How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Amedee Your Own Question
Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 26607
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
Type Your Car Question Here...
Amedee is online now
A new question is answered every 9 seconds

Hyundai sonata: traffic fine

This answer was rated:

Hi I have a 02 hyundai sonata 2.4L that when warm in a stop and go traffic wile waiting for cars to move engine will start pinging and shaking it will stall at times. starts right up
there is no codes, no engine light,when is not on gear engine seams to run fine.the problem is only under load.

I have tried coils,wires,plugs,found timing belt tensioner bad replaced thinking that was the problem but it does the same thing.



So the engine idling fine and the problem only happens under accelerating or under a load?

Customer: replied 7 years ago.
is weird becouse is only warm wile on gear at stop will ping so hard but when you get moving is ok no pinging but stell feels like no power
You could have a bad mass air flow sensor. Or the snorkel from the mass air flow sensor to the throttle body could be ripped. Both are very common and can cause you vehicle to loose power along with many other drive ability issues. First look for cracks or rips or anywhere air can enter the engine that is not accounted for by the mass air flow sensor. Next comes the Mass Air Flow (MAF) sensor. This is a very important sensor input to the computer. It uses a hot wire sensing element to measure the amount of air entering the engine. The MAF sensor then outputs an analog voltage signal to the PCM proportional to the intake air mass. The PCM calculates the required fuel injector pulse width in order to provide the desired air/fuel ratio. If the sensor is bad than this air/fuel ratio will be off causing severe performance issues. In extreme cases, I have seen these two problems cause a no start condition. This input can also be used in determining transmission Electronic Pressure Control, shift and torque converter clutch scheduling. The check engine light may even pop on if the sensor is bad, the snorkel is ripped or a tube has fallen off. This will result in a lean condition.
Customer: replied 7 years ago.
I have checked the snorkel for that all ready but is ok, also inspected the mass air flow sensor and found it dirty I cleaned the sensor and monitored with the modis and the parameters are within spects.
the check engine lite never comes on and there is not codes under history or pending.

SO its pinging under a load?


What is the front o2 sensor doing when this is happening?


What is the short term fuel trim?


What is the baro pressure on your scanner?


WHat is the engine load when its pinging?

Customer: replied 7 years ago.
ok. front o2 is 40

short term fuel trim is 1.6

engine load is 50

baro pressure is not available on the screen

map sensor is 3.6

O2 sensor is at 40? 40 what? 40 millivolts? Is this under full throttle or when accelerating?



Customer: replied 7 years ago.
40 millivolts. this is just sitting with the trans in gear.
Lets check the o2 sensor signal under load. Preferable when the engine is pinging.
Customer: replied 7 years ago.
it goes to 1000 millivolts WOT
and the readings I give you before were wile the engine was pinging wich is only wile in gear seating waiting for a green lite or cars to move.

So the engine pings while idle?



Customer: replied 7 years ago.
only when the trans is on gear
Is this just an unusual sound or is the engine actually pre igniting?
Customer: replied 7 years ago.
It is the engine pre igniting! I`m a tech as well I`ve been a tech for 16 years
but this problem is just someting weird.
What is the engine vacuum at idle?
Customer: replied 7 years ago.
It is 22 inches at idle and 10 wile pinging
I thought you said it pings at idle? Does it go from 22 inches idling and then down to 10 inches and start pinging? If so, then this is our problem.
Customer: replied 7 years ago.
no! it drops only afther trans is engaged and the engine will start to bug down then engine vacuum starts droping.
wile idle with trans in park. is ok. the problem only occures on this condottion:engine warm,transmision on gear (any) ,car is not moving meaninig at compleate stop don`t metter if you are in the gas or not will ping eader way.
Try adding some propane to the intake or in the air cleaner assembly see if that helps. See if the engine will stop pining and if the engine vacuum remains at 22 inches or stays in an acceptable range.
Customer: replied 7 years ago.
the pinging stops but the engine vacuum is still low and engine won`t normalize

Ok... what about wide open throttle? What was the o2 sensor voltage under load?


WHat is the engine vacuum under load?

Customer: replied 7 years ago.
engine vacuum goes to zero under load, o2 reading is 1010 millivolts
this is with the propane.

Without propane added, under load what is the fromt o2 sensor milivolts?


What is engine vacuum at 2500 rpm?

Customer: replied 7 years ago.
engine vacumm under load as well??
Right... is the o2 sensor still reading 1000 milivolts under a load without propane?
Customer: replied 7 years ago.
the engine will not race rpm up enogh to 2500rpm
the highest is 750rpm and o2 is 980 and vacuum is 20 inches

So when it bogs down with your foot on the gas pedal to the floor, what is the o2 sensor reading?



Customer: replied 7 years ago.
1010 mllivolts

Ok... good... this under under a load...correct?


And you cannot get it up to 2500 rpm?

Customer: replied 7 years ago.
not in a stall test! I can drive it and get it to 2500rpm no probllem.
Well, lets do that, lets check the engine vacuum while you are cruising down the road at 2000 or 2500 rpm. Let me know what its at.
Customer: replied 7 years ago.
is 18 to 22 fluctuating

SO it sounds like its less engine vacuum than at idle? If this is the case, I would suspect plugged exhaust.


