FJ62 Water temp sensor replaced but maybe now bad ECU?

[Swamp Possum]

First time posting a question.

I've got a 89fj62 that is having a hard time staring in the morning after sitting all night. It will run after multiple attempts at cranking and it not smooth until it warms up and then it's fine. I can drive it all day without further problems. The check engine light is on and the code flashes water temp sensor. I've replaced the sensor with new connectors and the problem still persist. I've checked the continuity of the sensor, the wires going back to the ECU, and everything checks out. I've followed the FSM steps and it lead me to believe the ECU is bad. Are there anymore test that I can run before buying a replacement and where is the best place to get one? Thanks.

-Mike

 

[SteveH]

It will run after multiple attempts at cranking and it not smooth until it warms up and then it's fine.

Have someone else start it while you smell and look at the tailpipe as it starts. Lots of black smoke could indicate a fuel problem (way too rich), and/or an sweet antifreeze smell could mean your spark plug(s) are wet when starting (head gasket). I would baseline a lot of stuff before I assumed that the ECU may be bad.

(You may have done all this, I'm just passing it along in case you haven't).

 

[Swamp Possum]

I definitely think its a fuel related problem.

So maybe I should give a bit more of back story. I recently replaced the front timing cover gasket, thermostat, water pump, water temp sensor, and replaced all the coolant. The starting issue came after those repairs. I also replaced the con rod bearings and main bearings (but really don't see how that would affect this).

When I crank it white smoke comes out for a bit, but just until it warms up. My belief is that the computer is not getting the signal from the water temp sensor to let run it rich upon initial start up, because its cold. It will also have a some hesitation when shifting through the gears (H55 Conversion) but that doesn't last long, and she starts to run fine.

-Mike

 

[fl4031003]

Have you cleaned your cold start injector? And/or checked that the CSI is getting a signal?

 

[CaptHamster]

I see you've already done this, but really check and make sure the connector is seated and the wires are run right. I struggled with a water temp sensor issue and ended up having to purchase a connector repair kit (thanks @ToyotaMatt ) and running new wiring out to the connector. My symptoms on an otherwise running FJ62 were the exact same as yours, starting was difficult and it ran terribly until it warmed up. It was very intermittent until I was able to replace the sensor and repair the connector.

When the ECU does not receive a water temp sensor signal, I believe it defaults to a pre-set temperature to tell the ECU; unfortunately I'm pretty sure that temperature is "hot" probably 190F, which means the mixture is leaned out until the engine starts warming up to that temperature. I can't imagine the ECU as a whole would be bad based on that one symptom but stranger things have happened!

 

[Swamp Possum]

I see you've already done this, but really check and make sure the connector is seated and the wires are run right. I struggled with a water temp sensor issue and ended up having to purchase a connector repair kit (thanks @ToyotaMatt ) and running new wiring out to the connector. My symptoms on an otherwise running FJ62 were the exact same as yours, starting was difficult and it ran terribly until it warmed up. It was very intermittent until I was able to replace the sensor and repair the connector.

When the ECU does not receive a water temp sensor signal, I believe it defaults to a pre-set temperature to tell the ECU; unfortunately I'm pretty sure that temperature is "hot" probably 190F, which means the mixture is leaned out until the engine starts warming up to that temperature. I can't imagine the ECU as a whole would be bad based on that one symptom but stranger things have happened!

I put on the new connector that came with the WTS but I'm curious how much it matters if I got the wires swapped on accident. Do you think that matters? I didn't think it would.

I have check the wires leading from the connector to the ECU and there doesn't appear to be a break and i checked the new WTS with my tester set on continuity. Wouldn't that tell me everything is good?

I'll look into the cold start injector this afternoon.

 

[Swamp Possum]

I think I've fixed the problem. The cold start injector switch and the water temperature sensor conectors are identical. I must have switched them during the reinstall. I also got the locations confused and put the new water temp sensor in the cold start injectors port. I'm going to swap them all around and we should be good. I'll keep yall posted and thanks for the help.

 

[cruisermatt]

That is a plausible cause, however they are not the same connector, they are close but not the same. The only way they could be swapped is if the connectors were broken or cracked.

 

[cruisermatt]

In the middle of this right now on @jesus888 FJ62.

 

[jesus888]

In the middle of this right now on @jesus888 FJ62.

View attachment 3120933

View attachment 3120934

Ha! I just read and "watched" this thread when I read his issue... Get r done!

 

[Swamp Possum]

That is a plausible cause, however they are not the same connector, they are close but not the same. The only way they could be swapped is if the connectors were broken or cracked.

You nailed it. My connectors are old and brittle, and they were damaged enough to fit in the wrong sensors. I've searched online but having a hard time just finding replacement wire connectors. I need one for the cold start injector switch and the cold start injector itself. Do yall have a good source for those?

-Thanks

 

[cruisermatt]

You nailed it. My connectors are old and brittle, and they were damaged enough to fit in the wrong sensors. I've searched online but having a hard time just finding replacement wire connectors. I need one for the cold start injector switch and the cold start injector itself. Do yall have a good source for those?

-Thanks

Yes, my shop carries them along with every 3FE electrical connector

We also restore 3FE harnesses for anyone interested in sending theirs in.

 

[Swamp Possum]

Yes, my shop carries them along with every 3FE electrical connector

Nice! I'll shoot you and email.

 

[Spook50]

Yes, my shop carries them along with every 3FE electrical connector

We also restore 3FE harnesses for anyone interested in sending theirs in.

Stumbled on this while searching around for data on the engine temp sensor (the actual sensor, not the sender); but as for the harnesses, have you considered if it's economically feasible to build and sell complete new FJ62 engine wiring harnesses?

I've toyed around with the idea of building an entire new harness for mine but since I'd have to have a complete harness to duplicate (and with the myriad other projects I have) it's gone on the back burner. The WAY back burner....

 

[toy_tek]

I've toyed around with the idea of building an entire new harness for mine but since I'd have to have a complete harness to duplicate (and with the myriad other projects I have) it's gone on the back burner. The WAY back burner....

We think alike. I have a spare harness that I want to go through for basically the same reason. However it’s also pretty far down the project priority list

 

[Spook50]

We think alike. I have a spare harness that I want to go through for basically the same reason. However it’s also pretty far down the project priority list

Just looking at the removal of the engine harness looks to be a bear of a job in itself, given how much it interconnects and the fact that it goes through the firewall. Sure wish it used a bulkhead connector at the firewall.

One good thing if I were to build a new one for myself is there are several unused connections since I desmogged that I could eliminate completely from the harness, along with using good silicon insulated wire and nice new wire loom to build the new one. THAT would be nice.