norcalz28

iTrader: (13)

After my header install I have noticed a drop in mileage. I still have the stock 22lb injectors on the car. But I am wondering if over time they can get to where they just dump fuel instead of precisely metering the amount which they release? I can't figure out why else I would be losing mpg after improving the overall breathing of the setup with headers, full exhaust(including new cat) and slp runners to help on the intake side. Any input would be helpful. thanks fellas

Will

91Z28-350

Injectors can fail, yes. If they do, you'd tend to run extremely rich, however. Look for an exhaust leak before the O2 or an intake leak first. It's possible that you may have a fuel leak. Torn o-rings are not unheard of. Did you lube them? It's also possible the injectors aren't properly seated.

There are lots of possibilities. You should also determine if your car is still misfiring and dumping fuel. Dumped fuel will make the O2 read lean, and the ECU will add more fuel to try and compensate.

Is your CTS hooked back up? The one by the #1 cylinder is what's important.

norcalz28

iTrader: (13)

The one by the #1 cylinder is onl for the gauge isn't it? The one on the front of the manifold is for the computer. Anyway the only exhaust leak I can detect is before the cat, far from the o2.
How can I check if the system is "dumping fuel?" I can see how the injectors might not have seated properly, but how can I check for the dumping fuel like you mentioned? Also how can I detect a misfire? I am wrking on getting an ALDL cable so I can look at things more closely.

Will

91Z28-350

Yeah, you're right. I always mix those 2 sensors up, I should probably make a note of it.

I think the easiest way is to pull the cat and run the car a bit in idle, and see what comes out. Let the car warm up first before doing that. If it's just water it's fine.

Another way is to run the car, turn it off, and check the spark plugs. There should be no moisture on the plugs. If it's wet, something is wrong, either it's misfiring or an injector is leaking.

eric305TPI

Also with headers the O2 can be moved away from the engine which can allow it to run cooler as well as slow its responce which in turn can reduce mileage.

norcalz28

iTrader: (13)

So I should just get a heated o2 and try my luck???

Will

91Z28-350

You could try that, but I doubt it'll make much of a difference. The general consensus is that you don't need heated O2 for shorties. I'd check for other things first. Get the scanner going before replacing your O2.

roarin_mouse

This problem is very common to closed loop operation. What changes when you improve the engine's scavenging (by adding headers, long duration cam, etc) is the charge that is being measured by the O2 sensor. During scavenging (exhaust to intake transition), some of the fresh intake charge is carried out the exhaust port. As scavenging is improved, this gets worse. This unburned charge presents a higher amount of O2 to the sensor which in turn, causes the ECM to increase the pulsewidth.

There is a solution. Contact me for more information if you are serious about fixing this.