P0171 and MAF (1 Viewer)

[VanIsleCruiser]

I've got the P0171. Mechanic thinks its MAF. Test on MAF is 4.8G/S @ idle says it should be 6-7; 13.2G/S @ 2000 rpm should be 17-18. Is this right? New MAF was $1100 CAD. , so bought a used one from wrecker, he says its better but still out of spec. (Dont have the numbers)And light still on.
Other things that have been done are O2 senors tested both come back good, one looks newer and one aged, smoke test(no leaks), fuel system pressure and engine vacuum all good. It has factory air filter and no cracks in intake pipe, fuel filter was changed(aged), fuel injection system cleaned, y pipe gasket replaced ( small leak). Still P0171. What do you guys think, should i try another MAF, or something else. Truck runs good like always has and if light wasnt on i proably wouldn't think anything. The only things i notice different are sometimes a very slight flutter at idle in rpm but most wouldnt even notice and increase in fuel consumption.
Thanks Mudders

 

[Malleus]

22250-66050? You can do better than $1100. Unless you're in a hurry.

Did you recently run out of gas?
What year?

 

[VanIsleCruiser]

22250-66050? You can do better than $1100. Unless you're in a hurry.
View attachment 1575963

View attachment 1575965

Did you recently run out of gas?
What year?

Never out of gas and its a 97

22250-66050? You can do better than $1100. Unless you're in a hurry.
View attachment 1575963

View attachment 1575965

Did you recently run out of gas?
What year?

 

[Malleus]

P0171 is lean mix. The code is indicated when the ECU compares two ratios to the sensor inputs, from a couple of sources.

Have you tries clearing the code and has it come back?

Has your fuel system been checked and does it check out? I'd look at fuel delivery before I replace the MAF.

Also, just because it's first on the list, have you confirmed that there is no leak in the intake (from filter to injectors)? You can lose a lot of money swapping parts on this problem.

Where did you get your performance specs?

 

[Malleus]

I guess my greater point here is that this isn't a dire emergency.

If it was my truck, I'd take all the time I could to completely check the SFI system before I replaced any parts. The benefits are twofold. First, you don't waste money throwing parts at a problem. Second, you get a really good baseline look at how the system currently functions, so you can compare that against the acceptable specs.

 

[VanIsleCruiser]

Thanks

I guess my greater point here is that this isn't a dire emergency.

If it was my truck, I'd take all the time I could to completely check the SFI system before I replaced any parts. The benefits are twofold. First, you don't waste money throwing parts at a problem. Second, you get a really good baseline look at how the system currently functions, so you can compare that against the acceptable specs.

Thanks for the reply Malleus, heres the specs from mech. We tried used Maf( mech still thinks no good), new fuel filter, new gasket y-pipe, clean fuel injection system. I think im going to try and find a MAF in town here (one other cruiser that i know about) and throw that in if i can convice buddy to let me try and rule out that. Maybe bad injector, very slight rough idle sometimes. They think Fuel delivery is good.

 

[landtank]

what is the long term fuel trim at idle? Also I've had dirty/fatigued connectors on the MAF plug. Pulled each wire out and bent the leaf spring to make a better contact.

 

[Malleus]

This is the point I was getting at. It looks like your mechanic's using a generic testing protocol. He needs to use the FSM. I doubt your problem is the MAF. It's more likely a fuel delivery problem. This isn't something a mechanic can "feel", the system components and operation have to be tested. There are explicit diagnosis and troubleshooting procedures for this code.

 

[landtank]

This is going to be a bit of a challenge to identify. I personally wouldn't fluff it off as not being a serious problem. Sure if it's on duty side of the equation and the ECU is compensating for a lack of fuel delivery then you are basically running normal. But what if it's with the control side such as a cracked Y pipe or leaking exhaust manifold gasket where the raw air is being drawn in pre O2 and now the ECU is over richening the mixture from that. Running rich will effect the lubrication of the cylinder walls.

And I also doubt it's the MAF sensor.

 

[VanIsleCruiser]

Thanks guys, ill have better look on control side (manifold) they were talking about possible unmetered air pre o2 on control side and we did replace leaking y-pipe gasket, no luck. I do think its running rich(smell fuel from exhaust maybe? and increase in fuel consumption) its frustrating that its going to
be some simple but proving difficult to identify. The shop is good and reputable and has experience with cruisers.

Another point that i havent mentioned is the cel did come on last year for a week or so and then went out for six months.

Still going to try and borrow MAF from vehicle that i know is good and see. Also going to have better look at the connections, they look great but two MAF's not being good seems strange. They test good manully but mechanic feels airflow numbers are off.

 

[VanIsleCruiser]

This is the point I was getting at. It looks like your mechanic's using a generic testing protocol. He needs to use the FSM. I doubt your problem is the MAF. It's more likely a fuel delivery problem. This isn't something a mechanic can "feel", the system components and operation have to be tested. There are explicit diagnosis and troubleshooting procedures for this code.

Fuel delivery has been checked, not sure on exact tests but will have a chat with them and see.

 

[Qball]

Just clean the maf with MAF cleaner.


Also check for intake hose and vacuum leak, that also gives you 171 every time. On these old beasts most of the time it's something simple.