GM MAF, now weird...

[Coldandafraid]

Just finished installing GM maf... admired my handywork for a few mins, and then took for test drive.

I was concerned with the translator to wire harness connection because the translator plug is so differently shaped, but my afc, and my pocketlogger were getting an air reading, so I assume all is good.

The car is all warmed up now. So, I drive. And now, whenever I drive (or rev the rpms higher than idle) and then take my foot off the pedal, the car drops to around 500 rpm and has a hard time idling for about 5 seconds and then it recovers and idles normally. But, its a blow thru maf, and it happens whether I have just been boosting or not.

I left all MAFT settings at zero, and left all AFC settings were they were. Pocketlogger tells me at low-throttle, my trims are atill balanced at all rpm points, except at idle, which is 750, (below my first increment - 1000) the car is adding quite a bit of fuel.

So, is it a simple case, of my car being too lean at idle... or something else?

 

[44pirate]

On the Translator your base knob setting should be at 4 or 5 which ever one it is for 550 injectors. The idle knob, what you want to do with that is, watch your LTFT, set it to +5 and see what your LTFT read. Adjust from there.

 

[Coldandafraid]

I just find it odd, that at all my rpm increments on the afc, the trims are balanced, but at idle, its way too lean .

Anyways, I did some tuning, and this is what happened:

On the idle knob on the translator it is +5 notches

And on the afc I had to take away 10% more than what I had previous at 1000 rpm to balance all the fuel added at idle.

And, all the other settings on afc, still almost the same.

 

[kpt4321]

If you're just tuning with the SAFC, then you don't need to touch the MAFT at all.

Sounds like a post-MAF vacuum/boost leak to me.

 

[Coldandafraid]

Originally posted by kpt4321
If you're just tuning with the SAFC, then you don't need to touch the MAFT at all.

Thats what I thought...

Sounds like a post-MAF vacuum/boost leak to me.

Thats also what I thought... but there isnt any place it can leak... only 1 coupler, and the TB connection, and they are solid.

And, for the ammount of fuel I had to add at idle, it would have to be one huge vac leak... I should notice it.

One Idea: Lets say a bov leaked under vac, and the air was sucked straight into the intake mani through the small bov tube... is this possible?

 

[44pirate]

Plug the little intake tube while it's idleing see if it changes anything. I doubt it. I'm not an expert I'm just going by my experiencees with the MAF-T. For my car I have to take out, at idle, on my SAFC -8% at the 1000 rpm setting with the MAF-T idle knb set at +5 on the to get my STFT to hover at 0.

 

[Coldandafraid]

Originally posted by 44pirate
Plug the little intake tube while it's idleing see if it changes anything. I doubt it. I'm not an expert I'm just going by my experiencees with the MAF-T. For my car I have to take out, at idle, on my SAFC -8% at the 1000 rpm setting with the MAF-T idle knb set at +5 on the to get my STFT to hover at 0.

This sounds like what I am doing... adding fuel at idle on the MAFT, and taking away fuel at 1000 on the afc. Except I am taking away a little bit more than you on the afc. But thats probly because I didnt change the base knob for the 550s, and left that to the afc.

When you say +5, do you mean +5 clicks, or +5% (1 click).

 

[kpt4321]

Originally posted by Coldandafraid Thats also what I thought... but there isnt any place it can leak... only 1 coupler, and the TB connection, and they are solid.

And the TB shaft seals, and the BISS o-ring, and all of the emissions vacuum line connections, and the BOV line, and the FPR source line, and the brake booster line, and the manifold gasket, and the throttle body gasket.....

And, for the ammount of fuel I had to add at idle, it would have to be one huge vac leak... I should notice it.

You're not pulling very much air at idle, it doesn't take much of a leak to mess up the mixture.

One Idea: Lets say a bov leaked under vac, and the air was sucked straight into the intake mani through the small bov tube... is this possible?

Only if the diaphram was leaking, which is unlikely and will show up in a pressure test.

 

[44pirate]

Originally posted by Coldandafraid
This sounds like what I am doing... adding fuel at idle on the MAFT, and taking away fuel at 1000 on the afc. Except I am taking away a little bit more than you on the afc. But thats probly because I didnt change the base knob for the 550s, and left that to the afc.

When you say +5, do you mean +5 clicks, or +5% (1 click).

+5 clicks

 

[44pirate]

Originally posted by kpt4321
And the TB shaft seals, and the BISS o-ring, and all of the emissions vacuum line connections, and the BOV line, and the FPR source line, and the brake booster line, and the manifold gasket, and the throttle body gasket.....




