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Unread 06-14-2014   #1 (permalink)
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Default Something Isn't Right still....

Hi AFM,

Short story:

Owned the car for 3 months (88' GT 5spd), did necessary maintenance to replace all the original things inside and outside of the engine bay to get the car roadworthy and reliable. I also added a BBK 70mm TB (now regretting) and original 93' Cobra intakes among other things.

It would seem ever since the intake install, I've been getting a backfire through the TB. It seems to "load up" under 2,000 rpms and it doesn't matter what gear it's in. Appears to feel sluggish many times when shifting from 1-2-3 gears when you depress the clutch, shift and accelerate. The engine is still very responsive and strong however once I get passed about 1,700 rpms. I also can't for the life of me get the car to idle under 1,000 rpms, which leads me to my main question. No coolant in my oil or out my pipes and no bent valves.

Could I have routed the vacuum lines incorrectly from the standard 5.0 H.O setup, when I installed the Cobra intakes? I have tried looking up a solid vacuum routing conversation but not really seeing much.

I noticed my brand new TPS sensor that came with the BBK TB is most likely bad as when I test it with a meter and a full sweep of the throttle blade--there's a point when the reading goes haywire and then smooths back out. That's certainly not correct.

Here's what I've done to update the car:

Intakes
TB
ALL ignition (including distributor)
IAV (IAC)
Most all vacuum hose
All unused vacuum ports are capped
PCV valve
O2 sensors
Cleaned salt and pepper shakers
*180 thermostat
Base idle reset didn't even get me to idle under 1,000 rpms
*13 advance on the timing

What's still 26 years old:
ACT
Temp sensor
MAP sensor
EGR valve

You have all been very great to me since I've recently joined; so any help is very appreciated.

Thanks,

Jon
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Unread 06-14-2014   #2 (permalink)
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The 70mm TB may not have been a great idea with only a Cobra intake for engine mods. Actual Mustang Cobras used a 65mm throttle body(not a 70mm), 24lb injectors, and a 70mm mass air meter to help balance out the air/fuel ratio with the bigger intake, GT40 heads, and more aggressive cam. It also had it's own unique computer to make sure everything worked harmoniously together. I suggest taking off that oversized TB and getting a bigger mass air meter and consider the 24lb injectors as well. Running a TB that is too large is almost like running a carb that is too big. That's probably why your low end power is suffering heavily and bogs.
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Unread 06-14-2014   #3 (permalink)
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Well, it doesn't bog but certainly feels like it's lacking something. I'm still speed density too. I could try putting the stock TB on. Thanks for that idea.

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Unread 06-14-2014   #4 (permalink)
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Run your codes first it is free and fast.

Secondly backfiring thru the intake is usually timing. I would check your balancer and the condition it is in.
It might have spun or is spinning meaning that when you bumped up your timing you really just messed it all up.

Make sure you have no vacuum leaks anywhere....hose, intake gasket, egr valve....check everywhere.

Oh and run your codes.
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Unread 06-14-2014   #5 (permalink)
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I had looked at the balancer as well but it doesn't look worn but that doesn't mean it may not be bad. I also thought this could be a problem. I did notice when I put my new distributor in, the rotor wasn't aiming toward the #4 cylinder but rather a bit left of dead center at the firewall. I believe it should be pointing more toward the #4.

I think if I was off a tooth it wouldn't run but what if my firing order at the cap is a wire off. Meaning I should move each wire clockwise around the cap.

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Unread 06-14-2014   #6 (permalink)
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Are you speed density or mass air?


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Unread 06-14-2014   #7 (permalink)
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Still SD

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Unread 06-15-2014   #8 (permalink)
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So I put my stock TB back on and as I'm letting engine warm up to adjust the idle, I hear a sucking noise. I located the sound it was my PCV valve hose collapsing on itself right by the PCV valve inlet. That hose is less than 2 months old and I'm not sure why it got so soft already.

I still think my vac hose routing might be suspect.

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