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).]
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?
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.
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.
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.
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.
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).]
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 :/
The proper one will have a brass end that sits in the coolant flow. The other temp sensor with an oval head that's acttually a 4th temperature sensor goes into the air filter canister. It has a mesh type shield over it's sensor.
The ECM temp sensor under the thermostat housing actually screws into a threaded reducer, so it may appear to have different thread sizes.
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.
A LOT of extra fuel. And the car will run like s***. I had a failed coolant temp sensor, and on my scanner the ECM was seeing a reported temperature of -40dF. Cold air is denser, so...lots of extra fuel and lousy gas mileage.
Same thing happened on my 87 and it was sudden while sitting at a traffic light. I made it to a friends shop and the scanner said it was -28*. It actually ran better when I disconnected it to go to the parts store to get another.
You can see the reducer for the Coolant Temperature Sensor in this illustration.
[This message has been edited by fierofool (edited 01-13-2020).]
I disconnected the correct one and it’s still giving me trouble. I still have to see what will happen if I put the new one in there. I just haven’t been able to get the reducer off the old one.
Yeah, it won't run great, but I think the ECM goes to a default mode if the sensor is unplugged. Not quite so rich.
The reducers are standard items at hardware or plumbing supply stores. If a vice and pipe wrench or 2 pipe wrenches won't sepadrate them just take along the new sensor to match the female thread and the old reducer to match the male thread. They are both standard pipe threads. Assemble them with some plumbers pipe dope. A brass reducer might be a good replacement piece.
[This message has been edited by fierofool (edited 01-14-2020).]
Yeah, it won't run great, but I think the ECM goes to a default mode if the sensor is unplugged. Not quite so rich.
The reducers are standard items at hardware or plumbing supply stores. If a vice and pipe wrench or 2 pipe wrenches won't sepadrate them just take along the new sensor to match the female thread and the old reducer to match the male thread. They are both standard pipe threads. Assemble them with some plumbers pipe dope. A brass reducer might be a good replacement piece.
Would the EGR valve be causing this problem you think? The previous owner told me a long time ago that there was something wrong with it but I brushed it off. Would it be causing the engine to run this rich.
Yeah, it won't run great, but I think the ECM goes to a default mode if the sensor is unplugged. Not quite so rich.
The reducers are standard items at hardware or plumbing supply stores. If a vice and pipe wrench or 2 pipe wrenches won't sepadrate them just take along the new sensor to match the female thread and the old reducer to match the male thread. They are both standard pipe threads. Assemble them with some plumbers pipe dope. A brass reducer might be a good replacement piece.
If you have a vice and the right size impact deep socket on the old sensor, you should be able to remove the fitting. You might need a "torque multiplier" - using a pipe slipped over the ratchet or preferably a breaker bar.
I got in my trusty '88 Formula this morning, started it up... and the engine sounded like it was running on somewhat less than six cylinders. It was very rough. I was quite puzzled as the car has always run so well. I turned off the engine, opened the decklid, and looked around. There didn't appear to be anything visually wrong. So I left the decklid open, started the engine again, and went to have another look.
And then I noticed something really weird.
It's probably the original EGR valve on this 2.8 engine... and it was looking mighty strange. I didn't take a picture of it on the car, but the picture below is what the EGR valve was looking like while the engine was running. There appear to be three rivets that hold everything together, and anyway... all three rivets had let go, probably due to 30 years worth of corrosion. (EDIT - I just noticed in my image below that two of the rivets had probably rusted away long ago, and the last one finally let go.) So while the engine was running, the pressure of the exhaust was pushing the entire diaphragm housing of the EGR valve up as far as can be seen in the image below. The end result was that the engine was struggling to run with the EGR valve wide open.
I pulled the EGR valve off a GT parts car here, and the Formula is now happily purring again.
