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Discussion Starter #1 (Edited)
This is a bit of a different one and I would like to request all responses to be respectful of my choices.
First a disclaimer: I used a professionally engineered kit to convert my 2012 Hyundai iMax (i800) to dual fuel. The first being normal diesel and the second being finely filtered (2 micron) and de-watered high quality vegetable oil. If you do not understand SVO systems, please do not comment. your comment is likely to be negative and ill-informed. I have converted so far 6 different cars and have driven them 300k without issue on SVO. I saved enough on fuel to get one of my children through university, this is my choice and I am happy to take the risks.

I have driven on the dual tank system for 40k now with this vehicle and I have not had any issues whatsoever. In the past few weeks a problem has started to occur that is increasingly getting worse. I will explain step by step what happens:
1. I start the car on diesel fuel (100%)
2. I drive the car for 5km until the engine is at working temperature.
3. The system automatically switches to vegetable oil.
3. After about 5-10km's the fuel pressure suddenly drops and the engine slows down until it stops.
4. I let the engine rest for about 5 minutes and then am able to drive another 5kms before the same issue happens.
5. I read the ECU with an OBDII reader but there are no error codes at all.
6. The car drives great until about 5-10ks after the engine is warmed up.

This is a dual tank system that supplies the 2 separate fuels via two separate systems out of different tanks to the CRDi pump.
Both lines have auxiliary pumps that operate at the right pressure.
Both lines have good filters and the SVO has an heat exchanger.
So far I replaced: both filters, the Common Rail Pressure sensor, the suction valve (all original Delphi). I removed the feeder hose to the CRDi pump and there is a good flow of both diesel and SVO, depending on how it is switched.
I tried driving on diesel alone and on SVO alone with no difference whatsoever. I checked all the hoses for kinks and replaced all the connectors + the hydraulic (SVO) filter housing.
Turbo sounds fine, no rattles in the engine. I bypassed the second tank and had the engine connected to just the diesel tank (as original) with no difference at all.

I just realised, the only thing that changed recently is the engine oil. I changed to 0w40 full sythetic from the normal 5w30 semi synthetic. I know that these engines have an issue with their oil intake, resulting in disintegrating turbos. Would there be a limp mode if the oil gets too thin? It has been between 30 and 40 degree celcius here for the past few months.

I would be extremely grateful if somebody has an idea what it may be. I considered bringing it to Hyundai but they quoted me $3000 (part price) for a new CR because they could not replace the pressure sensor on its own. A new Delphi pressure sensor is $40 on eBay so I kindly told them where to go. Plus, the first thing they would say is: get rid of the duel fuel system.

Like I said earlier, I respect your opinion, please respect mine. I do not need to be schooled in how bad SVO is for a diesel engine, everyone is entitled to their own opinion. A comment saying: "It's the SVO" is not helpful, please refrain from making these comments.
 

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After about 5-10km's the fuel pressure suddenly drops and the engine slows down until it stops.
I'm surprised that a significant drop in pressure isn't logging a pressure deviation trouble code. I assume fuel pressure is still controlled by the Delphi ECU even when it's running on SVO? Actually, I'm surprised your engine has a Delphi management system. I though the 2.5 used a Bosch system.

Gjalt said:
I let the engine rest for about 5 minutes and then am able to drive another 5kms before the same issue happens...The car drives great until about 5-10ks after the engine is warmed up.
This sounds kinda like the symptoms of a crank sensor failure. Quite a common problem on Hyundai engines. The sensor breaks down when it gets hot causing the engine to shut down, and it wont immediately restart. But once the sensor cools a little the engine is able to start again. It might be worth trying a new sensor on the engine just to rule that out before getting involved any further with the fuel system.
 

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Discussion Starter #3
I'm surprised that a significant drop in pressure isn't logging a pressure deviation trouble code. I assume fuel pressure is still controlled by the Delphi ECU even when it's running on SVO? Actually, I'm surprised your engine has a Delphi management system. I though the 2.5 used a Bosch system.


This sounds kinda like the symptoms of a crank sensor failure. Quite a common problem on Hyundai engines. The sensor breaks down when it gets hot causing the engine to shut down, and it wont immediately restart. But once the sensor cools a little the engine is able to start again. It might be worth trying a new sensor on the engine just to rule that out before getting involved any further with the fuel system.
Hey Autospark. Thank you for that excellent reply. you are completely right, just because the symptoms are similar to low fuel pressure, it does not mean that that is the issue. Of course the crank sensor warms up slower than the engine itself because it is attached to the (manual) transmission. I ordered a replacement sensor and will try it as soon as I get it. Thank you for your excellent suggestion!
 

