Air/fuel Swing In Wideband, Car Stutters

89gtsleeper · Aug 1, 2016

Ok guys. Decided to take a look at mass air and here are my findings. Engine running, voltage between pins A and B is 14 volts. I think I'm good there. Next, with the maf off the car and in the house, I checked resistance between pins A and B, then from C to D. The results were both at only around 4-5k ohms... Much lower than the 10k mentioned above. I put the meter back on the car, then probed between C and D with the car at idle. Only comes up with about .25 volts. Reached in and gave it a few throttle jabs while watching the meter, and it only jumped to around 1.1 volts at the most. Could this meter be the problem?

Noobz347 · Aug 1, 2016

89gtsleeper said:
MAF is a pro-m 75 mm calibrated for 42 lb injectors.

This is the elephant in the room. Does anyone know why? Where are the digital tuner dudes? @hoopty5.0

89gtsleeper · Aug 1, 2016

Or Is the low voltage simply pro-m's way of trying to trick the computer into altering the pulse width of the injectors?

hoopty5.0 · Aug 1, 2016

If you're still running with the a9l, unplug the MAF and see how it runs. If it's an improvement in limp mode, your MAF may be shot

89gtsleeper · Aug 1, 2016

hoopty5.0 said:
If you're still running with the a9l, unplug the MAF and see how it runs. If it's an improvement in limp mode, your MAF may be shot

Thx. That's the next thing on my list. I'll update tomorrow evening.

jrichker · Aug 2, 2016

89gtsleeper said:
Ok guys. Decided to take a look at mass air and here are my findings. Engine running, voltage between pins A and B is 14 volts. I think I'm good there. Next, with the maf off the car and in the house, I checked resistance between pins A and B, then from C to D. The results were both at only around 4-5k ohms... Much lower than the 10k mentioned above. I put the meter back on the car, then probed between C and D with the car at idle. Only comes up with about .25 volts. Reached in and gave it a few throttle jabs while watching the meter, and it only jumped to around 1.1 volts at the most. Could this meter be the problem?

That does not look good at all...
Use the diagram to locate the MAF output pins on the computer connector. Hook up your DVM or Multimeter, get a helper to watch the meter and go for a drive. Then compare your results to the figures posted in the MAF test path.

89gtsleeper · Aug 2, 2016

Haven't driven it yet, but with the mass air unplugged, the car is reasonably similar. Seemed to start up a little easier than normal, but it is still acting the same as far as swinging rich then lean. That aspect seems unaffected. I'll clear the codes then take her for a spin tonight with the mass air on and checking signal. If that still doesn't look good, I'll try driving around the block without mass air to see if any better.

Noobz347 · Aug 2, 2016

An A9L, 42 lb/hr injectors, and a calibrated MAF...

In my experience, it's going to run like crap until it's tuned.

Injector pulse minimums and injector pulse slopes differ too much from the behavior of 19 lb/hr injectors for this setup to run well without a tune.

Yes, your calibrated MAF will "lie" to the computer and tell it that there is only W amount of air versus X amount of air (this lowers the injector pulse so that the 42 comes down far enough to be equivalent to the 19s in this condition).

As the mass of air rises, the meter sends an approximate equivalent to compensate for the larger injector.

What the computer DOESN'T know is how a 42 lb injector really acts. The minimum pulse for a 42 lb/hr injector is much lower than that of a 19. The EEC doesn't know this and a tune is required in order to force the EEC to adjust for these differences.

Now... There are some mechanically tuned alternatives that work great on the race-track. You on the other hand, are shooting for power and streetability. You need a tune. If in doubt about the meter, send it in and have it checked. They can also provide you with a detailed 32 point transfer function (for your tuner).

Air Flow Research makes probably the best aftermarket meters but you still need to remember that 'calibrated' meters will sacrifice resolution (the more the better for drive ability) when they shorten the scale to accommodate for larger injectors.

Reliably, 30 lb/hr injectors are about as large as I would go with nothing but a 'calibrated' meter. The further you get from 19 lb/hr injectors, the more there is to compensate for than just a formula for calculating the mass of air being ingested.

