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My 1990 Laser RS-T won't start, help!

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GimpyTalon

Probationary Member
28
0
Sep 26, 2003
Des Moines, Iowa
Well, I came to a deal on a 90 RS-T FWD tonight even though I couldnt get her to fire up. Here is the background story: car was running decently, but occasionally started kinda hard. then one day.. no start period... and thats where it is today.

This is a pretty much bone stock RS-T, it has a test pipe, fart can and an MBC.. thats it. Heres what I've checked and tried so far.

1.) Compression test yielded 150psi accross the board, which is healthy in my book for a 7.8:1 compression motor.

2.) Tried a KNOWN WORKING ecu in the car, same no start results.

3.) Test lamp & metered the outputs on the MPI relay, according to the book all is well. Everything is getting power when it should, and everything is getting ground when it should (when starting or in the run position).

4.) While doing compression test, I testes each coil ouput.. and they did spark the plug.

5.) Removed the CAS, turned car to "run" and spun the cas and observed the car pumping fuel and clicking injectors as the CAS was rotated.

6.) Double checked cam to crank timing, appears to be right on the dot.

7.) Moved the CAS rotor 180 degrees to insure it wasnt installed wrong.

8.) Couldnt get a datalogger to talk to either ECU.... "ECU COMM ERROR". Is that normal for 1990's ... will be trying another cable wednesday night to make sure it wasnt the cable/setup.

---

Heres what I'm left with:

1.) Bad coils or igniter?

2.) CAS troubles of some sort?

3.) Fuel pump not giving the rail enough pressure (any suggestions on how to check fuel pressure since DSM's.. unlike every other ****ing car in the world... don't have a pressure test port?)? Bad pressure regulator?

4.) MAS/MAF possibly shot? I have heard of these dying, but my old 91 Talon would still start up in limp mode even without the MAS/MAF... just ran like **** obviously.

---

All suggestions welcome. I'm going to go ahead and swap the fuel pump with a Walbro255 to get rid of that possibility on Wednesday night.
 
Are you testing with a working 90 ecu? 90's are different from 91-94, you have to swap two wires.
 
Yes sir, I tried with a 90 and 91 working ECU. 91 ECU's will work in 90's w/o swapping they just idle obnoxiously high.
 
Thanks to a couple folks @ Fullthrottletech we determined it was the ECT (engine coolant temp sensor)!!!! It was seeing -78oF and as such dumping waaaay too much fuel to start :)

I replaced the ECT and spark plugs, and off she went!
 
GimpyTalon said:
Thanks to a couple folks @ Fullthrottletech we determined it was the ECT (engine coolant temp sensor)!!!! It was seeing -78oF and as such dumping waaaay too much fuel to start :)

I replaced the ECT and spark plugs, and off she went!


coolant temp sensors usually trigger a CEL, and mostly cause a no start condition after the car is up to operating temps.
 
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