I got an Actron fuel pressure gauge from Autozone today and hooked it up. I am consistently getting 56psi with a loss of about 3psi after 5 minutes. So the fuel pump should be ok.

I have been taking a look at the Long and Short Term Fuel Trim readings. I am noticing that the LTFT readings are consistently between 10-13%. From what I have managed to glean so far online after going through several articles, anything in the double digits indicates a problem. Now I have to try to figure out what is going on.

 

Not necessarily. The STFT + LTFT should = near 0, unless the difference is more than 10. That is adding negatives and positives. (at idle).

Not to mention that fuel trim CANNOT be used as a diagnostic without other inputs. It never tells you anything directly.

 

The difference between the stft and ltft is consistently 10-12%. I do realize this only gives some basic direction, but I am trying to get a list to go through for what to eliminate.

 

Sounds like fuel supply issue. Maybe a bad injector?

 

Given that I already changed the upstream O2 sensor not long ago, I decided to put in a new downstream sensor today given that it has 130k on it. It may have done the trick. I drove about 400 miles today, and the car is running smoother, and my mileage is definitely back where it should be. Been averaging 29.6 mph with 4 people, car loaded down, and a/c on doing 80 on the interstate.

 

BTW, I think there is a rule against multiple IDs.

 

(Didn't realize that I even logged in with the other ID. I never could get it to login which is why I use my current login).

An update. I did suspect the problem to be a injector related even though I never got any check engine lights. I went ahead and changed the spark plugs at 50k even though they didn't need it just to rule them out completely. I also cleaned my Specter K&N type air filter, ran Seafoam through the brake booster line to clean out carbon in the head/cylinders, ran Seafoam in the oil for about 100miles before changing it, and cleaned both the throttle body and MAF sensor. Car still ran a bit off. I ordered 4 new AC Delco injectors from Rock Auto and installed them.

We just took an 800 mile trip, and the car is purring perfectly, even when throttling hard on it with a loaded down car/AC running on the Interstate (not that I was exceeding any speed limits or anything ). I ran 2 tanks of Redline and several tanks of Lucas through her before, and it just didn't solve the issue. Replacing the injectors did the trick. One of them must have not been spraying quite right. Its nice to have it running smooth again.

 

Glad you got to the bottom of the problem.

FYI: If you kept your old injectors, you likely can find a local or semi-local place to test and rebuild them as necessary and hang onto them as spares if you are planning on keeping it long-term.

 

I did keep them and that is a good idea. I would think it would be cheaper to have them rebuilt than if I had to buy them again down the road.

 

Or post them up for sale?