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The pressure sensor is a replaceable part. Their attitude is replace the entire system but that's only when the high pressure pumps deteriorates and metal particles get pumped thru the system. My guess is they don't want to touch it. Nothing wrong with SVO it lubricates parts as good as if not better than diesel. I agree with autospark's comment about the crank sensor.
 

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Discussion Starter #5
The pressure sensor is a replaceable part. Their attitude is replace the entire system but that's only when the high pressure pumps deteriorates and metal particles get pumped thru the system. My guess is they don't want to touch it. Nothing wrong with SVO it lubricates parts as good as if not better than diesel. I agree with autospark's comment about the crank sensor.
Thank you for that information. I replaced the sensor without any difference whatsoever. I put the air hose on all the fuel lines and purged them completely, new fuel filters, cleaned mesh in pre-filter, adjusted oil pump pressure and completely cleaned the intake lines in the tank. Still the same issues. I am getting pretty desperate now and am considering bringing the fuel system to original and bringing it to the stealership and just bend over.

Does anybody have any idea why I have a sudden fuel pressure drop after 10-15k's?
 

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am considering bringing the fuel system to original and bringing it to the stealership and just bend over.
LOL...they'll just tell you you need a new ECU or a new high pressure pump. Their first "guess" always seems to be the most expensive part on the system then they work their way down the parts price scale from there until they, hopefully, swap the part that is causing the issue.

Gjalt said:
Does anybody have any idea why I have a sudden fuel pressure drop after 10-15k's?
Assuming it is a pressure problem, it really has to be something on the high pressure side since it sounds like you have two completely independent low pressure systems. I assume, since it's a Delphi system, that there is no pressure control valve on the fuel rail? If that's the case the only place the fuel could escape from the rail is via the injectors. Have you had those tested while the fault is present to see if one of them is leaking excessive fuel back to the tank?
 

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Discussion Starter #7
LOL...they'll just tell you you need a new ECU or a new high pressure pump. Their first "guess" always seems to be the most expensive part on the system then they work their way down the parts price scale from there until they, hopefully, swap the part that is causing the issue.


Assuming it is a pressure problem, it really has to be something on the high pressure side since it sounds like you have two completely independent low pressure systems. I assume, since it's a Delphi system, that there is no pressure control valve on the fuel rail? If that's the case the only place the fuel could escape from the rail is via the injectors. Have you had those tested while the fault is present to see if one of them is leaking excessive fuel back to the tank?
That is very interresting. The only issue is that the problem only occurs after 10-15k's at 100km/h. There are no problems at all before then. To me, this would indicate that the injectors work okay plus you would see a higher fuel return but not a restriction in the fuel supply. I have a couple of non return valves in the fuel supply that I will pull out and test to see if they are somehow restrictive.
 

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To me, this would indicate that the injectors work okay
Maybe they do...until they get hot.

Gjalt said:
plus you would see a higher fuel return
Exactly. That's what an injector leak off test is for. To check for excessive fuel being returned to the tank.

Gjalt said:
but not a restriction in the fuel supply.
You've seen a restriction in the fuel supply?
 

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Got it! Finally, djeez.... it was so simple. I finally ended up doing a leakdown test and found that 2 of the 4 were leaking horribly. This would explain the low pressure. They fuel system was probably having more issues as the engine warmed up and the fuel viscosity went down. I called the Hyundai dealer and asked the price of a single injector. They told me it was $1500 EACH. I made a cheeky comment and went to eBay where I found a set of 4 original Delphi's with less than 1000k's on them for $700 (for 4). Installed and the car runs like new again. Fun fact. The car just hit 150k and this is where these injectors fail. Normal maintenance. I wish I could bring this car to the stealership but they would have charged me 10k easily to repair it which is about the value of the whole van, would have been a write-off basically. That's why you find soo many modern diesels in the yard with not a scratch on them but a 'blown' motor. Thank you all for your comments and great ideas. I'm glad that it's running again.
 

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I finally ended up doing a leakdown test and found that 2 of the 4 were leaking horribly....I'm glad that it's running again.
Thanks for taking the time to update the thread and confirm the fix. I'm glad it's running again too, and glad I was able to help.
 
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