Intake MAF Adjustments needed

[DWebb]

I did away with the stock airbox. I installed a cheap spectre cone with a 2 3/4" I.D. MAF sensor adapter which to my surprised positioned the sensor quite well. I was able to locate the MAF sensor 7 3/4" from the throttle body. I lost a bit of hp, but wow it sounds really good. Now if only I could get the MAF to read the correct Air Mass.

My problem is this: The original MAF housing had an I.D. of 2 3/8". The new housing is 2 3/4". The stock housing area is almost 4.5 in. sq., while the new one is almost 6 in. sq.. The MAF sampling area is still only 0.2 in. sq.

Crap what is a better way to say this?

The computer calculations based on constants which I have changed, are now false and it is under estimating actual air mass causing the engine to run lean. nearly 20 : 1 or worse.

Now that the CEL is on and I have DTC P0171 ( No that is not caused by gas cap) < that would be gross evap system leak detected >
Having monitored O2s I see 1,1 switching, but unable to access mode 6 data on this vehicle I can't tell you for certain where I am on the switching threshold except that obviously its failing because I have a hard fault p0171.

I need help from some of you engineer types. I'm understanding the MAF to be a wheatstone bridge design and am accustomed to reading output as a freq.

Might I be able to install a resistor/capacitor in the harness to compensate for the smaller sampling area of the MAF in the new larger dia. bore. Sampling ratio went from 1/22 to 1/29 total.

I am quite handy with the 555 and have built many multipurposed freq generators in the past.

Or better yet can stock ECU be flashed to compensate.
Or would it help to install fatter injectors.

I could go on forever about why I really don't wanna put that monstrosity of an airbox back in.

Oh yea! That fin thingy doesn't fit in the new tube, it is same dia. as new tube. +++ don't wanna restrict air flow, just want more fuel to restore stoichiometric AFR.

Thanks in advance.

[darkSol]

Actually P0171 is system bank too lean...

You're running a dangerously lean condition - a wideband O2 sensor/display would confirm this but I have a feeling you're in the 14.5-15.2's wide open throttle... NOT good.

[turbophil]

Seems like just about every other vehicle on the market has an aftermarket MAF conditioner for the end user to tweak MAF signals to manipulate the AFRs on the car, so I know it *can* be done.

Here's the catch, the learn on the Lotus ECU seems to be particularly difficult to manipulate and tends to do the opposite of what the desired out put is when we try to play with it (after the learn "sets in")- like with the use of piggy-backs. That said, I don't know anyone that has tried to condition the MAF signal in particular as you're talking about. You should give it a go and see how it works. You'll likey get your desired result at first. The trick is to check back in a few hundred miles and see if the results are still there... then again in another few hundred miles... It would simply be awesome if it works and sticks...

Best,

Phil

[DWebb]

Yes you are correct, Darksol, it is running lean, which is what I'm mean to correct. Google "mode 6 data - O2 switching threshold".

Thanks Turbophil, very encouraging. Just to let you know I haven't tried to tweek anything yet, but I definately am getting some power back. The PCM does seem to be correcting for the lean condition and perhaps in the morning after I have visitation with my brother I will hook up the laptop and see where my Lft's & Sft's are sitting. Today it just sounded richer and seemed to pull harder. PCM corrections seem rather slow

Kinda wish my ass-dyno had a display screen or a printer port.

so I just finished taking a leak, and as I was standing there it dawned on me, " I don't need an engineer" I need a shop vac, a 12v battery and a Fluke.

I could condition the MAF signal on a makeshift flow bench without putting my engine, harness, or PCM at risk. That could save me oodles of time as well

[DWebb]

I had noticed on other posts that there were some problems with the angle the MAF sensor sat in the fixture. In order to prove first that this was not my problem i made a sleeve out of 2.5" coolant hose commonly used on detroit deisel engines. The CEL stayed off and throttle response and idle are both very crisp again at low RPM. Top speed suffers about a 4-6mph loss at 95deg ambient temperature. That is probably more due to the abrupt edge of the cut rubber hose than airflow restriction resulting from decrease of internal diameter. All in all the results do confirm my suspicion about the overall sampling ratio deficiency. Oilfield work is slowing down and I may find myself having much more time to tinker this winter. Hopefully i can have this worked out soon.

[brookester]

I'm using a MAF housing from a Subaru STi and a huge cone filter designed for trucks and I don't seem to have any trouble with CELs.

[JUNGLISTluder]

Simple solution. Read the whole thing.

Custom BBmod TS Pro1 Intake - SUCCESS!

[charliex]

You'd have to adapt the curve back to stock setting, which isn't going to be easy with a resistor, the ecu can be retuned to rematch but its a lot of work.

A 555 isn't going to help either, since its not a frequency.

If you're running a bigger tube, what is the end result/change for the MAF sensor output.