Engine running lean 96 supercarged series II

My cars diagnostic says it is running lean. This is not the case at all. Somebody before me (an idiot) cut off the catalytic converter and the O2 sensors might be bad. The computer is trying to comoensate for the "lack of fuel" and is running si thick with it the car is slow to start. Me and my "advisir" (lol) think that either the o2 sensors are bad or there is a fuel pressure issue. We are going to test the fuel pressure tomorrow if i can find out how. But i will definitely have to get a new cat. converter. Possibly the o2 sensors as well. Any thoughts?

The front O2 sensor is what monitors lean/rich conditions, not the rear O2. You can eliminate the cat without throwing lean/rich codes. The only code that may be set from cutting off the cat is a P0420 Catalyst Low Efficiency. Unless the front O2 is "bad", or the front of the exhaust was modified, you have a different problem that needs to be diagnosed before you go spending money and replacing stuff.....

If the car is telling you it's running lean, you can't assume that is not the case at all. If the PCM has detected a lean condition, it could be the case. If the fuel pressure is found to be low, that is in fact a lean condition - the PCM was right. If the O2 sensor (only the front sensor affects the A/F ratio) is found to be bad, that may be causing the PCM to read lean incorrectly.

Removing the cat converter will not cause the front O2 sensor to fail, so this would not be the cause of your lean condition report. A missing cat trips another code telling you the cat has malfunctioned.

How many miles on the car? If 150k or more, I'd replace the O2 with a factory one. If lower mileage, might try testing the O2 by watching its output using a scan tool. A healthy O2 should rapidly oscillate during normal driving, and read a steady ~900-930 at WOT.

The front o2 sensor read .4xx to .9xx with it unplugged or plugged in. O.o like i said i am getting a pressure test today. Thank you for the help. This is by far the best forum i have come accross.

O2 sensors are one of the most frequently incorrectly replaced parts. If the sensor is oscillating, it is doing it's job. If the voltage gets "lazy" or stops oscillating like it's supposed to you will get a bad O2 sensor code from the computer. Something else is most likely the problem, do not waste your money on O2 sensors at this time.

Look for vacuum leaks and fueling issues. Check the fuel pressure - look for 50 PSI at idle with the vacuum line removed from the FP regulator. Vacuum lines are nylon tubing and both the tubing and their rubber connectors are prone to cracking. There are plenty of other places the intake might leak, lightly spraying carb cleaner around the intake area should help identify any air leakage. Also make sure your MAF sensor is clean.

Maf sensor is clean, and i have traced all the vacuum lines with no results. I do hear something that sounds like and air leak around the backside of the intake. The intake gasket is known to go bad but i have checked it because it seems there are alot of line on top of theintake/supercharger. But as i said before, the comouter showed the same reading with the o2 sensir plugged in as when it was not plugged in.

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But as i said before, the comouter showed the same reading with the o2 sensir plugged in as when it was not plugged in.

This could be a bad connector or wiring going to the O2 sensor, although SES lamp should be on if this is the case. One thing you might try: unplug the O2 wiring, secure it, and drive the car 3 trips. The PCM should throw a DTC and illuminate the SES lamp if this wire is disconnected. If no code, something's not right with the PCM.

PCM as foolish as this sound i am not familiar with thus acronym.

PCM = Powertrain Control Module, GM speak for "ECU". This is what reports codes. I'm not saying to replace the PCM - they rarely go bad, but it would be strange if you pulled the connector and it didn't notice the problem.

I am starting to lean to the maf sensor being bad. It is unfortunate because of the high cost. This still doesnt explain why the o2 sensor is acting up. But the engine is consuming ALOT of fuel.

Why do you think the MAF sensor is bad?

If the MAF sensor is dirty, a scan will show LTFT value reading high (lean). Cleaning with electronic parts spray should fix. If the MAF sensor has totally failed, or is disconnected, the SES lamp will illuminate, and a DTC is logged, pointing to the bad sensor input. I've had to clean my MAF sensor several times, but it's still original and works at 235k miles.

How do you know the O2 is acting up?

