Intake Questions

[a91what]

OK im relatively new to the performance scene and need some help getting my ducks in a row with my car. Starting with the intake I have a 75mm throttle body attatched to a hand ported cobra intake the port job was done here in my garage in a few hours. The transition to the plenum is relatively smooth but im concerned with velocity problems. I am currently running a 73mm C&L MAF after doing some research i concluded that i either need a larger MAF or i need to port out the housing so it is larger than the TB. The sampling tube for the 73 and 76mm housings are the same for my setup, so no problems there. Will making this modification help my setup at all? or am i wasting my time... ( currently have stock e7te heads on engine, cnc'd gt40 irons on work bench..).

I have a slew of other minor problems as well.. cold idle issues (starts and dies), pop/ backfire only when cold, and a rich smell (no matter how low i set fuel pressure) might be lean smell not sure?.

Any Info would help Thanks.

 

[a91what]

BBK cold air intake has a 73mm tube between the tb and maf so it would be pointless to mod the maf.. the tube feeding the maf is 87mm going to radius the entry of the maf it is only 76mm then a flat wall, so plenty of material to work with on that side. also making my own velocity stack using a pipe spreader to radius the entry on the tube feeding the maf on the filter side. Trying to get results without spending any money.

Still trying to hunt down cold start/ idle issues car has no vac leaks ive checked maybe a dozen times.... is there a sensor that might affect cold start? It also pops but only when cold and only when i hammer it down.

 

[foxna6]

The cobra intake will be a great upgrade for your set up as far as throttle hosts a 75 mm is a little big for your set up a 65 or 70 would be much better suited and will perform much better but yes your MAF should be bigger then TB for better flow

 

[a91what]

I already have the cobra intake on the car, ( the car came rolling with boxes of parts in it.) the tb was on sale so i bought it after ordering the maf. (realized my mistake after the fact) so now im stuck with that for awhile. the intake is port matched to the tb. i have excellent throttle response and plenty of power but some idle problems i cant seem to shake.

 

[Noobz347]

Do NOT port the MAF housing. Doing so will create more problems that what you have. MAF assemblies don't measure all the air that's coming into them. They take a sample of that intake air. The element is tuned for the housing that it's in. For instance:

If the housing allows 400 CFM, the MAF element is going to sample the 1% of that air entering the housing (the portion that actually flows over the element). That sample is turned into a voltage reading.

Let's say that the housing is widened and we're now flowing 500 CFM. Now you're sampling that same 1% of air that the element sampled when the housing was smaller --AND-- the air is moving slower over the same element than it was when the inlet was smaller (because there's more room).

So not only are you getting a smaller sample of the air entering the inlet, but the air is moving slower and producing a completely different voltage.

It's the perfect scenario to cause everything to run lean.


Currently, you're running a 75mm TB into a necked intake. There's nothing wrong with that. Air velocity will increase slightly in the necked portion of the intake (slight benefit) and your throttle response will be good.

Because of the necked inlet, the intake won't move the same volume of air that the TB is capable of. In that scenario, it's not necessary for you to do anything to the MAF. The bottle neck is the inlet and your MAF housing will out-flow that bottle neck.

Leave it alone. It should all function just fine.

 

[foxna6]

Your idle problems are probably do to your base idle setting have you ever tried to reset base idle

 

[a91what]

Ok thanks for the info on the maf. I will just leave the setup alone. As for the idle problems i have tried everything, the car idles very well after it has warmed up it is ONLY when the car is COLD (as in first thing in the morning) i have problems. It seems like it doesnt want to fast idle when its cold it will also START and DIE a few times before running. I have to let it warm up before driving it. I also get a POP when i hit the gas to far when it's COLD and it only happens when the car is under LOAD i.e. (only in gear)..
I have not scanned the car to see if there are any codes... dont know how. i remember reading somewhere there is a tool you can buy or you can use a test light and count the blinks but not sure how to go about that..

 

[Noobz347]

You can pick up an OBD1 scan tool at Walmart for about $30. If it's only doing it when cold then I'd guess that there's a problem with the open loop portion of your tune.

Question: The C&L that you're running. Does it have removable/replaceable sample tubes or is it of the fixed variety?

Some things to look for:

Pull codes

Check your TPS. Turn the ignition key to ON position (don't start the motor) and check to see that the voltage scales. You do not need to adjust for voltage. All you're doing here is ensuring that it does infact scale and that it's not DOA.

Check the condition of your cap, rotor, and plug wires. If they look at all old/worn, replace them.

