Ok guys I want to see if anyone has any input/experience on this one.

I am working on a '96 Pontiac Sunfire with 2.4L/auto for a friend.

Car was running fine and then all of a sudden wont idle and only runs if you keep feathering the gas to get it into the (much) higher rpms. When first started it will idle normally for a few seconds and then start surging which gets more pronounced and then will finally die. He has replaced the TPS and MAP. He then talked to a mechanic friend of his at work who suggested to spray carb cleaner into the throttle body and if it idled smooth it needed a fuel pump ( he had seen it a million times I was told). He replaced it and the filter with no change so he decided to change the pressure regulator as well, also with no change. At this point he is a few hundred $$ in and asked me to bring my scanner over to maybe help figure out what is going on. So I stopped by last night and plugged her in. I am thinking either bad ECM or connections at it…

First some details…

My scanner will not "communicate" with the ECM according to the display when I try to access any SES diagnostic codes. There is no light in the dash as supposedly the previous owner removed it.

BUT, I can access the live data with the car running. I had him spritz carb cleaner in the TB to keep it idling so I could see some date.

With the car idling this way I found some really weird data.

Front "precat" O2 shows 1.0475 volts

Rear "aftercat" O2 shows .445 volts

Neither moves at all…. both flat line at that voltage when viewed in graphing mode on my scanner.

So at this point I though maybe the cat was clogged and suggested he drop the cat pipe and with open manifold we fired it back up… no dice. Not a single change except it was now loud.

So he kept it idling while I looked at other data…

Ign Adv at idle is - 34 degrees. With a small rev and let off it will raise to -9 but that was as high as it went. Negative timing, WTF?

Short term fuel trim is - 42% and hardly moved

Long term fuel trim is dead seat at 0% and never moved

MAP reading was pretty steady at 9" which seems low to me for a lil 4 but I also do not know what normal is for that car. It was steady reading. I did not bring a vacuum gauge to verify this true.

TPS read as normal with movement.

RPMs seem to match what I saw on the tach.

Load varied and as expected would raise as the car ran rough.

So with all this known I feel there are too many faulty readings for one sensor to cause this. Could very well be wrong, but the gut says ECM at this point.

But as we were talking after we shut it down he brought up that the ECM is under the fender apron and that the plastic stone guard/splash shield has been missing for awhile and he did his best this past winter cleaning the snow, ice and salt off the ECM and its wires !!!!!!!!!!!! I asked him WTF? .. and got an empty stare with a "yeah I know"….

So I myself am kind of leaning towards either a failing (or failed) ECM or just faulty ECM connector wiring. My advice was to pull the ECM out of its location and look for obvious corrosion. Then to disconnect any wiring to it and again check for corrosion. If all looks ok I then suggested to pick up a DVM ( he loses my tools when borrowed so we stopped that years ago ) and check continuity from a spot where the wires are good and clean from the harness ( I suggested a good 6" before the ECM connector) and its prong in the connector. Wiggle the plug and make sure all seem solid. Then check the ohms for each if solid. Any doubt I suggested to hit the boneyard and find the same car and cut these plugs off and graft them into his car. That way we would know the wiring is solid.

So I come to you guys,,,, anyone ever experience something like this or otherwise have any other advice?

Agree on the checks to the ECM I would open it and clean it with a electronic cleaning spray and close it using some silicone for a water proof seal.BTW coil cover fails once a year in this cars so it is a suspect. I would also check IAT and all vacuum hoses for a leak. Definitely get it scanned to get the codes....

John Winship wrote:First some details…

My scanner will not "communicate" with the ECM according to the display when I try to access any SES diagnostic codes. There is no light in the dash as supposedly the previous owner removed it.

BUT, I can access the live data with the car running. I had him spritz carb cleaner in the TB to keep it idling so I could see some date.

Part of the reason I lean towards a failed ECM.

My buddy pulled the ECM out of the car. Was pretty dirty and corroded all over. Not a surprise considering the splash shield is non existent. He then went to unplug it. 3 plugs in total and 2 came right out. The 3rd one was pretty much corroded in place. Said it took him all of a half hour working it back and forth and whatever else needed to get it undone. He said that the connector itself and the terminals in the cavity of the ECM were very badly corroded and he saw a lot of green in there. So I ordered him a used ECM and he sourced (used) new plugs from a boneyard as well as a splash shield. Considering what he saw and showed me on the connectors I said my best suggestion was to get the wiring and ECM back to solid before we go any further. ECM came in today. He also called to say he got the ECM plugs from the junkyard after work today. I get over there and figure take the one bad plug and one at a time cut the wire and splice onto the new (used) plug in the same location till all of them are hooked up.

Simple right?

Well, it turns out he thought it would be a good idea to cut the plug off his car and take it with him to the JY to make sure it matched up!!

Problem I am having is I have 3 GRN/WHT wires all next to one another, 2 GRN and 3 WHITES all next to one another as well. The other 13 wires match as far as color and location so I am pretty comfortable there.... but damn. I need an ECM pinout to know where these common wires go.

John Winship wrote:My buddy pulled the ECM out of the car. Was pretty dirty and corroded all over. Not a surprise considering the splash shield is non existent. He then went to unplug it. 3 plugs in total and 2 came right out. The 3rd one was pretty much corroded in place. Said it took him all of a half hour working it back and forth and whatever else needed to get it undone. He said that the connector itself and the terminals in the cavity of the ECM were very badly corroded and he saw a lot of green in there. So I ordered him a used ECM and he sourced (used) new plugs from a boneyard as well as a splash shield. Considering what he saw and showed me on the connectors I said my best suggestion was to get the wiring and ECM back to solid before we go any further. ECM came in today. He also called to say he got the ECM plugs from the junkyard after work today. I get over there and figure take the one bad plug and one at a time cut the wire and splice onto the new (used) plug in the same location till all of them are hooked up.

Simple right?

Well, it turns out he thought it would be a good idea to cut the plug off his car and take it with him to the JY to make sure it matched up!!

Problem I am having is I have 3 GRN/WHT wires all next to one another, 2 GRN and 3 WHITES all next to one another as well. The other 13 wires match as far as color and location so I am pretty comfortable there.... but damn. I need an ECM pinout to know where these common wires go.

that was stupid.

Solution: Make smart friends.

freelancer1988 wrote:that was stupid.

Agreed. And only a touch more than your very useful reply.

I am glad that we are on the same page. Glad I could help.

BEING SERIOUS... I personally would go back to the junkyard and mark each pin and trace them down one by one on where they go. Obviously on the same year and not the cut one, lol. I would also bring a multimeter. Draw a nice little diagram of the pinout and where they all go. I can try and get the diagram for a 1996, but you will still have to trace them.

I seriously can't believe he cut all the wires without at least marking them. I still think that was stupid and I will not retract what I said, but you are right about me not being helpful. I will apologize for that. Good luck and hope you get it fixed.