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Discussion Starter · #1 · (Edited)
Hello,

I've been having problems with my '02 Elantra. It shudders and doesn't accelerate well (or at all) going up hill, or attempting to accelerate quickly (like passing a car on the interstate). If I try to push it through these situations it will run worse, engine light flashes, and sometimes will stall. In the past, when it stalled, it would start up again in about 30mins or so.


Codes it has thrown were P0304, P0303, and P0420.


When I took it to mechanic, he really couldn't figure it out. He ended up testing and replacing fuel pump motor in November. Got it back and within a few days it was throwing same codes and having same symptoms.

Everything else from this point as been DIY. I bought a manual, researched these forums, learned as I went, and did the following myself:

I changed the spark plugs and wires. Still ran as described above but at this point when the engine light comes on, I am only down to the P0304 code right now.

Thought perhaps it was a vacuum leak. I have very few tools, and Autozone said I could use seafoam as a means to tell if I had a leak if smoke came out of vacuum lines as I put it in. I tried this, none came out of vacuum lines that I could tell. I drove it after seafoam, some white smoke came out tail pipe from solution but dissipated after driving a little while, and then I had the shuddering issues and loss of power while driving the interstate. It literally would act like I wasn't pressing the gas peddle, then suddenly surge as if it realized I was... engine continued to run until I pulled over and then it stalled. Normally it would start right back up after 30mins or so. But this time it didn't, I had to tow it home.

With a crap load of starter fluid and jamming the gas peddle to ****, I finally got it to start. It ran horribly at idle, had a weird knock. So I didn't drive it and did the following instead.


I replaced the coil pack.
Replaced crank position sensor.
I confirmed that I have spark on all 4 cylinders.
There are no obvious oil leaks (nothing on garage floor and I don't see any obvious signs of wet oil on engine or smoke when it runs)
Temperature is fine, coolant level is normal & hasn't needed refill or topping off.

I pulled the fuel pump again, noticed that the fuel sock had holes and was full of muddy/pasty type crap. Gas was dark, cloudy in spots, and appeared to separate in some areas.

Replaced fuel sock.
Syphoned gas.
Thoroughly cleaned out gas tank.
Put premium gas in.
Manually cleaned fuel injectors.

Reassembled and it started right up, runs strong, no more weird knock, but the other symptoms start to reappear... the shuddering, loss of power, and stalling. Its intermittent... sometimes when I jam on the gas peddle, sometimes when I'm cruising at low speeds. I can force it to stall by jamming on the gas peddle to the floor, acts like it's choking, engine light flashes, lose power, then it stalls. Pretty much every time I push it like that.

I can continue to limp it to Autozone for codes, but the engine light currently isn't on.... and it usually takes it a hard drive pushing it through the symptoms for the light to appear, and it's always been the P0304 code at this point.

Is there anything else I can do from home with no special testing equipment?

Anyone else have this issue in the past and find a different solution than the things I've already tried?

Is there a part or sensor that would cause these symptoms and NOT throw a code other than the misfire?
 

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Discussion Starter · #2 ·
Not sure if this detail is important... but it does NOT stall at idle. Not even when I jam on the gas peddle. I can get it to shudder slightly at idle, but never stall.
 

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Since it got better after cleaning the fuel system, I think that is where to keep looking. Did you replace the fuel filter and purge the fuel lines, fuel rail etc? Probably should clean the injectors again after that.
 

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Busted intake manifold gasket between cylinder head and intake flange..

0420 is catalyst lost efficiency because you killed the cat with the misfire... cats dont die on their own, they killed by something.

Can of carb along intake seam while at idle will tell story if gasket broken.. $10 part and 2.5hr labor (gravy ticket for me)...

Look at plastic wire ends too for nasty looking burn marks or discolor of the plastic sticks. NGK platinum or IRIDIUM only, and Hyundai wire set too.
 

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the P0420 bad cat code could very likely be caused by the misfires alone. i'd start troubleshooting other things before going there.

i'm going to say what i always say here - stop replacing parts at random. replacing parts as part of a diagnosis should be the last ditch effort and even then avoid it. unless you just don't like money, in which case you're welcome to send it my way.

also quit with the fuel cleaners. you've been down that road and it hasn't helped much....which is usually what those do.

the fact that it has done anything is a clue however. i would suspect a partially failed injector. its well and good to clean them, but it doesn't really prove anything. you may have an injector that is not functioning 100% or may be clogged with crap inside that you cannot see. the easy way is to put a mechanic's stethoscope (very cheap and useful tool) on it and listen for the snapping sound of it opening and closing. compare with the other ones and see if it sounds badly off.

sbr has some great suggestions. that gasket can cause untold headaches, sure did for me. putting something like WD-40 or starting fluid along the seam where the intake manifold mates with the head will cause the idle to pick up if you have a leak. if you have welding equipment, another option is to spray some argon gas around that area and watch the idle even out if leaking.

after all that is done, i'd start looking at first the coolant temperature sensor **with a multimeter on resistance at both hot and cold** and then i'd give it a compression test. compression tester is another very cheap and useful tool.

i'd also start looking for a new mechanic. if he replaces a fuel pump, no result and then just gives up he should find a new line of work.
 

