95 motor with 97 ecu and harness?

[jakes97gs]

Hey guys, I just installed a 95 motor (420a) in my 1997 gs, i used the harness and ecu from my 97 motor, and for a while i couldn't eben start the motor. Now I replaced the cps and i can get the car to start if i hold the gas pedal to the floor, then when my car starts i have to keep the rpms above 2500 or the car dies, after about 20 seconds of higher rpms the car idles smoothly, but if i give it gas, just tap the throttle, my rpms drop and then they race to like 3-4000 rpms and hang there for a while (it varies how long they stay there). I have tried a number of things, and im wondering if maybe the ecu/harness is not compatible being a 2gb with a 2ga motor. Any help would be GREATLY appreciated

 

[95TalonOwner]

Hey guys, I just installed a 95 motor (420a) in my 1997 gs, i used the harness and ecu from my 97 motor, and for a while i couldn't eben start the motor. Now I replaced the cps and i can get the car to start if i hold the gas pedal to the floor, then when my car starts i have to keep the rpms above 2500 or the car dies, after about 20 seconds of higher rpms the car idles smoothly, but if i give it gas, just tap the throttle, my rpms drop and then they race to like 3-4000 rpms and hang there for a while (it varies how long they stay there). I have tried a number of things, and im wondering if maybe the ecu/harness is not compatible being a 2gb with a 2ga motor. Any help would be GREATLY appreciated

Did you reuse the fuel rail from your 95?

 

[jayson427]

Probably map sensor or you need to wire something differently I know when you change stuff around like that the pcm doesn't always compute with the motor. There were a few things different from the 95 motor compared to the 97. Search the forums on here.

 

[boost97gst]

i think you may have a really bad vac leak bud. Sounds very familiar to something ive experienced. With the 2ga and 2gb 420a's there are a few connectors that need to be soldered from one to the other. Ive done it several years ago. The ecu should work and all the sensors should be compatible but the connectors are different on a few.

 

[95TalonOwner]

You shouldn't have to change a single thing as long as you reused your original sensors and fuel rail. Long block wise, they are all virtually the same.

 

[jayson427]

regardless of the sensors he may or may not have used he still shouldnt have to hold it at wot to start it up. if he didnt change his fuel rail im sure he would of found out pretty quick that it wouldnt work since they are different fittings. i think you have a vac leak or your map and iac are junk. i had the same problem on my stock 420a motor.

 

[jakes97gs]

I changed the entire intake manifold including injectors and fuel rail from the 1997 onto my 95 motor, and they seem to be working properly. as far as vacuum leak goes, we tried a smoke test (with a cigarette and compressed air to force it through the lines) and we didn't see anything strange. if my map sensor was bad would i be experiencing these symptoms? thanks guys

 

[Abe'sGST]

Yes you map sensor can cause those symptoms. Did you make sure the pcm you put in is good?

 

[95TalonOwner]

I changed the entire intake manifold including injectors and fuel rail from the 1997 onto my 95 motor, and they seem to be working properly. as far as vacuum leak goes, we tried a smoke test (with a cigarette and compressed air to force it through the lines) and we didn't see anything strange. if my map sensor was bad would i be experiencing these symptoms? thanks guys

That's your problem. You need to switch back to your 95 fuel rail because the fuel pressure regulator on the 95's is on that rail. So unless you added the 96-99 fpr back by the tank, you have no fuel pressure regulator right now. Also, you'll need to connect the fuel return line on the 95 rail back to the steel line on the firewall. You NEED to switch the fuel rail back to the original one.

 

[jakes97gs]

its a 1997 car though so the fpr should be 96-99, I used the 97 fuel rail, and i don't think i have the fuel return line on my firewall. does the fuel rail have to match my motor or the ecu/car? thanks

The Ecu/pcm (correct term?) that i put in worked fine before the new motor, I did have a brief short when i connected my battery during installation though because i had power to a little ground. I just touched the positive cable to the terminal cautiosly and instantly removed it when i saw sparks, is that enough to fry my ecu? I also checked my map sensor like my haines manual said, by checking the power supply from the plug and I didn't get any voltage. The manual said it was either bad wiring or my ecu

 

[jayson427]

That's your problem. You need to switch back to your 95 fuel rail because the fuel pressure regulator on the 95's is on that rail. So unless you added the 96-99 fpr back by the tank, you have no fuel pressure regulator right now. Also, you'll need to connect the fuel return line on the 95 rail back to the steel line on the firewall. You NEED to switch the fuel rail back to the original one.

you have even me confused. if its a 97 420a car and he swapped the fuel rail and intake from his 97 on to his 95 motor why would he need to change it back? its a 97 car it should have the fpr on his car currently? he has the 97 pcm and harness too?

 

[95TalonOwner]

Aww damn I read it backwards. Thought it was a 97 motor in a 95. The fuel rail should match the car not the engine. In your case, it is correct.

Disregard my previous post.

 

[jakes97gs]

I did a scanner test to view the live data while engine is running and it shows zero long term and zero short term fuel trim. It also reads -36 degrees F for the coolent temp and +66 degrees intake temp. O2 sensors?, ECU? I don't know what to check next?

 

[95TalonOwner]

I did a scanner test to view the live data while engine is running and it shows zero long term and zero short term fuel trim. It also reads -36 degrees F for the coolent temp and +66 degrees intake temp. O2 sensors?, ECU? I don't know what to check next?

Coolant temp sensor and/or wiring is bad for sure. That would be the 2 wire one.

 

[jakes97gs]

that was it! i replaced the coolant temp sensor because the 1995 one didn't actually fit with the 97 plug, switched out the sensor and the car runs great now. it was running way too rich to compensate for the cold temps it was getting. thanks for all the help guys