Okay, here goes. I have a 1994 Pontiac Firebird Formula which is in dire need of help. I have not done much to this car, since it is a newer car and I am a novice mechanic, I have not worked on it for fear of breaking it more.

The car has run like crap since I got it. I have put about 2 or 3 thousand miles on it since then and it has been parked for a month or so. It has a very rough idle just sitting and when I'm going down the road, it stumbles and shakes at about 1500 to 2000 when accelerating. I took it to murray's and scanned the PCM for codes, since I noticed my check engine light has been off and on since I first got it. Keep in mind, I had disconnected the battery a couple of days before I took it to get the codes read in order to clear the computer of any codes.

When I scanned it the scanner gave me 8 codes, but only showed 7:

Code 13: Bank 1 (left) Heated Oxygen Sensor (HO2S) Circuit (open circuit)

Code 16: Distributor ignition system (low resolution pulse)

Code 32: Exhaust Gas Recirculation (EGR)

Code 41: Ignition Control (IC) circuit (open circuit)

Code 42: Ignition Control (IC) circuit (shorted or grounded circuit)

Code 48: Mass Air Flow (MAF) sensor circuit

Code 83: TCC PWM Solenoid Circuit Fault (automatic transmission)

This car has about 130K miles on it and I have a feeling the guy that had it before me did not drive it nicely. All I have done is replace the spark plugs pretty much and change the fluids. I need to do the driver side manifold gasket but the dude broke a bolt off in the head so I am not sure if I wanted to attempt it yet or not. The car also has a security system, not sure if it is aftermarket or stock, but it is not hooked up. When I hook it up (connect the wires going to it that are obviously disconnected and laying in the engine compartment) all the lights just flash on the car.

Please help me get my bird runnin' right! Thanks!

 

Im not sure on this, but the code 16 sounds like the opti

 

Okay, this is something I was wondering when I read through some of the other threads. How hard is the opti to replace? Don't they cost excess of $200 plus?

As far as the other codes, could my MAF Sensor be bad? And should I just start unplugging wires and connectors and checking grounds? Thanks.

 

Checking grounds and inspecting wires/connectors couldn't hurt, since that could explain a lot of the problems. Definitely go over all that stuff, especially the PCM connectors. Unfortunately there's still a good chance the Opti is having problems. Replacing it requires removing the water pump; it can be done but it's a pain.

 

Okay, I've removed water pumps on other vehicles, hopefully this one won't be too much different for me to get to the opti. Is there any way I can test the opti before I replace it?

Any more help on the codes other than 16 anybody? Someone mentioned the EGR code may just be my EGR solenoid or EGR valve? Does this sound correct? Thanks.

 

Multiple codes, particularly two that contradict each other (DTC 41 and 42) are often a result of poor electiorcal connections, including the grounds for the engine and PCM. That would be a good place to start.

Code 13: Bank 1 (left) Heated Oxygen Sensor (HO2S) Circuit (open circuit)
Swap the bank 1 and bank 2 O2 sensors side-to-side. If the problem follows the sensor, its a sensor problem. If the problem stays on bank 1, its a wiring problem.

Code 16: Distributor ignition system (low resolution pulse)
This is for the Opti. But if the engine is running, its a "stored" code. It isn't unusual to find this one. Clear the PCM and see how quickly it comes back.

Code 32: Exhaust Gas Recirculation (EGR)
The PCM is sending the signal to operate the EGR valve, and it isn't seeing the expected change in manifold absolute pressure (MAP). Did you check to see if the engine still has the EGR valve and all its components? Its fairly common for people to delete the EGR system, in the erroneous belief that it will increase power. If the system appears to be intact, make sure the vacuum connctions are good, the vacuum lines are not cracked, the solenoid is not plugged (apply +12V to open it), and the EGR valve is working (apply a vacuum to see if the EGR valve opens - engine idle will get extremely rough if it does). If all the parts are there and working, it could be a plugged passage in the intake manifold, or an extremely low back-pressure exhaust system.

Shoebox has details of the EGR system (and most anything else you need ):

http://shbox.com/1/egr1.jpg

Code 41: Ignition Control (IC) circuit (open circuit)

Code 42: Ignition Control (IC) circuit (shorted or grounded circuit)

These are among the hardest codes to track down. It can be a problem anywhere from the Otpi low and high res pulse signals, to the IC module, to the coil, to the PCM, to the white wire that connects the PCM to the IC Module. There are some diagnostic logic diagrams in the factory manual. Getting copies of those would be a place to start.

Code 48: Mass Air Flow (MAF) sensor circuit
With the key on, check the pink wire in the MAF harness connector for +12V.

Code 83: TCC PWM Solenoid Circuit Fault (automatic transmission)
Is your car an A4 (automatic) or an M6 (manual)?

Suggest you add a "signature" with basic info about your car, including year, tranny type and any known major mods.

Second suggetion.... don't screw with the language filter.

 

As far as code 16 goes, like I said, I cleared the PCM only a couple days before taking it to get the codes read so I would assume the code would come back quickly. I do not have insurance on this car right now so I can't really drive it too far, if at all legally.

Those diagnostic logic diagrams are in the factory manual? Are they not in my Haynes service manual? I have not been able to check, I am at school. I'm not sure if the car came with the factory manual.

The car is an automatic.

Which one of these would be the cause of it's rough idle and ride?

Thanks everyone!!! I will try the trick swapping the O2 sensors and start checking my grounds when I get home tonight.

 

Everything except the TCC lockup code could cause rough idle and poor performance.

