emc53

I have a 94 lt1 engine in my car and when I get on it it will stumble and then when I slow down it will shut off. I don't have any codes but when i checked my readings there was a big difference between the left and right oxygen sensors. Is there a range that they should fall in ?

Injuneer

In closed loop, your O2 sensors should be rapidly (up to 10 times per second) cycling between 0xx - 9xx milliVolts. Since each bank of the engine is independently controlled, the left and right O2 values will not be the same.

At WOT (power enrichment, or PE mode) they should both climb into the range of 900 mV, and should be close, within maybe 20 mV.

emc53

My code reader said the left sesor was 569 mvolts and my right sensor was 176 mvolts.

SilverZConvertible

Get a data cable and do some data logging. Let it idle, drive around and run it WOT in PE mode. You'll be able to see what the sensors are doing in real time as it happens. Might even be able to post it up here and ask someone who really knows about this stuff.

Maybe I read your post wrong but you said you had two constant values? They should be bouncing back and forth at idle like Injuneer said.

The data cable is well worth the money.

Injuneer

Was that simply a snapshot of a single frame of data, using a scanner? If so, a single frame of data from the O2 sensors is virtually useless. You need a full data log to evaluate what they are doing.

Read this to understand what your scanner is telling you:

http://www.injuneer.com/ScanMast.html

emc53

Thanks Fred
i read the article about scanmaster and it explained quite a bit. I have a Auto Xray scanner and I went for a ride with it hooked up and checked my readings with the ones in the article and they were very similar except for one. The Mass Air Flow Sensor 471gr/sec. My problems is I don't have one installed.

Injuneer

That is the result you will get for the MAF sensor when it is not connected. I don't run an MAF sensor any more, and my ScanMaster shows a similar number.

You may also get a reading of -40*F for the oil temp sensor, because you don't have one of those either.

emc53

So is there a benefit to having a MAF or not?

Injuneer

The MAF directly measures the mass air flow into the engine. As a result, if you make significant changes that improve engine breathing (intake, exhaust) the MAF sensor measures the improved air flow, and the PCM can proportion the fuel accordingly. No PCM programming required.

The alternative is to run "speed-density". In that system, the PCM calculates the volumetric air flow from the displacement, the RPM, and the volumetric efficiency (VE), then converts the volumetric flow to mass air flow by using the perfect gas law to calculate air density from the absolute air pressure (measured by the MAP sensor) and the absolute air temperature (measured by the IAT sensor). If you tune the engine correctly, programming the volumetric efficiency table correctly, you will get the same results whether you are running MAF or speed-density.

The problem comes when you alter the engine's breathing. The equation for calculating volumetric air flow requires the VE tables to match the engine's specific intake and exhaust capabilities. If you change either, you have to program new VE tables, and that's not easy to do. The correct way would be to put the engine on an engine dyno, and measure the air flow directly. A good tuner can get pretty close though.

So.... MAF minimizes the need to reprogram for breathing changes. Speed-density requires the extra step. Nothing wrong with running speed-density - I'm making about 500HP at the flywheel, normally aspirated. But the engine uses a high end aftermarket engine management system, and was tuned extensively on both an engine dyno and a chassis dyno. Unfortunately, the car has probably made more dyno pulls than its made passes at the track.

You can run speed-density on the 4th Gen PCM's simply by disconnecting the MAF sensor. But you better have the right values in the VE table.

No MAF......



MoTeC M48Pro.....

emc53

What started out as questions about the 02 sensors turned out to be my MAP sensor, the connector was not locked in .

Injuneer

The entire connector dries out and crumbles. May be time for a replacement pigtail.

emc53

I have a new painless harness on it, I am sure I didn't lock it in.