Have I hydrolocked my diesel from overpressurised rail?

[boxerbeemer]

Hello all,

I am turning on you with one question, which I really cannot solve by myself. I hope there is someone who knows stuff about diesel engines and will be able to explain some things.

So, I bought a used Opel Astra 1.7 CDTI, common rail turbodiesel engine with 110 hp. It is an Isuzu - derived engine using Denso fuel supply sistem, icluding Denso high pressure diesel pump and suction control valve. The car was running powerfull but it had the problem with idle. These engines often suffer idling problems from faulty suction control valve, which is basically a fuel pressure regulator for the fuel rail. I heard on some forum, that I could just unplug this regulator to see if this is the cause of the unstable idle problem. And this move was a big mistake.

When the engine was shut off, I unplugged the connector of the suction control valve. Then I started the engine. As soon as it started, it started to produce really loud, tractor - like sound, even louder than a tractor. It is obvious why - namely the absence of the suction control valve resulted in overpressurised fuel rail. The injectors were really loud. So with the engine running at about 1200 RPM ( normal idle is around 750 - 800 RPM) I was trying to figure out what is going on. Everything lasted for about 30 - 40 seconds, untill the engine died by itself. After that I plugged the connector back on the suction control valve and started the engine. The start - up was normal.

So my question is: since the fuel rail was way overpressurised and the idle was at about 1200 RPM, 400 - 500 RPM higher than normal and the engine then died, is it possible that I hydrolocked it on one of the cylinders? Why would it stop otherwise? I still have some hope that the hydraulic lock didn´t happen. My opinion is, that if the amount of fuel was way too large, the engine would have first raised the RPM even more resulting from the increased fuel flow, like it would, if I pressed the gas pedal, am I right? Namely the diesel combustion process is controlled by the amount of fuel, so wouldn´t all the extra fuel (injected at the right time of course - I pressume that since injectors are ok, they opened and closed at the right crank angle) result in increased RPM of several thousand RPM and not in hydrolock? At least this is my hope, since the pressure was really high, I thing the fine - atomised fuel would have raised the RPM istead of accumulating in the cylinder and thus hydrolocking the engine. The engine is running ok for now.

I am feeling really bad for what I did. The engine is really torquey and fuel efficient. I like it a lot.

I would like to hear your opinion. Thank you all.

 

[Racecarfan2]

If you hydraulic the engine it stops running because there is too much diesel in the cyl to compress. You probably washed out the cylinders and need to change the oil. The noise was likely spark knock from too much fuel.

 

[boxerbeemer]

So why did the engine come to a stall then all of a sudden? If I was the one that shut it off, I wouldn't worry about that now ...

 

[Racecarfan2]

So why did the engine come to a stall then all of a sudden? If I was the one that shut it off, I wouldn't worry about that now ...

It was too rich. If you filled the cyl with fuel you would have a bent rod/locked up engine. Change the oil and move on if the engine sounds like it always has.

 

[boxerbeemer]

If a turbo diesel runs rich it increases revs, because the power of a diesel engine is regulated by the amount of fuel injected.

 

[Trav]

Hello all,

I am turning on you with one question, which I really cannot solve by myself. I hope there is someone who knows stuff about diesel engines and will be able to explain some things.

So, I bought a used Opel Astra 1.7 CDTI, common rail turbodiesel engine with 110 hp. It is an Isuzu - derived engine using Denso fuel supply sistem, icluding Denso high pressure diesel pump and suction control valve. The car was running powerfull but it had the problem with idle. These engines often suffer idling problems from faulty suction control valve, which is basically a fuel pressure regulator for the fuel rail. I heard on some forum, that I could just unplug this regulator to see if this is the cause of the unstable idle problem. And this move was a big mistake.

When the engine was shut off, I unplugged the connector of the suction control valve. Then I started the engine. As soon as it started, it started to produce really loud, tractor - like sound, even louder than a tractor. It is obvious why - namely the absence of the suction control valve resulted in overpressurised fuel rail. The injectors were really loud. So with the engine running at about 1200 RPM ( normal idle is around 750 - 800 RPM) I was trying to figure out what is going on. Everything lasted for about 30 - 40 seconds, untill the engine died by itself. After that I plugged the connector back on the suction control valve and started the engine. The start - up was normal.

