I have been getting a code 13 and running rich. I changed out the sensor but the signs remain. I put a pin into the computer side of the o2 pigtail and measured DC volts. I chose the computer side to make sure the pigtail was ok. When the car was cooler (below 200) the car would not stay in closed loop, and ran at .836 volts fairly steady. There was some variance in volts but it would lock in at .836 for several seconds at a time. I ran the car at idle and there was the most variance, at 2k RPM less, and at 3K RPM she held steady at .836. When the car was (to me) really hot (230) the computer showed even pulses of the SES and closed loop with the volts varying nicely. I tried differing RPM's with good variance. Now, is this telling me I need a heated o2 sensor? I have stock manifolds! Today it is very hot here (85F!) and it's the first time I was able to sustain closed loop in this test. I turned the car on at one point at 243F. I normally run at 190 at cruise. On other tests of this nature I'd enter and then drop out of closed loop after ten seconds or so, at 2K RPM. While driving I get an intermitant SES light. Are there any other conclusions? Thank you!

 

With stock manifolds, you don't need heated O2 sensors (I assume that your car is pre-94). Any other mods that might require a custom chip?

 

Mods in sig. I don't have any cats at all. This is the first time that I've got her to stay in closed loop with these tests. It's really hot here.

 

Move to Phoenix area. Then you'll know what hot really is.

 

No, I don't think a heated O2 sensor will help. Do you have a FSM? If so, just follow the code 13 troublshooting and if not I/we can help. You are going into closed loop if the O2 sensor is sending signal to the ECM. It look like is on the rich side and is probably working correctly. I think you have a different problem besides the O2 sensor. Anything that will add more fuel to the cylinders.

 

When the exhaust temps get to 600* and the engine temp gets to about 140* if should go closed loop. It doesn't really matter about the outside air temp. Also if the engine got to 243* there is a problem there also. The fan(s) should kick on before it gets that hot. All the heated O2 sensor does is self heat to get into closed loop quicker. As with headers where the exhaust doesn't get as hot as with stock manifolds.

 

Yes I'm following the code 13 trouble shooting. The 243 temp. was when the car was turned off, the temp. goes up some then. This is the first time in two years of testing that the car stayed in closed loop. I'll try driving around in diagnostic mode today instead of just testing in the shop. The code 13 flow chart sends me to intermitants. On that, it could be a bad computer?

 

I'm having a rich exhaust problem too. I don't have any codes and fuel pressure is at 40 at idle with 24 lb injectors. I switched out the ECM (had a spare) and nothing changed. I will be getting it on a scanner soon and see what the computer is seeing. Good luck.

 

Today I drove in diagnostic mode, the SES light light solid then flashed closed loop, then dropped right back to open loop as usual. I drove 80 miles and never once did it attempt to enter closed loop again. I tried turning the car off for 30 seconds and entering/exiting diagnostic mode, nothing made the SES light solid again. Then on the way home I drove in normal mode, the SES light came on (code 13) and stayed on for 80 miles. That is new. It normally would light intermittantly. I think I'll call around for a scan. Any ideas? Computer seems more likely?

 

You say that you have been troubleshooting using the Code 13 chart. Are you using the Factory Service Manual (FSM) or an imitation? Troubleshooting the Code 13 should be pretty easy using the 88 FSM. There are only 3 main steps in the book. What were your results for each step?

An open sensor circuit or cold sensor causes "Open Loop" operation.
-FSM page 6E3-A-24

Based upon what you have posted so far, I'd guess that you have an intermittant open on circuit 413, the tan wire from the ECM for O2 ground. Or possibly a faulty ECM.

Code 13 FSM chart results for step 3.
-> Ign "on" Engine "off"
-> Voltage check of circuit 412 (purple wire) at O2 sensor connector harness, using a 10 MOhm DVM.
=> Should be between 0.3 - 0.6 volts.
=> Over 0.6volts = Open Circuit 413, Faulty Connection, or Faulty ECM

 

I had a local dealer print out the code 13 chart for '88. I'm not an expert with a multimeter on these tests. I just got one. Step three, it doesn't say but is that with the car warmed up? For this test I would stick a pin through the purple o2 wire, attach my MM to that and check DC volts? If I do read over .6 would it be a good idea to try running a temporary ground for 413 to test that?

 

It doesn't matter. The ignition is "on"; the engine should be "off". The voltage you are testing for is the circuit voltage, not the O2 sensor voltage. I'd do it cold.


Yes. I'd try to connect at a terminal, rather than putting a hole in the wire. Notice in the printout that any voltage is a bad sign. The value helps point to the cause.

Have you had the transmission worked on? I believe the 413 circuit grounds via a connection to the transmission casing. Not reconnecting that ground, or a bad connection/loose connector at that point might be the cause of your lack of ground at 413.

