Low speed stumbling

[hemi_fan]

My car is stumbling on acceleration, but only at low rpm's, below 2000 or so. It lurches a little, similar to if you engage the clutch to quickly. Once it's over 2000 or so rpm it runs smooth as butter. The exhaust also smells extremely rich. I have punched 1 cat as it was clogged but the other 3 are still in tact, I'm not sure how much of a noticeable difference that would make in the exhaust fume smell though. Any ideas what could be causing this?

 

[Mustang5L5]

Run the check engine codes and perform a cylinder balance test.

 

[hemi_fan]

KOER

32 (R) EVP - EGR not responding properly during test - EVP
(O,R,M) EVR - EVP signal is/was low - EVR
(R,M) PFE - PFE shows low pressure, EGR not seating or memory, not seating intermittently - PFE

44 AIR system inoperative - Air Injection

94 AIR system inoperative - Air Injection
Transmission TCC circuit/solenoid problem - Transmissions

KOEO

32 (R) EVP - EGR not responding properly during test - EVP
(O,R,M) EVR - EVP signal is/was low - EVR
(R,M) PFE - PFE shows low pressure, EGR not seating or memory, not seating intermittently - PFE

Cylinder Balance Test gave a 9, a-okay.

The miss only seems to happen when I'm at low rpms accelerating lightly. If I'm higher in the rpm, or on the gas a bit it drives fine. Fuel smell is constant.

Could the AIR codes be causing the problems? I am running 3 stock cats, 1 punched. Seems as though the entire smog system is malfunctioning. I'll try to check everything over, found some nice threads describing EGR and AIR operation;

http://www.stangnet.com/mustang-forums/821443-5-0-running-rich-pulled-codes-21-31-44-22-66-a.html

http://www.stangnet.com/mustang-forums/789737-1990-5-0-mustang-vacuum-emissons-issues.html

Do you think this could cause the problems? I'll have to fix it anyway as the car will have to pass a smog test next spring.

The fuel smell is noticeable on the highway so its making me think the bypass valve is constantly open since I wouldn't expect to smell tailpipe emissions from the cabin at speed. Does that make sense?

 

[Mustang5L5]

The 44 and 94 Cpdes are harmless. They do say your smog pump setup is not working, but shouldn't affect the way the car runs.


The code 32 is worth looking into. Imwould remove the egr and clean it. If it's hanging open slightly it could cause your stumble.

 

[Haus]

codes 44/94 could be cause by a clog of carbon up in the cross over tubes attached to the back of the heads. been there done that haha

which probably caused you clog up one of your cats. so I would get that fixed. the codes are not harmless when you have cats

 

[Mustang5L5]

Ah, I read that as the stock smog hpipe...all punched out.

 

[hemi_fan]

Nope, its just one of the cats thats punched. The honeycomb came loose and turned sideways completely restricting flow so I had to knock it out. So I suppose the smog system could be causing the problem? I should fix it regardless I guess since next year it'll have to pass emissions.

 

[Mustang5L5]

Well, I would fix it all, but i would wager the low speed stumble could be caused by the egr hanging slightly open at near idle.