What have you done to your vehicle today?

[TransAmDan]

From what you said, I would think O2 sensors or that area. They control the fuel trims +/-20% in the ECU. If the PCM is reset, these go to zero. They don't learn until up to temperature, then it's in closed loop learning. Obviously is the mixture goes too far either way then idle troubles will happen. Did you say it seems to run fine when driving? This would then point me in a direction of an exhaust leak before the O2 sensor(s), the amount of air on idle compared with exhaust fumes would be higher than driving so it may affect it more on idle. Does the O2 sensor have a single wire? if so it needs to get an earth to read correct, usually it gets it from the block conducted via the exhaust, if there is corrosion then community could be impacted. Perhaps use an Ohmmeter between the base of the sensor and 0V battery, if this isn't close to zero it will affect the reading from the O2 sensor(s) fooling the ECU.

 

[AmericanThunder]

Its really interesting you mention the O2 sensor as this is the other area I need to explore.
The O2 sensor is new'ish replaced in the last 18 months, but the Fiero is known for cracking one of its exhaust manifolds, the forward one (transverse V6). And yes this car is no different.
Its been like it for over 5 years which is why I'm hesitant to replace it but also because they are hard to come by, and although headers are available they are expensive.
Its entirely possible that the exhaust crack is pulling air in which is giving the O2 sensor incorrect readings, too lean, and therefore its trying to compensate.
It is a single wire O2, and I have checked resistance between the block and the negative battery terminal before and its minimal. I suppose I could disconnect it, but would that throw a code and keep it in closed loop? If so that would stop it reading other sensors too so wouldn't help diagnose it.

Its not a job I'm looking forward too, as its easier to remove the head than just the exhaust manifold. And of course that means pulling the 3 plenum intake manifold and all its associated vacuum hoses and plumbing of which there is stacks!!
I might see if disconnecting one of the dog-bone engine mounts would enable me to tip the engine far enough back to avoid pulling the head.

On the other hand....... its insured......:flame::flame::flame: :clown:

 

[an88fiero]

On the other hand....... its insured......:flame::flame::flame: :clown:

Watch it :jaw:................ note to oneself - hide the lighters and matches lol

 

[an88fiero]

Oh - I might have sourced a cheap "pair" of exhaust manifolds - he's checking on shipping costs ..............

 

[TransAmDan]

How does the engine come out of the Fiero? does it drop out the bottom? maybe it will make it easier to change the manifolds. Although probably a lot or wires to unplug and get back correct without crushing them. Not a job I would like to do. I see you have a keen inhouse mechanic.

 

[AmericanThunder]

You can drop the engine out of the bottom by removing the entire cradle and transaxle. You can pull it from the top leaving the cradle and transaxle in place.
It would easier to just pull the heads again - they have been off in the last few years when i rebuilt the top end. I just didn't want to do it again right now - I'd rather be driving the Challenger!!! :burnout:

 

[July92RS]

Get it to your MOT guy on a Friday night,See if he will let you go down there the following morning and do a live reading test on the emissions from cold so you can see what is happening as it warms up

 

[AmericanThunder]

Get it to your MOT guy on a Friday night,See if he will let you go down there the following morning and do a live reading test on the emissions from cold so you can see what is happening as it warms up

Not a bad idea - I actually could do this at home as I have one of the Gunson exhaust sniffers.

 

[July92RS]

Does that give you HC CO O2 and A/F ratio

 

[AmericanThunder]

Just CO IIRC - Its been ages since I used it properly.

 

[July92RS]

Just CO IIRC - Its been ages since I used it properly.

Get it on the 4 gas,do a search for some "good "live readings so you can compare them as see where you go from there

 

[AmericanThunder]

Get it on the 4 gas,do a search for some "good "live readings so you can compare them as see where you go from there

Well the spare parts will arrive before my MOT man returns from holiday, so if nothing else I will have eliminated 3 other possibilities.

 

[CorvetteAl]

Hi Thanks Chris, not sure about doing it myself, will tackle most things but a carb is a little complex for me.

 

[AmericanThunder]

And the Fiero is fixed!
Replaced 3 sensors at once so no idea what the faulty part was!!

The three sensors replaced were the IAT (intake air temperature), the temp sensor (PCM not the gauge), and the MAP (no MAF remember). I had previously tested the IAT with an ohm meter and a hot air gun and found the readings in tolerance but it looked like it had seen 28 years of service so it got replaced. The MAP was replaced as it was a possible fault and cheap, but the real culprit in my mind was the temp sensor. If this sensor was failing/failed then as the PCM moved into closed loop it would believe the temp to be something Arctic and put the engine into an extremely rich mode!!
We'll likely not find out unless it plays up again as this point it's just a reliefs and I'm not going to muck with it. I suspect the TPS has a little more learning to do and I think a 'blat' down the local dual carriageway is in order over the weekend.

Now..... Beer assistant!!!

 

[Chriswrx123]

Are well done ... Another headache fix fingers crossed

 

[an88fiero]

A very happy bunny here ........... Now to drive her and get my enthusiasm back as she almost got sold!!!!

Woohoo!!!!!

 

[saleen 192]

:clap2::clap2::first::clap::thumbup::thumbup:

 

[Chriswrx123]

Car washing today yippee got 3 cars and 1 caravan to wash inside and out still it will be a good test for the di vessel

 

[TransAmDan]

And the Fiero is fixed!
Replaced 3 sensors at once so no idea what the faulty part was!!

The three sensors replaced were the IAT (intake air temperature), the temp sensor (PCM not the gauge), and the MAP (no MAF remember). I had previously tested the IAT with an ohm meter and a hot air gun and found the readings in tolerance but it looked like it had seen 28 years of service so it got replaced. The MAP was replaced as it was a possible fault and cheap, but the real culprit in my mind was the temp sensor. If this sensor was failing/failed then as the PCM moved into closed loop it would believe the temp to be something Arctic and put the engine into an extremely rich mode!!
We'll likely not find out unless it plays up again as this point it's just a reliefs and I'm not going to muck with it. I suspect the TPS has a little more learning to do and I think a 'blat' down the local dual carriageway is in order over the weekend.

Now..... Beer assistant!!!

Brilliant, sounds like its fixed. If a temperature sensors goes it thinks its -40. Mine broke down inside, the problem would come and go until I replaced it.

i bet you are glad that fix is complete. did you get your beer?

 

[Chriswrx123]

Well washed all 3 black cars in an hour using the two bucket method and rinsed off with hose pipe going though the di vessel and left to air dry. Tested the water coming out of the di vessel and it contained less than 10 ppm of tds total dissolved solids before di vessel was 456ppm any thing under 500 and southern water is happy.. The result