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Discussion Starter · #1 ·
I’m having an issue with my 2004 Hyundai Elantra cutting off, and am out of ideas of what to check for next. Basically I have a very intermittent issue where the car seems to lose electrical power for a split second (or possibly total loss of gas – as in, it doesn’t seem to be misfiring, just seems to totally lose all power). If it happens when I first start the car up, the car will start up for a second and then cut off. It also happens randomly when driving at any speed, and when it happens while driving, it just goes out for a split second, and then cuts back on and I can keep driving, so the RPMs Rev up for a second as a result when it kicks back on, but then goes back to normal. But it is completely intermittent, as in, some days it will not do it at all on my 30-min drive to work. I even went a whole week without it happening. But this week it has come back. Some days it will do it 3 times, some days 20 times. Some days its hard to get my car started, because it keeps cutting off when I start it. But so far after I try around 5-10 times it will start up and keep going. Also, this may indicate nothing, but when it goes out for that split second, I can hear a click, or electrical sounding click coming from the dash/instrument panel area. Which is what makes it seem electrical in nature, but I could be wrong, could be a spark/gas thing.

This has been happening it seems no matter what the weather is outside (its been anywhere from the 20s to 60s here in the last few weeks) and it doesn’t seem to matter if the car is warmed up or not. Also, so far the check engine light has not come on, so it makes me think it might not be a sensor, since those will usually trigger the light when they start going bad. Also, when the car is running, it runs perfect. Idles perfect, drives perfect, no misfires, no hesitation, etc. The ONLY problem is it cutting out. Also, it doesn’t seem to matter if the fuel tank is full or half empty. I had read in one place that if the vapor recovery charcoal canister gets full of gas, it will vent liquid fuel instead of vapor, which can result in car cutting off or running rough, but this usually only happens when fuel tank is full. So I suppose it could be this, but I doubt it.

The car has 180k miles. Iridium plugs have 60k on them. Wires have 60k on them. Original fuel pump and fuel filter. I wouldn’t think it would be the filter since when it runs it runs perfect. I guess could possibly be the pump having an intermittent issue. Trying to avoid replacing that for now unless I knew it was the problem.

What I’ve done so far:
• I made sure the battery cables are tight and clean at the connection
• I checked as many grounds as I could find, they all seem good
• Alternator puts out a perfect amount of voltage
• I swapped the ECU main relay and fuse with another relay and fuse in the fuse box that were identical
• I swapped the Fuel Pump relay with an identical one in the box
• I replaced the Crankshaft position sensor
• I cleaned the Mass Airflow sensor (though it looked spotless)
• I looked around for any vacuum hoses that were disconnected. Didn’t find any
• I’ve tried resetting the ECU (unplug battery for a while) and I thought that fixed it at first, but then it came back a few days later. And now resetting ECU seems to have no effect.

Some possibilities of what it could be:
• Fuel pump intermittent issue?
• Camshaft position sensor?
• ECU problem?
• Catalytic convertor going bad?
• Some other sensor going bad?
• Possibly the vapor recovery charcoal canister is full of fuel as described above
• ignition coils – but I doubt it since you’d usually get a misfire/engine light when those go bad (from experience)
• Fuel pressure regulator – but I doubt it, based on the symptoms. Seems like I’d have other symptoms.

I’m not convinced of any of these above, and some of them I wouldn’t know how to check (like for a bad ECU). Does anyone have any suggestions of what you think it might be? Getting nervous driving 75mph on the interstate with someone behind me and the car cutting out. Luckily so far it doesn’t cut completely off when I’m up to speed with someone behind me!
 

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I'm not sure what to tell you. A similar thing happened with my wife's HD a year or so ago in San Diego. Come to find out the battery was bad and her ground cable was bad. We replaced both and I scraped off more paint where the ground connected to the chassis and it has not had a problem since. She had the same problem though, the car would just cut out. A few times it only cut out for a few seconds, other times it cut off and died completely. Then she had to restart the car and it worked. I know you checked the battery cables so I am not sure what else to say. Have you run a scan?
 

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Discussion Starter · #3 ·
I've tried jiggling all the cables, including the battery cables and ground cables to try to replicate it. I have an ODB scanner and have checked it probably 4-5 times in the last few weeks and so far has reported no error codes, and have not gotten any check engine lights this whole time.
 

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That must be frustrating. You might have to take it to the dealer. Ther only problem is that the problem might not happen while you are there.
 

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This is just spitballing and I'm no expert by any means, but since when it "cuts out" the revs go up could it possibly be a transmission or clutch issue? Or maybe I didn't read that right...

The clicking sound from the dash makes me think solenoid, or because it's under the dash, electrical short so it never hurts to pull all the fuses and check them. If you have a short I'm sure one will be blown.

Also a while back my wife 2004 GT had a dead battery because of a bad alternator and it would barely run. Not sure that the alternator still can't be bad even though it's putting out appox. 14 volts at idle.

I know. Not very helpful... :)

Maybe someone with a bit more experience will post an exact solution. Good luck!
 