You wouldn't get a factory service manual with your car.... you would buy it from Helm, for a price in excess of $100. You can find used copies on eBay, or you can just ask if someone who has the manual would send you a copy of the charts.

http://www.helminc.com/helm/Result.a...0MJE68BJR07SV2

 

I would take this on one thing at a time. My car had the factory O2's on it and they had over 100K miles. I replaced them since they have are recommended to be replaced at around 80K miles. I would assume most everything is origional since it wasn't been worked on much if at all. I would replace the water pump and opti if it turns out to be bad. If you just do the opti the water pump will leak all over it since you left it. You could have rotted wires on some of these causing them to not function correctly. I have seen where the opti harness will be ruined so check that connection carefully. I usually replace any part that i find to be questionable if it has over 100K miles and was a pain to get to. The O2 sensors are $40 on Ebay for A.C. Delco so the cost is pretty cheap if you do it yourself. The bolt on the exhaust manifold probably just broke off like so many others. The only good option is aftermarket headers that don't use the two rear bolt holes. What one exactly is broken? All your problems are pretty easy to do if you have so mechanical skills and you won't believe how good i will run if you find all the problems.

 

The bolt all the way towards the back of the manifold is broken. That header idea sounds really good to me! I didn't know they made aftermarket's that don't use those holes. That would save me pulling the head and drilling it out.

As far as the O2 sensor's go, the driver side appears to be right in the side of the manifold with only 1 wire coming out of it. The O2 sensor on the passenger side is in the manifold after it turns down. These look like 2 different sensor's and like I won't be able to switch them.

Also, after I started it up today, I remembered some other things that were strange with it that I forgot. One being that it tends to run much worse and idle badly only after it warms up. Also, when the car is first started up, the voltage is easily around 14 or 15 volts. After the car warms up and starts to run poorly, that voltage drops to 13 and waaaaay below at times, especially if I sit at a light or stop sign in drive with my foot on the brake.

I didn't realize the computer wasn't grounded through it's chassis. I checked the resistance going from the negative on the battery to the casing of the computer and it seemed fine. I also looked at the wiring harnesses on the computer and they seemed to look OK, no missing wires there. However, I did find a wire coming out of a group of wires near the computer that is not hooked up to anything. Also, it looks like the guy that had the car before me had opened one of the panel's on the computer because the torx screw holding it on has had it's head snapped off.

- Strange Stray Wire???
- Dude broke this torx screw head

 

The sensors on both sides should be identical 4-wire sensors, AC-Delco # AFS75 or GM # 25312184. If you have the correct sensors, one in the base of the driver's side exhaust manifold, and the other down a few inches on the passenger side of the Y-pipe, they will interchange. If you don't have identical sensors on both sides, you may have found your problem.

Running bad after it warms up could be directly related to the faulty O2 sensor. When the engine warms up, the PCM goes into closed loop and uses the O2 sensors to tweek the A/F ratio. If the sensor is faulty, your A/F ratio is wrong.

Its normal for the battery voltage to be higher on cold start. The voltage regulator ramps up the voltage to replace the charge the battery used to start the engine. As the battery recovers, the voltage regulator brings the system voltage down to about 13V. If your voltage drops significantly below that at idle, you may have a faulty alternator, weak battery, or someone may have installed underdrive pullies.

The gray wire/connector near the PCM is the fuel pump prime connector, for testing the fuel pump. Should not have anything connected to it.

The Torx screw holds down the cover for the knock module. You should replace it, so that you get a water-tight seal, and keep moisture out of the PCM.

The PCM is grounded at pins A2, A18, C32 and D1.

 

This Ebay auction shows a picture of the two O2's that go in my car. Just put this in the search box to view it "CHEVROLET CAMARO Z28 Oxygen Sensor ACDELCO AFS75". I bought an datalogging cable on Ebay for $75 and it came with a disc with around a dozen programs for monitoring and programming your car. I use the Freescan since it works and its FREE. My laptop allows me to see what a lot of sensors are doing and you would be able to see the O2's working in real time. If you are serious about working on your car this is a cheap and fun toy. I got the Pacesetter headers since they were the cheapest ones that looked like the best quality.

 

It was alluded to earlier about grounds and again regarding voltage. I'll add here that a poor alternator can cause a problem in another way. The alternator has diodes that convert AC to DC. As these diodes break down, they allow AC out on the DC lines. The PCM does NOT like AC. It will cause all sorts of problems. Many seemingly unrelated codes can be traced back to low or incorrect (AC leakage) system voltage.

First you should concentrate on the voltage at the PCM then measure the grounds at the PCM as well.

Next check the alternator for leaking AC voltage. Do this by setting the voltmeter to AC and measure from the output post of the alternator to the negative battery post. Any reading over 0.03 VAC is time to replace the alternator.

Once you have satisfied those conditions, it's time to go after sensor faults. But don't just replace the sensor to find out is was a wiring or connector issue. Check to see the proper voltages and grounds are at the sensor first. Then be sure you have continuity to the PCM from the particular sensor.

 

OK Speedy, I checked the AC voltage at the post on the alternator with the black on the battery negative and I read 31.72V!!!!!! So I guess I will pull the alternator and go get it tested at Advance Auto. Could this cause my car to run so poorly? Or maybe my O2 sensor could still be bad? Injuneer, I was looking at the wrong sensor before, I found both the O2's and they are the same. I will swap those after I have figured out my alternator situation.

Also, another thing that is strange about this car is that someone wrote on the Air filter box under the hood "all clamps must be tight to run right" talking about the intake assembly hose clamps. I don't know why this would be, maybe someone has an idea?

Thanks for the input guys, really helpful!

 

your meter should be on a DC scale.