alright, so i got this problem lately where my car pretty much falls flat on its face under 2500 rpm. it will stutter and hesitate and it basically sounds like a misfire. so it keeps throwing a code. anything above 2500 rpm it runs perfectly fine tho…
p0138 which is high voltage for the second o2 sensor, which means a rich condition. so i pulled the code’s freeze data from the scanner at work twice.
heres the readings from the first time
throttle 18%
rpm 2596
load value 45.4%
map sensor 44 KPA
coolant temp 190
intake air temp 100
short term fuel trim 1 -12.1%
long term fuel trim 1 3.9%
(heres where the problem lies i think) short term fuel trim 3 -100.6%
long term fuel trim 3 -100.6%
vehicle speed 38mph
fuel system 1 closed
fuel system 2 n/a
and the second time
p0138
throttle 25%
rpm 2532
load vaule 77%
map sensor 78KPA
coolant 183
intake temp 69
short term fuel trim 1 -10.9%
long term fuel trim 1 10.9%
short term fuel trim 3 -100.6%
long term fuel trim 3 -100.6%
speed 48 mph
fuel system 1 closed
fuel sytem 2 n/a
im not entirely sure how the fuel trim readings are supposed to be, but i was told from a couple mechanics that the ones for the trim 3 readings are pretty far off. the numbers are supposed to balance each other out or somehting like that. i dunno, the sensor is relatively new, as is the cat. i’m open to ideas here, or an explanation of what the trims mean so i can start to track down this problem. its pretty annoying
for those of you that don’t know, 96 gsr
might be a small vacuum leak? those are some big big trim corrections…
what exactly do those trims do/mean?
As I understand it:
Fuel trim basically comes down to injection duration. A positive value means a longer duration which means the ECU is adding fuel above its anticipated “normal” level. A negative value means a shorter duration so the ECU is adding less fuel than “normal.”
Over time, the ECU will “learn” what your engine needs to maintain A:F at 14.7 (usually the target A:F for a stock ECU on an NA car, but technically a stock ECU could target any A:F that it was given). This knowledge is stored as the Long Term (LT) fuel trim. The ECU uses this as its “normal” fuel trim. The Short Term (ST) fuel trim is what your ECU uses to adjust “on the fly” in order to tweak your A:F when the O2 or another sensor reports out of range.
If your issue is at low RPM it sounds like a vacuum leak. The other option would be a bad O2 or bad MAF?
Correct, The ECU “sees” the A/F ratio as reported by the O2 sensor, and takes information about vehicle speed, throttle percentage, load etc to make a correction to reach a A/F ratio that is acceptable for mileage and power (within a certain range). Small vac leaks trick the ECU into seeing more air, and thus delivers more fuel (positive trim numbers). Trims in the area of 10-15 percent are slighly high, let alone 100%…so you’ve got to find the source. Try hooking up a vac gauge and see what the needle does and begin the troubleshooting routine.
I dont think its a vacuum leak because he is seeing the computer pulling fuel. His car is running rich. I would say you have to check a few things. MAF sensor, MAP sensor, and TPS sensor.
if it is a mass air flow system, then I would go that direction first. Pull it out of the housing and see if you have a lot of dirt on the wires that the sensor uses to determine the amount of air going into the engine. If it is dirty you can clean it with MAF cleaner you can get at a auto parts store. I would prefer to use my vantage to check the MAF, TPS, and map sensors, but you can do it with a multimeter or scan tool. Sweep the TPS with the key on and engine off and read the voltage coming out of the sensor. If there is a quick jump or drop off, then it is bad.
I just looked at your post again, and look at the difference in the MAP sensor readings. I think the MAP might be your problem.