My 1989 FJ62 4.0 straight 6 runs rough and smells rich until it warms up. After that it runs great. Any ideas/suggestions?
runs rich and rough (2 Viewers)
- Thread starter Michaelinlv
- Start date
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Is this how it has always run or did it just start happening? How are your air and fuel filters? Plugs, cap, rotor, wires, battery cables and connections? Have you checked for vacuum leaks? Does your state smog test?
assuming the above is ok then you might have a bad coolant temp sensor.
assuming the above is ok then you might have a bad coolant temp sensor.
- Thread starter
- #3
It's a new vechicle to me. It's done it since I got it. I'll try a coolant temp sensor
Before you go throwing parts at it you can measure the resistance across the sensor when its cold and when its warming up. Other problems could be bad grounds or low battery charging. If the voltage is low it can send all the efi sensors out of wack. Do you have the Factory Service Manual (FSM)
- Thread starter
- #5
I replaced/
cleaned the grounds when I changed all the belts and hoses. I have a FSM. I'll check it. Thanks
- Thread starter
- #6
Filter was clogged! Washed and dried. No difference. I did find a wire, no connector, that was folded and tucked under the he thermostat housing. I didn't find anything that it looked like it had a a wire missing.
I looked over all the vacuum hoses and all where connected and not cracked. I ordered the coolant temperature sensor. I read all the trouble shooting steps. Any other suggestions?
- Thread starter
- #7
No check engine light when key is on, no jumper in diagnostic port. I'll pull the dash cluster and check the bulb tomorrow,
- Thread starter
- #8
Disconnected the coolant temperature and it started, ran at high idle(1,200rpm) smooth. I shut it off, reconnected the sensor and it ran rough. Maybe Ill disconnected it until the sensor comes in.
- Thread starter
- #10
Did all of that before I posted.
- Thread starter
- #11
I did. Checked all the hoses where tight and not cracked. Sprayed carb cleaner all around the engine in hopes of finding a leak, no change in RPM. Changed cap and rotor, has new plugs. Runs much better when warmed up for 10 minutes.
- Thread starter
- #12
It's rich even when warmed up.
If all the basics are good then the coolant temp sensor is something that is used by the efi computer along with the throttle position sensor and airflow sensor to start and run the truck. Once it’s warm the efi also uses the oxygen sensor to adjust fuel. But a bad coolant temp sensor can cause a lot of issues.
- Thread starter
- #14
Replaced the check engine light. It comes on with the key on but goes out when the engine is running.
So it passes its internal checks at least. Also probably indicates that no sensor has truly failed. As a back seat driver I feel this is related to the coolant temp sensor...which is either sluggish or not reading properly.
I need to look at the 3FE manual but usually you can measure the resistance across the sensor while heating it up in a pot of water on your stove and you should see the resistance change. If you have a fancy DVOM with graphing capability you can plot the resistance over time and inspect the curve for issues.
and even more simply measure the resistance across the sensor when engine is cold and measure it again when its hot and see if it aligns with the FSM
- Thread starter
- #17
The vechicle is running rich all the time. I'm cleaning the throttle body and replacing a cracked air intake hose.
I've got no check engine light. What would cause it to run rough but not cause a check engine light?
I've got one coming.
I don’t know the 3FE efi computer well enough to know the triggers for the check engine light. But a vacuum leak could result in a rich running condition. The extra air would tell the O2 sensor that the engine was too lean and needed more fuel. Or you could have leaky injectors. Or a bad coolant temp sensor. Or an out of wack air mass meter. Or a bad ground or a battery voltage problem. Or a bad fuel pressure regulator or incorrect fuel pressure.
so a few possibilities.
so a few possibilities.
- Thread starter
- #20
I could smell it, used 1/4 tank in 20 miles
