Hello, I am trying to fix my friends 1998 Grand Cherokee and Im having a hard time hooking up the obd2. It connects and reads computer with the key on and engine off. When I start the car though and try to connect it will not connect at all. Its a decent scanner with live data read and works very good on all of my cars. I should add that I have already soldered the first 3 pins inside the ecm because if you even touched the connector the car would die and it had random stalls prior. Now it does not stall and does not die if you wiggle the connector.

 

Has the vehicle been involved in a collision or had other previous damage? Certainly sounds like a wiring and/or connector issue.

 

Im not sure about a collision or other damage. Its just weird that it connects while the key is on but not when running.

 

"Its just weird that it connects while the key is on but not when running."

You are right, I've got nothing. That last time I scanned my '01 I used a 3140 once it establishes protocol you're good engine running or not.
Have you checked to make sure the connector still has a good ground and you have power with the engine running?

 

ok this connector only has pins 3-4-5-6-11-12-16 Here are the KOEO readings #3=2.27v #6=4.74v #10=2.26v #16=12.27v. Here are the KOER readings #3=2.27v #6=4.74v #7=.20v #10=2.27v #16=13.92v

 

Perhaps somebody can point me in the direction to another place for information on this ? I seem to have all the correct voltages and not sure where to go from here

 

Pins 4 & 5 have good ground?
Any codes KOEO?

 

try just connecting it switch it to on position and jiggle the wire behind the connector and see what happens try getting another scan too and plugging it in as well

 

I will recheck pins 4 and 5 for ground because I honestly dont remember how I checked. Different scanners yield the same result, and I removed the 2 screws holding the connector up to the dash and checked for loose pins and wiggled while car was running and that did not seem to change anything. No codes. I have unplugged the tps and no codes threw and unplugged my upstream o2 and no codes. It threw codes when I unplugged the map, IAC and IAT and also ECT just not the other 2. Will check tomorrow and re post my results. Thank you for your help so far it is much appreciated.

 

Pins 4 and 5 both have a solid ground.

 

The only thing I noticed as unusual was with the engine running I had my meter on beep continuity on the pins 4 and 5 and it was pulsating but steadily. This could be normal Im not sure.

 

It's not normal. You do NOT have a solid ground. Work on that.

 

Ok. So I know that the abs module shares the ground with pins 4 and 5 so I unplugged it and that made no difference. Next question is where is the next best place to check ground for thosr?

 

Hmmm. Not sure where that grounds. Wiring diagram needed!

You are seeing fluctuation because of voltage that shouldn't be there because of resistance that shouldn't be there. That fluctuation is going to give your PCM fits.

 

I should note that I watched numerous videos on testing obd2 ports and all have said I should have voltage on the k line #7 pin. I have none. I am in process of unplugging the BCM and checking voltage after that.