Problems after exhaust install and 02 harness

[djj62478]

Hey guys, just put a new to me of off road h pipe on(last one didn't fit correctly to the cat back) and put the cat back on. Also I recently learned the 02 harness plugs into a 8 pin connector I believe on the passenger side under the maf, so while the car was in the air I switched that from the driver side 8 pin connector near the strut tower coil area I had it in, to the other by the maf. Now previously with it running out of the h pipe and the 02 sensor harness on the wrong connector the car seemed to run fine. I started it up now with the cat back on and the 02 harness plugged in where it should be it surges like crazy and then eventually dies and won't start again without help from the throttle. Does the connector I moved the 02 harness from go to anything important that is now not plugged in? Here's a pic of it

 

[djj62478]

Disregard the 8-pin connector I found the other end it was under the battery tray hooked it up I could see it's something for the dash setup all good there. Just don't understand this problem didn't start happening until I reconnected the o2's to the other side and put the H pipe in. Could I have put them in backwards? Also to know when it does start and surge till it dies it has a strong smell of fuel

 

[djj62478]

Also one thing I did leave out is when I re-ran the oxygen sensor harness I noticed that it obviously had two plugs for each sensor but one of the plugs had a thinner wire sticking out of it that was frayed at the end? Would that be my problem what does that go to?

 

[General karthief]

Check codes, tell us what you find.
Check for vacuum leaks.
Have you reset the computer?
This should cover it....

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...

www.stangnet.com

 

[djj62478]

Just checked codes, got 85, 66 and 96. And like I stated earlier the only thing I did was install another off-road h-pipe move the O2 sensor harness to the other side of the car where it was supposed to be and put the mass air meter and cold air induction back on after I plugged in the O2 sensor harness. Only thing I could think of is that mystery wire that comes off the one 02 sensor plug not really sure where it goes and it's cut and frayed. Thinking maybe since it was plugged into the wrong plug originally it didn't cause an issue because the 02s were technically not working and now that it's in the correct one it has to go somewhere? I don't know maybe I'm wrong. How do I reset the computer, just take the terminals off the battery?

 

[General karthief]

Computer reset is in the link but correct, disconnect the battery for several minutes.
What year and got pics of that frayed wire?

 

[djj62478]

That's the single wire there. Any research is telling showing me it's supposed to have a plug on the end and go into the oil pan? Not sure though, if that's the case then would that cause any issues or is this just a coincidence that the wire is frayed and it's making me think that it's causing an issue?

 

[djj62478]

So I just went back to the car reconnected the battery after about 15 minutes, seem to run better still surged a lot and will eventually stall out but definitely better than yesterday, also check the codes again and got the same 85 but then it blinked once then once paused then once and once I'm guessing that's 11 for all codes clear?

 

[Praetorious]

That wire is for your low oil level in your pan, once it goes down a quart that light should come on,i dont understand how the o2 harness can be plugged into some random plug and be working fine before but now that its were is supposed to be its not?

You are correct about the placement of the harness, its plugged in under the mass air and runs around the front of the pan to both banks where the o2s plug in,have you owned the car long? sounds like someone monkeyeed with it and didn't do things correctly, if you are going to keep the car you might want to invest on a INNOVA code reader (part number 3145), they are cheap and beats that counting flashes and beeps scenario.

When resetting the computer disconnect the negative wire and then turn your headlights on or hit the brake pedal a few times, that will drain whatever power is stored in the car, if the car was changed from auto to standard and someone used the wrong harness that could also be cause for other issues, something else to look for.

 

[djj62478]

Do you think it could be an 02 sensor issue? Any way to rule that out?

 

[Praetorious]

When you swapped them out to your new off road pipe did you happen to see what they looked like? if they are completely carbonized and covered in soot it could cause some smaller issues but i wouldn't say major stuff like bucking and jumping, o2 sensors help the computer develop the proper fuel ratio for the engine by reading the oxygen present in the exhaust etc and adjusting accordingly so you might have detonation issues but i think your problem is elsewhere.

You mentioned before you did all this work the car was running fine,so it wasn't missing or nothing? i know this is not the right way to do things but have you tried to start it with the o2 sensor wiring disconnected? just for grins? might be worth to see if it changes anything, these cars are really easy to work on but sometimes you get a gremlin and it can make you question your sanity,lol

 

[djj62478]

I'll try that when I get home I'll just disconnect it from where the main harness plugs in under the mass air flow sensor

 

[Praetorious]

Sounds good, Yeah sometimes it takes trial and error,i have a 89 and a 91,i have had just about every issue these cars are famous for,lol

 

[djj62478]

Sounds good, Yeah sometimes it takes trial and error,i have a 89 and a 91,i have had just about every issue these cars are famous for,lol

Yeah it's a tough situation because when I got the car it needed a head gasket and it was fairly stock except for a possible cam didn't really know trick flow intake full exhaust 75 mm mass air and throttle body. Then I went and put a 306 in it with forged internals Edelbrock aluminum heads Comp cams and trick flow upper and lower shorty headers off road H pipe and kept pretty much everything else that was on there.

 

[Praetorious]

Sounds like you have a nice setup, i tell you a story about my 91,many years ago i had this issue were i would drive a few miles and it would die,if i pressed the brake pedal it would either die or the radio would cut out,i was at my wits end and i was throwing parts at it which is not the thing to do,one day on my lunch break at work i was messing with it and i went to start it and this coworker was walking by and he said "man, your car just arced bad by the firewall" it turned out to be the 3 dollar ground strap that goes from the intake to the firewall, after i replaced that i had no more problems with it, the old one was green with corrosion.

Some car brands i have seen dragging ground straps on the ground and they run perfect but these cars we own are not that way,they are very picky about grounds and clean electrical contacts.

 

[AeroCoupe]

Make sure the ECU ground behind the battery is in good shape as well. There is also a ground wire that is part of the injector harness that is typically grounded on the back of the passenger head or bell housing or on the intake. Make sure that one has a good ground as well. Believe this wire is orange?

 

[djj62478]

There is none going from the head to the intake.

 

[Praetorious]

Yes, like Aerocoupe said,your injector harness should have a orange wire coming out of it around the drivers side towards the back, this wire needs to be grounded, its usually grounded to the last intake bolt or behind around the bellhousing like previously mentioned, in the picture im sending you,see that lone wire around the middle that has the eyelet ? thats the wire you are looking for, needs to be grounded, its not easy to see, look at it from the passenger side, just lean in and you might see it bolted somewhere.

 

[djj62478]

Yes I have that grounded.

 

[General karthief]

Most surging issues are a vacuum leak, look over the link I posted read the directions and stop jumping around hoping to fix it, it details the step by step diagnostic tests