Hi all,
My bone stock (as far as I know) 87 started running oddly a few days ago. Sometimes at idle it would be erratic while pulling into the garage (RPM varied from 5xx to 1xxx).
It did this after I noticed while crusing (not on criuse control) at a steady speed the engine would surge and stumble. As soon as I moved throtle position it would disappear. The SES light would come on for awhile and after a few minutes go out.
I paper clipped the ALDL and got a stored 44 code (O2 lean).
I did some very basic checking (ohmed out the fuel injectors, sprayed WD40 all around the intake/top end/hoses looking for a vacume leak), checked for melted plug wires etc but found nothing.
I did pick up a new fuel filter and that will go on this weekend as well as a get myself a fuel pressure guage. I DO have the FSM as well as the electrical supplement.
In the mean time I did manage to home brew myself a USB ALDL cable and get TunerPro RT working.
I have never used it before so I basically started logging, started the car, let it idle a bit and then snapped the throttle to see what would change on the screen (it stalled-never does that!).
Started it and repeated it complete with stalling.
Started it again and then wasn't so agressive with the throttle.
I'll try to attach the exported CSV here and I'm hoping something will stand out and I can get a clue where to start.
Thanks in advance!

 

I would say your TPS is hosed. For one, the base voltage setting that the ECM sees should be about .540 volt and yours starts at .61 volt base setting, so that needs adjustment. But then, later on, when you say you snapped the throttle open and then it stalled, I can see the engine RPM go to 0 but the TPS position did not change much at all (line 41 in your .csv file). So if you stepped on the gas but you only saw .61 to .63 voltage increase in the throttle position sensor I think that's a sign of trouble.

I'd start there....

 

I forgot to mention (I found this out after more reading) that I didn’t remove the 10k ohm after I got communication between the car and the laptop.
Apparently that causes the RPM to be slightly higher and a few other settings are changed.
Would that be reason for the higher reading or is the resistor not even an issue for the TPS?
Like I said TunerPro is completely new to me and I’m impressed I even got my home built cable to talk. (I used $32b data but apparently I can use the $6E to get the full 8192 baud rate).
Thanks again for taking the time to look it over.

 

UPDATE:
Every time I had the time to do a drive and data log, the weather wasn’t cooperating.
I hate throwing parts at a problem but after reading the O2 sensor is a service part and since I have no idea if/when it was changed I decided to pick one up for $30 when I was out this weekend.
Ran it up the ramps after work today and went to change it. Literally as I cracked it loose it broke in half with just a touch as my hand passed it.
Put new one in and on a shortish test drive, the surge is gone and SES light did not trip.
Still need to change the fuel filter (not fun on a vert because of the X brace) but that’s on tap after the long weekend.
I may still do a run with logging but for now I can tell(smell) it isn’t running as rich as it was and the annoying surge at steady speeds is gone and idle is back to how it was when I got it January.

 

You won't learn much scanning in ALDL mode at 160 baud due to the low sample rate and limited data (only 25 bytes), but its a start.

Here's your log: https://datazap.me/u/tequilaboy/87-s...8-9-18&solo=18

Nothing too remarkable. 1,000 rpm idle (due to the ALDL idle rpm setting). BLM initially lean at 150 in open loop from previously stored sam cell data (Note: 150 is the upper limit for sam cell data), then drops to a slightly rich 122-120 during warm-up in closed loop which is reasonable for the conditions.

98 IAC counts at 1,000 rpm seems reasonable for the coolant temp and tps (0.61 volts). A bit high, but not your problem. O2 behavior looks ok.

From the scan id, the broadcast code is ADJR which fits for an 87 y-body, auto trans car. $32B mask.

BCC Year Release Date Eprom ECM Prom ID Scan ID Platform Engine Disp. Trans Trans Type Gear Ratio
ADJR 1987 31628 16071823 1227165 1825 1711 YB L98 5.7 MD8 AUTO G44

Look around for an appropriate 8192 baud adx file and be happy that its not an 86. You will also need a cable capable of 2-way communication in order to invoke 8192 baud. You mentioned a home-brew cable so this may be a limitation depending upon the design.

 

I should have mentioned that I gave the throttle body a blast of cleaner and cleaned it up (didn't remove it form the car). It needed it but wasn't horrible.
I reset my TPS (I think it ended up at .55 volts, not perfect but close)
I did get a 8192 adx file working but haven't taken it out to do a new log.
As I mentioned, yesterday I got the time (and good weather) to run it up the ramps and change the O2 sensor. The old one literally crumbled in 2 as soon as it touched it with the wrench.
I cleared the stored codes and then I took it out for a shortish test run. The surging didn't happen and it didn't set any codes. I will take it for another run today and see if it keeps behaving.
My plan (after the long weekend) is to take her out for a run with the 8192 logging and see if everything else looks good.
Thanks!

ps. That graph you created is awesome! Thanks for doing that. Makes the raw data easier to understand.

 

Hello Shrav!

Just so you are aware the oxygen sensors on the C4 were designed with a 24 month life or 50 k miles. They wear our and do strange things as they go out. First the signal becomes weaker and then it starts to lag behind the ECM and that is when you have drive-ability issues.

Any time you have issues and your O2 is older than the 24 months or 50 k miles I would start with a new Oxygen sensor! be careful with the new one as they are easy to poison and damage before installing it.

Being able to see the raw data in action is the best way for me to find a problem so I have a 1320 Electronics ALDL Cable and a Snap On MT2500 just so I have the ability to see the raw data when I need it. The Snap On is ancient technology but works for what I use it for. I can even see the OBD2 in my newer cars.

 

Yea, TB is our early C4 tuning GOD! We’re lucky to have him.