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Discussion Starter · #1 ·
Hello guys,

I have lost all hope. I tried everything.

I have a '05 V6 with the automatic transmission. When the engine gets warm, on idle, the voltage slowly drops down to 12V. I've replaced the alternator, radiator fan, alternator cables, ground cables (both engine and battery), relays (A/CON1, RAD, A/CON2), and fuses. I've also disconnected the subwoofer and replaced the belt and the pulley - no change. On a freshly started engine, the charging voltage seems fine - around 14V. When it gets warmer, on idle, the voltage starts to slowly drop, then goes back up when I add some throttle. Red light - I use the brakes and stop the car - the voltage goes back down (now almost instantly) to 12V. The problem is the most visible with the AC on, but it also happens with AC Off. Could you give me any tips on what to look for now?
 

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Try to check the other accessory pulleys that the serpentine belt drives (A/C compressor, alternator, idler pulley, power steering pump) and see if one of them is binding up. Could be one of them binding and causing the belt to slip and therefore not spin the alternator like it should.
 

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Discussion Starter · #3 ·
Try to check the other accessory pulleys that the serpentine belt drives (A/C compressor, alternator, idler pulley, power steering pump) and see if one of them is binding up. Could be one of them binding and causing the belt to slip and therefore not spin the alternator like it should.
I eliminate AC pulley, since it also occurs when AC is turned off (coil works fine, draining 3A when I short the relay), same with the alternator, since I've tried this on two different alternators. I've also checked this on 3 different idler puleys.

Ill check the power steering pump. That is some kind of idea.

BTW. I noticed, that the RPMs do not go up when I turn on the AC - shouldn't they raise? Could loose throttle lines be the issue?
 

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2006 Hyundai Tiburon SE
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On an automatic, your RPM will stay the same if you're up to operating temperature of 90C. If you are still warming up at around 60C your RPM will change as much as 60RPM with a load on the engine (such as power steering or A/C). Meanwhile, on manual cars (or autos in neutral/park), the Idle speed without load should be 750RPM and with a load should rise to 800 RPM. Otherwise an auto in any gear will stay at 650RPM with and without a load. Here are the OEM temp (Celcius) vs RPM settings. The left two are for manuals or autos in park/neutral and the right are autos in gear:

Rectangle Font Line Computer Screenshot


I would check to make sure your power steering pressure sensor is hooked up and operating correctly. It's the single wire that leads to the power steering pump on the V6's. Loose throttle cables do not affect idle. Your IACV does all the idle adjustments. If your IACV is starting to fail it may also be a contributing factor.
 

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Discussion Starter · #6 · (Edited)
So, today I replaced IACV and power steering - no difference. Any idea what can also cause the issues?

To make things clear - voltage drops firstly to around 13V, then goes down progressively down to around 12V. When I change to Neutral or sth, then the voltage goes up back to normal.

I think it might be the same issue as here: Voltage drops when engine's hot
 

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Did you reset your ECU after replacing the IACV and let the car idle for 10-15 minutes from a cold startup? If not, try that first as the IACV minimum and maximum values need to be recorded by the ECU in the adaptive values section of memory.

Do you have an A/C pump? If so, set your fan settings away from defrost and disable your A/C button. The defrost setting will activate the A/C clutch to condition the air blown onto your windshield. It's possible that the A/C pump is bogging down your motor.

What size diameter crank pulley do you have? If you have one of the all aluminum undersize pulleys it may be underdriving your alternator to the point it provides less power at idle. What size diameter is your new alternator pulley? There were a few variants of our alternator with difference sized pulleys from different vehicles. Our higher revving "sports" motors typically came with a larger alternator pulley compared to the passenger cars to prevent overspinning the alternator at the rev limiter. I've seen rushking pull several 2.7L alternators from Sonatas and Tucsons in the junkyard with varying pulley sizes.
 

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Discussion Starter · #8 ·
Did you (...)
I'll try to reset ECU - I forgot about it. However, I think the issue is not related to the AC - first of all, the voltage drop also takes place when AC is not turned on at all.

I also do not think that is the alternator issue - I also had my alternator regenerated beforehand, but the issue remained. The new one is AS-PL A3217. Voltage regulator was replaced on both alternators.

Pulleys are brand new originals, I do not remember the diameters.
 

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Discussion Starter · #10 ·
So, today I've measured the current that the alternator is giving. It is around 83A on idle, so I think it would be weird to complain about it.

The voltage still drops tho. I will replace IACV to the used stock, the replacement I've put there is probably malfunctioning (buzzing loudly on ACC).

Does anyone know the standard current draw on 2.7 with automatic transmission?
 

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Not sure if it was already mentioned but I would also check the grounds. Especially the negative battery terminal and the strap from the intake manifold to the firewall. If they're dirty or greasy etc you can clean them up and make sure they're getting a good connection and that may help.
 

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Discussion Starter · #12 ·
Not sure if it was already mentioned but I would also check the grounds. Especially the negative battery terminal and the strap from the intake manifold to the firewall. If they're dirty or greasy etc you can clean them up and make sure they're getting a good connection and that may help.
Yea, both gnd cables replaced ;/
 

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Discussion Starter · #13 ·
Update:

I've checked the alternator - on the measuring table it works fine.


Replaced everything I could, but the issue still persists. I'm out of hope.

It is looking like the engine is not giving enough RPMs to supply the alternator. IACV was replaced twice, but nothing changed.
 

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What changes to the electrics? Things like bigger stereo, lights, etc. If anything was changed, turn it off or disconnect for now.
What RPM's is it running when cold and warm?
 

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Discussion Starter · #15 ·
What changes to the electrics? Things like bigger stereo, lights, etc. If anything was changed, turn it off or disconnect for now.
What RPM's is it running when cold and warm?
When it's cold it's running around 1000-1100 RPM. It seems like the RPMs are too low for idle on hot engine, but as @chase206 said, 650 seems normal on AT.

Electrics - added LPG installation and stereo - no changes no matter if they are connected or not.

In addition - the same situation with the engine running on gasoline and LPG.
 
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