Hyundai Repair: Loss of power once engine starts to warm up, hyundai excel, self diagnosis

Question
Hi again HT,

Thanks again for your advice.

As you asked, I have reset my ECU (by doing the 5 minute battery disconnection thing).  I have then checked that there were no fault codes by doing the self diagnosis shorting of pins 4 and 15 on the ECU connector plug in the cabin.  There were no faults (as evidenced by a code 4444).

I then took it for a ride around the block, and experienced the fault I previously described.

Upon returning, I then re-shorted pins 4 and 15 to find the only fault code was for the knock sensor, ie; 3211.  

I will replace it, but could you please advise me of where abouts on the block I might find it?

Again, the car is the last of the single cam G4 engines and it is a 1997 Excel (Accent).  I think it might be the one next to the oil presure switch toward the back of the block, but I'm not entirely sure.

Thanks in anticipation...

Regards,

Adam
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Followup To

Question -
Hi there,

I have a 1997 model Hyundai Excel 12-valve (Accent in other countries).  For the first minute or two, it runs fine, but after that it experiences a fairly radical drop in power (to about 70% in my opinion), and will continue in this fashion until it is once again cold.

If it is test driven, it really feels like the timing is getting severely retarded.  It is almost as if you can tell it wants to go, and has potential, but is holding back.  It revs, but not enthusiastically.

I have done the following checks/changes already:
- Checked cam timing against BTDC (it is ok)
- Checked ignition timing at idle and not under load (it is ok - varies from about 7/8 degrees to about 12-14 degrees when revved)
- swapped coils from another car as I thought they may be breaking down under load when hot (no change)
- leads are already new... and it doesn't feel like an ignition miss anyway
- spark plugs are all a nice light colour
- swapped the EFI temp sensor for another (secondhand) one (no change)
- checked the resistance of both EFI temp sensors under various temps (ranges from about 300R when hot to about 3.5kR when cold, as they should
- Changed the O2 sensor in the exhaust (no change, although I can feel it working when power is down because the power that's left rises and falls slightly as the mixture changes while driving along)
- Pulled the cat converter off to look through it.  It has not collapsed, and looks fine.
- Swapped the Air Flow sensor off another car (no change)

Other useful info:
I also went to the Hyundai dealer and the diagnostic gadget came up with a number of sensors, including:
- Mass air sensor (which I swapped already)
- Knock sensor (which I'm not sure of the location of, but could be the culprit, I guess - what would the symptoms be... just retardation under load?) I can't hear pinging, by the way.
- EFI temp sensor
- O2 sensor

Final tests I did today:
- Tested and re-installed the original EFI temp sensor, which tested fine.
- Drove the car with the O2 sensor disconnected (no change)
- Drove the car with the EFI temp sensor disconnected, and, although it got a "check engine" lamp showing on the dash, which would be obvious, the car thought it was running hot (which it wasn't as the guage was still connected and I was watching it), but the thermo fan came on, and the mixture obviously changed, as the car ran as it should!!!!

Unfortunately, I'm not sure how to recognise what this might be, given this final result, but any help is appreciated.

Kind regards,

Adam
Sydney, Australia

Answer -
G'day, Adam.  I don't have any experience with Australian spec vehicles, so I cannot verify how similar the EFI system is, but here's my thoughts:

Your reported symptoms match the typical fuel pump failure symptoms.  If you've got a fuel pressure gauge handy (and the proper fittings), I'd recommend tapping in at the fuel filter and watching the readings while you drive.  Compare those when the condition is happening to those when it's not.  Typical fuel pressure is about 30-35 psi.  If you see anything near 20 psi or lower, you've almost certainly got an issue with the fuel pump.

As for the sensors you say were reported to be needed, I doubt any would cause this large a lack in power other than the mass air flow sensor, which you say you've replaced already.  If you've got the actual trouble codes, that may help me give you more accurate information.

For you sensor diagnosis, you'll probably want to do the following:

-Check the connection at the mass air flow sensor.  Make sure the terminals in the connector have enough tension to grab the pins on the sensor tightly and that you don't have a large amount of wire tension pulling on the connector.  

-Just go ahead and replace the knock sensor.  I don't recall an instance of setting a code for this that replacing the sensor didn't correct the issue.

-I presume that EFI temp sensor refers to the coolant temperature sensor.  I'd recommend replacing the sensor (even though it tests good).  I've seen many of these sensors work great in the shop and then just flake out once the owner gets the car back.  Just like for the air flow sensor, make sure you've got good contact at the terminals and that there's not excessive wire tension pulling on the connector.  If you've got too much wire tension, move the harness a little to relieve it.

Good luck.  Send me the trouble codes if you have them, and let me know if you need any more info.

Answer
I don't recall where the oil pressure switch is, but the knock sensor is on the back of the block (I believe cylinder #2) and is attached with a single 12mm head bolt.  I believe the wire connector is on a clip attached to one of the intake manifold bolts.