Backfire under load W/ PO 171 & PO 174

[Toronado3800]

Here is a week or two of background.

I had a random misfire and then mercifully a misfire cylinder 7 code a week or so back.  The primary resistance on the coil pack tested well and it was only one cylinder so I inspected the plug wire.  Resistance was in range but every once in awhile it would lose connectivity when I moved.  So I replaced the wire with a good testing old ones and the car has run better if not perfect since.

What I have been feeling is a bit of a miss or hesitation on acceleration and today a couple backfire like pops climbing a hill.  For several years my CEL has largely been on with a permanent PO139 HO2S Slow response bank 1 Sensor 2 and po1139 HO2S Insufficient Switching Bank 1 Sensor 2 error.  The previous owners' failed attempts at fixing this is why I got the car so cheap. 

Now I also have a couple new ones, PO171 Fuel Trim System Lean Bank 1 and PO174 Fuel Trim System Lean Bank 2 errors.

My fuel filter is less than 5 years old.  Is the correct plan to change it then check fuel pressure?  Anything else I should look out for? Or what would your order of operations be?

[AUROD X]

OK I had a similar issue, so after checking everything I finally got to the fuel injector and it was bad. Replaced, erase code, fired up and drove it since with no problems.😅

[tigger]

Both banks lean at the same time is a good indication of a vacuum leak somewhere after the MAF.

And I guess a dirty or faulty MAF could cause lean codes.

GL

[Toronado3800]

Nov 14, 2018 12:50:28 GMT -6 tigger said:

Both banks lean at the same time is a good indication of a vacuum leak somewhere after the MAF.

And I guess a dirty or faulty MAF could cause lean codes.

GL

My fuel pressure off was 45psi and at idle maybe 43.  Running at different throttle positions it seemed to hold rather steady also, never below 40 and I don't think ever above 50.

Then, thank you for the lead, I took the MAF off, cleaned it and reinstalled.  Then I cleared the codes.

Since I've driven the car about 20 miles with tons of time idling picking up the kid at school and a couple hard launches.  It never backfired or had a bad miss running and no CEL activity, although 20 miles might be enough to pass emissions around here but not really tell if you have an O2 code.  I still don't think its part throttle acceleration off idle is perfect but it is 30 degrees and icy out and a 20 year old car.  

So I THINK following your lead to fool with the MAF I have fixed it.  Tomorrow I have about a 60 mile round trip to make in the snow so we'll see!

At least now I have a car which if I took it to the mechanic he'd probably send me home to wait for it to actually do something tangible before paying him to do maintenance I should just do myself while guessing.

If it comes back is there an effective way to check a MAF sensor or injector with a multi-meter and a cheap scan tool?

Thanks guys.

[RCA1186]

Yeah I was going to suggest a vacuum leak as well. Maybe the backfire valve, intake gaskets, a grommet/elbow on one of the PCV hoses. Good that cleaning the MAF took care of it (so far) hope it stays that way!

[Toronado3800]

I'm about 90 miles in now and I think the imperfection is a miss, or I should say it definately has a miss I can feel at idle in gear and I think thats what I feel when driving.

It has not thron a code yet. My plan is to look for pending codes every so often and try to guess which cylinder next time I feel like playing with my old school timing gun.

[Toronado3800]

Ah, this morning was rough on the Olds lol.

First the CEL came on while warming up. Then after about 20 minutes of driving it had a back fire/pop/miss noise and feel while axcelerating around 40mph today and I pulled the codes. It had a random misfire, the O2 sensor as usual and a new one, P0741, Torque Converter Clutch system stuck off.

Is my order of operations for that P0741 is to check the trans fluid and wiring to the switch then pretty much see if its just overdrive affected and live with it I imagine? FWIW, I have not done any transmission fluid changes on this car over 5 years and 50k miles but that sounds like a non fluid dependent part, correct?