Hi guys

So I have an intermittent P0171. Actually, I don't know if its intermittent becuase i think it comes back every 3-4 drive cycles consistently. So ... its a P0171 that I'm wrestling with. I've googled and googled and all the P0171 threads are a couple years old at this point so **** it, let's make a fresh thread.

My 04 MT RX8 has a Revi intake from racing beat. other than that, its stock. Well, lowering springs but thats not going to be causing issues here.

Things that i have done.

1. I've ensured that the VFAD nipple is capped off and that the cap is still present.
2. I've smoke tested the car from the accordion tube (the one with the three hoses running off it) back and I do not see any smoke seeping from any discernible places under the hood. I'm using the Autopro smoke machine. The little red box one.
3. I measured my LTFT and it points to a vacuum leak for sure. Its sitting at +20% at idle. MAF is reading ~4.7 to 4.9g/s though....

I need some ideas as to how to chase this down. I know P0171 codes are notoriously difficult to track down.

Some thoughts:

1. I just replaced the fuel pump in October so its still relatively new...would leaky injectors maybe cause this?
2. I did just replace all of the UIM gaskets with new OEM ones but those are pretty easy to seat in their respective grooves so I dont believe thats an issue. Also that wouldve showed up in my smoke test if it was.
3. SSV was replaced recently with new solenoids. Could the solenoids at the back of the upper intake manifold be a cause of the random lean condition?


Car idles fine. Pulls to 9k smoothly no hesitations. Warm starts just fine. I'm not naive to the fact that compression could play a role here but I think thats jumping into the deep end before looking at possibly easier solutions.

Let me know what you guys think.


Thanks in advance.

 

4.7 is just about 20% short of the 5.7 g/sec airflow you should have at idle. So yep, vacuum leak and not a small one. Trace every vacuum hose. Smoke doesn't work super well for the far away or hidden vacuum lines.

Is the MAF firmly seated and do you have the air straightener screens ahead of it?

 

@Loki I'm actually glad you responded. Ive noticed you chime in on every one of the P0171 threads I came across hahah

Ive heard that 4.7 - 5 was the expected range? Maybe i'm completely wrong.

i've even considered putting the stock intake back on because i wasn't getting a lean code until after the REVi intake was installed. but i was getting a different code with the stock intake which was P0456 which was a small leak in the evap....

MAF is definitely firmly seated. The REVi has a nice aluminum mounting tube that lets me seat the MAF pretty well and yeah the screens are also installed ahead of the MAF.

When you say "trace every vacuum hose", what should i look for if smoke isn't helpful in that regard? A visible check of how the hose looks?

 

5.7g/sec at 800 rpm is the reference. Yeah, examine the hoses. A leak that big should be apparent. Some folks have had a cracked vacuum block under the UIM where the intake valve solenoids get their vacuum.

 

Do you think the solenoids themselves would be suspect?

Ill tear into the manifolds this weekend. What a pain

 

Self induced problem. Ditch any and all intakes that aren't OEM if you're not bothering to recalibrate the maf for them.

 

Plenty of people run the Racing Beat intake without recalibrating.

 

Or so they think they do. In between rich and lean misfires there's room enough to park a lorry. Doesn't mean the engine runs at its best. I get that isn't the top priority for most, but at least when it runs so poorly you notice it without any logs... some light bulbs should turn on.

 

thats what i fear too.

how do you go about recalibrating the maf? i assume you mean some kinda tuning....

 

I have one, have looked at logs. It's fine. Have you?
Other intakes - maybe, but RB and MazdaSpeed have the same dimensions and the same straighteners the stock intake does. There's not 20% of noise in the signal.

You can back to stock or calibrate the MAF if you want, but that's a long way to find out that wasn't the problem.

 

random thought - does smoke test before the throttle plates effect the results? i put the tester into the accordion tube that sits in front of the throttle body. i wonder if the throttle plate being closed effects how much the smoke can propagate through the system.

 

Most of the vacuum connections are before the throttle, so in theory, shouldn't affect it, but if you have a damaged gasket in the intake manifold, the smoke wouldn't get there. Has the intake manifold been taken apart ever?