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Discussion Starter · #7 ·
So i havnt reported back in a week or so...to try to answer all your questions:
-There are no check engine lights. And no old stored trouble codes.
-The connections to the battery are nice and tight, no corrosion anywhere. More on the battery further down in this post.
-I've pulled all the fuses and checked, and also swapped relays around to try to pinpoint if a certain relay was bad (more on that further down in this post)
-I've cleaned the Mass AirFlow sensor, though it seemed spotless, but i cleaned it anyway


A guy told me he was having a very similar problem and it was his ignition switch. So I replaced the Ignition Switch and that wasnt it. Thought it was since I drove a day without a hiccup, but by day 2 the problem came back.

As a next troubleshooting step, I have a Bluetooth ODB scanner and the "Torque" Android app, so i got the idea to plug it in and turn on logging and have it log a data file while I drove and experienced the cutout. It logs stuff like speed, rpm, voltage, sensor data, etc of the car every 1/10 of a second. So I started driving, and I noticed that when it cuts out, the Bluetooth ODB scanner loses connection and has to reconnect. So the logs arent helpful since the ODB scanner loses power when it happens. But the fact that the scanner loses power for that split second during the cutout is very good troubleshooting information I think! I think this means that the ECU itself is losing power, which is why the ODB scanner loses power, since the ODB connection is what powers the Bluetooth scanner. This tells me one of two things. Either the ECU itself has some type of issue, or it seems there is a bad connection to the ECU. I say this because I dont lose power anywhere else when this happens (radio, headlights, dash) and normally the bluetooth ODB scanner has power when plugged into the ECU even if the car is turned off with no keys in the ignition. In other words power is always going to the ECU, and power is always going to the ECU's ODB port. But when the cutout happens, it seems that power goes away for a half second. Bad ECU? Loose connection maybe? Wiggling the harness and any wires under the steering column doesnt replicate it. I will say that about a month or two before this started happening, the voltage regulator on my alternator went bad and was actually putting out too much voltage to the car. I got a check engine light and looked up the code online and it said something like "Voltage exceeded 17 volts for more than 3 seconds". So then i tested with my multimeter and it was 16.8 which is higher than the 13.5-14.5 range it should have been in. So I put in a new alternator and that fixed it. So one possibility I'm thinking is that the high voltage could have damaged something in the ECU, though I'm not really convinced of that. But still contemplating getting a used one off ebay just to see what happens.

So I think this must be an electrical issue and has to do with the ECU or power to the ECU. As i think I said in my first post, I've already tried swapping the ECU relays and fuses, so its not that. Also, what about an internal short in the battery. Possibly? But wouldnt the power to the other components be lost in that split second as well? I had considered the battery, since the high voltage can ruin a battery, but it has been working just fine, as in cranking just fine ever since the ordeal with the alternator. Any thoughts?
 

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I am going to have to agree with you. I would say it's the ECU or the wiring to the ECU. That bad alternator probably did burn something out. It's just like having a power surge to an outlet. If there is no surge protector those extra volts can burn stuff out. I would agree to get a new one.
 

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Hello elantraGLS2,

Been a while and wondering if you were ever able to solve your problem. Sounds exactly what my 2003 has started to do.

Thanks,
 

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I had something very similar to what you describe and it's wasn't easy to know the problem cause there wasn't any error code in the computer so I start to replace stuff and first was the crank sensor but the problem still occurs.. So I replaced the ignition cables and since then the problem solved but I'm not sure if that the problem with your car .
My car could just died with no sign in the middle of the road or in the highway doing 80mph... And again no check engine was lightened and after restarting the engine it's like nothing happend.
Good luck and don't give up .
 

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I had something very similar to what you describe and it's wasn't easy to know the problem cause there wasn't any error code in the computer so I start to replace stuff and first was the crank sensor but the problem still occurs.. So I replaced the ignition cables and since then the problem solved but I'm not sure if that the problem with your car .
My car could just died with no sign in the middle of the road or in the highway doing 80mph... And again no check engine was lightened and after restarting the engine it's like nothing happend.
Good luck and don't give up .
I’m having the same problem on my 2002 Elantra GLS. What do you mean when you say you replaced ignition cables? The ignition switch itself or wiring harness?
 

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Well, I had similar problems on my 1991 Mitsubishi Mirage 18 years ago - it randomly died for a fraction of seconds and then immediately come up. Sometimes it was not immediately, but it was pretty similar symptoms like described above. It was clearly electrical issue. It took a few weeks, but finally we figured out this problem. Long story short: some capacitors on ECU board failed, but not completely. They been swell up and start leaking.. Acid from these capacitor damaged ECU board and initiate all these symptoms. When we opened Engine ECU cover we immediately seen these bad and swollen capacitors. We clean ECU motherboard and replace these capacitors with new one from Radio Shack (as I remember it was 3 capacitors, about 40 cents each), and problem was fixed. I did some research and found that it was a common problem with these type of capacitors in 1990-s - after 10-12 years they fail and leak acidic electrolyte on the main board around them. Not only Mitsubishi but other manufacturers had this issue too.

I don't know if Hyundai use the same type of capacitors in ECU, I never had problems with my Elantra and never open any ECU's on this car - just share my experience. It also may be a problem with ECU connectors or wiring.
 
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