98 3.9 auto.

Thing runs great 1/3 the time.

Other 2/3 the pedal just goes dead, thing backfires out the intake, and acts like you cut the key unless you mash the pedal to the floor.

Once you jab the gas it'll take off like a rocket... but anything under ~3000rpm just pops and farts.

The codes I'm getting are for misfires, evap leaks, and both o2 sensors.

I don't want to just go throwing new parts at it as I'm sure several of those codes are caused by one of the other ailments.

So... where do I even start??

Thanks!


P0132
P0300
P0301
P0138
P0455
P0305
P0306
P0172

20170701_194054_zpsc1rsqbg8.jpg

 

I like your choice in toys there. Can't tell what you have covered, but do I spy an early 3rd gen firebird up on jackstands?

I would start at the O2 sensors. Circuit high means that the sensor is unplugged. Check the wiring harness, one of my wires had laid up on the exhaust and burned right through. Or it could be that the O2 sensors are just wore out.

The computer uses the pulse signal of the O2's (synced to the ignition coil signal) to determine the existence of a misfire on each particular cylinder.

EVAP is usually due to cracked hoses in the vicinity of the battery tray (the LDP and filter are in that vicinity) or going to the charcoal box under the cab, driver side frame rail, behind transmission.

 

Thanks! That's my 83 Firebird that's in the middle of a 383 upgrade. Hopefully that'll be done soon!

Ok, wasn't sure if the o2 sensors had FAILED due to the engine running rich, or if they were CAUSING it!

How many o2 sensors are there total? I see some are marked driver's side; are there more on the passenger side?

Also seeing Rockauto has several varieties... any one that's known to work best?

The EVAP code worried me. Hoping it isn't the intake manifold or some hidden hose somewhere. Might have to smoke it.

Thanks for the reply!

 

Stick with OEM for engine management sensors.

 

P0132 O2 Sensor 1/1 Circuit Voltage High
P0300 Multiple Cylinder Misfire
P0301 Cylinder #1 Misfire
P0138 O2 Sensor 1/2 Circuit Voltage High
P0455 Evap Leak Monitor Large Leak Detected
P0305 Cylinder #5 Misfire
P0306 Cylinder #6 Misfire
P0172 1/1 Fuel System Rich

Start at the plenum, There are tons of posts on it. The v6's didn't have as much of an issue as did the v8's but it still needs to addressed. It alone can cause a lot of issues like PO300.

http://www.hughesengines.com/Index/p...T&partid=26194

Use only NTK 02's, Others don't last especially Bosch.

Check the vac line coming from under the throttle body(left lower side standing in front) it supplies the vac for the evap system. Follow it back to the evap canister/s and check all hoses. You didn't say the last time it got a tune up so new plugs cap rotor and wires wouldn't hurt.

 

On the EVAP side, there's a 5/8" hose that loves to crack at the charcoal canister, as well as the 3/8 hose at the green inspection port next to the battery.

It's possible that the plenum gasket or possibly intake gasket has failed, usually that would be more indicative of a lean condition and/or oil in the intake.

 

Ahh, so no Rockauto then. Dealer? I can't find any online, unless I'm not looking in the right place.


Yes, I have that plenum bookmarked. Really hoping that isn't the case... all this wiring and fuel injection stuff scares me a bit when it comes to teardowns heh

Good to know not to use Bosch.

NTK would be 23099 downstream and 23506 upstream, according to Rockauto. Those are the only two, correct?


OK, I'll check into all the evap areas you've mentioned!

 

But follow magnethead’s tip and fix the O2 sensor problem first, then tackle the Evap problem. Check your harness to the O2 sensors. Since two different sensors are throwing codes it seems unlikely they both went bad at the same time. Look for broken/melted harness wires, bad or loose connector. Know how to use a VOM? Unplug the connector at the O2 sensor and look back into the harness and you will likely see the problem as an open or a short circuit. After you have verified the harness is OK, then spend money on new O2 sensors if needed.

BTW, the reason it runs when you mash the pedal to the floor is that the PCM switches to open loop control and ignores the the O2 sensor output.

 

The 3.9L magnum. Gotta love this engine. I had similiar codes, did a tune up and changed O2 sensors. Still had the problem so I took off the intake....waste of time as it was tight but redid it anyway with new gaskets. Easy engine to see if it's a vacuum leak or not. You can more or less seal the intake holes and ignore all the vac lines just to see if it solves your problem. I've been through this.....no vac leaks causing the problem for me. Sensors for this engine are really inexpensive and there are not that many. The hardest to change is the crank position sensor. It takes allens by the way should you decide to change it but you can't see them. The bolt is a hex head but again if I would have known the allens were there it would of made it a lot easier. Anyway.....I had a bad crank sensor and to make things worse I had to do it twice before I got a good one from advance I believe it was. Misfires and codes were all over the place but never an indication of a bad crank sensor. The only thing that led me to this was the timing jump looking at live data on an actron scanner. It went fron like 14% and then jumped to 23%.....something in that order. It sort of led me to a timing problem and on this engine the cam sensor and crank sensor are responsible for this. Hope this helps.

 

If it's been awhile, I'd start with a full tuneup, plugs, wires, cap, button, air filter, and O2s (especially since you have a code). This could rid of basically all your codes minus the P0455. The O2 sensors being clogged could indeed lead to a rich system, or at the same time, be fouled by a rich running system. Worn plugs/wires/cap/button would cause a weak spark and not burning all the fuel, leading to the O2 reading a rich system. Similar if your air filter is clogged, it's not getting enough air so too much fuel. You'll want to get it done before too long as a rich system and unburnt fuel could lead to a damaged catalytic converter, and that can be an expensive fix.

For the EVAP code, P0455, double check or simply replace the gas cap. The rubber seal could be cracking or simply not holding tight enough to seal the system. Most common evap codes are from a bad fuel cap. Otherwise, vacuum lines between the tank, charcoal canister, and purge valve on the firewall. I was getting P0300, P0301, 303, and 305 (all bank 1 cylinders) if I ran over 70mph, turned out the purge valve was upside down, hasn't returned since flipping it (still testing, been a week, here's hoping). I would assume it being bad/leak could cause it as well.

Best of luck, at least all these repairs are fairly cheap and decently easy.