can you tell us what the color wires are coming from the O2 sensor? It should be a 4 wire, meaning it has one power, one ground, one signal and one for the internal heater of the O2. If you do have the 4 wire, check the black/dark green wire from the O2 sensor and backprobe the connector with a paper clip and read the feedback voltage with you voltmeter. Like I said before it should bounce around between 0-1 volt DC

 

Hi all.
Here's the info from today's attempt. Scanner readings are:

O2 wiring is good check resistance back to terminal strips .
o2 voltage when ignition turned on 13.7 V (Good per manual)

Crank sensor checks out (Good per manual)

Snap shot from Scanner not running when engine craps out.

RPM 625
TPS v .7
% 0
ECT 45 C
v 1.58
Map 22 kpa 12.4 " hg
1.72 V

Barometric pressure 92 kpa 27.4 "hg

up o2 lean
2.10v

TAT 38 c
1.94 V

Total advance 24 degrees
ASD relay energised


Any thoughts????

 

Tried a new Cam Sensor today. Tested Crank sensor (Static test when warm and it's a new Chrysler one). No Change

At wits end ;-)

 

since you don't know what sensor is causing the issue i would do this. when it stalls unhook your o2 and see if it runs. if not the go to the map sensor and do the same. then the coolant temp. if you feather the gas can you keep it running? also if you have acess to a lab scope or oscilloscope back probe the crank sensor and dist pickup and see if you have a good sig when it stalls. you need someone to crank it while you watch it though. do you have another pcm laying around you pulg in after it stalls? i doubt it's the pcm but if you have one (ivenif for the 5.2) it'd be easy to ruel out. what it comes down to is something is lying to the pcm once it hits closed loop. the o2's have been know to short out and cause this (had it happen myself and it never set a code either). i doubt the ect is bad (coolant temp) but easy to check.

when you unplug these things the pcm will just make up a default "safe" value to limp the engine to a shop. so you won't hurt anythinhg by doint this. just shut the key off between sensors so the pcm can recheck and see you hooked it back up.

 

here's what's not making sense: your MAP sensor is also your BARO sensor and the readings between the two are not the same. The low MAP is OK because it's saying that because of low RPM, the vacuum is low, however the BARO reading shows high vacuum and the only time vacuum would be that low is if you were -480 ft below sea level. Also, the O2 sensor voltage is reading 2.1 volts is super high, telling the computer that it's running pig rich.

Before you go any further in throwing parts, check all your grounds both on the body/frame and on the engine. I ran into a similar problem a few years ago on a 1996 Chrysler LHS that another shop replaced the heads. It would run for a few minutes and then shut off and wouldn't turn on until the engine cooled. Making a long story short, there was a braided ground cable that was loose on the back of the RH cylinder head that caused the PCM to loose it's ground and start running funky. Just FYI.

 

All grounds are good. There is no ground between the computer case and the chassis as the computer is housed in plastc.

Tried a new computer today. Exactly the same results. Runs for 8 minutes ish then quits. Will continue to run ( up to the 8 minutes) even with the sensors being unplugged, except crank position. When the CPS is unplugged it dies.

Will NOT restart until something changes several hours later. Then the cycle continues.

 

ok, as far as the MAP & BARO sensor readings, I double checked with a scan tool on my truck and I see similar readings, so unless my truck is secretly dying on me, those readings are OK, and I correct myself.

Here's what I find interesting, after 8 mins, your engine is only at 45 C or 113 F. It should be around 180 F or 82 C. What temp thermostat or you running, if any at all? Try using a 180 or even a 195 (82-95 C) and changing your coolant temp sensor and see what happens.

 

hmm. ok here's how you can checck your grounds once and for all. take a dvom and put the neg lead on the neg bat cble and the pos lead on the engine. like the intake of alt. something with a good engine ground. you have less than half a volt if i remember correctly. now heres the part some ppl shy from. print a connector pin out for the pcm from the fsm and find all of your power and grounds. not sensor grounds just grounds. now once it's dead check them with the key on and see what you lose if anything. if all is ok then check your sensor ground ckt and your 5 volt ref ckt. i would check those at like the oil pressure sensor or tps (tps is easily accesible) and see what you have. if you find a dead ckt then go to the pcm connecter and see if it's dead there. if so then pull the wire out of the loom so you have good acess to it and if your able to solder and comfy with it snip it. now see what you have at the pcm with the ckt isolated from the vehicle. if it comes back up and you have comunication with your pcm congrats. you've found the ckt thats causing issues. from there you trace it to sensors and find out if it's a sensor or a short. good luck if you decide to go on with your diag and please let us all know what you find out.

 

Well after 2 more days of fooling around (we had to wait 5 hours between start ups) we gave up. Some erratic readings on the Crank Sensor and we tested it and could not get it to swing between 0 and 5 volts (out of the car). Used the metal in front/move away test). 8 volts were there on the reference power to ground signal ground. It would read 5 volts on the signal one time and stay there then after a few minutes would MAYBE move on its own to 0. This was out of the mounting in the block. No action when the steel was passed in front of it.

Owner has decided to convert to carb/conventional ignition. Thanks for all your help. It's too bad as this would have been a neat set up if it worked :-(.

 

I'm not to sure if you check the O2 and the temp sensors. But oh well, I just hate to see another POS carb on a perfectly good MFI system.