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CATEGORY LISTINGS > GM DIESEL > Have I hydrolocked my diesel from overpressurised rail? [ REFRESH ]
Thread Title:

Have I hydrolocked my diesel from overpressurised rail?


Created On Sunday November 01, 2020 10:30 Diesel Talk
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Joined: Nov 2020

Note Sunday November 01, 2020 10:30 View thread in raw text format
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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 (former GM subsidary) 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.
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