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Discussion Starter · #6 ·
Since it got better after cleaning the fuel system, I think that is where to keep looking. Did you replace the fuel filter and purge the fuel lines, fuel rail etc? Probably should clean the injectors again after that.
On my '02 the fel filter is built into the fuel pump. There isn't another fuel filter outside of that. I replaced the fuel sock, which is at the bottom of the canister, because it was packed full of crap and had holes in it.

I did purge the fuel lines & fuel rail when I cleaned the injectors.
 

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Discussion Starter · #7 ·
Busted intake manifold gasket between cylinder head and intake flange..

0420 is catalyst lost efficiency because you killed the cat with the misfire... cats dont die on their own, they killed by something.

Can of carb along intake seam while at idle will tell story if gasket broken.. $10 part and 2.5hr labor (gravy ticket for me)...

Look at plastic wire ends too for nasty looking burn marks or discolor of the plastic sticks. NGK platinum or IRIDIUM only, and Hyundai wire set too.
The 0420 code went away after I had changed the plugs & wires, cleaned injectors, etc. However, to rule that out, I did use WD-40 on the intake seam to check for leaks and have not found any sign of one.
 

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Discussion Starter · #8 ·
the P0420 bad cat code could very likely be caused by the misfires alone. i'd start troubleshooting other things before going there.

i'm going to say what i always say here - stop replacing parts at random. replacing parts as part of a diagnosis should be the last ditch effort and even then avoid it. unless you just don't like money, in which case you're welcome to send it my way.

also quit with the fuel cleaners. you've been down that road and it hasn't helped much....which is usually what those do.

the fact that it has done anything is a clue however. i would suspect a partially failed injector. its well and good to clean them, but it doesn't really prove anything. you may have an injector that is not functioning 100% or may be clogged with crap inside that you cannot see. the easy way is to put a mechanic's stethoscope (very cheap and useful tool) on it and listen for the snapping sound of it opening and closing. compare with the other ones and see if it sounds badly off.

sbr has some great suggestions. that gasket can cause untold headaches, sure did for me. putting something like WD-40 or starting fluid along the seam where the intake manifold mates with the head will cause the idle to pick up if you have a leak. if you have welding equipment, another option is to spray some argon gas around that area and watch the idle even out if leaking.

after all that is done, i'd start looking at first the coolant temperature sensor **with a multimeter on resistance at both hot and cold** and then i'd give it a compression test. compression tester is another very cheap and useful tool.

i'd also start looking for a new mechanic. if he replaces a fuel pump, no result and then just gives up he should find a new line of work.
I hadn't thought about the injectors.... when I cleaned them, I had also tested them with a 9v battery. They all "clicked" but two of them had a different tone in sound than the others... it was sort of a duller noise. Didn't think much of it at the time, but now the engine light is back on with multiple misfire code, cylinder 4 and 1 now..... it's moved. (used to be 3 & 4), so I'm thinking since I didn't mark or take care to put injectors in same spots, maybe two of them are bad, the ones that sounded different?

I don't know how they are supposed to sound, so I guess the best way to figure it out is to mark them, swap them, and then reset light and see which cylinders misfire after driving?

Whatever the issue, it's inconsistent.

Thanks for your help. I'll go check out some compression tester's at the part store and see if I can figure out how to do it. I've never done any of this stuff before. Learning as I go.
 

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Discussion Starter · #10 ·
Hello everyone, just wanted to return with a follow up regarding this issue I had with my Elantra.

When I dug back into the fuel injectors for the new misfire codes (1 & 4) I discovered that debris from previous issue with bad gas had found its way back into the injectors & fuel rail again. Injector #4 was visibly clogged after having just cleaned them all out a few days prior.

I cleaned them all out again and moved #s 1 & 4 into the 2 & 3 positions. This way, if I have misfires and they move to those cylinders, then I know that the injectors need replacing.

It's been a few days, I've taken this car out for a beating, and I have not had any issues at all since the final cleaning. I guess there was just residual crap somewhere in the system that made it's way through. Hopefully that's the end of it!

Note to self, no more sale price gas.... :dry:
 

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glad to hear it was a cheap fix :) love those ones.

at the expense of being a pompous ass, this is a prime example of why diagnosis should be done before any part replacement.
 

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Discussion Starter · #12 ·
glad to hear it was a cheap fix :) love those ones.
at the expense of being a pompous ass, this is a prime example of why diagnosis should be done before any part replacement.
Ahahaha! Are you all puffed up and proud of yourself? :D

At the expense of being optimistic, the parts I replaced were as old as the car... so I figure I'm covered on those for the time I keep it on the road, since they have a warranty and all. If they DO malfunction, I wont have to dip into my pocket again.

BUT, the wires did look pretty bad. Two of them had cuts into em, one having been pinched in the top cover and screw driven through side (bleeping careless mechanic!)

Anyway, 200+ miles later and I'm dealing with a new code now P0420. Car isn't running any differently or badly, engine light just came on suddenly when I started it up after having breakfast out this morning. I'm researching other threads now to see if there's info to get me started on diagnosis. But I'll post a new thread of my own if I need help :)
 
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