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MECHANIC GUYS > Engine misfire issues - DIAGNOSED: Broken valve spring (1 Viewer)

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Insoxicated
BACKGROUND:
4.6L Hyundai Genesis V8 (Multi Port Injection)
Has been an awesome car without issues for a long time. Recently threw a Coolant temp sensor code. Coolant was low. Topped off. Engine never overheated. Next day cold morning suddenly ran very rough, blinking check engine light. I pulled over and towed it to the dealer. 

OBD CODES:
Codes read random/multiple misfires, misfires largely contained to 4/6/8 with a random one on 3. Also got a injector 6 circuit malfunction code once but that seems to have cleared. 

DEALERSHIP:
The suggested plugs and replacing the sensor. Did that. No help. I asked them to flash the ECM (common issue), supposedly did. No help. Talking to them they're clueless. Want to play parts-darts and talking replacing injectors, Replacing the ECM/computer, thousands of dollars of ####.

Car SEEMS to run smoother when warm, or at higher RPM. Seems to lug worse under load at lower RPMs. Never runs smooth though. Idle gets rougher when put in gear. 

I purchased an OBD2 Code reader and Dash Commander App and hooked it up and noticed these things: 
• Short Term Fuel Trim swings from 0 to +13ish.. holds then drifts back down. AT idle and seems to have the same swings when driving. 
• O2 sensor voltage runs up and down when idling, but so does Engine RPM due to the stumbling/misfires. Seems to stabilize a bit when driving. 
•Timing swings a bit from +25deg to +45ish deg. Sometimes seems to be throttle dependent but can't tell for sure. Maybe due to VVT? 

Here is a video going through all gauges... perhaps I'm missing something. 

Here is a CSV/Excel data dump of all sensor output during a short 1 min drive around the block where I pushed it a bit. 

I have a couple buddies who have given me their thoughts on where to start, but wanted to try here too... HELP! Thoughts? 

 

 
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ECM would be my guess based on your video.

ETA-Timing findings concern me most. 

 
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squidrope said:
ECM would be my guess based on your video.

ETA-Timing findings concern me most. 
Click to expand...
God I hope not... I too am kinda alarmed by the timing numbers. Any other factors outside ECM that should be looked at as possible Cause for that? I have it in the hands of a pretty knowledgeable guy now but I’m still digging.

I’d hate to have to dump $1500+ into a new ECM for this thing as a shot in the dark. 

 
what about the throttle position sensor if that is off or not working it can result in the wrong mix of gas and air and cause an engine to run rough check that one out bromigo take that to the bank 

 
SWC said:
what about the throttle position sensor if that is off or not working it can result in the wrong mix of gas and air and cause an engine to run rough check that one out bromigo take that to the bank 
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Thanks GB, I haven't checked that but I'll drop a text to the fella taking a look at it. He drives a Hyundai himself and talking to him, he seemed to know his ####. Going to be testing coil packs and injectors this morning and moving down the line from there. I like that his approach is to test #### instead of just replacing it and hoping that was it. :lol:  

wilked said:
Try a Hyundai forum 

looks like a mess though. Good luck 
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I have posted on genesisowners. They're usually pretty active over there but seems to have died down the last year or so. Thanks for the suggestion, GB. 

 
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God I hope not... I too am kinda alarmed by the timing numbers. Any other factors outside ECM that should be looked at as possible Cause for that? I have it in the hands of a pretty knowledgeable guy now but I’m still digging.

I’d hate to have to dump $1500+ into a new ECM for this thing as a shot in the dark. 
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As Wilked said, I think a Hyundai forum would be worth a shot.  You might be able to pick up a used ECM there, or get one from a junk yard. Would you consider parting a wrecked car yourself?   A bit of work, but you'd probably make a few bucks and would have numerous parts you could try swapping.

 
squidrope said:
As Wilked said, I think a Hyundai forum would be worth a shot.  You might be able to pick up a used ECM there, or get one from a junk yard. Would you consider parting a wrecked car yourself?   A bit of work, but you'd probably make a few bucks and would have numerous parts you could try swapping.
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I would have zero issues with purchasing a used ECM assuming it was from a reputable (guaranteed not DOA) shop and had a guy who was capable of installing it and doing any necessary recoding (vin match necessary?). 

Hoping the ECM isn't the concern... curious to hear what "Daniel" (the guy who has my car this morning) comes back with. 

 
Mechanic said the advance timing was normal. 

Coils, Plugs, Injectors passed testing. Compression / Leak down underway... valve cover may be next. ugh. 
 

 
ChiefD said:
Exactly what I was thinking.

Good work Daniel.  :thumbup:
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No ####... in a matter of a couple hours he drilled straight down to the issue. I'm very impressed. 

$20 in parts. 
Will only be in it "several" hours if he can avoid pulling the head. Apparently it's nearly a 20hr job "by the book". 

 
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sbonomo said:
Super impressive he was able to nail that so quickly....wow. 
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This kid is legit.. particularly given he went into it thinking coil pack or something simple. This wasn’t him getting lucky and guessing right. 

Loved that he actually diagnosed and eliminated all the options that dealers will just try to replace-and-pray in an hour or two. 

 
Picked up the car today.... 

Total tab to diagnose, repair, retest... $620 out the door parts and labor :wub:  

Car is back to running like a dream. As an aside, he was drooling after the test drive and is now in the market for a Genesis. :lol:  

 
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