ported tb + no screen = bad

[John_D.]

With all the debate on whether removing the maf screen is good or bad, I had left mine in for the last few months. However, after porting the tb a couple of weeks ago, I decided to test it now and see what happens in combination with the porting.

Let me tell you, it is very bad. (bad as in "not good")

The first problem is an unstable idle, to the point that the headlights would dim as the rpm's dipped up and down and the engine would almost die.

The second (and much bigger problem) is that the top end was way off. Yes, the top end... I thought the problem would be limited to idle and low flow conditions.

I had audible ping for the first time.

And more telling, were the autotap readings for the o2 sensors at wot. I broke way out of the .88-90 range that I'm normally in. And I'm not talking like .7's or .6's even. More like .3's!!!!

Without the autotap I would never have known how bad it was. The reported air flow readings were nearly 20% lower than the flow numbers when the screen is in, which of course told the pcm to add much less fuel, even though the same (or more) air was flowing into the engine.

Put the screen back in, and readings went right back to the .88-.90 range.

So the moral of this story is keep the maf post intact, or keep the screen, but don't get rid of both.

[ June 19, 2002: Message edited by: John_D. ]</p>

[slacker69]

my question is does this apply to the 98+ f-bodies cause we dont have a post, but after i took the dremel to my throttle body i do have a uneven idel and it sometimes feels like it is gonna die but never does. My main question is that if it is bad then can i put the MAF screen in even though I spray a 75-100 wet shot of nitrous. I have really bad topend right now and if you say it is really killing topend i will put the screen back in. Please let me know thanks.

[pgriffith]

I would assume it apply's to '98 cars because he has a '98 arctic white camaro. I took my screen out. I got a little rough idle but WOT seems the same. But my TB is not ported. It is all stock.

[John_D.]

Mine's a '98 so I would say it applies to the '98. We are cursed with the angle tb, so it might be better in the 99+ with the straight intake. They seem to tolerate it better, from what I've heard on here.

About the wet shot, are you spraying before or after the screen? I would think if you spray after the screen, then it shouldn't matter. If you're spraying before, I can't answer that one, maybe one of the other wet shot members will know.

I'm putting an 85 dry shot on mine, before the screen. (the nozzle is mounted in the silencer at the moment, but may get moved if I ever get rid of the silencer.)

I was amazed at how bad the top-end was. Not so much seat of the pants bad, although it did seem to take longer to wind out, but bad as far as running so lean. I'm sure it would make a big difference at the strip, and eventually hurt the engine too.

My port job was both the top and bottom half of the post, so the problem may be more pronounced in mine.

[Skinny]

I took my screen out when I put my nitrous on only for one reason: I KNOW that screen can't handle a nitrous backfire. I'm afraid that if it was to backfire then the screen would blow to bits, then get sucked right into the engine. BAAAAD.

[Ironman24]

So you completely ported out the whole MAF post? And you just have the 2 MAF wires hanging down into the TB? Very interesting. I left the top half of my post intact and have no screen. My flow numbers went up a bit but I didn't see any change in O2 readings.

OH, I don't consider the angled TB a curse, I dynoed with the whisper lid hooked up and also with just the TB open and there was no change in the numbers. So it's not hurting us like I used to think it was.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Ironman24:
So you completely ported out the whole MAF post? And you just have the 2 MAF wires hanging down into the TB?

Oh, I don't consider the angled TB a curse, I dynoed with the whisper lid hooked up and also with just the TB open and there was no change in the numbers. So it's not hurting us like I used to think it was.<hr></blockquote>

I did port the whole thing out. When I started on it, I had asked for some advice on finishing the job, and Magnus asked if I had done just the bottom or the whole thing. That got me thinking about it for the first time, and the more I thought about it, the more I wanted to try it... The maf sensor plastic stub is still hanging in there, but it's really small compared to the post. I even ported down that flat spot where the idle air passage starts.

The angled tb is not really that bad... Except for the disturbance in the airflow, regarding the maf. I'm curious if the straight intake would be better with the missing post. The bulk of the air must be missing the maf wires, the way it has to round that corner, based on the incorrect readings I was getting without the screen.

[Magnus]

Very interesting.. Could you do some more testing John?

I really don't see the screen making THAT much of a difference.

Perhaps it is because of the bend in the intake, the air is directed downard where as the maf sensor is more toward the top.

Very interesting.

[pgriffith]

WOuld it be possible to use a 99 TB and put it on our 98 cars? Reason being is because 99's are streight.

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Magnus:
Very interesting.. Could you do some more testing John?

I really don't see the screen making THAT much of a difference.

Perhaps it is because of the bend in the intake, the air is directed downard where as the maf sensor is more toward the top.

Very interesting.<hr></blockquote>

I don't mind testing some more. Are you thinking some other variations on the test, or just repeating the results? I will have to richen up the wot dial on the maft before running it that way again, because I'm scared of hurting the engine with any wot runs at .1-.3 o2's.

