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I have a 97 civic DX coupe with a y8 motor installed. When I start the car the brake light will pulse hard along with the headlights, occasionally if the car has been running for a little bit the lights wont pulse as such. Initially I replaced the alternator to no luck. Occasionally when I drive, the car will jerk when accelerating or will lurch forward so to speak when accelerating. I seen something online about the ELD switch and when I went to replace it if anyone may know or have pulled that big brown fuse there's a plug on the bottom of it. Initially 2 of the 3 wires were totally disconnected so I replaced that plug and fuse and still I have the same issue. Couple things to note are when the lights do not pulse on the dash the car drives perfect, however when they pulse hard the car drives hard. Its worse at low speeds but at freeway speeds it doesn't really seem to be an issue. all the wiring to the ecu is connected and nothing has been de-pinned from the ecu leaving stray wires. Last thing to note is when I drove the other day it was fine but it started to bang limiter at about 2.5k rpm. Any suggestions would be helpful, I just want to drive the dang thing.


-p0500 Speed Senor (Speedometer doesn't work even after I installed a brand new one)
-p1298 Electric load detector High circuit
-p0453 Evap emission control system pressure sensor high
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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Charge and test the battery, clean all the grounds, and check the charge line from alt to underhhood fuse panel and clean its contacts. What is the output voltage when lights are pulsing? When its running steady?
 

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93 Civic HB SI, 95 Civic HB CX
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Are any of those faults Active when you check them? Are they always Active or sometimes inactive or pending? Can you read Counts? Freeze frame data?

"High" on those circuit faults indicates their input to the ECU is voltage high, meaning feedback to the ECU on their respective circuits is pegging out or exceeding their range.

If these "High" faults are Active, you likely have a short to power somewhere in the wiring harness. I would confirm this by testing at the ECU pins for each of those circuit inputs. The service manual will tell you the expected feedback and operating range from each of those devices, and if your reading at the ECU is higher than its supposed to be, then you need to find the cause.
 

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None of this seems to be an ELD or alternator issue at first gut feeling, given it is random or intermittent.

If it were over voltage, you would have physical damage to inspect if it were to cause the car to act up. Most sensors are not happy with a high voltage, and will be damaged if they react in such a way (example, injector circuit through the ecu, if they shut down due to overvotlage, likely the circuit is damaged and they wouldn t work again)


This really seems like a wire is rubbing a ground somewhere, and the right kind of vibration or temperature leaves it alone.

Or this is a pinout problem, and something is pulling down the 5v reference voltage. Check ALL sensors that need 5v, and be sure all are indeed getting 4.8 to 5.2 volts.

If you want to verify this, simply yank the alternator belt off. Make sure the 12v battery is fully charged and happy, hell, toss a second battery inside with a pair of jumper cables.

Then go drive around for 10-20 minutes at a time, or if you have a multimeter or votlage gauge, drive around until it shows 11.5 or so volts under load. That is your que to stop and charge the 12v battery so it doesnt get damaged.

If it never experiences the lights pulsing issue, then I can then agree it is something with the charging system.



But it really feels like a grounding issue, something with power is touching the wrong spot at times.
 

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Had this same problem In my 97 HX coupe.
Luckily it just stopped.
I tested all the wires everything was right.
Drove me nuts to the point I said fuck it and kept driving it. Was getting 16v at the battery when the head lights would pulse.
It stopped for me but is a on going problem
I've been through about 8 alternators in the last 3 years. Changed ecus same thing.
Will be following this.
 
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