2000 Hyundai Sonata 4 cyl hesitation, poor acceleration

Tiny
DSTATION
  • MEMBER
  • 2000 HYUNDAI SONATA
  • 244,000 MILES
Major hesitation from 0 MPH, then takes off like a rocket; checked compression, manifold vacuum, exhaust restrictions, installed a new TPS, and now we are trying to determine what the readings should be on the MAF sensor. Should there be a 5 volt reference signal to it? This MAF is integrated with the IAT sensor (5 wire)
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Monday, July 15th, 2013 AT 2:53 PM

7 Replies

Tiny
SATURNTECH9
  • EXPERT
Should be 5 volts to the maf. Have you checked plugs wires/spark plug boots etc yet?Any codes in the computer?
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Monday, July 15th, 2013 AT 3:01 PM
Tiny
DSTATION
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No codes and we checked all the obvious things. When I asked this question I had a clue but wanted some confirmation. I spent much of the day on Mitchell-on-demand and AllData. Here's what I figured out (but won't be able to confirm until tomorrow). It is a combo MAF/IAT with 5 wires. One 12V and an input wire for the ECM (IAT), and three for the MAF, a ground, a 5V, and another input for the ECM. We had no 5V signal, in fact that wire was grounded. Until we unplugged the ECM. When we tried manually applying 5V, we popped the 15A ECM fuse (didn't see that at first). So, tomorrow we cut the "gray" 5V signal wire at the ECM, apply 5V from one of the other lines (such as the MAP) and see what happens. We might be able to cheat the system, but my diagnosis is a bad ECM!
I asked this question on justanswer. Com a few days ago and they were all clueless until today when I hinted at the answer. I wish someone would have steered me in the direction on how to check a MAF in the first place!
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Monday, July 15th, 2013 AT 9:11 PM
Tiny
SATURNTECH9
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Yeah if you unplugged the ecm and the 5v reference wire was no longer grounded sounds like a bad ecm. You really can't cheat that maybe get a used ecm?Is your car a automatic or manual transmission?
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Monday, July 15th, 2013 AT 9:34 PM
Tiny
DSTATION
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Automatic. I'll find out today about "cheating " the system. Theoretically, if all I need is to get 5V to my MAF, my throttle response might be resumed. Odds are that that isn't the ONLY problem with the ECM!
I was sooooo close to buying a new MAF (after having purchased a TPS); this was a big lesson for me!
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Tuesday, July 16th, 2013 AT 7:34 AM
Tiny
SATURNTECH9
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Sometimes there is multiple failures in the ecms othertimes jus one. But when they start failing best to just replace them.
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Tuesday, July 16th, 2013 AT 12:38 PM
Tiny
DSTATION
  • MEMBER
One last question- I've ordered the replacement ECM (the only reason I was considering the 5V jumper wire was to confirm my diagnosis, but then I thought, why?)
Will I have to have the new (used) ECM flashed on this particular vehicle?
Thanks
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Wednesday, July 17th, 2013 AT 7:51 AM
Tiny
SATURNTECH9
  • EXPERT
I would say to give a honest answer on the reflashing on the used ecm. From what I have seen/experienced usually it all depends on how the options from your car differ from the donor car. For instance abs cruise control etc. Those little things can cause issues.
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Wednesday, July 17th, 2013 AT 12:23 PM

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