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modifiede30
07-24-2004, 10:43 AM
My car is begining to act a bit strange. After my track day Monday, I started to notice a bit of hesitation at speed. This only occurs at a constant speed, and it seems a bit worse when its humid or raining. Its not a severe hesitation but occasionally, it feels like someone grabed the crank and held it still for a split second making it feel as though the engine's about to cut out.

At the same time, I'm noticing that more often than not, the idle is loping in unison with my A/F ratio gauge at idle. Now this I see as very odd since the A/F gauge isn't supposed to be able to read anything accurately unless at full throttle. You can tell that the lope to higher idle is consistent with a rich meter reading.

Lastly, before the car is warmed, the A/F meter reads perfectly stoic, and idles very smoothly. Again, the A/F meter shouldn't be reading anything.

The entire engine has about 3500 miles on it at this point. The 02 sensor is brand new but I've always noticed they tend to burn out a bit faster with the headers but this quick seems odd.

Nothing has been checked yet diagnostically, but I'll begin the process tomorrow, likely starting with the O2 sensor, AFM, and thermo-time switch. Anyone have any other suggestions?

AdamF
07-24-2004, 04:51 PM
The A/F gauge should read just fine at idle, and it should fluctuate a little bit with the mixture changes. The reason it doesnt do that when cold is because the O2 sensor has a warm up period where the ECU ignores the reading.

modifiede30
07-24-2004, 05:15 PM
Mine doesn't, it swings back and forth from totally rich to totally lean constantly. The only time it is steady is before warmup and at WOT.

JSF252
07-24-2004, 05:37 PM
Mine doesn't, it swings back and forth from totally rich to totally lean constantly. The only time it is steady is before warmup and at WOT.
That's exactly what mine does. I crank it, and it will sit still, then as the engine warms, it will cycle (ECU is in closed loop) from lean to rich, over and over, unless I floor it (WOT).

It seems we have the exact same problem with our cars, even though you have headers. I've replaced the thermo-time switch, and it didn't change much.
I've not had a chance to replace the O2 sensor, so If you do so, let me know if you notice a change.

Josh F.

decay
07-24-2004, 06:40 PM
Mine doesn't, it swings back and forth from totally rich to totally lean constantly. The only time it is steady is before warmup and at WOT.

every narrow-band o2 meter i've ever seen did that.

modifiede30
07-24-2004, 07:17 PM
I'm not sure what AdamF is using, but I've never had one that didn't act this way, whether digit or LED. I did unplug the O2 sensor today and what a difference it made. I'm thinking that there may be some interference caused by the A/F meter's wiring setup that may be causing some of the problem. I'll be regrounding it tomorrow and I'll likely replace the O2 sensor if it doesn't help. Its definitely related to the O2 sensor.

JSF252
07-25-2004, 02:56 PM
OK, So I want to replace my O2 sensor. What was the Ford O2 sensor that is a replacement for our cars? Was it a 5.0 Mustang?

Josh F.

modifiede30
07-25-2004, 04:42 PM
Well, did all the possible diagnostics on the O2 sensor, checked the plugs, vacuum lines, etc. Everything checked out okay except one of the throttle body intake vacuum lines (from the brake booster), seemed pretty loose so I wrapped it in teflon take to see if that may be a part of the problem. I ran it for a few minutes and the idle was definitely smoother, with no loping. However, if I keep it at a constant position of about 3000 rpm, you can hear the engine running smoother each time the A/F ratio meter reads rich as it moves back and forth. When it swings back to lean, it sounds more unsteady. I can't figure this one out, totally puzzled by it. Does anyone elses car seem to do this time of steady/unsteady engine tone? Its a pretty subtle difference but its really annoying me.

iXer
07-25-2004, 05:10 PM
My car acted this way when the contact surfaces of the fuel or main relay were bad (fixed them both at the same time). I cleaned them up and have had no hesitation since.
I had occasional hickups but finally the car suddenly just died, knocking on the relay (in front of the left front shock tower) caused the engine to stumble. It was definately an electric problem.

/Mattias

diegom6
07-25-2004, 05:34 PM
Mine doesn't, it swings back and forth from totally rich to totally lean constantly. The only time (http://www.ntsearch.com/search.php?q=time&v=56) it is steady is before warmup and at WOT.

yup! same here!!