suddenly runs rich
suddenly runs rich 1973 corvette with a 1999 ls1 4l60e out of a TA.rans for 3 years no problems.suddenly runs super rich.burns my eyes.all 8 plugs Black.I changed the plugs.still super rich.stumbles.off the start like it wants to stall.I did nothing to the car except for cosmetic things.No codes with a simple code reader.I pulled one o2 sensor.sooted up.but wiped it off with a rag,no spray and it still looks good.what would make this happen so suddenly?where do I start to look?TIA
TECH Fanatic
Joined: Jan 2009
Posts: 1,063
Likes: 475
From: Bostwick, GA.
"I pulled one o2 sensor.sooted up.but wiped it off with a rag,no spray and it still looks good".
Not the way to verify the sensor operates correctly.
A scan tool that will read activity is needed.
Not the way to verify the sensor operates correctly.
A scan tool that will read activity is needed.
On The Tree
Joined: Jan 2006
Posts: 180
Likes: 16
When checking for vacuum leaks, do not just check engine vacuum, also check any vacuum accessory, like HVAC switches or (maybe) the system to pop up the headlights. I had that in my '70 Impala with a LQ9, the vacuum leak that made the engine run extra rich was under the dashboard!
My fuel mileage was horrendous, too... I only got a code when the computer could not dump enough fuel anymore to compensate for the lean signal...
My fuel mileage was horrendous, too... I only got a code when the computer could not dump enough fuel anymore to compensate for the lean signal...
I really looked hard for vacuum leaks.Nothing found.BUT.I found a blown fuse.I replaced it and the car does run better but the scan too still shows -39 short term fuel trim.long term 0 at idle.under load it stumbles at take of.and when I let off the throttle.it wants to stall ans back fires out of the right side.Did i already ruin the o2 sensors?Doe the ecm need to relearn?thanks
some numbers from the code reader all at idle.
TPS 0.0
RPM 800
MAF (lb/m) 2.33
MAP (HG) 11.5
TEMP 201
IAT (f) 97
Short term 1 -39.1
short term 2 -39.1
long term 1 0.0
long term 2 0.0
02S 11 0.945
02S 12 0.443
02S 21 0.945
02S 22 0.445
TPS 0.0
RPM 800
MAF (lb/m) 2.33
MAP (HG) 11.5
TEMP 201
IAT (f) 97
Short term 1 -39.1
short term 2 -39.1
long term 1 0.0
long term 2 0.0
02S 11 0.945
02S 12 0.443
02S 21 0.945
02S 22 0.445
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update.replaced the MAF sensor with a known good unit.numbers dropped.but still something off.I listened to wave 1957 and systematically checked for vacuum leaks.Brake booster NG.probably the only part that is oringinal to the car.well 50 years was a good run
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If it's running that rich, -39 on the STFT, the 02's probably aren't going to switch.
Have you checked the fuel pressure?
What does the MAP sensor show, key on engine off? It should be 99-102kpa depending on your elevation?
What does it show with it running? The size of the camshaft will determine that. Stock should be around 40kpa, a big donkey dick cam would be around 70kpa
Make sure the MAP sensor hasn't popped out of the intake and the little orange grommet isn't missing.
Have you checked the fuel pressure?
What does the MAP sensor show, key on engine off? It should be 99-102kpa depending on your elevation?
What does it show with it running? The size of the camshaft will determine that. Stock should be around 40kpa, a big donkey dick cam would be around 70kpa
Make sure the MAP sensor hasn't popped out of the intake and the little orange grommet isn't missing.