The ol' girl is at it again

Matt_aka_Dale

SCCoA Member
To start, the car has just straight up died on me twice. Once backing out of the garage and a week or so later dying about to pull into the garage. After the second time, I decided to check if there were any codes. Interestingly enough there weren't any.

Next we have an issue of it going very rich to very lean at idle. Sometimes it plays nice and won't do it, but if it does, it might fix itself. It also won't show up when cruising. It doesn't seem to bog down or hesitate in acceleration.

I'm willing to try anything at this point
 
What year?

When it dies, how many tries to get it running?

What was the last work you did on it, and what were you attempting to fix at that time?

Mods? Running a chip/tune?
 
It's a 1989.

If I remember right, it took about two tries to restart.

I think the last work that I did to it was;
-Replaced the forward harness to the DIS and crank sensor.
-I swapped out the DIS, crank, and MAF sensor. Also replaced the O2s.
-Replaced the fuel pump, sock, and filter just to make sure none of those would be an issue. (I have the old pump just in case)

I vaguely remember why I did all that...might have been another drivability issue. Hell, it's probably the same issue if not the same. I did notice that after replacing the O2s, it ran much better and I felt that was the final fix.

It does have a chip (supercoupesunlimited)

Mods
-a/c delete
-egr delete
-double intercooler w/ raised sc top
-screaming demon coil pack
-March pulleys
-10% sc pulley
-76mm MAF
-75mm throttle body
-38lb injectors
-255 fuel pump
-Long tube headers
-built trans w/ shift kit
 
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Good evening


It appears you need an OBD 1 scanner with live data capabilities or access to datalog information. Your problem might be a suspect engine coolant temperature and or barometer sensor readings.
 
I should have access to a scanner no problem. But a bap sensor? I've only ever heard of this one other time, though it wasn't for my vehicle. If these 'suspect sensors' are in question, would backprobing with a multimeter show any signs of an issue?
 
..would backprobing with a multimeter show any signs of an issue?

Perhaps - see this post for process:http://www.sccoa.com/forums/showthread.php?140602-Sold-IRCM-used-93&p=1121893#post1121893 - note I would use a DVOM, tho.

Keep in mind...

Which is Not a Symptom of a Potentially Bad ECT Sensor
  • Continuous rich air-fuel mixture
  • Continuous lean air-fuel mixture
  • Rough idle
  • Engine misfire
  • Engine stalling
  • Increased emissions
  • Increased fuel consumption
Answer is: misfire…


Also see this one: http://www.sccoa.com/forums/showthread.php?140824-Yet-More-Cooling-System-Fun

And since you're running a chip, I'd keep expectations low if you see what's up using an OBD-1 code reader.
 
I've had a code for the sensor coolant before, but was from KOER and I might have forgotten to plug it in or something. I don't recall exactly, but there was a code. Plus it continues to give me a code 19.
 
Why would you do that? You have 38# injectors, 30# is stock, so something could go wrong if you take out the tune. Plus your using 75mm throttle body stock is 65mm.
 
I didn't think I would anyway, but like I said, I'll try anything at this point. Just fire the parts cannon it. I've lost what little free time I've had to try and test things and honestly might sell/trade the car. Pretty tired of it. Can't continue any other work on it when something mechanical keeps happening.
 
Could this be a sign...

It has been pretty cool/cold these past few days, and on a particularly cold day, the car ran flawlessly. No a/f spikes or drops. On just about any other day, it has been showing very lean and starting to run poorly. Hope this helps
 
Finally got around to replacing the coolant temp sensor. There was no change. Unless it's supposed to be the one on the water neck? I might just try injectors. It's one of the few things I haven't replaced hahaha.
 
If your mixture is hunting, the first thing I would change would be the O2 sensors. I had one quit without notice and the car went pig rich and would barely run. The computer is only smart if all the sensors are working correctly. Those O2 sensors live in a pretty hostile environment.
Alan
New O2 sensors are no guarantee that they work right. Check the wiring to them is not shorting to the manifold.
 
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O2's where replaced not that long ago. The wiring for them is all in order as well.
Update:
ECT was replaced. No issues during first and second drive test. On third drive test, there were no problems until I went to pull into my garage and the problem showed back up(poor a/f with bogging). I'll try testing more tomorrow.
 
So this should be the end of this thread(hopefully). Time for a little backstory.

A day or two before Christmas, I once again revisited this issue. This time I decided to look at the O2 wire extensions, because after installing them and my longtube headers, I melted one a decent amount. It was enough to expose a little of the metal wires. After discovering that, I tried to fix what was left with heatshrink and electrical tape. Anyway, me and our one technician looked over my beautiful work to the extension. Checked continuity and nothing was showing any problems. After removing the electrical tape wrap I did, plugged the extensions back up, hooked up an actual scanner, ran self tests, and cleared codes. Then drove home.

It has been 5 days of absolutely no issues. No wacky a/f readings or running issues. Runs like a champ.

So it looks like I need new O2 wire extensions.
 
Congrats Matt, im glad you finally got it fixed! Its cool that you got it running good after you modded your engine. I cant wait to get my new engine finished.
 
Hey Matt, saw you're from Cincinnati, always nice finding local guys. I've had my 93 bird for 10 years (5.0 lx Bill Elliott edition heavily modded) but just picked up a 94 sc in nice shape except the motor needs completely reassembled. That being said, I know I'll have some questions along the way since I've never built one of these motors and will probably be looking for some recommendations and advice. Plus once shows start up again it's always awesome having multiple mn12s lined up!!! Three of us have v8 cars here in Harrison plus I just picked up the sc.
 
Hey Matt, saw you're from Cincinnati, always nice finding local guys. I've had my 93 bird for 10 years (5.0 lx Bill Elliott edition heavily modded) but just picked up a 94 sc in nice shape except the motor needs completely reassembled. That being said, I know I'll have some questions along the way since I've never built one of these motors and will probably be looking for some recommendations and advice. Plus once shows start up again it's always awesome having multiple mn12s lined up!!! Three of us have v8 cars here in Harrison plus I just picked up the sc.

Sweet! I'm in the Fields Ertle/Loveland area. Feel free to ask me anything, though there are plenty of things about the car that I still don't know, but I'll do my best to help. Otherwise this forum and the FaceBook page are quite helpful and a pool of knowledge. Just let me know?
 
Cool, I actually work in west Chester. I've been around mn12s for about 20 years. You might know my buddies cougar, the white 91 that has about everything from Bill's that you can imagine and then some. I know the cars very well, just not the sc motors (yet anyway). Also been to many shootouts as well so got to meet a lot of cool people already as well. I'm sure well be able to help each other out in the future for sure!!!
 
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