If not, then check ignition timing on your scanner. Maybe the harmonic balancer or the trigger wheel some on shifted causing wrong ignition timing?


Also, I would recommend to check valve timing. Make sure the marks are dead on.


If all checks out, I would lean towards a fuel deliver issue. If fuel pressure is up to par, maybe your mass air flow sensor is at fault here causing all of this trouble.

Another idea would be the egr valve sticking open causing an internal vacuum leak?

(Just had a friendly expert bring this theory up to me.)


Let me (us) know what you find! :)


I am sure that there are a lot of eyes on this post.

Customer: replied 7 years ago.
I just checked timing marks and there all lined up!
I also checked for exhaust back pressure and is normal no back pressure.
the scaner shows advanced timing of 12 to 16 depending on the throttle

What about the egr valve? Have we checked this as well as for other vacuum leaks? Have we smoked the intake?


What about the fuel pressure regulator? This engine has a fuel pressure regulator....correct? Not leaking?



Customer: replied 7 years ago.
I all ready performed an egr test from ALLDATA and seams ok. I just installed a fuel pump and does the same thing. all though! there is someting I though is weird.

before the engine starts pinging the timing on the scanner is around 35 degree's and as soon as the engine starts buging down the timing moves to 10 and then goes to 0 and the pinging continues

Sorry for the delay!


That is very odd. Can you scope the crank sensor? Is the harmonic balancer loose? WHat about the timing belt gear that sits on the crank? Is the key way nice and secure?

Also, watch the timing retard on your computer to see if the computer is actually purposely retarding the timing maybe because of an input like the knock sensor? If the engine is making noise maybe the knock sensor is picking it up and retarding the timing? I have also come across the know sensor torqued too tight causing it to be way to sensitive and it will cause the computer to retard the timing causing a drive ability issue.


Just a thought.

Customer: replied 7 years ago.

no is not lose Ijust replased the timing belt tentioner and I just re checked everything and seams fine.

Here is some information on engine pinging.


Likely Causes

Ignition Timing, If Adjustable -
Incorrect ignition timing can cause the engine to ping or have spark knock. NOTE: OBD II vehicles do not have adjustable ignition timing.

Exhaust Gas Recirculation (EGR) Valve -
Lack of EGR flow can cause the engine to ping or have spark knock.

Knock Sensor, If Equipped -
A failed knock sensor can cause the engine to ping or have spark knock.

Fuel -
Low octane fuel can cause the engine to ping or have spark knock.

Cylinder Head -
Carbon deposits in the cylinder head increases the compression ratio which can cause the engine to ping or have spark knock.

Radiator -
An overheating engine will increase the likelihood of spark knock or pinging.

Overlooked Causes

Injector(s) -
Any injector(s) with poor spray pattern or restricted flow can cause pinging.

Here is a awesome test to help us pinpoint this problem. It will tell us which way we should go in this diagnoses. Lean, Rich or a mechanical. Its called the flat raters test drive.


Get the engine to act up under wide open throttle and look at some of the parameters on your scan tool and compare them to the readings I have below.


Here is the test. ( have to be off line for an hour or two. I will check in with you later tonight.)


The flat raters test drive..........


Under safe road conditions, a wide open throttle acceleration is performed. Try to maintain WOT for at least 5 seconds. 10 to 20 seconds would be better.


What will the pre cats do?

Will indicate rich


Should the barometric pid change?

Should remain stable! Very important!


What will air flow do?

Max out. Volumetric efficiency. Engine load 100%
(Engine load Parameter on scan tool should go close to 100%)



Poor acceleration, rich exhaust, and good Barometric pressure = restricted exhaust or late ignition timing.


Poor acceleration, rich exhaust, low or decreasing Barometric pressure = intake path restricted


Poor acceleration lean exhaust and good barometric pressure = fuel delivery concern.


Poor acceleration, lean exhaust and low barometric pressure = air flow measurement error. (Ford has this problem with Mass air flow sensors)


Note: Some vehicles Barometric pressure is not updated until Wide open throttle.

Customer: replied 7 years ago.

Hey! tanks for all the effort and you help with this problem.

I won`t be able to do anyting moreto this car till tomorrow so I will have an enswer for you bright early tomorrow tanks againg and hope to find you online tomorrow.



THat is just fine. I will be on line all day tomorrow. Let me know what you find.


You can hit the accept button any time and we can still continue our conversation. I will stick with you until we get this thing handled!


Talk to you tomorrow!





Amedee and 5 other Car Specialists are ready to help you
Customer: replied 7 years ago.
tanks for you time and effor I just got jumped (they want someone else look at this car) so I guess this is the end of the rad. tnak you and I wanna pay you for all you work and hope some other time I get better luky.



THanks for the accept!


I know we tried hard to get ot the bottom of this thing and we did all we can do.


Please let me know if you have any further questions!

Customer: replied 7 years ago.
yeaH! tannks. I`ll let you know if something comes up.
SOunds good!