Come to think of it, how did the issue start?

 

Yeah, i took apart my whole upper intake manifold system to replace the three solenoids in the back. I also replaced the SSV while i was in there and the purge valve solenoid.

I bought new gaskets for the upper intake manifold assembly and made sure they were seated in the grooves. They're pretty hard to mess up because theres a tab on each of the gaskets that keeps you aligned.


I hate to say it but the issue started after i installed this racing beat intake.

With the stock intake, i did have a P0456 code but that was due to a defective purge valve solenoid that i bought.

 

so embarrasingly...i went to go and perform a smoke test and i notice my oil cap was completely missing. it was (fortunately) laying on top of the engine and ive been driving like that for the past day while running these tests.

im going to re-do my readings and.....re-evaluate myself. lol

 

That'll do it lol. Was not on my bingo card for this one.

 

Unfortunately, that didn't resolve it.

I tightened the oil cap, reset my fuel trims by disconnecting the battery and waiting for 45 minutes (i also pulled the room fuse for good measure) and i'm back at 4.6 g/s at the maf and at idle right after resetting fuel trims, I'm seeing +10% LTFT. This is the same result as before.

Smoke tested again - this time behind the throttle body (jurys still out on whether that makes a difference) and there isnt any smoke coming from the manifold. VFAD is capped still.

ill throw the stock intake back on and see if it numbers return to normal.

 

Threw the stock intake back on.

Maf readings still low and LTFT sit at 16%. At what point does the ECU trigger the lean code for a high fuel trim?

I wonder how long my LTFTs have been elevated but i never noticed because i never saw a CEL.

Ill continue to work on the upper intake manifold and check vacuum lines.

 

Agree with Ciprian .... ALL aftermarket intakes need recalibrating ... Racing Beat is no exception. I've tuned multiple cars with multiple intakes so have seen this first hand.
A lot of the time ...you get away with it. That doesn't mean it's optimal though.

 

See if you can borrow another maf sensor to try.

 

Fair enough, but would that cause the airflow to be 20% out? We're far from optimal here

 

When in doubt: revert to OEM. E - v - e - r - y - t - h - i - n - g. Hardware and software. If not sure, log both maf voltage and maf flow and compare with stock scaling.


If you say it does the same with stock intake I'd check this table out before chasing other far less probable culprits: 22+ yo worn and tired fuel pump, poor fuel pump voltage, dirty injectors.

 

It would appear it's not the case here, given the stock intake didn't fix the issue. But, yes I've see a Racing beat intake where airflow was MORE than 20% out - actually caused by a mechanical installation issue/poor design. Once that was resolved the error was below 10%.

 

To OP's question : the code triggers when fuel trims (which max at 25%) can no longer compensate for the unmetered airflow that isn't coming through the MAF. So whatever gap there is is still there. I don't believe this is a fueling issue since your MAF is actually reading not enough air for sustaining 800rpm idle - yet the car idles.

What you could try to narrow it down is pinching each of the vacuum hoses at the intake to see if any of them changes the sound or fuel trim. Quick way to isolate the problem circuit, or figure out which ones aren't the problem.

 

Thanks for all the input guys. The stock intake doesn't lean out the engine enough to trigger the CEL anymore but I'm still reading high LTFT. So something is causing a vacuum leak but...JUST enough to not trigger a light? I must have been driving like this for a while and never noticed until I swapped the Revi intake over....

Its also important to consider....I used some cheap amazon solenoids for the 3 solenoids in the rear of the UIM. could that be a source of a vacuum leak? i know they're one way solenoid valves but...if it fails wouldnt that throw a CEL?

@ciprianrx8 I use the Torque App connected to an old samsung phone i have. I dont think the app provides MAF voltage but thank you for putting that chart up. Ill figure out a way to measure MAF voltage.

The photos below were taken after driving the car for a couple days. The particular data set below is after a 45 minute drive. No issues with drivability. No check engine light. Revs all the way to 9k just fine. Idle is solid at 780-800

 

Measured the maf voltage by backprobing the signal wire on the maf sensor. After the car warms up, im at 1.12 - 1.13 volts so the maf reading is correct at 4.4g/s.