I'm still surprised at the wot difference. I would never have figured it would be that much. The idle was very bad too.

If I had an old tb to experiment with, I might try to put the maf sensor in the bottom of the tb somehow. Another thought is to put something like a ls1 maf on it, but not sure how far experimental I want to go with this thing...

[John_D.]

<blockquote>quote:</font><hr>Originally posted by pgriffith:
WOuld it be possible to use a 99 TB and put it on our 98 cars? Reason being is because 99's are streight.<hr></blockquote>

I've thought about this. If I had access to one, I would probably eventually try it. The throttle by wire (vs. cable)would be one issue. I'm guessing the '98 throttle cable assembly could be fitted to the 99+ tb with only a little work.

The throttle blade shaft would be the part that needed to be the most similar. If it protruded out the same distance (or further), and had the same diameter with the same 2 flats on it, then the assembly would fit with no problem. The next hurdle would be the cable bracket, but that could be fabricated if needed.

The maf sensor and tps would probably need to be the ones that came with the '99, and then tied into our wiring, if the plugs don't already mate up.

If anyone can add some factual information to this, please do.

[ June 19, 2002: Message edited by: John_D. ]</p>

[Ironman24]

<blockquote>quote:</font><hr>Originally posted by pgriffith:
WOuld it be possible to use a 99 TB and put it on our 98 cars? Reason being is because 99's are streight.<hr></blockquote>

I looked hard into this and the result was, PITA. You need the intake also and a 99 computer and the electronics to convert to the fly by wire setup and harness for new sensors on the TB. The main problem is not the TB itself but the flange on the intake is cast at an angle on the 96-98 and the flange on the 99+ is straight. I checked the bolt patterns and they don't match either.

John,

The MAF sensor, it is in 2 pieces. The bottom half of it actually comes off. You will notice a seam in the sensors plastic. I would highly suggest pulling off the bottom half before it gets sucked into your motor. Mine did when I had a nitrous backfire. This pic may help you understand what I'm talking about. In the pics the lower half I'm talking about is missing.

http://www.carolinafbodyclub.com/iro...es/maf_jpg.htm

I'm also curious in more testing. I'm baffled why you had that low of O2 readings.

[ June 19, 2002: Message edited by: Ironman24 ]</p>

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Ironman24:
I looked hard into this and the result was, PITA. You need the intake also and a 99 computer and the electronics to convert to the fly by wire setup and harness for new sensors on the TB.

The MAF sensor, it is in 2 pieces. The bottom half of it actually comes off. You will notice a seam in the sensors plastic. I would highly suggest pulling off the bottom half before it gets sucked into your motor.<hr></blockquote>

Oh yep, I was thinking intake and all, to do the swap. Something else I'm thinking which is opposite of what everyone else has said so far --instead of having to inherit the wired throttle control and tie it into the wiring and pcm, is going the other direction and putting the '98 cable onto the throttle shaft itself, doing away with the throttle by wire.

Thanks for the tip on the plastic thing! I will check that out tonight. It might be glued on though... I don't want to break one of those wires trying to wrestle the plastic thing off. Your explosion might have loosened yours up? :D Man, what a mess, from those pictures you posted. Whew!

p.s. The maf sensor will be easier to take off now, because I used the "tit-less" screws that used to be on the maf metering plate to put it back on. Since I have no metering plate anymore... (for those of you who have tried to take the originals out, and found that little raised piece of metal where your torx bit is supposed to go).

[ June 19, 2002: Message edited by: John_D. ]</p>

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Ironman24:
The MAF sensor, it is in 2 pieces. The bottom half of it actually comes off.<hr></blockquote>

Ok, more experimentation, as a result of this comment. I took the maf sensor out, cranked on the bottom half with pliers, and broke the bottom half off. It was glued or stuck, but came off without breaking the wires. [img]smile.gif[/img]

There were still 2 little ears/tabs sticking up on the sides, so I whittled those down too, with a box cutter. Couldn't stand to see them just left sticking up there, interfering with the airflow around the sensor wires.

Too bad I forgot that rule where you don't put any body parts in the line of fire if the knife slips... I guess if the car ever turns up missing and recovered, I can prove it's mine by the dna residue all over the inside of the maf sensor. Hey but my thumb should heal up ok in a day or two...

So anyway, next round of testing will be to see if removing that excess plastic from around the wires made a difference. -- If the air is bouncing off the bottom of the maf up towards the sensor, the plastic would have shrouded the sensor, and now it's opened up.

So we'll see. No autotap tonight though... Will autotap in the morning.

[Dominic]

Both my 2000 and my 2002 have had no issues with the !MAF Screen, so it must be an issue only on the angled throttle bodies of previous years. Sorry you cut your finger!