Hello All, I just replaced the engine in my sc 400 because the original threw a rod. After the new V8 was installed the car began to do very weird things after it would warm up. When we first started the motor after the install it started right up with no issues. After we drove it a while the temperature gage would go up all the way pass the hot mark and then the car would start to miss (idling very rough with no Power). The gage will then come back down to normal and the car will drive fine. Even though the gage reads hot it really is'nt overheating. If you drive the car and the temperature gage reads hot the car will idle really rough and there will be no power but then the gage will come back down and it will run perfectly. This problem has baffled about 4 different mechanics so far and at this point I do not know what to do. Another issue that we think could be the culprit is that there is a sensor that is in the intake manifold right between the coil (under the coil) at the front of the engine and the thermostat which has nothing conected to it. My mechanic that did the install said that there was nothing in the wire harness that connected to it. I find it hard to believe Lexus would just put a sensor there for no reason. As you can imagine coils, injectors, sparkplugs etc have been checked. PLEASE HELP. Thanks.

 

What year is the new engine from?

 

I am not sure what year the engine was from but I had to use my original intake manifold because it was a little different from the one that came out the car. I got the engine with the car and I tried to call the salvage yard to find out which car and year it came from but nobody was able to help.

 

I had this same problem, after I installed my modded engine in my 97 SC4 that I use to have :

http://www.lextreme.com/forums/showthread.php?t=4865

Drove me crazy for a few days. Scary cuz you think the engine might be over heating, but its not. Will run fine sometrimes just like you said then temp guage shoots up and engine starts running like crap. I put a temp guage in the thermostat housing when it read hot and it was at normal temp.

This was the problem and fix :

The motor had a ground wire that is ground to the motor on the back behind the Tranny upper housing that actually did not need to be disconected to remove the motor because it come from something on the motor and is ground to the motor. I found out by taken it to the Lexus dealer and the shop Guru researched and pointed the tech to look for it. Sure enough he found it but could not get to it, and thought that the tranny had to be removed to get to it. After awhile he was finally able to get to it, ground it back and problem was fixed. I forgot which wire it was, but it does not ground to the frame or engine bay, it grounds to the morot from the motor on the back upper end behind the Tranny.

 

dmcclymo, do you still have your old motor that blew ? If so do you have the Crank pulley/Damper. I'm trying to find out how much the stock Damper pulley weights, and get some front, side and back pics of it.

Also possibly want to buy one from somone if they have one. Can you let me know.

 

If you used your old intake manifold, you might have gotten a 92-94, did you see an extra injector on the new engine's intake manifold? That's a sure sign of 92-94, you might have gotten a 95 too, I don't know myself, but I've HEARD (cannot verify) that the 95-96 had different intake manifolds too.

 

That not his problem, has nothing to do with it.

 

Thanks for the help. I will call the shop to see if they still have the motor and i will let you know.

 

Thanks, will wait to hear from you. When I saw your thread I knew excatly what you were talking about. If you don't figure it out, post up and I'll try to call the shop and ask if they have it Documented or remember. That problem drove me crazy. That disconected ground throws the ECU off.

 

jgscott, I spoke to my mechanic and he told me the recycling guy picked up the motor and the only thing he kept was the intake manifold from the donor motor. I forgot to mention that the engine and the transmission was taken out together so I guess when it was put back in they forgot to reconnect the ground. Anyway, tomorrow we will try to find the ground. I will keep you posted if we find it. Thanks to you and everyone elso who gave help.

 

i was just curious on what motor he might have had. But if you think about it the motors change compression, and cams. And don't the 97+ have vvti? or is it 98+?

 

The 98+ came with the vvti. I am still trying to figure out what motor I actually got. I am thinking it has to be 93 to 95.

 

I'd go with the suggestion above about the tranny ground.

Your mechanic should keep your existing wiring harness and plug it to the newer motor. That way, everything will be the same. As long as the existing harness completely plug its plugs, even there's a non-used sensor on the new engine, it'll be ok. You can not have an extra harness plug, but you can have an extra sensor. Different ECU has its own wiring and sensors.

For example, the LS400 JDM engine that I currently use has an extra temp sensor on the front water bridge and I didn't use it. There's no problem because I use my existing SC400 harness and plug all of its plugs. There're not many different sensors between cars, including the JDM engine. But if you omit 1 harness plug, the ECU can behave differently. Or you can have the complete ECU and harness that orginally came with the engine.

 

We used my oringinal ECU and wire harness whick plugged up to everything on the new motor so i will not not worry about the extra sensor at this point. I have not found the tranny ground as yet but the symtoms that jgscott described is exactly what I am experiencing so I will try to get the car on a lift today to try finding it.

 

spiking needle can also be caused by air in the cooling system. Did you guys bleed it and properly refill the cooling system after install?