You're not pulling very much air at idle, it doesn't take much of a leak to mess up the mixture.




Only if the diaphram was leaking, which is unlikely and will show up in a pressure test.

Are you using a MAF-T? I didn't see it in your profile.

Nevermind I saw it on your website.

 

[kpt4321]

44Pirate - Why would you set the MAFT to +25% at idle, and then use the SAFC to pull it back down -9%? Why not just set the MAFT to +15% (which is probably close enough) or at least +20% and -4% on the SAFC?

That doesn't make sense to me.

Yes, I am using a MAFT. I think it's a great tool and one of the best mods I have done, and my car run and idles AWESOME with it. It saddens me to see people having trouble with it.

 

[44pirate]

Well when I log my STFT, it seems to give me better #'s and idle better. Maybe I have alot of intake leaks and it's compensating. If I set the Base for 660 injectors and set the Idle knob to 0 the car dies. I have to increase the Idle knob 5 clicks positive to idle good. 4 clicks and it idles real lumpy. So I adjust me SAFC negative and it idles better and I get STFT and LTFT to 0 at idle.

 

[Coldandafraid]

what about the breather filter, in place of the hose that used to spit oil into the intercooler? Will that make a big diff. I did a pressure test, and it seemed like I could hear air coming from there.

Originally posted by kpt4321
And the TB shaft seals, and the BISS o-ring, and all of the emissions vacuum line connections, and the BOV line, and the FPR source line, and the brake booster line, and the manifold gasket, and the throttle body gasket.....

As for these places, they didnt leak before the maft install, so I assume the only place that ould leak after would be the things I had to touch to install the new pipes. Basically, the one coupler, and the TB gasket.

So, I take it, you do not need to add fuel at idle then, and me and 44pirate have something odd going on?

 

[Coldandafraid]

ok, hows this theory sound...

The new gm maf does not have an accurate reading at very low air flow, but works good at 1000 rpm flow and above... so thats why we have to add air at idle.

ok, it was just a theory...

 

[kpt4321]

Originally posted by Coldandafraid
what about the breather filter, in place of the hose that used to spit oil into the intercooler? Will that make a big diff. I did a pressure test, and it seemed like I could hear air coming from there.

The valve cover breather?

I bet you a hundred bucks that your PCV valve, which goes out the back of the valve cover, is leaking. That gives you a boost leak under positive manifold pressure, and a vacuum leak the rest of the time.

You can buy a new valve, or re-route yours to a catchcan or filter. Your choice, there are lots of topics about that as well.

http://home.comcast.net/~tarryo/kyle/pcv.html

 

[kpt4321]

Originally posted by Coldandafraid
ok, hows this theory sound...

The new gm maf does not have an accurate reading at very low air flow, but works good at 1000 rpm flow and above... so thats why we have to add air at idle.

ok, it was just a theory...

Nope, vacuum leak. See my last post.

 

[44pirate]

Originally posted by kpt4321
Nope, vacuum leak. See my last post.

I have my PVC and Breather T'd together and going to a catch can.
I'm gonna do a boost leak test today and see if I have any leaks.

 

[Coldandafraid]

Originally posted by kpt4321
I bet you a hundred bucks that your PCV valve, which goes out the back of the valve cover, is leaking. That gives you a boost leak under positive manifold pressure, and a vacuum leak the rest of the time.

I will check that, however, I did change my pcv about 8 months ago.

 

[Coldandafraid]

Ok, I bought a new pcv, and then I took my existing one off and compared them. Both the same. Tell me though, you can easily blow out, and can hardly suck in, but you can suck in just a little. Is this normal, or is this a crappy aftermarket knockoff made by our local cheapo store?

 

[Coldandafraid]

Ok, here is another idea I had.

I have to add fuel at idle (750 rpm) to balance the trims, yet I have to take away fuel at all the other rpms (1000+rpm) to keep the trims balanced. So, you would think vacuum leak, making unaccounted for air getting in at idle, needing more fuel. But, if I am free reving to 1000 rpm, no load on the engine, isnt the vacuum the same... meaning, I should have to add fuel when free reving as well? What is the difference in vacuum from our engine at idle, and our engine in free rev?

 

[44pirate]

So I did a boost leak test. And I had a leak between the MAF and TB at the coupling. I clamped good and tight. It idles alot better. I haven't yet messed with the settings. My trims are still the same.