question:
this is for a 87 trans am with a 305 tpi auto

I just changed my spark plugs, wires, and O2 sensor and now the car is running very rough, not so bad in park until it warms up, all around bad in gear.
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Things ive checked so far
vacuum-20 in at idle
fuel pressure 45 psi
continuity(sp?) of o2 sensor wires(purple and the ground)
coolant wires(black and yellow(?))
proper tps operation(starts at around .6 i think and ends up above 4 volts at full throtle)
voltage across o2 is-
with key on run- .4v
with engine running- constant .45v from cold till whenever
engine isnt switching to closed loop(or is it open loop?)
had ign mod checked at autozone to!
no codes at all exp once when i drove it i got a code 13 or 14 for open o2 sensor cirucit
plugs are autoliute spp 26(changing to rapid fires(2)
o2 is a bosch
car ran fine before this with occasional code of open o2 sensor on the highway above 2000rpm after about 2 mins

what do you think o2 or ecm or something else?

Thanks
BM

 

anyone?

 

I know it might sound dumb but here are three things I would check or make sure of before I went father.

1) make sure all the plug wires are ordered correctly on the distributer. I screwed this up once and it took me FOREVER to figure out, and I really felt silly later.

2) the spark plugs were correctly gapped right?

3) check the wiring from the O2, looked for burnt, grounded, or other wise screwed up wires.

If these all check out I'd try to get a hold of a scanner to try and see what the ECM is or isn't seeing.

 

I had the same problem for a while. Was a cylinder not firing. If you have a timing light, you can check each cylinder to make sure you are getting spark to it. If not, try a cap and rotor.

 

If you are measuring O2 voltage, while the sensor is connected, and it always reads .45, then the ECU is fine, and the O2 sensor has an open inside it, or the connection sucks (unless you are measuring on the sensor side of the connector). The ECU will output a bias voltage of .45v all the time, and the O2 sensor has to basically over power it by pulling it low when lean or pushing it up to about 1 volt when rich (in simple terms). When the sensor itself is cold the sensor will not be causing any voltage change. When it reaches a few hundred degrees, it will.

My advice: Check the connection at the O2 sensor, first. Measure O2 voltage on the O2 sensor side of the connection second. If the voltage on the sensor side does change (basically does not read .45 v), then the problem is in the connection. If it also reads .45 V when the engine is running and warmed up, then the sensor is bad, and replace it.

 

dumb ? maybe, but do you measure the volts on the O2 sensor with the key on? i'm only getting .17V at the connector... with a new ecm...

 

If you're just checking the sensor continuity, you can do that with just key on (check for .45V on boths sides of the connector - with the connector still connected of course).
If checking the sensor functionality, you must have the engine running for a few minutes, and check it while running. If the sensor and ECU are working with closed loop on, you'll see the voltage go less than .3V, then switch to greater than .6V, and it should keep doing that back and forth. A single wire O2 sensor may not be able to remain hot enough just at idle, so if it's not switching, try revving the engine to about 2000 RPM and check again. If it ALWAYS stays .45V or so, the sensor is shot. If it always stays low, or always high, the ECU is fighting a lean or rich condition respectively (or it isn't getting into closed loop for some other reason). The ECU has a limit to how far it will try to correct the fueling to get the voltage to switch from low to high and high to low, before it gives up and sets a trouble code.

 

My '89 got to the point where it would stall every time i stopped. Tried everything. Here, it was the EVAP cansiter. The purge solinoid can get stuck open, causing a silent vaccum leak. You don't hear it, and it looks like its ok, but it acts just the same way as a vac leak. I'd say, plug up the tube from the canister to the TB and see if it improves.

Took me a year to figure out this stupid thing was bad.

 

guess i shoulda' said i was checking the lead from the ecu with the O2 disconnected, cold engine (had not been running at all) with the key on, and only getting .17V. i was expecting to get the .45 at least... i believe it can be fighting the rich/lean condition, because i do believe that exists and is not corrected yet, but like i said, it's a cold engine. trying to get a "baseline" to start from. so i'll reconnect the O2 and read it cold again when i can get back to it tonight. thanks. good info on the purge solenoid, too.

KAM

 

I was getting a really bad surging idle, and it ended up being the IAC. ECM was saying it was moving, but it really wasn't. Probably not your current problem, but thought I'd mention it.

 

yea, that IAC issue seems to come up a lot... mines not that old, but isn't there a way to check it for proper operation? seems to me there is a way, but may replace it anyways...

KAM

 

Hey, just and update, the o2 sensor i put in was new, maybe 10 miles on it. I ended up doing the shop manual test on it and acording to the book its the senor. So last night i started to take it out, i move the wire coming out of the o2 and it fell out! Ouch that sucks, so i start taking the o2 out, it isnt moving, ended up rounding it off! that sucks, now its take the manifold off or drive it to my mechanics. grrr

anyways i found out the other day that if you jump the aldl with the engine running, the check engine light will flash fast for open and slow for closed, so i do this test and after about 2 min it will flash slow, then go back to flashing fast, and will keep repeating this. Odd, anyone have this before

 

oh yeah, triple check the plug wires, sparks are gapped at .035 or is it .35 anyhoo, and wireing is fine

anyone know about how much a scanner is? and where do you get one?

 

i did this today, and when disconnecting the tube from the canister, the idle increased til i plugged the tube with my finger, then it almost stalled out - is that how it should work, or if it stumbles like that it means it's bad? when i pulled the tube and the idle increased, it ran fine. for the most part, it still runs fine with that stuff being connected... mine's not stalling each time i come to a stop, but there's been a few occasions where it wanted to.

KAM

 

The "Official" way to check the EVAP canister is:

Place a bit of tube on the bottom inlet. Try to blow into it. If you can, its bad.

If you can't, apply 15"hg of vacuum to the top inlet. It should hold for 20sec. If not, it's bad. IF it holds, try blowing through the bottom again. You should be able blow air into it freely this time. If everything checks out, the canister/solinoid are ok.

Next, you check the Fuel Pressure Control Valve. Its a black disk looking thing plumbed inline just before the EVAP. Pretty much same deal. Shouldn't be able to blow through the bottom unless you have 15"hg of vacuum on the top inlet, and it should hold vacuum for at least 20 sec. Otherwise, its bad.

If you just plug up the line going into the bottom, which actually leads to the Throttle Body, you are essentially removing the EVAP from the equation, and you would have to drive the car around some to see if your problem has been fixed or not.

 

well i guess mine's bad cuz i can blow in to it like there's no tomorrow. no resistance whatsoever. as for the fpcv, both hoses are "tee'd" together in to one, which goes to the lower inlet of the solenoid, so they're not separate.

KAM

 

Yeah.. thats how it is suppose to be. If the canister solinoid is energized by the 'puter, it lets the canister purge, which means it lets the canister suck up fuel vapor into the throttle body using the vacuum. The bottom hose, going to the other vavle would have the same amount of vacuum as the rest of the lines, and thus open the valve and let addtional vapor in from the gas tank, at the the same time. The T is just a good way to do it with less hose.

 

I don't know if they are all the same but I have a canister from an 85 Iroc-Z that's for sale if anyone is interested

 

yea, mine's different than that. got a new one on order, but thanks for the offer.

KAM