Ford Mustang Forums banner

1 - 16 of 16 Posts

·
Registered
Joined
·
62 Posts
Discussion Starter #1 (Edited)
notice the A/F? The weird thing is, I have never heard the car detonating. A little background, 93 cobra, bonestock, 21,000 miles, all original........due to the fact that my A/F is off the chart without any audible detonation, could bad cats be causing this? I was told by my dyno guy that if the cats are burning up, the heat generated could burn all of the remaining fuel outta the exhaust causing it to "show" a lean condition on the dyno. Funny thing is, I did get a loud backfire from right near the cats a while back. How can you tell if your cats are trashed? Judging from the jagged graph it appears that it's time for a tune up (car has it's original plugs/wires). I just don't know what the cause of the jacked up A/F could be? Any help is greatly appreciated. Anyone in SA that could help me out with a little h-pipe switch?

on the good side the car dyno'd 227rwhp 268rwtq bone stock probably with bad cats!
 

·
Registered
Joined
·
62 Posts
Discussion Starter #4
50 views.....nobody knows anything about this?
 

·
Registered
Joined
·
544 Posts
Yeah, I 'd definetly suggest you find an off-road h-pipe from somewere. I don't think that idea about the cats could happen. Of course I don't know for sure, but I don't see that happening. I think a simple switch to the off-road and another A/F test will let you know right away, there not expensive if you have to buy another one anyway.
 

·
Registered
Joined
·
111 Posts
where was the O2 sensor mounted for the dyno runs? If it was installed in the factory O2 location, it's BEFORE the cats, so even if the cats were bad, it shouldn't affect the readings.

I also think a missfiring cylinder could be the real cause.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #8
the sensor was installed in the tailpipe. The car doesn't feel like it has a miss, but something has to be making the graph look like it does.
 

·
Registered
Joined
·
63 Posts
An exhaust leak would cause the A/F ratio to read lean from the tailpipe. It could also cause backfiring.
 

·
Registered
Joined
·
62 Posts
Discussion Starter #10
the back fire I'm referring to was more a load "pop" from right under the drivers floorboard.....it has only done this loud once and maybe two other times but those where real quiet. The car doesn't sound like it has an exhast leak???
 

·
Registered
Joined
·
381 Posts
My 91 GT had a slight exhaust leak from right after the second cat drivers side. I could hear a slight pop...pop once in a while(more so under load), finally I drove it onto some sand, and while it was running I looked under the car, when it made the poping noise I could see the sand move.

Try that...if you can't tell if you have a leak or not.
 

·
Premium Member
Joined
·
5,822 Posts
Hi there,
Ask the dyno operator where was the smoothing function set at. If it was set to 1 or 2 that could be your problem. If it was set to 3 (most shops use this setting), I would change the stk. H-pipe out, give the car a tune-up and use the highest octane available at the pump.
Good luck. Michael Plummer
 

·
Registered
Joined
·
62 Posts
Discussion Starter #13
Michael Plummer said:
Hi there,
Ask the dyno operator where was the smoothing function set at. If it was set to 1 or 2 that could be your problem. If it was set to 3 (most shops use this setting), I would change the stk. H-pipe out, give the car a tune-up and use the highest octane available at the pump.
Good luck. Michael Plummer

the dyno guy did play with the smoothing.....I think that I am just gonna drop it at the svt dealer in town as it would cost about the same as another dyno pull to have them diagnose it.
 

·
Registered
Joined
·
594 Posts
I have seen several X3Z and Cobra mass air combos running extremely lean not quite as lean as U R but close, have U pulled any plugs if your car is as lean as the graphs indicate the plugs should be white, check them out, when I had my car dynoed the A/F was right in the 12.5-1 range! Good Luck!
 

·
Registered
Joined
·
62 Posts
Discussion Starter #15
well, I took the car by a dealership today to have a diagnoses done. I was interested in seeing if the car threw any codes (I was told that excessive backpressure would throw a code). Result......everything is perfect. Tech pulled a plug and said that it was perfect. So I'm thinking that maybe I have a minute exhast leak that is jacking with the reading???
 

·
Registered
Joined
·
62 Posts
Discussion Starter #16
just by looking at my power curve I decided that something is not exactly right....so I went ahead and changed the cap, rotor, and wires (it was all original). Driving the car, it sort of feels like I might have a miss somewhere. When I got back from my test drive I checked to make sure I had secured my wires properly and noticed that the plug wires on the drivers side were to hot for me to push on.....on the passenger side they were hot but not finger burning hot......hmmmm. Now the interesting part is that the drivers side is the side that the A/F sensor was hooked up to on the dyno. Could one side of the motor be lean?
 
1 - 16 of 16 Posts
Top