Electronic spray on the two smalle wires that are exposed to air? The car is rough maitenancewise and it could need a spray. Just tue symptom of high fuel consumption said that to me. I got an error 7170 or 1707 something like that. I dont have an ses lamp. But i do have a lean code. . . The code given was told to be either an o2 sensor maf sensor or.injector i beleive

A lean code is NOT an O2 failure code. If the MAF is bad, that will also throw a different code, NOT a lean code. A lean code does NOT indicate that you need a replacement for either sensor.

You need access to a good scanner, it would cost about as much as a MAF sensor and O2 sensor. With that scanner you would be able to see how much airflow the MAF sensor is reporting, what A/F ratio is being called for, the MAP value (would help indicate a vacuum leak), among other useful things.

My opinion is still for a vacuum leak, possibly at the intake manifold gaskets.

Would that cause a high fuel consumption? My brother seems to think that the intake gasket is bad too. Its just a real pain to get to. And another question. How DO you replace that gasket.

Well, if your Intake gaskets are bad and have a vacuum leak (or just a vacuum leak somewhere), it's unmetered by the MAF, and the O2 is reading the lean condition caused by the extra incoming air. The PCM then adds fuel to compensate for the lean readings by the O2. So, yes, you could absolutely get excess fuel consumption from the situation.

So there are more than one intake gaskets? This is going to be absolute joy. Have any of yiu had to replace these/know which is the most common to go out?

It is a V6 with a central intake manifold, so you have two intake gaskets, one on each head. It is not an easy job, but is also not a hard job. Both are common to go out, as the OE gasket design sucked. Replacement gaskets are aluminum instead of plastic. If you get plastic gaskets, return them and ask for aluminum ones. (Typically from an '04 GTP if you have to specify a vehicle for them.)

You'll also need a supercharger to LIM gasket, and probably the plastic coolant elbow that comes off the front of the intake.

The Lower Intake set consists of 4 main pieces. 2 for the Intake runners and 2 rubber pieces for where the Intake meets the block. Every songle 3800 I've ever known or seen has needed or had the LIM gaskets replaced at one time. It's a GM thing....It's not all that hard, but if you've never done it before, you'll need someone to show you so you don't have to take it all apart again in 6 months. There's a write-up on the site for them.



Look around and under the base of the supercharger with a flashlight. If there's oil or coolant (or both) built up ot sitting in the LIM pockets, the gaskets are bad. They can also leak oil into the coolant internally.



HOWEVER, the chances of the LIM gaskets causing a Lean condition is quite rare.....if they were leaking air that badly, you'd more than likely have a mad oil/coolant leak somewhere.

I have checked all the vacuum lines i could find according to the diagram on my car to no avail. And i do not have a bad oil/coolant problem. However every once in a while i will get white smoke when i start the car. I csnt tell a smell with the cat cut off because all i smell is gas.i do kniw i am getting roughly 8 mpg right now and this car snt THAT bad on gas when it is running tight.

dtrumbo wrote:

I have checked all the vacuum lines i could find according to the diagram on my car to no avail. And i do not have a bad oil/coolant problem. However every once in a while i will get white smoke when i start the car. I csnt tell a smell with the cat cut off because all i smell is gas.i do kniw i am getting roughly 8 mpg right now and this car snt THAT bad on gas when it is running tight.

sounds like you are "dumping" fuel and doing almost all city driving. Did you say you checked the fuel pressure regulator and the injectors? Kinda wonder if one or more is stuck open.

I havent checked.the fuel.pressure i am not sure hiw to check the regulators and injectors. And i do mostly city driving but even then the average is rated to 17 mpg. The car is slow to start and an injector could be stuck on but wouldnt it give an ses lamp? Plus the diagnistic is saying the engine is running lean. From what you guys have told me i beleive i might have ine massive (or several small) vacuum leaks. Some of the lines seem way to easy to pull out and i suspect that they could be worn and causing a leak which causes too much air, which causes the engine to dump extra fuel to compensate. If i sound wrong or if you have any better suggestions let me know. And thanks alot for the great info.

