Hyundai Elantra 2000 GLS temperature related ignition control problem[/b] Can anybody help me with a curious problem with the ignition/control system on my Elantra that started immediately after a visit to the dealer for a dealer recall and routine service? First the symptoms: I live in deep south Texas where the land is flat as a pancake and there is a nice 10 mile stretch of four lane divided highway close by that we have been using as a 20 mile test track. The only “hills” are four overpasses. 1) The car starts easily and getting on to the test track we accelerate up to the posted 70 mph and engage the cruise control. For the first 20 minutes the car behaves perfectly. The throttle position on level road is about one third. 2) After about 20 minutes at the next overpass when the cruise control asks for more throttle the car appears to hesitate as though it was miss firing. As soon as the throttle demand goes away the hesitations go away. 3) On the following overpass the hesitations are more severe and engine rpm drops. The transmission shifts down and when the hesitation goes away the rpm screams as the power comes back on. This all repeated about once a second with ride becoming increasingly jerky Not wanting to trash the transmission I disconnect the cruise control 4) At this point the engine will accept up to about half throttle before the hesitations start. Beyond half throttle the engine appears to die for may be half a second before the power comes back on briefly in a die/return, die/return cycle. 5) Over the next 30 minutes the useable throttle range decreases to the point where any throttle beyond idle causes it to die and then finally it won’t even idle. 6) If the car is allowed to rest and recover its sense of humor (or more likely to simply cool down) the whole one hour process can be repeated What the dealer did before the problem started 1) Routine 50,000 mile service 2) Installed a new timing belt 3) The dealer recall was to lengthen the harness pigtail to the Mass Air Flow Sensor What we have done to attempt to rectify the problem 1) Checked all electrical and hose connections 2) The engine starts throwing error codes as the problem develops. Trouble is it throws too many codes apparently randomly. Using the codes as guidance, we have replaced: a. The TPS (throttle position Sensor) b. The ECM (Electronic Control Module) c. The MAFS (Mass Air Flow Sensor) 3) Replaced the fuel pump and fuel filters 4) Cleaned the fuel system We think we may be looking for an ignition/control system component that goes bad when it gets too hot. What do you think? Thanks Archie

 

I think the subject line should have been called "Stump the Chumps". You have pretty well covered all the possabilities I was thinking of. The obvious is the Mass AFS harness extension, since you indicate this scenario started with that modification. I suppose that wiring has been checked numerous times with all the other replacements you've done. The only item that comes to mind is the fuel pump relay, but I don't think it would keep tripping in and out for the extended period of time you describe. If you replace any more parts, Hyundai should start the warranty clock all over.

Sorry, but you've done everything I would do to diagnose this problem. I really can't think of what else the problem would be. I hope you respond with the answer if this situation gets sorted out.

 

Thanks for your observations. The last thing I can think of before sending it off for scrap is the Crank Angle sensor. Years ago I had one that was temperature sensitive and needed replacing. Have you had any experience with that sensor? Take care and glad you follow Car Talk!

 

Actually, there are two such sensors on your Elantra. The aforementioned Crank Position Sensor and the Cam Position sensor. Both detemine rotation of the respective shafts and both control timing of the iginition and fuel systems through the ECM. When these go bad, the engine usually just stops dead because the ECM simply shuts off ignition and fuel. I've never heard of an intermittent problem that goes on for an extended period of time like you describe. I've noticed that these two sensors do tend to develop some heat sensitivity when they start to go bad. Perhaps you need to carry a scanner with you on the test track and try to pull the very first error codes when the hesitation initially occurs.

"Click" and "Clack" are on the local NPR station in 30 minutes. Perhaps a call to them would be appropriate...

 

Thanks again for you observations. I will try replacing both sensors, one at a time, and if that doesn't work I try the Tappet Brothers. Take care.