1991 Toyota Corolla



April, 11, 2009 AT 3:17 PM

Engine Performance problem
1991 Toyota Corolla 4 cyl Front Wheel Drive Automatic

1991 Toyota Corolla - 4FAE Engine Type. Automatic.
VIN: 2T1AE94E6MC074888. Mileage: 216,834 kms

Concern: Failed emissions test

1st test:
ASM2525 Curb Idle
Limit Reading Limit Reading
HC ppm 68 39 200 19
CO % 0.38 0.02 1.00 0.00
NO ppm 789 1305 N/A N/A
RPM 1876 RPM 898
Dilution 14.5 Dilution 14.4

Repairs Performed:
• Replaced Catalytic Converter
• Replaced 02 Sensor
• Changed Oil & Filter (Synthetic)
• Replaced Spark Plugs
• Replaced Air Filter
• Drove vehicle 150kms

2nd test:
ASM2525 Curb Idle
Limit Reading Limit Reading
HC ppm 68 67 200 23
CO % 0.38 0.00 1.00 0.00
NO ppm 789 2374 N/A N/A
RPM 1865 RPM 1023
Dilution 14.0 Dilution 14.0

Other Notable Issues and Repairs:
• Slow to start cold: Turns but doesn’t fire. Leave ignition on for 3-5 seconds and its okay.
• Fans come on with ignition (Defrost and A/C not engaged) Replaced Fan Switch - Okay
• Cleared all codes - Ran to operating temp and re-tested: Code 43 (Starter/Ignition/ECU) Didn’t repair, Code 22 (Coolant Temp Sensor) Replaced Coolant Temperature Sensor – still get Code 22. Check engine light only comes on when accelerating from standstill, goes away at cruise or decel.
• Oil Light comes on (solid) as vehicle warms up. Not noted earlier as: Check Engine Bulb & Oil Lamp Bulb had been removed. No engine noises noted. Replaced Sender - Okay
• Compression 180psi all cylinders.
• New plugs and oil exceptionally clean (lean burn?), However, has only been run for 250kms.

Other Repairs Performed:
• Cleaned Throttle Body
• Ran 2 cans of combustion cleaner through engine
• Replaced Fuel Filter and PCV Valve
• Rewired 02 Sensor (Connector had been crossed I verified on known good car & wiring diagram)
• Retarded timing 2 degrees
• Filled with 91 Octane fuel
• Drove vehicle 150kms

3rd test:
ASM2525 Curb Idle
Limit Reading Limit Reading
HC ppm 68 66 200 42
CO % 0.38 0.48 1.00 0.07
NO ppm 789 1136 N/A N/A
RPM 1895 RPM 930
Dilution 15.5 Dilution 14.4


5 Answers



April, 12, 2009 AT 6:43 AM

I would change the distributor including the module and coil.

But the main problem is the coolant temp sensor, if the sensor is new and you are still getting the code, it will make the engine run rich and fail emmissions.

Might be worth a try to return the one you bought as defective, put a new one in and see if code goes away. Clean the electrical connections to sensor with electronics cleaner. If code still appears, then wiring or ECM.

If coolant temp sensor fails, ECM will set a default coolant temp so engine will run. This is usually very low temp (-40), so as not to damage the engine with a lean condition.

If you can, check fuel pressure with mechanical gauge (a special tool set is required since there is no factory test port in rail).
Set timing back to factory specs, 10 degrees, I believe.
Run 87 octane, 91 is not necessary. High octane gasoline burns slower than 87, 93 octane burns slower than 91.

Many people believe that high octane burns cleaner. This is not true. It is only true on engines designed to run on it e.G. High compression or turbocharged/supercharged engines.



April, 13, 2009 AT 9:13 AM

In your response you recommended changing out the Distributor, Module and Coil is this to correct code 43? I initially retarded the timing and increased fuel octane in an attempt to cool the cylinders and reduce NOX.I will now set back to specs. There are a number of (4) 'coolant sensors/switches' in and around the thermostat cover. I have identified the cooling fan swich and of course the temp guage unit however just to be sure can you confirm the location of the coolant temp sensor as located in the front of the stat housing pointing to the front of the vehicle and wired Green/Black? I replaced this from a known good vehicle (not new) and did clean all connections as you suggested, should I check with an ohmeter or just replace with new? Thanks for your timely reply!
PS The vehicle runs extremely well regardless of the current issues.



April, 14, 2009 AT 7:37 AM

I believe the coolant temp is orange connector on front of housing, there is also a green one on rear of housing, can't exactly remember what it is but I have never changed one on a 91.



April, 15, 2009 AT 8:03 AM

I still have a small dilema that hopefully you can assist. There are 4 swiches/sensors in the stat housing: The Fan Controller Switch, the temp guage sender and 2 coolant sensors. The dealer only has a listing for 1 coolant sensor: the smaller one at the rear of the stat housing (lower rad hose) I had to replace this one as I broke it upon removal however it tested good with an ohmmeter. The larger one is not listed it is located at the front of the stat housing (upper rad hose) and is wired green/black. I tested this also and cannot get a resistance change when cooled/heated. Finally my question: Which is the correct sensor and could you provide me with a part #?
Thanks in advance,



April, 16, 2009 AT 6:53 AM

The front one (dark orange) is coolant temp. the one that is closest to radiator. The one wire is gauge sender, then fan switch (points towards battery) next is Bi-Metal switching valve, has two vacuum lines coming out. The rear one next to waterpump hose is the one I can't remember, the connector is green.

Toyota should have all these, I have purchased most of them in the last year.
Talk to a different Toyota dealer parts dept.

You can also get these at junk yard from 90-92 Toyota Corolla or 90-92 Geo Prizm.

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