 

I checked the o2 sensor with the car off it read 82.1 DC mV and with the key on 102.1 DC mV. I took apart the grounds at the transmission and cleaned the stud, nut, and ground wire flanges. Now the reading is 0 DC mV with the car off and 20.1 DC mV with the key on. My problem remains though, I still get intermitant SES light with code 13. I reset the computer before test driving. The car acts slightly better.

 

My MPG is higher now after cleaning that ground.

"Code 13 FSM chart results for step 3.
-> Ign "on" Engine "off"
-> Voltage check of circuit 412 (purple wire) at O2 sensor connector harness, using a 10 MOhm DVM.
=> Should be between 0.3 - 0.6 volts.
=> Over 0.6volts = Open Circuit 413, Faulty Connection, or Faulty ECM"

I am not reading .3-.6 volts with the key on. Next I will check at the ECM for that, if that doesn't read .3-.6 then it is the ECM having a problem? I'm heading out to do that now.

 

After reviewing the FSM the easiest check of the ECM and O2 wiring was to run 412 (ECM pigtail to O2) to ground. I ran a wire to the neg. battery and the test is: with car warmed up and in diagnostic mode, the SES should flash for 1-4 seconds then go out for atleast 30 seconds. I did this and mine does exatly that, repeatedly. This tells me that the ECM and O2 wiring are ok, yes? So I have another bad O2. That is three in a row. I did now clean the ground, could a poor ground ruin the sensor? I can't find anything else wrong with the car.

 

I am reading your post, what strikes me is solid 800+ mv reading this is a scanner reading correct? I'm sure you know the 02 should be bouncing and not steady. Rich and became sluggish/froze
The test sounds correct. What I found was I went through 2 sensors. First one due to contaminents on fresh build , second one after relaocating location(bung on collecter). It took out a new one and froze the readings @46 and threw a lean code. Mine seemed to be particularly sensitive to tuning and adjustments. This last one seems to be fine w/the tune being better/stable. don't know if this helps,BTW all are bosch 02's

 

here is some info on O2 operation that may be helpful:

"When you first hook up your ScanMaster, and start your car, you will be convinced either the ScanMaster is broken, or your car is "possessed". Don't worry…… the unit is SUPPOSED to be flashing constantly changing O2 sensor values. The sensor is extremely sensitive at an A/F ratio of 14.7:1. Go very slightly richer than that (14.6:1) and the voltage can soar to 700mV. Go very slightly leaner than 14.7:1 (say 14.8:1) and the sensor output voltage plummets to 200mV. Since the PCM is constantly juggling the fuel up and down to keep it right at 14.7:1, the voltage is going to jump up and down too. So, you will see that, since the PCM updates it's calculations nearly 10 times per second, the O2 sensor voltages are going to be cycling rapidly back and forth between 100 and 800mV, and you might even see values as low as 050 mV, and as high as 950 mV. THIS IS NORMAL."

"Remember, the O2 sensor can only measure OXYGEN. It can't measure fuel, or other components of the exhaust, so if you have a cylinder that misfires, there will be all the oxygen that was in that cylinder, and all the fuel that was in that cylinder, in the exhaust. The sensor will see that oxygen, and the voltage will drop, indicating "lean", but it is not really lean."

 

I tested a known good O2 today from a friend and it acts the same way as my other sensors. With code 13 set the car will not try to enter closed loop. If I reset the computer then the car enters closed loop and then drops out after at the longest so far, 30 seconds. Without code 13 set I can repeat this test with varying times of staying in closed loop. When I pull the O2 it is coated in black soot.

"The sensor will see that oxygen, and the voltage will drop, indicating "lean", but it is not really lean."

Mine sticks at .836 V for a few seconds, shows rich. This leads to me to believe the problem is not in a miss, because it would be measuring the extra oxygen and reading lean.

Would a vacuum leak show up as rich or lean? I tried spraying water around the intake but noticed nothing.

This could be three things right? Mechanical (cracked head, vacuum leak?), computer, or ignition related?

Can anyone think of a way to make the problem worse? I tried varying the fuel pressure with no change. Also I tried removing a vacuum line with no changes.

 

...regarding 3 things you need for combustion...
<air> <fuel> <spark>

the good news is you got all 3! Problem is you may have more of <fuel> than the ECM can compensate for. If it were me, I would be looking for leaky fuel injectors. Sounds like your O2 is screaming rich, but your ECM can't lean out your AFR. Also, use carb cleaner or starting fluid to check for vacuum leaks, water may not be enough to notice a small leak.

Sounds like you should consider your O2 sensor as the "messenger" and not the "culprit". Time to look at your fuel equation.

 

Thanks for the reply! I visually checked the injectors for leaking, none did, when I put the new intake on. I put in a Holly AFPR. That is working well. I adjusted the FP today, up and down, with vacuum and without, that all works well.

Regarding checking for leaks, will carb cleaner make the engine running faster or slower?