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2002 Sonata #2 #4 cylinder misfire

Old 12-22-2018, 07:24 PM
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Join Date: Nov 2018
Posts: 5
Default 2002 Sonata #2 #4 cylinder misfire

I couldn't find my old thread so I am starting a new one. I finally figured out the #2 and #4 cylinder misfire on my 2002 Sonata V-6. It turned out to be quite simple, but let me recap.
1. I was getting trouble codes for #2 and #4 misfire, as well as random misfire. The car had poor acceleration and idled rough when put in gear.
2. Did a compression test, all cylinders showed 155 - 165 psi
3. Decided to change spark plugs, and while I was at it and since the rears require removal of the intake plenum, I replaced the wires also. Same problem.
4. I purchased a scan tool with live data feed and saw that the B1S1 (front upstream) oxygen sensor was reading high at .7 - .9 volts, while the rear upstream sensor was acting normally, fluctuating between .1 and .9 volts. Replaced the oxygen sensor, but readings did not change.
5. I took the rear upstream sensor out (known good part) and put it in place of the new sensor. While I was at it, I removed the exhaust and did a visual check of the catalytic converters to see if they were plugged. Replacing the new sensor with the one from the rear yielded the same results, still reads high all the time.
6. I tried removing the plug wires one at a time, I could hear the engine rpm change on all but #2 and #4, a definite sign they were not firing.
7. I purchased a new coil pack, although it would seem to me if I had two bad coils I should have four misfiring cylinders. As I suspected, the new coil packs made no change either.
8. Even though the plugs appeared wet whenever I removed them, I tested the fuel injector harness with my "noid" light. They both flashed as normal indicating the injectors were receiving power and were being triggered by the PCM.

A couple of weeks ago, I picked up a couple of injectors at the salvage yard. Today, I finally got a chance to work on the car again. Once again, I looked down into the cylinders and also down the injector bungs to see if perhaps water was getting into the cylinders causing the misfire. Everything looked clean.

So...I installed the two salvage yard injectors and holy cats!! It runs like new again!! I drove in through town and on the freeway, took her up to 85 mph, climbed some steep hills, and really gave her a romping - excellent reaction, super acceleration, lots of power climbing hills, the whole bit. And no check engine light.

Had I owned this car for a long time, I might have been able to diagnose it quicker. However, I bought this to re-sell so have no personal history with the car. The young fellow I bought it from had had an issue with it dying at stop signs, and he told me he had replaced the MAF, TPS, and yes, the fuel injectors, which is why I didn't suspect them. But it just goes to show, you can't trust new parts all the time either (or the seller's word?) The funny thing is, it seemed to run okay when I bought it, this came up AFTER I had spent money on new tires, and replacing some other broken trim pieces, etc. It was after I power washed the engine that the problem cropped up, which is what made me think I had caused some damage to the electrical system or the coil pack. Also the harness plug on the coil pack was badly deteriorated, so it might have been a good idea to replace it anyway.

I wanted to share this with everyone in case anyone else has a similar issue. Remember to always check the basics first - compression, spark, fuel, before you start throwing money away on expensive parts. And, you can always get parts at a salvage yard for testing purposes. By the way, since the salvage yard injectors work, I am just going to leave them in there.

Thanks for all the advice I received.
Old 12-23-2018, 08:22 AM
Senior Member
Join Date: Sep 2013
Posts: 341

Thanks for the update and sharing the fix.
Your procedure was sound and yielded good results.
It's easy to overlook the basics , compliments are in order, thanks.
Old 12-23-2018, 10:12 AM
Senior Member
Join Date: Aug 2015
Location: Iowa
Posts: 186

Thanks from me as well! Feedback is so important to the learning process. This is one of the better lessons I've received.

Happy Holidays!
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