85 GT running rich? (Page 1/3)
GravityKat JAN 10, 12:18 AM
Hello! This is my first post here and I’ve come here because I’m completely clueless on what is going on with my fiero.
Ok so. I’m not very experienced with cars whatsoever. This is my first project.
So what is going on with the car is. It seems to be running very rich in the beginning when the engine is cold. To the point where it gets flooded every time I crank it cold. I have to hold the throttle to the floor to get more air in the mix and crank it for a while for it to finally start.
After I get it running it will immediately die unless I keep giving it throttle. Once it warms up however it will idle. Very poorly. It isles at about 500-600rpm and dies most of the time after idleing for about 3 min or so.
Now if I give it throttle it revs up nicely but if I give it steady throttle the rpms will rise by itself and eventually die.
I can put it in gear and take off semi easily but it will buck really hard and start to die. When I give it throttle to try to get it going it will eventually catch again but only for a little before it starts to buck again.

So far this is what I’ve replaced in the car to try to fix the problem.
Fuel pump (45 psi)
IAC valve
O2 sensor
Distributor cap and rotor
Spark plug wires
All the spark plugs
Fuel filter
Coolant temp sensor

I tested the throttle position sensor with a meter and it has all the right voltage and has a smooth increase and decrease when I move the rocker arm.
If anyone has any suggestions on what might be going on please help me out here.
Thanks :/

[This message has been edited by GravityKat (edited 01-10-2020).]

fierobear JAN 10, 12:30 AM
Assuming all of the above listed are not a problem, and no engine codes being set, maybe a stuck cold start injector?

[This message has been edited by fierobear (edited 01-10-2020).]

fierosound JAN 10, 01:05 AM
MAT (Manifold Air Temp) sensor in air cleaner.
Sounds like ECM thinks it's really cold out.

Check sensor's resistance across it's connections with an ohm meter.





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[This message has been edited by fierosound (edited 01-10-2020).]

GravityKat JAN 10, 01:07 PM

quote
Originally posted by fierosound:

MAT (Manifold Air Temp) sensor in air cleaner.
Sounds like ECM thinks it's really cold out.

Check sensor's resistance across it's connections with an ohm meter.







I’ll check it out for sure. I was getting an error code for it but I didn’t think it would affect the vehicle that much. Would it be possible to run the car without that sensor connected?
fierosound JAN 11, 07:38 AM

quote
Originally posted by GravityKat:

Would it be possible to run the car without that sensor connected?



That's basically what it is IF it's not working properly.
You already know what the answer is.

[This message has been edited by fierosound (edited 01-11-2020).]

fierofool JAN 11, 09:27 AM
You say you replaced the coolant temperature sensor. The one on the head or the one under the thermostat housing neck? The two are often referred to by the same name. Just wondering.
GravityKat JAN 11, 04:25 PM

quote
Originally posted by fierofool:

You say you replaced the coolant temperature sensor. The one on the head or the one under the thermostat housing neck? The two are often referred to by the same name. Just wondering.



I only replaced the one on the head... I didn’t know there was another one.
fierobear JAN 12, 03:16 AM

quote
Originally posted by GravityKat:


I only replaced the one on the head... I didn’t know there was another one.



Technically, there are *3* temp sensors. One goes to the ECM (coolant temperature sensor), one goes to the gauge on the instrument panel, and the third turns on the radiator fan.
fierofool JAN 12, 08:07 AM
The one on the head doesn't affect the runability of the engine. It is only for the gauge and temp light. The one underneath the thermostat housing, just above the water pump sends engine temperature to the ECM and that controls the fuel injectors. If that sensor is reading cold, it will dump more fuel into the engine.

If the sensor they sold you for the head required cutting and splicing on a new harness end, they sold you the one that should be installed above the water pump. The gauge sensor has a round plastic head with a slot in the side. The ECM temperature sensor has an oval plastic head.
GravityKat JAN 12, 09:03 AM

quote
Originally posted by fierofool:

The one on the head doesn't affect the runability of the engine. It is only for the gauge and temp light. The one underneath the thermostat housing, just above the water pump sends engine temperature to the ECM and that controls the fuel injectors. If that sensor is reading cold, it will dump more fuel into the engine.

If the sensor they sold you for the head required cutting and splicing on a new harness end, they sold you the one that should be installed above the water pump. The gauge sensor has a round plastic head with a slot in the side. The ECM temperature sensor has an oval plastic head.



That is the one I bought! I never fully spliced everything so I’m gonna go see if I can swap them.

Update: I looked and the thread size is different on the one they sold me. It has the oval head but it doesnt fit in the hole for the spot under the silver coolant cap :/

[This message has been edited by GravityKat (edited 01-12-2020).]