89gtsleeper · Aug 3, 2016

I've been thinking a lot about the injector size and plans for the car. I agree 42 is really stout unless I install a blower cam and turn the boost way up. I'm going to drop this thing down to 30 lb injectors. Found a deal on some solid frpp 30 lb and a matching 75 mm pro-m. Keep it simple at 5-6 lbs boost and this should be a good combo. It will also give me an opportunity to redo some vacuum lines and plugs on the upper intake and work over the PCV config. I'll have this knocked out in the next week or so, and will report my findings.

Gearbanger 101 · Aug 3, 2016

Leave the injectors and MAF where they are. They aren't the problem. You need to have the car retuned. You know as well as anyone, that 5-6psi will keep you satisfied until about the next pay check, then you'll be looking for more. Only you won't be able to, because after you swap to the 30's, you won't have the injector to support it. Spend the money you're thinking of dropping on the injector/MAF combo on a new tune. Your drivability issues will be gone and you'll be back into boost before you know it.

The 42's can be tuned to run just like stock. I've got 60's in mine and they'll tune up just fine. Heck, the new thing is 80lb injectors now for the forced induction crowd. No such thing as too much injector anymore.

a91what · Aug 3, 2016

Very true... hell I just tuned a 1.6l Honda with a mega squirt ecu, 75lb injectors idles like stock.

Noobz347 · Aug 3, 2016

Gearbanger 101 said:
Leave the injectors and MAF where they are. They aren't the problem. You need to have the car retuned. You know as well as anyone, that 5-6psi will keep you satisfied until about the next pay check, then you'll be looking for more. Only you won't be able to, because after you swap to the 30's, you won't have the injector to support it. Spend the money you're thinking of dropping on the injector/MAF combo on a new tune. Your drivability issues will be gone and you'll be back into boost before you know it.

The 42's can be tuned to run just like stock. I've got 60's in mine and they'll tune up just fine. Heck, the new thing is 80lb injectors now for the forced induction crowd. No such thing as too much injector anymore.

What he said

89gtsleeper · Aug 3, 2016

So I can't believe this, but it think I figured out a large portion of my issue... Though I'm still trying to make sense of why this issue would have just started out of nowhere. So a few weeks ago I was reading about crank case pressure and I read how most people that install a blower remove the vacuum line from the throttle body to the valve cover oil fill tube, then install a breather filter on the valve cover. At the time, I immediately noticed the car ran much better once I did that. Then suddenly I have all this issues weeks later, mid drive. Today I put that vacuum line back on, and voila. Car runs like it did right before the issue started.

However, I'm still cant get it to ever run much more rich than 14 under any throttle condition I've tried. I shouldn't have to put it all the way to the floor and get into 4-6k rpm in order for the car's computer to start pushing toward 12:1 AFR should I? I won't do that until I have the tune in better shape in terms of pulling the timing during boost and possibly installing fmu or chip to get fuel pressure increased on the top end.

a91what · Aug 3, 2016

if your getting into any kind of boost then you will show lean....
consider this 7psi has the effect of adding 50% atmosphere into the engine.. that means your engine is consuming 50% more air [generally speaking theres a lot more to it than this] you need more fuel to make it even out.

Don't go into boost without a FMU/ TUNE.

89gtsleeper · Aug 9, 2016

Got the msd btm installed to handle timing. Car is running fine for daily drive duty. Fmu with discs will be here tomorrow, and also have a new fuel pressure regulator for peace of mind. Prob going to try the 4:1 disc first. Going to tackle all that this weekend and see what she does. Trying to figure out if I want to alter my pcv setup while I've got the upper intake off.

elarm1 · Aug 11, 2016

Woah, I think your in dangerous territory without a tune. What fp, spark plugs, heat range. Your playing with fire....ask a man who's popped two sets of hgs playing with settings.

89gtsleeper · Aug 11, 2016

Running new autolite plugs a heat range colder than stock gapped at 35. Fuel pressure a little higher than stock, about 42 with vac removed. Car seems happier there than 39 for daily use. Btm set to kick in at 0 boost and pull 1.5 degrees per pound of boost. Mityvac will be here tomorrow so I can verify and calibrate this setting. Still running base timing at 10 degrees.

a91what · Aug 13, 2016

Start with the 10:1 disk in the fmu... remember rich will save the motor lean kills. Afr in boost shoot for 11.5

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