I forgot to mention i have a bad coupling in my supercharger. I doubt that could be the case, if it could let me know because thats a reasonably easy fix.

dtrumbo wrote:

I havent checked.the fuel.pressure i am not sure hiw to check the regulators and injectors. And i do mostly city driving but even then the average is rated to 17 mpg. The car is slow to start and an injector could be stuck on but wouldnt it give an ses lamp? Plus the diagnistic is saying the engine is running lean. From what you guys have told me i beleive i might have ine massive (or several small) vacuum leaks. Some of the lines seem way to easy to pull out and i suspect that they could be worn and causing a leak which causes too much air, which causes the engine to dump extra fuel to compensate. If i sound wrong or if you have any better suggestions let me know. And thanks alot for the great info.

One of the problems with giving 'advice' over the net to fix a car is that the advice by necessity is not always complete.

I mean, you've noticed problems with the vac lines, you oughta go ahead and fix that problem since it affects so much else. You'll fix the lines, performance will improve somewhat but not all the way and then we'll find something else. After several iterations things should be all fixed.

But...

You have to start by fixing something.

On Sept. 2 you wrote that you checked vac lines to no avail. On Sept 3 you write that the lines are easy to pull off. So... now that you have established that the lines are easy to pull off it's time to repair/replace them. One way to do that is go to an auto part store, hopefully a NAPA or a neighborhood type store, and tell teh clerk you want to replace all the vac lines on your car's engine for maintenance because it's 15 years old and could he/she look at the engine with you and figure out how many feet of which diameter line to buy? You'll end up buying a foot or 3 of the popular sizes and it won't cost much. Next, in the HELP section of the store you'll need to get an assortment of vac line caps and an assortment of adapters. And if you don't already have one a tube of black RTV (form-a-gasket). Using the old vac lines as your guide, cut lines to fit and glue adapters in place on those new lines as needed to make up replacement lines. And install them... IIRC there is a writeup on this site with more detail.

Good luck & let us know how it goes. Again - keep at it - it will take a while to get your car all sorted out.

When i checked the vac lines i was looking for holes and didnt think thwt the lines could be leaking at the fittings. Some of the lins are hard molded plastic and probably do not need replaced (around the exhaust ir other hot areas) but i am going to keep at it as long as it will run without breaking me. (as if i have money) this is going to be a classic car someday.

The supercharger coupler won't cause anything like your experiencing.

Before we decide a vacuum leak is causing your lean condition (I'm not sold on it), are you experiencing any obvious symptoms of a vac leak? A serious vac leak should make the engine RPM fluctuate at idle, and hesitate under throttle application, but then things will seem fine once you get into it. Are you experiencing a rough idle situation? If so, you haven't told us about it. It also effects shifting of your trans. I once had a cracked vac line, which made my some of my shifts feel "harder" than normal.

Have you tried spraying your vacuum connections with carb cleaner with the car running? A leak might respond with a change in idle RPM when you find the leak area. This same test can be done for the intake gasket, and I assume the LIM gasket too, if it's that bad that it's leaking to the outside air.You can also combine this test with the use of a scan tool to check changes in STFT (short term fuel trim). STFT should change quickly if you spray the leak area. If you're not able to get a response from spraying the carb cleaner around the engine, I wouldn't start tearing apart and replacing gaskets just yet.

Another test you can do is use a scan tool to simply watch STFT & LTFT (short/long fuel trims) while running the engine. If you are truly running lean, your STFT & LTFT numbers should be very high (above +8 or 9). If this is only the case at idle, and the STFT gets closer to zero at higher RPM, it suggests a vacuum leak. If the STFT continues to stay high at higher RPM, it probably represents a fuel related condition.

You say there is a starting problem, or delay. Here is a big clue that makes me think fuel delivery (although a vacuum leak could also cause this). One thing to try is to take a fuel pressure meter and mount it to the pressure valve on the fuel rail, with engine off. Start the engine and get a reading - should be above 40 PSI at idle (mine showed 44). Turn the car off and watch the needle. Does it lose pressure quickly? If so, one of your injectors may be leaking fuel, which might explain all of your problems. BUT.. you can't know this until you perform the test.