Gasoline/Fuel Diluting Oil - 3FE Cold Start Injector? (1 Viewer)

Joined
Nov 22, 2020
Messages
8
Location
Birmingham
Hi MUD, 1991 FJ80 with the 3FE and 235K miles on the clock. I’m getting measurable and visible gas in the oil (and crankcase). Using Rotella 15w40 and the viscosity was so low that the oil was dripping from the dipstick after about 1,500 miles. Oil was black and smelled like gas during the resulting oil change. I’ve read that it’s probably either worn piston rings or a stuck injector. Also, I may have a thermostat stuck open (could that result in the excess fuel?). Hoping you can point me in a direction here to diagnose. Thanks MUD and appreciate you all!
 
Joined
Nov 9, 2012
Messages
13,239
Location
Olathe, KS, USA
Hi MUD, 1991 FJ80 with the 3FE and 235K miles on the clock. I’m getting measurable and visible gas in the oil (and crankcase). Using Rotella 15w40 and the viscosity was so low that the oil was dripping from the dipstick after about 1,500 miles. Oil was black and smelled like gas during the resulting oil change. I’ve read that it’s probably either worn piston rings or a stuck injector. Also, I may have a thermostat stuck open (could that result in the excess fuel?). Hoping you can point me in a direction here to diagnose. Thanks MUD and appreciate you all!
Stuck injectors, period.

One or more are shorted open. Check wiring harness.

Change oil before running it more or bearing damage will occur.
 
Joined
Jan 19, 2005
Messages
3,666
Location
South west utah
What he said ☝️☝️☝️
 
Joined
Nov 22, 2020
Messages
8
Location
Birmingham
So doing a little more reading and looking at the engine bay this afternoon. I think the issue may be the cold start thermo sensor at the thermostat. The connector is broken and is hanging down. This sensor opens the cold start injector (7th injector) on the 3FE intake manifold. I think the cold start injector is stuck open because the sensor is broken or grounded. I’ll test this and report back hopefully in a couple of weeks when I have some time. Thanks @BILT4ME for getting me on the right track.
 
Joined
Nov 9, 2012
Messages
13,239
Location
Olathe, KS, USA
So doing a little more reading and looking at the engine bay this afternoon. I think the issue may be the cold start thermo sensor at the thermostat. The connector is broken and is hanging down. This sensor opens the cold start injector (7th injector) on the 3FE intake manifold. I think the cold start injector is staying open because the sensor is broken or grounded. I’ll test this and report back hopefully in a couple of weeks when I have some time. Thanks @BILT4ME for getting me on the right track.
That sound very logical. I was thinking the 7th injector, but I don't know enough about the 3FE to diagnose everything.
 
Joined
Sep 17, 2016
Messages
6
Location
Fort Collins, CO
So doing a little more reading and looking at the engine bay this afternoon. I think the issue may be the cold start thermo sensor at the thermostat. The connector is broken and is hanging down. This sensor opens the cold start injector (7th injector) on the 3FE intake manifold. I think the cold start injector is stuck open because the sensor is broken or grounded. I’ll test this and report back hopefully in a couple of weeks when I have some time. Thanks @BILT4ME for getting me on the right track.
My FJ62 needed new water pump & thermostat so I left it parked over the winter. Got everything done this week and found the car to be very hard to start. It has never failed to start in all kinds of horrid temperatures (I'm in northern Colorado close to Wyoming) so I was baffled. Car started after weather warmed up a bit and I finally figured out I had busted the 'cold start injector time switch' connectors. Live & learn...

Also, the water pump job sucked...
 
Joined
Mar 11, 2022
Messages
139
Location
California
So doing a little more reading and looking at the engine bay this afternoon. I think the issue may be the cold start thermo sensor at the thermostat. The connector is broken and is hanging down. This sensor opens the cold start injector (7th injector) on the 3FE intake manifold. I think the cold start injector is stuck open because the sensor is broken or grounded. I’ll test this and report back hopefully in a couple of weeks when I have some time. Thanks @BILT4ME for getting me on the right track.
The cold start injector circuit only works off the voltage from the key in the start position. If the key is not in the start position, the injector will not get voltage, regardless of the thermo time switch. The injector could still be stuck open, however. For the rings to be bad enough to cause fuel in the oil, the engine would be running like utter poop. I'd pull the injector rail with all injectors and cold start injector attached. Zip tie the injectors to the rail so the fuel pressure doesn't pop them out. Turn the key on, and then either push the airflow meter flapper open, or jump the fuel pump terminal in the check connector to turn on the fuel pump. Check for any fuel coming out of any of the injectors.
 

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