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Discussion Starter #1
Hoping I can get some help from the community diagnosing an odd CEL issue I am having.

My 93 MKII (purchased 2 weeks ago) with JDM 2nd Gen 3GSTE full rear clip swap (performed by ATS in 2012) is throwing a CEL, but when I attempt to pull the codes per EG-178 no codes show. The CEL just blinks repeatedly without pausing.

I have also tried pulling codes in "Test" mode per EG-179, but no luck. The CEL rapidly flashes when the car is turned on, goes solid after a bit of driving, and stays solid after jumping TE1 and E1 (note: car still running; TE1, TE2, and E1 are all jumped).

Under normal driving (not trying to pull codes) it seems to take the CEL a few seconds to turn on after turning the car on. It also flickers on and off under hard acceleration / boost. Oddly it will slowly de-illuminate when I boost hard and will re-illuminate quickly a few seconds later.

I understand that there are a few codes that are not stored in the ECU after throwing a CEL when the car is turned off (43, 51, & 53). But I can not get my car to even tell me the codes for the CEL it is currently displaying when running or otherwise.

Also had a one time occurrence 2 weeks ago after driving on the highway in stop-and-go traffic. Traffic started picking up speed and I began to get on boost. Car started stuttering really hard and would not go above -10inHG. Jumping, etc... Had to pull over and restart the car. Issue went away and has not re-surfaced. Could have been a hick-up in the fuel filter. Or perhaps AFM issue? Has new dizzy, plugs, wires....

Thoughts???

Thanks in advance
 

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... it seems to take the CEL a few seconds to turn on after turning the car on. It also flickers on and off under hard acceleration / boost. Oddly it will slowly de-illuminate when I boost hard and will re-illuminate quickly a few seconds later...
This sounds like inadequate power supply to the ECU. For example, maybe the ECU is powered from the same circuit as the fuel pump, and the pump is overloading the circuit at full demand.
 

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Discussion Starter #3
This sounds like inadequate power supply to the ECU. For example, maybe the ECU is powered from the same circuit as the fuel pump, and the pump is overloading the circuit at full demand.
Let me clarify, the CEL comes on when the key is placed in the "ON" position as it should. Upon start up it de-illuminates for a short period of time (~5 to 10sec) and then re-illuminated.

Could be an error that takes a period of time to produce a CEL.


  • As an example No.22: "Open or short in water temp. sensor circuit for 0.5sec. or more. (THW)"

Though this code should store in the ECU.

The car is running without issue apart from this ghost CEL.
 

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Did you try tracing and inspecting the wiring that powers the ECU? I don't have any better ideas than what I have already laid out. Look for bad connections or signs of heat damage, and see if there is anything else on the same circuit that could be hogging power. Since you have a swapped engine, there is no guarantee that everything hooked up right.
 

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If the ECU has good power connections, then it has to be an internal malfunction of the ECU. I understand that the ECU internal power supplies fail when the large capacitors dry out or leak. Many people have had success with opening the ECU and replacing all of the electrolytic capacitors. Another option is to try a known working ECU.
 
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