Things to try:

If these things check out, try cleaning the IAC. If that makes no change, bump the throttle stop screw a 1/4 turn at a time, to see if your cold idle smoothes out at all.

 

[a91what]

Ok my tps voltage has been adjusted then readjusted (.9) The engine has less than 6000 miles on it so everything is new i assembled it myself. The iac has been replaced with no change to cold start. The sample tube is replaceable and i verified that it is the correct tube for 24# injectors and cold air kit. The car has been chipped but its one of those bama tunes i have tried to start it with the stock tune function in place and i get the same issue. The car will run/idle fine on cold start if i cycle the tune on start up..

I have installed a A/F ratio gauge on the car and it does not read properly, (swing back and forth while cruising) it only reads when you hammer it down i know the ground for the o2 sensors and the iac are common would a weak ground possibly cause both issues?

 

[a91what]

Expand on symptom: ok so if it does not die it seems like the idle is "wandering" it will drop as low as 400rpm then shoot up to 1000rpm or so.. i will verify that the computer is sending the signal to close the ground loop with a voltmeter. hopefully the iac is faulty (both of them).... maybe. i regrounded the pigtail no real change..

 

[stykthyn]

have you tried to set the base idle with the IAC and the SPOUT unplugged? What is your base timing set at? What is your total timing?

 

[foxna6]

You need to set base idle with spout out and iac unhooked also pop may be caused but a bad water temp sensor have you dumped codes I'm sure you have some

 

[a91what]

OK. no i have not tried to set bas idle with the spout or iac unplugged. i will warm the car up in the morning and start with that..

The BASE timing is 14* ^how do i read for total timing^ (The car has a chip from bama custom tunes so im sure they adjusted it)

I need instruction on how to dump and read the codes I dont want to fry the computer.......

The car has the same issues with the stock tune in place. It ran perfect when i first put it together but we all know how that goes...

Also my A/F ratio gauge reads rich when i let off the throttle, It reads nothing when im at idle (reads lean on startup then nothing) and reads lean then stoick then rich when i put my foot down.... But its just a light show anyway.

On my way home from the hall tonight the car started running so rich my eyes were watering its a convertible and i had the top down doing 70.

 

[foxna6]

Ok first unhook the battery for at least ten minutes lose that chip as it may be causing your problems the bama chips are known for that as its real hard to tune a car that's not right in front of you make sure to dump the code both with just the key on and with the car running I'm betting you reset base idle replace some bad sensors and lose that chip it runs like a raped ape but that's just what I'm thinking tomorrow is Saturday so spend it with your Fox I have been for the last 3 years its like tharapy to me good luck hope this helps and let us know how it goes there all kinds of info on this site to help you go over the surging idle.check list do every step of it that thing will run I'm shore of it

 

[a91what]

do i need to dump the codes before or after i reset the computer? Are you sure the chip causes problems it cost an arm and a leg...... LOL

 

[jsw81]

Ok first unhook the battery for at least ten minutes lose that chip as it may be causing your problems the bama chips are known for that as its real hard to tune a car that's not right in front of you make sure to dump the code both with just the key on and with the car running I'm betting you reset base idle replace some bad sensors and lose that chip it runs like a raped ape but that's just what I'm thinking tomorrow is Saturday so spend it with your Fox I have been for the last 3 years its like tharapy to me good luck hope this helps and let us know how it goes there all kinds of info on this site to help you go over the surging idle.check list do every step of it that thing will run I'm shore of it

What the Expletive deleted am I reading??

OP: The bama chip is probably ok. I have zero issues with mine, and my setup is not stock. Have you tried clocking the MAF 45 degrees? The C&L is known to cause stalling issues. I had the same problem and clocking it fixed it. Many people have done this.

 

[foxna6]

Dump codes first I'm shore bama chips cause problems do a search on here a read for.your self and you know everything I.tell you is just my thoughts on it I've only built 3 foxes I don't know everything use the surging idle check list clocking the c&l's can also help but more then likely its the base idle and or chip again do a search on any Fox forum of your choice

 

[foxna6]

There's nothing wrong.with.act chips its.the.tuning problem again it hard to tune a car that's not on a dyno in front of you there also a reason Bama will not send you a tune if your car is heavly moded

 

[Mark Palmer]

Outstanding thread, thanks all for joining. I'll visit often.

 

[a91what]

Having an issue getting the codes from the car.. found the diagnostic port but the other wire im supposed to jumper it to is nowhere to be found.... from what i read they are supposed to both come from the same group of wires...