage, not what's been modified by the ESM). This is a quick and easy way to monitor boost - it's ~0.2v per PSI. Bear in mind this is absolute pressure, so "0 boost" would read about 3 volts, below that is vacuum, above that is real SC boost. With a stock pulley you should expect to see boost start around 4k and build as rpms increase. Max boost should get you to 4.0 to 4.2 volts.

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Thanks for the advise guys, I'll check into the ideas. This thing is driving me crazy. Anybody wanna buy a car?