97 Civic Ex - pulsing lights, not typical fuse 15
 

97 Civic Ex manual d16y8

Pulsing lights, crazy speedometer, blown fuse 15 as suspected. If I disconnect the wiring clip from the alternator, the crazy speedo goes away and it doesn't blow the fuse. As soon as I plug the alternator back in, pops the fuse, runs like crap for a minute and then dies. I have completely removed the engine harness, not a single wire had been rubbed or melting or anything, again, engine harness removed from car and all looks good, even the c115 connector area.
Could it actually be a bad alternator/voltage regulator?
Could it be a bad ecu or electronic load detector (ELD)?
Thank you.

Re: 97 Civic Ex - pulsing lights, not typical fuse 15
 

Replacing the alternator will likely solve the problem.

Re: 97 Civic Ex - pulsing lights, not typical fuse 15
 

Did you check for rubbed wires at the secondary and primary O2 sensors?

Re: 97 Civic Ex - pulsing lights, not typical fuse 15
 

you're voltage regulator is fried. the voltage got too high and you're fuse blew. then the car ran like crap because it doesn't like the high voltages, and most likely the voltage was fluctuating. i got a 19 year old alternator in my car (the original, thank you honda), and occasionally my voltmeter will read between 14.0 and 14.5 and jump around a lot. Most of the time though it sits steady at 14.2 or 14.3 volts. it just means my voltage regulator is slowly dying. i got at least another year on it though..

Yes I checked primary and secondary o2, I even unplugged them to see if the pulse would go away, it did not go away. The car actually had a non-vtec automatic harness in it, I'm ordering a vtec manual one now. I'm replacing the alternator and wiring harness and crossing my fingers. I'm getting the alternator bench tested later today. Also, car has a 96 manual ecu, I have a 97 but from what I've been reading I'm okay since it's still 96 - 98.

97 Civic Ex Engine Diagnosis - Will pay for Advice
 

97 Civic Ex d16y8 - 5 speed manual
96 manual p2p-a31 ecu

I will pay you via PayPal if you can help me diagnose my problem, anyone that's interested can PM for a phone number and we can discuss it. Here is what I got...

Turn the key after a night of sitting, runs like a champ, tons of power and not a single problem or even a hint of one. After running for about 5 minutes, in neutral it will still rev up perfectly and sounds great, put it in gear and begin to drive... stumbles, jerks, sounds like cut-out. <Cannot drive, it has no power to go, it moves, but I could get out and walk next to it with you flooring it in first gear. Not a clutch slipping, rpms just won't go.
New alternator and battery, starter, used computer. Pulled the harness, installed another used harness and thoroughly examined near c115 connector.

I have checked:
Air/fuel filter- free and clear, even removed the air filter. Fuel filter is new.

Clogged Cat - Removed 2 bolts on flange before cat and removed 1st o2 sensor

Timing- both engine and ignition are spot on, re checked ignition with timing light twice

Spark- replaced plugs, wires, cap, rotor, and distributor. Ohm tested ignition coil and it reads perfect, 0.9 a to b and 16k a to secondary winding

Fuel/injectors- I pulled the pump and examined the tank as well, injectors were pulled, bench tested and cleaned.

Also to note, I'm getting a p1298 code for a bad eld. Will sometimes blow fuse 15. Could a bad ELD really cause my symptoms?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Is the car completely stock aside from the ECU?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

An aftermarket aluminum air duct, and that's it. Stock exhaust, stock injectors, stock fuel pump, stock fpr. Hell even the stock 14 wheels are on it.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Is P1298 thrown regardless of whether fuse 15 is blown or do they go hand in hand?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

It comes on within about 10 seconds of running after the codes are cleared, the fuse is still in tact at that time. Then if I try to drive it, fuse will blow and then give me the heater element code for each o2 sensor.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Have you carefully inspected the power wire for each O2 sensor heater element for signs of a short?

Have you tested different segments of the Blk/Yel wire from uncapped C115 for a short to ground using a multimeter?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

I have checked the o2 wires, I have even unplugged both o2 connectors to see if my problem would still be there, it was. I did not un-cap the c115 connector though. Didn't think to. I will tomorrow if I have time.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

The car would constantly blow fuse 15 and pulse all the lights, that was pinpointed to being a bad voltage regulator in the alternator. Replaced alternator and that problem was solved, and then I could at least drive it for a few minutes now.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

The fuse 15 circuit diagrams below may help you. Although the O2 sensor heater and alternator wires are the most common cause of the problem you're having, let your multimeter guide you to the short by doing resistance to body ground tests on various segments of the Blk/Yel wire.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Thank you for the charts. Looking at them just reminded me that my speedometer still acts up, even while sitting still, jumping to 30mph or so.
Would my problem of it running and driving perfect for the first few minutes and only after it warms up make sense for what I'm checking for? I feel like it would be there almost always or even when it's vibrated loose, but not only when it warms up and goes away on cold starts.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

There's a short somewhere in the complicated fuse 15 circuit. I believe the short is always there. It just doesn't immediately blow the fuse.

If you understand how to read a circuit diagram, there are numerous resistance to body ground tests that can be done with certain connectors (e.g., C421, C501, and C115) or components (O2 sensors, ELD, cluster, EVAP valves/solenoids, and/or VSS) unplugged. These types of tests should help you pinpoint the short. Keep an open mind about possible outcomes for the tests.

With the VSS and both o2 sensors unplugged, the car is a bit more manageable and it does not blow fuse 15 anymore, nor does it set the p1298. Still cuts out in low rpms (idle to 3000), then after 3000rpms it has full power and runs great. Any ideas or are you still set on checking fuse 15 wiring?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Try unplugging these^ one at a time to see whether blowing fuse 15 and setting P1298 can be linked to a single component.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

I plugged the VSS in first, drove the car for 10 minutes, it runs great and I finally had a working speedometer (not jumping). Plugged in the primary o2 sensor next (VSS still in as well), car still drives but not as well, my voltage on my voltmeter dropped a bit lower than usual. Unplugged o2 and volts went back up. Never did I blow a fuse or set another CEL besides the sensors I unplugged. Could I buy a new primary o2 and wire it straight to the ecu?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Did you also do the unplug/plug test of the secondary O2 sensor?

Why would you rewire the primary O2 sensor directly to the ECU?

1. Dust off your multimeter.
2. Unplug the primary O2 sensor and measure resistance to body ground at each of the 2 black wires for the sensor heater element.
3. What are the two readings?

For comparison, make the same two black wire Ohm measurements on the secondary O2 sensor.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Primary o2 harness side unplugged. 0 ohms on black/green, and 16.58 M ohms on solid black.
Didn't have time for the secondary, still at work.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

You tested wires on the wire harness side of the O2 sensor plug (Wht, Grn/Blk, Blk/Yel, Blk/Wht). The tests need to be done on the 2 solid black wires in the unplugged sensor connector (Blk, Blk, Wht, Lt Grn).

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

With the other connector lead where?

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

Not sure what you mean.

Key off. Unplug the primary O2 sensor connector, and then do the tests on the unplugged sensor-side connector, not the wire harness-side connector.

Re: 97 Civic Ex Engine Diagnosis - Will pay for Advice
 

So I have one of my ohmmeter leads on one of the black wires, where does the other ohmmeter lead go to, B-, sensor body, other black wire?