Granatelli MAF question

[prophiseer]

I recently bought a Granatelli MAF w/ cold air tuning for my '99 GA 3400; I installed it per their instructions (disconnect both + and - batt terminals), fired it up and let the computer re-learn its idle. Well, after letting the motor run for about 45 minutes, I drove it around a bit (every time I can to a stop, the motor would surge for a coupla seconds until it finally evened out, also bogged down something terrible when I'd go WOT), came back home and cut it off. I couldn't get it to restart unless the motor cooled for about 30 minutes. Odd. Never kicked a DTC (no pending, either). Put the factory MAF back in and the motor runs fine again . . .

Anyways, I'm also running a DHP 1.0 PCM. I called customer service at Granatelli and they said there's nothing wrong with their unit (based upon the same description that I gave them), and DHP states something along the lines of if I'm not pulling enough air to justify the MAF, then I really don't need it (or something to that effect). Currently, my motor is mostly stock, 60mm TB, CAI, plenum spacers (I thought I was running my ported manifolds, but realized Sat they're still sittin in the motor room at the shop ).

Anyone else have this type of problem with a Granatelli MAF w/ a DHP PCM? Just curious for some thoughts 'fore I box it back up and send it out . . .

[Darin]

All a Granatelli MAF does is send false information to the the PCM tricking it into thinking it's running lean.

If you are tuning the car yourself the granatelli will only cause you problems.

[prophiseer]

Yeah, I was just looking for a little more unrestricted air flow to the motor. I ran into the same problem a month ago when I bored out a stock MAF. The sensor couldn't 'read' the change in airflow, and the PCM kicked a sys too lean code (plus the sensor smelt like it was burning ), ran the same way too.

Same reaction with the Granatelli MAF, just no code.

[IsaacHayes]

tampering with MAF's will give you headaches. They seem to be very sensitive to things. Does the Granaelli have a screen in it? Putting one back in will help unless the adjustable thing is just totally defeating the purpose of the MAF giving an accurate reading.

I'm not a big fan of things that fake sensor values to give you "extra hp". Nothing is free by faking a value. Just like the IAT resistor mod....

[SE'sarecool2]

Two things I'll add my .02 on:
1. Have you done anything to the exhaust? Trying to get as much air as possible into the engine and doing nothing to help it get out is kinda pointless. No wonder it won't run right with the Granatelli MAF.
2. Send that Granatelli MAF back and go get a Pro-M one. I've been running mine now for about a year with no drivability issues.

[prophiseer]

Yeah, I've done work with the exhaust; SLP cat-back system, and I've removed the catalyst material from the cat. In essence, she's straight pipes with a SLP muffler.

I don't think the MAF is really "tricking" the computer into squeezing out a few more hp, it's supposed to have a broader range that it can read. I kind of get the feeling their unit might be defective, but that's hard to accurately diagnose with an aftermarket MAF.

DHP made it sound like their PCM isn't compatable with an aftermarket MAF, but they didn't come right out and say that either.

[tejohnson]

If you can change the PCM (as in, you are a powrtuner/hptuners owner) How about sending the MAF back, and pick up an LQ4 maf from a junkyard... Thing is, if you can get to 100kPa at WOT, no MAF upgrade will make you any faster...

The only time this is really necessarry is when you push more then 12-13PSI of boost. Then you need an upgrade...

[prophiseer]

Yeah, it'll prob go back in the mail tomorrow. I was just trying to remove a slight restriction in the intake (hence the ported stock unit), ain't no bigey; there's much better things I can spend the $300 on

thanks for the help, y'all

[AaronGTR]

Porting the stock unit is also a big no-no. The screen is there for a reason. It is supposed to keep air flow straight going over the wires. If you remove it that can lead to an incorrect reading and throw your fueling off. The surges and inconsistent idle you feel is probably the pcm using the O2 sensor and MAP sensor to adjust fuel when it sees the air fuel ratio is off compared to how much air the MAF is telling it is coming in.

The granitelli MAF causes the same problems. It isn't intended to "trick" the pcm and lean out the fuel as someone suggested. They recalibrate the electronics inside the MAF so that it puts out a signal similar to the stock size MAF so the pcm can calculate the correct air flow. This is an imperfect way of doing it though, and of course there's no screen, so again the signal is slightly off. If you have a tuner and can tune your own pcm then it's not a problem because you can adjust for it yourself. As has already been stated several times though, on a mostly stock NA engine you aren't going to see any gain from a larger MAF. I'd send it back for a refund.

[Darin]

It isn't intended to "trick" the pcm and lean out the fuel as someone suggested.

I have been dealing with these POS MAF sensors for years with the f-body's. I am quite sure they are exactly the same as these units. In simple terms, They send a lean reading to the PCM so in turn the PCM will richen the A/F ratio. (Adding more fuel)

The surges and inconsistent idle you feel is probably the pcm using the O2 sensor and MAP sensor to adjust fuel when it sees the air fuel ratio is off compared to how much air the MAF is telling it is coming in.

This is due to the false reading the MAF is sending as I stated above

[tejohnson]

If the MAF is too far off from what the PCM expects, you'll go into speed density mode. Not fun while the cruise control is on and passing folks on the interstate. The CC increases the throttle, the car stalls...

[RednBlack]

So, I guess using a 75mm MAF is out of the question.

I could have saved 10 bux.

[prophiseer]

The surges and inconsistent idle you feel is probably the pcm using the O2 sensor and MAP sensor to adjust fuel when it sees the air fuel ratio is off compared to how much air the MAF is telling it is coming in.

Yeah, but on an OBDII vehicle, even at idle the PCM should be able to bring the motor down to an even idle; not that rough. And anyways, if the PCM detects too much airflow through the 02's (enough that it would cause that rough of an idle), it'll kick a DTC in a heartbeat; the PCM wouldn't be able to compensate for it. Even in open loop, the PCM still monitors the forward 02.

I know I'd have to buy the equipment to tweak the PCM myself, but that's kind of above and beyond my current budget. The beast is back in the mail though, sent it out this mornin.

[tejohnson]

So, I guess using a 75mm MAF is out of the question.

I could have saved 10 bux.

Actually, no. That is not the point. I'm going with an LS6 MAF myself:

http://groomlakelabs.com/index.php?q=gallery&g2_itemId=1790

You can always go bigger, you just need to modify the MAF table in the PCM.

I'm going this route for two reasons... I was seeing ~11kHz at times at 11PSI, and it has a built in IAT. Much easier to deal with when you have to deal with IC piping...

[AaronGTR]

Yeah, but on an OBDII vehicle, even at idle the PCM should be able to bring the motor down to an even idle; not that rough. And anyways, if the PCM detects too much airflow through the 02's (enough that it would cause that rough of an idle), it'll kick a DTC in a heartbeat; the PCM wouldn't be able to compensate for it. Even in open loop, the PCM still monitors the forward 02

The pcm doesn't react as fast though to O2 readings as it does to MAF readings. You'd be surprised how long it can take between the O2 sensor reading rich or lean before you see the correction in short term fuel trims. And no, you won't see a DTC from that. There are many factors that can cause a rich or lean condition and the pcm doesn't automatically blame the MAF if the O2 sensor reads a lean condition for a certain MAF value. I've seen people have this idle problem time and again with these MAFs. Bottom line is you shouldn't buy one unless you plan on tuning the pcm too.