I have a blazer that struggles a lot and thrown misfire codes before. I checked the distributor and changed everything to get good spark.

I am investigating a lack of power under load and I have these values for Fuel Bank, does that point to a possible problem with injectors ??

Long Term Fuel Trim

LTFT Bank1 -2.3% min 0.2 max 11.7
LTFT Bank2 -3.1% min -0.2 max 11.7
LTFT Bank3 60.2% min -97 max 97
LTFT Bank4 -73.4% min -96 max 97

The Short Term Fuel Trim on those are strange as well!!


How do I interpret this data ? Fuel leak at injectors??


I'd go as far as say that all fuel trims are bad, in OL the short terms are fixed (normal and the truck runs like crap) as soon as it goes in CL it's going better but still not optimal. Thus the Fuel Trims adjust to the specific problem present.
Which is most likely a vacuum problem or an injector one . I'd say injector personally, but have no previous experience with this!

 

Looking at the Bank 1 and 2 LTFT readings, they look normal.
You don't have a Bank 3 or 4 so you can ignore those readings.

Same for the STFT readings on Bank 3 and 4, ignore them.

 

^^^+1
Details Man! You have a Blazer, most of us do. What is the year, when did this start, how does it manifest itself and what has been done to it in the past?
Sounds like secondary ignition or fuel delivery. Very hard to tell with lack of DETAILS!!!~sorry, first day off the cig's

 

Negative fuel trim numbers means that the fuel mixture is richer than expected and the PCM is decreasing injector pulse width to lean it out. Your readings of -2.3% and -3.1% are nearly perfect. Rule of thumb is if trims exceed 10%, there's a problem.

Was the problem present when you took those readings?

 

Ok more details.

I will ignore bank 3 and 4.

So here's what happening:
- Start the truck, when in Open Loop it stumbles and throw random misfire code, it lacks power. I changed and verified everything in the ignition system and since then it seem to start better and run better but it lacks a lot of power and the problem is the same, just a bit less bad.

- When hot the truck seem to run almost normally, but it clearly isn't stable, as it will sometimes lack power while accelerating.

So there's a difference when Open Loop and Closed Loop.


Now, I checked the short fuel trim Bank 2 accross many captured frames and it goes from -30% to 26% and that's when accelerating with engine in Closed Loop. Bank 1 is better but still goes from -14 to 28.

Let's see that snapshot :

RPM : 600 (idle)
Bank 1 : 18.5%
Bank 2 : -30.5%
Temp : ~60 celsius

So one bank is rich the other is lean .. Strange thing!

Is that the symptoms of leaky injectors?
Btw my fuel economy is atrocious.. I get 200km per full tank, which is extremely bad!

Timing advance varies a LOT from 7 degrees to 42.5 degrees. While accelerating it goes up and comes back down after accelerations.

Engine coolant temperature for this test was from 60 to 85 degrees.

Also, the fuel trim data at idle for about 65 celsius is : -14.1 and -30.5

Fuel Trim seem to be perfect at 1200 RPM approaching 0%
At 1900 RPM it's at 18% and 14%
On deceleration (933 RPM and down) -10% and -11%
Acceleration 2500 RPM : 14% to 17% and 14% to 18% (That's where it starts to lack a lot of power, up to ~3000 RPM)
Heavy Acceleratin ~2600RPM : 25.8% and 25.8%

And the last few frames when I let it idle and temps are 84 celsius the trim is -8% and -8%

 

HAhaha, ok it's a 2000 Blazer LT, I had this problem for a little while, it was subtle at first, and suddenly the engine wouldn't start, I went to the garage, they replaced the distributor cap and rotor and it ran again, however, shortly after, it started to throw misfire codes and run like crap (before bringing it to the garage, it was misfiring and was lacking power as well).

Now it lacks power but I think I solved the major misfires since i replaced the coil, clean distributor cap and rotor, checked distributor gear and bushing, change all spark plugs (driver side spark plugs are a bitch to change), put dielectric grease everywhere etc.

It's not misfiring at the ignition, it's more like a stumble now and a general lack of power, people must think I am 90 years old and don't see straight when I drive on the road, it's that bad.

 

When the PCM operates in open loop, oxygen sensor data is ignored. Fuel mixture is calculated by using data from MAF, MAP, throttle position, IAT and ECT. When the PCM switches to closed loop operation, the PCM relies heavily on oxygen sensor data for calculating fuel mixture.

Long term fuel trim shows data averaged over a long period of time. Short term fuel trim is live, (real time) data. Short term fuel trim data is far more accurate. Acceleration & deceleration fuel trim data really doesn't tell you anything, the engine needs to be at a constant speed.

Coolant temperature: When the engine is at operating temperature, the ECT should show ~93C to ~94C (~200F). Yours at 85C (185F) is too low. Low coolant temps will cause rich fuel mixtures. Here's how to determine if the problem is the thermostat, or the ECT sensor: After the engine has been off for at least 10 hours, don't start the engine, turn the ignition to the RUN position and check the ECT, IAT and ambient temperatures. They should all be within 1C (2F) of each other. Post your results.

Open loop is where you're experiencing most of the trouble, which may indicate that the ECT is faulty. If it's calibrated low, it will cause a rich mixture all the time, moreso in open loop, than in closed loop. The colder the coolant temp, the richer the fuel mixture.

EDIT: Don't get your hopes up too high on the coolant temp, there may be other problems involved.

 

Stop scaring me!!

Ok tomorrow I'll post these values, hopefully it's a simple sensor problem.

Btw, I have an exhaust leak, seems louder when it's the engine is not operating well (I don't know if that's relevant or not, just posting every details I recall..)

 

In front of the oxygen sensors or behind? Where exactly is the leak?

 

The muffler has a weld and weld points on it, it's on the back, just before the tip. The tube that goes from the tip to the oval "box", this weld is cracked.

Maybe there's another leak somewhere, I will confirm this tomorrow.