So my question is: since the fuel rail was way overpressurised and the idle was at about 1200 RPM, 400 - 500 RPM higher than normal and the engine then died, is it possible that I hydrolocked it on one of the cylinders? Why would it stop otherwise? I still have some hope that the hydraulic lock didn´t happen. My opinion is, that if the amount of fuel was way too large, the engine would have first raised the RPM even more resulting from the increased fuel flow, like it would, if I pressed the gas pedal, am I right? Namely the diesel combustion process is controlled by the amount of fuel, so wouldn´t all the extra fuel (injected at the right time of course - I pressume that since injectors are ok, they opened and closed at the right crank angle) result in increased RPM of several thousand RPM and not in hydrolock? At least this is my hope, since the pressure was really high, I thing the fine - atomised fuel would have raised the RPM istead of accumulating in the cylinder and thus hydrolocking the engine. The engine is running ok for now.

I am feeling really bad for what I did. The engine is really torquey and fuel efficient. I like it a lot.

I would like to hear your opinion. Thank you all.

I would not loose any sleep over it. You did 100% not hydrolock the engine, not even a little bit. At worst the oil is a bit loaded with diesel and should be changed. Do not listen to internet blather without looking into carefully.

 

[atikovi]

The noise was likely spark knock from too much fuel.

In a diesel?

 

[clinebarger]

Unplugging the Pressure Control Solenoid was a bad idea but likely didn't cause any harm as it has a Pressure Relief Valve. There are Rail Pressure Sensors for a reason & can be used to diagnose Rail Pressure/Pressure Regulator issues.

 

[boxerbeemer]

Thank you. I just can't explain myself how it stalled all of a sudded at 1200 RPM?

 

[Jetronic]

Hello all,

I am turning on you with one question, which I really cannot solve by myself. I hope there is someone who knows stuff about diesel engines and will be able to explain some things.

So, I bought a used Opel Astra 1.7 CDTI, common rail turbodiesel engine with 110 hp. It is an Isuzu - derived engine using Denso fuel supply sistem, icluding Denso high pressure diesel pump and suction control valve. The car was running powerfull but it had the problem with idle. These engines often suffer idling problems from faulty suction control valve, which is basically a fuel pressure regulator for the fuel rail. I heard on some forum, that I could just unplug this regulator to see if this is the cause of the unstable idle problem. And this move was a big mistake.

When the engine was shut off, I unplugged the connector of the suction control valve. Then I started the engine. As soon as it started, it started to produce really loud, tractor - like sound, even louder than a tractor. It is obvious why - namely the absence of the suction control valve resulted in overpressurised fuel rail. The injectors were really loud. So with the engine running at about 1200 RPM ( normal idle is around 750 - 800 RPM) I was trying to figure out what is going on. Everything lasted for about 30 - 40 seconds, untill the engine died by itself. After that I plugged the connector back on the suction control valve and started the engine. The start - up was normal.

So my question is: since the fuel rail was way overpressurised and the idle was at about 1200 RPM, 400 - 500 RPM higher than normal and the engine then died, is it possible that I hydrolocked it on one of the cylinders? Why would it stop otherwise? I still have some hope that the hydraulic lock didn´t happen. My opinion is, that if the amount of fuel was way too large, the engine would have first raised the RPM even more resulting from the increased fuel flow, like it would, if I pressed the gas pedal, am I right? Namely the diesel combustion process is controlled by the amount of fuel, so wouldn´t all the extra fuel (injected at the right time of course - I pressume that since injectors are ok, they opened and closed at the right crank angle) result in increased RPM of several thousand RPM and not in hydrolock? At least this is my hope, since the pressure was really high, I thing the fine - atomised fuel would have raised the RPM istead of accumulating in the cylinder and thus hydrolocking the engine. The engine is running ok for now.

I am feeling really bad for what I did. The engine is really torquey and fuel efficient. I like it a lot.

I would like to hear your opinion. Thank you all.

