CPS testing...

Anyone know how to or what values I should be looking for when testing a 91' CPS. Everything I find is for a "hot" test. Can't start it to get it hot.
Heres whats going on, the ECM shorted out, have tested everything we can think of, but have had two people say to check the CPS, it could be the prob.( one was a dealer, the other was a NAPA). Have another ECM coming (thx 8 UP), but want to rule out CPS b-4 installing ECM, any thoughts?

1. Place an ohmmeter across terminals B and C of the CPS connector. The meter reading should be open (infinite resistance). Replace sensor if resistance is indicated.

. A bad CPS will not ruin a ECM, what part of the ECM is bad a input or output or power supply?

That was a new one me too, had never heard of that. When you hook up the batt. the ECM would start smoking,now it does nothing.
You can crank engine, no spark, could smell gas so figure the injectors are working, pulled the fuel pump relay so as not to hydrolock it with gas.
We tested everywhere we could think for a short. Pulled all the fuses, tested them, all OK. replaced them one at a time, more test,nothing. Went between the batt. cable and batt. post looking for a draw, miniscule at best.
Hate to put the new(used) ECM in and have it burn up too.
About the only thing we haven't tested is the CPS, but I still don't believe a sensor would kill the ECM. Im really surprised a fuse didn't blow b-4 the ECM.
The last time this ran was a year ago the day after the girl had a new alt. installed. The she was driving down the street, said she turned on the radio and it died. They tried to jump it ( wonder if they got cables crossed) ECM started smoking, so she put it in her barn, I just picked it up for $200. Only has 101k on it, mint interior.

wonder if they got cables crossed? That would do it, do you have 12v on pin 3 on the ECU?

I don't have the test findings right here with me, but I do remember pin 3 being a hot pin. Son just called and seems to remember 12V+ on pin #.

12.6 volts on pin #3

Just a thought, since the trouble seems to have occurred after a new alternator was installed which apparenly didn't work: make sure it's the right alternator and that it isn't mis-wired.

I think your correct to not want to install a new ECM, without determining why the old one "smoked". I'd disconnect the battery and pull the connectors off of the ECM. Using an ohm meter, I'd test each pin to engine/chassis ground. I'd investigate every circuit that was other than open (no continuity). By investigate, I mean trace the circuit to its component and determine why your getting a reading. You could have a shorted component/sensor, a shorted pin on the component's socket, or a short internal to the wire harness. The CPS should read ~200 ohms across pins A & B(Renix system); an open indicates a bad sensor. I doubt seriously that a shorted CPS or O2 sensor input to an ECM would "smoke" it. These are inputs to the ECM. Something like a relay driver, or injector driver might. Reversing the battery cables probably would. Since the last work done on the Jeep was an alternator install, I'd definitely double check all wiring to ensure correct connections.

We're gonna go thru it one more time with fresh batteries in all of our equip. and in the vehicle.
Sidenote: put a batt. in it the other day and was testing for spark( the I did not ahve). When I was done I disco. the POS cable and left the NEG connected. Went to crank it yesterday and it was pretty much dead, I DID leave the ECM connected. I'm gonna throw a charge in the batt and disco the ECM and leave it overnight again. We didn't show a draw when going between the cable and post, but if I remember we had the ECM disco. Have to do it again.

hooked up to dagnostic port, nothing...it just tells us to turn key off if its on, Don't think the is any output from ECM, got the new one today but will fight the urge to connect it 'til we're totally sure that there is nothing else going on.

SHE LIVES !!!! Got it started about an hour ago. We went thru everything again, a few times.. to the point where we were getting stupid(er). Finally said the hell with it , put the other ECM in, cranked it, saw we were getting spark, and not coming out of the ECM...lol, put everything back to where it should be hit the key again... about three cranks and it fired up.
Was a little rough, but that was to be expected, hadn't run in a year and swapped ECM's.
Hooked up to diag. port, but couldn't communicate....took us few then we realized we were using the old VIN#, have to try and get the one for this ECM.Quit laughing ...we were tired. Did the key thing, pulled a 12 &14, batt had just been changed( which by the way is junk), and the other is low MAP voltage, not bad for something that sat a year.
Will drain & flush cooling sys. and oil+filter. Has one lifter that sounds bad, will add MMO, I heard this eng. Run b-4 being put in mothballs and it was real quiet.
Just wanted to say thanks for all the replies on this thread.