Two different codes and detonation

[jj98cobra]

I have a 98 cobra. It threw a p1143 a few weeks ago which is an evap system concern. And it began hesitating under light throttle probably 1/8 to 1/4 open. It's kinda like a misfire or detonation. After I cleared that code a p1151 popped up and has since been the case. I believe this is an o2 bank 1 code. But I don't know if it's upstream or down. I have an o/r x pipe with MIL eliminators. Anyone else have or had an issue like this?

 

[jj98cobra]

So no opinions or input?

 

[mwolson]

P1151 - Lack of HO2S-21 Switch, Sensor Indicates Lean

A HEGO sensor indicating lean at the end of a test is trying to correct for an overrich condition. The test fails when fuel control system no longer detects switching for a calibrated amount of time.

Some possible causes:

Electrical:
● Short to VPWR in harness or HO2S
● Water in harness connector
● Open/Shorted HO2S circuit
● Corrosion or poor mating terminals and wiring
● Damaged O2 Sensor
● Damaged PCM
Fuel System:
● Excessive fuel pressure
● Leaking/contaminated fuel injectors
● Leaking fuel pressure regulator
● Low fuel pressure or running out of fuel
● Vapor recovery system
Induction System:
● Air leaks after the MAF
● Vacuum Leaks
● PCV system
● Improperly seated engine oil dipstick
EGR System:
● Leaking gasket
● Stuck EGR valve
● Leaking diaphragm or EGR
Base Engine:
● Oil overfill
● Cam timing
● Cylinder compression
● Exhaust leaks before or near the HO2S(s)

I'd smoke test the evap system first.

 

[jj98cobra]

Would the evap system really affect the cars performance the way it has been?

 

[mwolson]

Actually it sounds to me like you have at least two different problems. The prior DTC leads me to suspect your evap system, and the part throttle detonation makes me suspect your EGR system.

EGR cools the mixture and allows the PCM to run extra spark to get more power from less fuel at part throttle. If the PCM is adding the spark and the EGR is not working properly, it could cause part throttle detonation.