Code 31 trouble

[vilant]

Was curious if anyone gets an intermittent Code 31?
I finally started to attack this problem in mine. My symptoms were: the code sets after just starting the car, I turn it off, clear the code, and it comes right back. Clear again, and it stays off for @20-30 min then sets again. Turn off the car, start it, and it's gone, then will come back again. A true intermittent. I followed the procedure in the FSM. Ruled out the ECM, and according the procedure I have a faulty cam sensor or faulty cam sensor connection. Bought a NOS one and cleaned up grounds points. The ground for the sensor is that fun one to get to behind and down from the center of the plenum. Cleaned the other 2 behind the battery while I was at it. Lightly sanded all parts and used De-Ox on all connections and added a lock washer (even scraped the paint off the frame on the lower ones). Re-seated all connectors on the ECM (even re-seated the PROM) and I still set a code intermittently. The only thing I can think of is the actual connector that connects sensor to the harness is bad. I tie wrapped the two halves of the connector together tight, which seemed to make it last longer between settings than usual, bit still sets. It's just annoying cause as soon as the SES light comes on, the secondaries won't come on (everything works normally, but it's like having the power key off). I got to turn the car off then on, or clear it to get full power again. I'll try re-pinning a new connector and if that doesn't work, then I'm completely stumped.
Anyone have any ideas? Would another sensor (there are several that are part of the same 10 amp fuse) be somehow interfering with the cam sensor?
Thanks, Joe

[Schrade]

Remember there's 8 grounding straps behind the plenum...

5 x D side


3 x P side


And it might help if you shoot snappics of each FSM diags step - someone might see something (why I shoot all my stuff )

[vilant]

The ground for the cam sensor (blk/wht) is G105 which (I thought), was the 3 together down behind the plenum where the trans connects to the block, but I looked again and I was wrong. That's G106, 105 is one of the 2 behind the battery (according to the wiring diagrams manual). Not sure where the other 5 are, that you're holding or what point that is, G109?. I followed the procedure for testing Code 31, but if it's an intermittent (which it is) you go to "Intermittants" section B. And that narrows it to just about everything, lol. There's a whole slew things that could be causing it. I guess maybe I should scan it while it's running and pull up the sensor and see what it's doing. I just can't believe it's the sensor, because it's brand new (I guess anything's possible though).

[Schrade]

I can't remember ATM what the code is for the D Side 5 x in my hand - or even where they bolted, without looking at more posts in that Top End Rebuild Thread.

But unless there's a common 31 trigger, that no one has posted about yet, then scan & post the FSM chart, and TAKE and SHOW SNAPPICS of diags for EACH STEP. NO shortcuts - EVERY STEP. And you can start right now if you want...........................

[pan9101]

My 92 had the same problem last year. I've replaced the cam sensor, and then I reset the code on the ECM but I still get the H31 code almost everytime especially after I've driven the car for about 20-30 mins on the highway. I've finally solved this issue by replacing the ECM.

[vilant]

That's what I'm praying it's not. I tested point D3 from the ECM, if it varies in voltage from 0-5V while starting the car, the ECM is faulty, but I had a steady .22V. Maybe it starts going buggy later. What sucks is the ECM circuit board is coated in some kind of resin. The only thing that can be replaced easily is the PROM chips. I'll try re-pinning the connector first, cause that's cheap. If that doesn't do it, maybe a new PROM or IC chip will. ECM's are expensive. Thanks for your input, even if it is bad news for me

[Mystic ZR-1]

Have your injectors ever been replaced?
Code 31 was one of the many I got on my '90
when they finally crapped out. Replacing the injectors
cured all the different codes that came up. Some codes came
up alone or together with others.

[vilant]

Yea, they've been replaced. I changed the injectors, coil packs, wires, and plugs a little over a year ago. Code 31 didn't start popping up until after this winter. This winter was colder than usual so I didn't have it out as much as the previous winter. But I would still start it up from time to time if I couldn't take it out.
On a side note, my ECM is a re-manufactured one. Have no idea when the original was replaced.

[vilant]

For you Schrade.


Just to clarify, I followed the procedure on the chart to the right when I first had a steady Code 31, which led to faulty cam sensor or cam sensor connection. Bought a new cam sensor, then it became intermittent. I just realized I can't "re-pin" the connector. I need a whole new connector instead. Instead, I tried cleaning the inside of female connector, used De-Ox, and bent them down a little bit for a tighter connection. The 3 arrows below are what I thought might be causing the intermittent. Also found I can't read what the cam sensor is doing on my scanner, it's just a malf flag (on my scanner at least). We'll see how the cleaning and bending works out.