The engine didn't hydrolock. The ecu can't control fuel timing properly because of the high pressure and this is producing the knocking sound. What you hear is what that engine would sound like with a rotary direct injection pump and mechanical injectors. If there's overfueling, the RPM will rise. That's how a diesel regulates it's rpm, through fuel delivery. x amount of fuel = x rpm... 2x fuel, 2x rpm...

Normally around idle with a warm engine the ecu will aim for 200 bar fuel pressure but now the pressure was 1300 bar or more. The engine was gaining some rpm which probably increased pressures even further and the ecu stopped the engine when the max pressure was reached.

What is the issue at idle?

 

[boxerbeemer]

So there is no chance it could have hydrolocked in this situation of overpressurised rail? It then shut itself off by closing the injectors, or?

It idles fine now, because I replaced the suction control valve.

Thank you for the answers!

 

[Skippy722]

No, if it hydrolocked it wouldn’t have restarted and been okay, usually a hydrolock results in bent and broken parts. It’s possible the ECU sensed it couldn’t control the engine speed so it shut itself down as a safety measure, but I’m not familiar with them to know for certain.

 

[Trav]

So there is no chance it could have hydrolocked in this situation of overpressurised rail? It then shut itself off by closing the injectors, or?

It idles fine now, because I replaced the suction control valve.

Thank you for the answers!

That's it. A true hydrolock while running would likely break or seriously damage internals, damage from bent or broken rod(s), broken piston to a hole through the block. The ECM shut it down, I suspect just going by your post it possibly had a defective SCV to begin with.

 

[boxerbeemer]

Yes, it really did have a faulty suction control valve (SCV), which I have replaced later next week. But I was worried it could have stalled from hydraulic lock, since it came to a sudden stop after running at 1200 RPM and massive pressure in the fuel rail ...

 

[boxerbeemer]

Now I am getting a strange sound, like a turbo whistle but it is not. Could it be a conrod bearing from a broken rod? Happens every now and then with no logical sequence.

 

[Trav]

You do not have a broken rod and a rod bearing failure would be a knocking noise, bearing noises do not come and go.
Look for a leak in the turbo pressure system, a loose clamp, split hose, anything you may have disturbed or moved while working on it.

 

[boxerbeemer]

Sorry I meant a bent rod. It is interesting that the sound occurs randomly, but mostly under no engine load or only a little load. It sounds like someone would rotate a rope in the circle in the air. I am not a native english speaker so I really can't explain the sound any better. It occurs mostly around idle to about 1700 RPM. It usually doesn't occur at higher revs, but since this diesel has most torque around 2000 RPM, I ofren don't drive it much higher than that. If I hear the sound and then increse the revs in neutral or with the clutch pressed, it goes away as the RPMs are raised. When the RPMs drop back down it is often hearable again.

Is it possible to be a diesel high pressure pump or maybe a water pump or some ball bearing on the belt drive?

 

[boxerbeemer]

But I have no idea why it started to happen now, because I really wasn't moving any hoses, pipes or whatsoever. It was really a straight forward 5 minute job. So you really don't think that a small hydraulic lock could occur and bent the connecting rod just a little bit (since it was only idling)? I just can't explain that sound which started the day I replaced the SCV. Plus, I have heard of engines hydrolock due to the faulty pressure regulator ... I really don't know but I am really concerned about that. Any suggestion and thought is welcome.

 

[Jetronic]

Sorry I meant a bent rod. It is interesting that the sound occurs randomly, but mostly under no engine load or only a little load. It sounds like someone would rotate a rope in the circle in the air. I am not a native english speaker so I really can't explain the sound any better. It occurs mostly around idle to about 1700 RPM. It usually doesn't occur at higher revs, but since this diesel has most torque around 2000 RPM, I ofren don't drive it much higher than that. If I hear the sound and then increse the revs in neutral or with the clutch pressed, it goes away as the RPMs are raised. When the RPMs drop back down it is often hearable again.

Is it possible to be a diesel high pressure pump or maybe a water pump or some ball bearing on the belt drive?

it's not the engine cooling fan?

 

[boxerbeemer]

No, I checked that also.

So you are saying there isn't a slightest chance it got hydrolocked from overfuelling? Thanks!