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Munipit
10-22-2015, 10:15 PM
I pulled the codes and I get not one, not two, but six different failures all at once. These are the "key on" codes in no particular order (actually, the order I get them in)

51 - Coolant Temperature sensor circuit open
22 - Barometric Pressure Sensor out of range
53 - Throttle Position sensor out of range (high)
54 - Air Charge Temperature sensor circuit open
35 - EGR Valve Pressure Transducer/Position Sensor voltage out of range (high)
67 - Neutral Drive Switch circuit open

Codes don't seem to clear which made me think it's the pcm I bought a second pcm (but the fuel pump priming circuit stays on in koeo) and it runs like poo and still has a CEL but the new pcm won't even pull codes so I already know it's bad.

But what I'm trying to find out if there is any common point on the wiring harness that could cause these codes I have swapped every sensor and still same codes so it's either the wiring harness or the pcm any ideas?

KMT
10-22-2015, 11:43 PM
If you don't have an EVTM for that car, common points in general are always grounds.

Check:
- the black lead to the header panel next to the driver's side headlight and hood support
- ground strap from the pass. side motor mount over to the body
- since the computer was swapped, be sure the center bolt is there and tight...it's ground too

As for the codes, work them in order.

With those errors, I'd want to know that the multi-wire ignition switch down on the right side of the steering column isn't coming apart...older ones tend to do that. Did you inspect the engine harnesses you can reach with the hood open?

You said those are 'key on' - they might be ok with a cold engine, not running. Did you mean 'key on, engine running'? Was it warmed up well?

But there isn't much point in all this, I think, really, if the latest pcm is bad too.

Munipit
10-23-2015, 10:19 AM
I have checked the 3 grounds on the wiring harness for the 89 sc being

1. behind the driverside headlight labeled as main pcm ground

2. ground at pcm in passenger side kicker panel

3. the ground on the drivers side cylinder head

Ignition swith also replaced brand new unit

Heck even the engine ground on the passenger side frame rail even installed test jumpers at all contact locations (need a pinout to test at pcm connector) but my fuel pump circuit works and I'm sure that the sensors and fuel priming and fan circuits are all grounded by a common point by the pcm so if some work and others don't it doesn't seem to be a loose ground (but I could be wrong)

I have even swapped the entire engine(long story) with all different sensors and a different engine and injector harness the only things that haven't been replaced well at least with a good unit are the pcm and engine harness that passes through the firewall with the pcm connector

So what happens on a cold start the car will start and run like a million dollars after its warm it won't start until the gas pedal is held down and it's cranked for a minute or 2 then huge clouds of black smoke rough run then cleans out back to running

The codes explain this as default values for the ect put temp at -40 so it's flooding a warm motor because it thinks it's in Alaska during winter

I have been fighting this gremlin for 8 months and is the reason I got a sc with a mp3 blower(and a bunch of other goodies) for 1000 bucks.

I have also seen 3 other posts with these exact codes all 89s and 90s so it seems to be a repedetive problem but none of them have posted a resolve

jman2000
10-23-2015, 11:43 AM
Had this exact same problem before I sold my '89 5 speed. When it was started it would run rough, idle like ~~~~, sometimes die, and when it was warmed up it would stay running but run rough and seem like it was missing, I think I had a lot of these codes. Car also ran rich if you stepped on the gas black smoke would come out. I couldn't figure out the problem so I sold it. No one seems to have the answer. Made me hate SC's after all I had done to it.

Munipit
10-23-2015, 06:11 PM
Ok so after poking around I found all 6 sensors share a common wire splice which goes to pin 46 of the pcm and is the blk/white wire anybody know this wires function( ie ground or reference voltage wire or signal wire)

Munipit
10-23-2015, 08:46 PM
Ok so pin 46 is the ground circuit for all 6 sensors and it's grounded internally in the pcm. Pin 60 is the main pcm ground which is properly grounded so I jumped ground to pin 46 and now I have reference voltage on all 6 sensors which should indicate the pcm internal ground for pin 46 is bad however does anybody know if pin 46 is constantly grounded and if not what prompts the pcm to ground pin 46

Munipit
10-24-2015, 08:05 AM
Looks like I fried pin 46 in the ecm it failed the ohms test between pins 60 40 and 46. With 46 having a burnt trace common with voltage on the signal return.

Verified voltage on signal return wire now all I need to do is find out were it's coming from......

Munipit
10-24-2015, 07:11 PM
So silly me I spent some time chasing voltage on pin 46 that was supposed to be there since I left the pcm connected (2nd step in test procedure is to remove pcm) so anyhow I ended up finding my mistake(a few hours later) and discovered that there was no foreign voltage on pin 46 so thanks to stang.net (I tried to post the picture sccoa doesn't like the format) there is a photo of what the burnt trace in the pcm pin 46 looks like and how to repair it with a jumper.

So I took the pcm apart and soldered the jumper in place and now all of my sensors have reference voltage.(and ground)

So I took the car for a spin and noticed it ran much much better(as it should) but I still had a CEL and a wot stumble.

So I pulled codes and got codes 22,49,32,34 and 41

So only one of the original 6 the baro was throwing a code and I now had 4 new codes

So I preformed a circuit test for the baro and dis both ended up being bad luckily I had brand new ones on the self since I swapped them out before and what do u know I only have codes 32,34 and 41 and the CEL only comes on after the car reaches temp

Codes 32 and 34(both egr) are because I bypassed my egr when I put my mplll blower on

So another circuit test for code 41 and I will still have a CEL for the egr lol