[billyNOTnice]

So about 2 years ago i posted about this before. Anyhow i've not ran o2 Sensors in that long, and i've been through a few setups now, but i'm back to using a pms and I thought about trying to run o2's again with this new motor to try and improve my poor fuel economy. Anyhow here's the deal. The car runs great without the o2's hooked up. The car runs at a commanded value that i set in the PMS. When i plug in the o2 harness, the car will pop through the intake, sputter, and my wideband will read from stoich to lean just flipping back and forth and the car develops what feels like a breaking up missfire feel and it shakes a bit.

SIDE NOTES: Bought car had a completely different motor, ecu, meter etc.. had the same issue origionally. I now have a new motor, differnt ecu, brand new meter, and i'm still having the same problem as before.

I just bought brand new o2's for the second time, and the car just runs like dog#### when i plug them in. Does anyone have any idea what could possibly be causing the car to go nuts? I'm going to try and find a wiring diagram for the o2 harness tomorrow and see if i can't test some wires and see if maybe i got something wacked out. This issue is killing me. I've been trying to chase it down since i bought the car, and i'm just clueless.

One other thing i've noticed.. (Possibly related, but not really sure) My Autometer tach jumps around every so often. I'm not sure if it's being half broken, or if it's the what seems to be an electrical issue effecting my cars operation. It does it with both the o2's hooked up and unplugged though.

Please and thank you for the time, and suggestions. I would be thrilled to get this issue put to rest finally.:hammer:

 

[jmbaltz]

PM me with your email address and I send you the wiring diagram from the '92 EVTM.

 

[terryr]

Are you using the same firing order as stock? Using the 302 order makes the car lean out. Does the 93 cobra have its' own computer?

 

[cocomojak]

I have a 93 coupe.306 NA.PMS and a wideband on board.I havent ran stock O2's for about 5 years now.Car runs great.I just tune to what i see on the wideband.And standalone is turned on at 3500RPM and 50% TPS.And its pretty deadly in the brackets.I know that doesnt awnser what is wrong with your car,but my setup,has really no tune or driveability issues since I have done that.The only other thing I had to do for good driveability,is remove the tube from the oil fill to thottlebody.I have it setup to + or- 14.7 at light throttle cruise speeds,and 12.9 to 13.1 WOT.

 

[billyNOTnice]

terryr, i have no idea what you are talking about, but I am using an A9L PCM.

cocomojak, my problem is not tune related. I've got some electrical issue.

 

[wick]

Billy, I had an issue last year sort of similar to this and it was a ground issue. Like I said on SCS, is the o2 harness for your year? The pinout is different. It could have always been screwed up and just not ever caught. Whats the rest of the history on the car?

 

[FASTFOX91]

i believe this is a ground issue as well

 

[gray86hatch]

Didn't you have issues with your AEM?

Tim

 

[terryr]

terryr, i have no idea what you are talking about, but I am using an A9L PCM.

Old 302s have a different order on the camshaft than 5.0s. So 4 injectors are wired to different sides. So when the O2s read they adjust the wrong injectors, and lean out the engine over a short time.

Also, check if the engine is grounded properly.

 

[billyNOTnice]

I'm going to do some testing here with the diagram i have. I had a clutch destruction issue this past weekend, but i'm getting to it lol

 

[red9250]

Run a ground strap from one of your rear h-pipe/cat-back bolts to the body. You can thank me later.

 

[billyNOTnice]

i'll give it a shot as soon as i get my clutch back together

 

[billyNOTnice]

just an update, i got my clutch in, and car is back running again, so i'm ready to tackle this o2 issue. I'll post my progress once i have any lol. i'm gonna get crackin.

 

[billyNOTnice]

well i'm not really sure where i'm at right now. I've tested the voltage with KOEO and it is at 11.8 testing with the ground in the o2 plug. The color of the loop on my o2 sensor harness is light blue with a yellow stripe. I pulled the ground off the back of the head and inspected it, and it appears to be fine. I've tested the ground by the washer fluid reservoir and it also seems to be just fine. So what to do now?

 

[billyNOTnice]

Well guys i'm still completely baffled as to what to do about this problem... I didn't try running a ground strap yet, but that's because i'm running a downpipe, it has no bolts anywhere close to the o2's until you get back to the mufflers. I still had this issue before I went turbo though, so I know it's not the turbo kit.

 

[billyNOTnice]

anyone here have any idea of what i can do to figure this issue out?

 

[34blazer]

dont know much about the tuning setup you are using, but, since you had unplugged the O2s you were putting the ecm into open loop. what do you have your closed loop parameters set at? try and bump your timing up a couple of degrees at idle. what is your idle timing set at now? and the base timing? does PMS have initial timing scaler or main spark bias?

 

[wick]

What fan are you running? Is it on with the key or on a "proper" relay set up? Where is it grounded to? Does this happen when the fan is on? Off?

 

[billyNOTnice]

it's a manual switch, and It's relayed. It's not the fan though. I'm at the point now where i almost want to just tear my harness in car and engine bay out and replace with other ones.

 

[flasch192]

it's a manual switch, and It's relayed. It's not the fan though. I'm at the point now where i almost want to just tear my harness in car and engine bay out and replace with other ones.

Get ahold of joel5.0 on here or sbftech.com he can help u out im sure, if all test pass and the fuseible link for the o2s are good i would have too say open up the computer and check for burnt diodes, if ur car was ever switch from a auto to manual or vise versa its a good possibility