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car hesitates/jerks while driving


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abgreene07
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Dec 18, 2012, 7:04 PM

Post #1 of 11 (25379 views)
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1999 Hyundai Sonata
GLS v.6

So i cannot figure out whats wrong with my car and it is really bugging me.
When i am driving it seems like my car hesitates when accelerating, then when i am driving it will randomly jerk at low rpms sometimes even when at high speeds. BUT IT ONLY DOES IT AFTER WARMED UP. Also, i recently had my trans rebuilt, so the monitors arent ready because whatever is the problem is preventing them from resetting. This is a problem since i have to get it inspected soon.
Had spark plugs and wires changed, put a lucas fuel treatment in tank, and air filter was changed. Also cleaned MAF too. Still having the problem. Took it to a shop and they wanted to rip apart the engine for a fairly pricey amount. Im just trying to figure out if theres any other options i have before just throwing a ton of money at it without knowing whats wrong.
There are no codes being thrown. The problem was present before i had the trans rebuilt as well and still no codes were being thrown then either. The timing belt has been changed, although i have no idea if that changes anything.
Please help!!


Discretesignals
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Dec 18, 2012, 7:14 PM

Post #2 of 11 (25363 views)
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Re: car hesitates/jerks while driving [In reply to] Sign In

When it hesitates does it feel like it is skipping, surging, bucking, and/or delay before your accelerate?

This one might be hard to diagnose over the internet if there are no trouble codes popping up without monitoring scan tool data. Which monitors are not readying?

One thing that you could have done is to check the fuel pressure to be sure it is in range when the engine is warm. They'll need special adapters to connect up a gauge to that one.





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abgreene07
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Dec 18, 2012, 7:23 PM

Post #3 of 11 (25351 views)
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it feels like a delay in accelteration. ill step on the gas but it wont accelerate as fast as it should be. then if i give it more gas it will go. but sometimes it takes entirely too long and too much gas to get it to move faster. and then the jerking happens at low rpms at all speeds but only after warmed up.


abgreene07
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Dec 18, 2012, 7:24 PM

Post #4 of 11 (25347 views)
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the evap, o2, and catlyst monitors arent ready, the mechanic said an engine problem would be causing them to not reset and until fixed they wont be ready....?


Discretesignals
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Dec 18, 2012, 7:47 PM

Post #5 of 11 (25327 views)
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The cat monitor won't ready until the O2 tests pass.

EVAP monitor is one of the harder tests to get to run because of the criteria that has to be met. EVAP problems usually don't cause drive-ability issues unless the purge valve is stuck open.

Like I mentioned before the data stream is going to need to be monitored while the problem is occurring to see if anything stands out.

Would be interesting to watch the short and long term fuel trims when this is occurring. Just need some data or clues to go on to get some direction on where the problem is.

Most of the time if you have a secondary ignition issue a code would be set. I've seen crank sensors on those start to go bad and have those symptoms when it gets hot, but you really would need to use a lab scope to confirm that before replacing something like that.

There is a whole slew of possibilities, but someone with the knowledge and right equipment should be able to pinpoint the problem.





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abgreene07
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Dec 18, 2012, 7:57 PM

Post #6 of 11 (25318 views)
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another thing i noticed also was that when i get gas it takes forever for the gauge to actually go to where i filled it to. could that have to do with fuel pressure?


Discretesignals
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Dec 18, 2012, 8:04 PM

Post #7 of 11 (25314 views)
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A fuel level sender problem could cause the EVAP monitor to not run. There has to be a certain amount of fuel in the tank for the EVAP tests to run which the PCM monitors through the fuel level sensor in tank. That shouldn't cause your drive-ability issues though.





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Discretesignals
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Dec 18, 2012, 8:25 PM

Post #8 of 11 (25305 views)
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I take that back. On this vehicle the PCM doesn't monitor the fuel level in the tank. There could be a sender problem, but that still shouldn't cause a drive-ability issue.

You might want to check the connections at the fuel pump. Wiggle the connections around to see if your fuel gauge changes. Inspect the connector and terminals also. Fuel pump is behind the access cover underneath the rear seat cushion.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


abgreene07
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Dec 19, 2012, 11:40 AM

Post #9 of 11 (25254 views)
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So i just heard back from my mechanic and he says its the crankshaft positioning sensor. he said this should take care of the performance issues and he found this out by running diagnostics. so hopefully this actually fixes the problem for good because i really cannot afford to put much more money into this car. does this sound accurate?


Discretesignals
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Dec 19, 2012, 7:02 PM

Post #10 of 11 (25240 views)
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Like I mentioned they did have crank sensor troubles on those vehicles. If your mechanic took the time to diagnose it correctly, then you should go by his/her word. If you don't feel comfortable with your mechanic's find, you can always get a second opinion.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


abgreene07
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Dec 19, 2012, 9:26 PM

Post #11 of 11 (25225 views)
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Nevermind it didn't fix the problem. They ran diagnostics and still no idea what's wrong!




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