Engine Check engine light with no stored codes


Feb 5, 2020
Looking for some help on a check engine light issue.

1993 mustang cobra
Smog delete
Threw all the normal codes for smog delete. Chipped it. Now no more smog codes.
Replaced 3 capacitors on A9L compu
After chipping had a code for idle out of limit and map out of limits.
Set timing (10 btdc), check fuel pressure 42 psi, set TPS .975 ohms, set idle to about 800 rpm. MAF cleaned, throttle body cleaned, vacuum checked good. Reseated map sensor
Idles smooth.
Codes check 11 key in engine off
Codes check 6 and 11 key in engine on
Balance check 90.

Not sure about 6 vs 8 code on key in engine on?

I have cai

Previous owner added a external phantom automated tach, fuel pressure and oil pressure sensor.

The oil pressure gauge on dash reads zero with external gauge jumpered off instrument panel. Removed the jumper the oil pressure on instrument panel goes up but not very much.
Tested gauge by attaching to neg battery terminal goes to full high.
Points to a oil pressure send failure.

Replacing oil sender and idle air control tomorrow. But don't think oil pressure would trip cel. IAC may help but idle is in limits.

Replacing speedometer cable can't this weekend but once again I don't think that would affect cel.

Overall, cel comes 3 seconds after start goes out when accelerating through 1600 rpm back on at 2200. Stays on during deceleration. No stored codes. I have cleared codes.

Looking for any ideas or places to go next. Thanks for any input in advance.
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Put lubricant all over the balls
Mod Dude
Feb 18, 2001
Most likely it's EGR related. The other smog components don't trip the CEL if they display, but EGR will. Usually when you get RPM dependent CEL it's one of two primary causes. O2 sensors, or EGR.

The resistors you are using to remove the CEL probably aren't returning the correct values. I would remove them completely. The CEL should be constantly on. Drive for a bit, and then pull codes. See if you get the various code 33/34 for the EGR.


Feb 5, 2020
Lots of tuners prefer to work with the A9L, not an issue for running the car as the program is running off chip. That is second hand knowledge so please don't attack. I have never programed a chip.

I fixed the problem last night. I realized that the Barometric Air Pressure sensor was hooked up wrong. It had manifold vacuum pressure to it, like a MAP. I removed the pressure to give it ambient Barometric Pressure, now everything is running perfect.
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