Original high pressure pump (HPP) will not be able to maintain selected pressure level if we increase the amount of fuel going it to the engine. That is why we needed to find bigger HPP. Mercedes 400cdi has one that fits our 320cdi pretty easily. It is capable of producing bigger fuel volume at same pressure as our original pump. Roughly this HPP is 30% bigger than original. This means that we can run 30% more fuel through injectors without problems with maintaining the pressure. From the software we can adjust the pressure even higher than it originally is. 1600 bar is the standard max pressure with this system, we have raised it to 1800bar. Mounting the pump was a pretty easy job, at the same time we added vacuum pump from 270cdi to get brake booster to work. Originally this engine does not have vacuum pump because of its electrically boosted brakes.
We tried to find some bigger injectors for our use from MB catalogs. We even ordered a new set , but after testing those at injector test bench we decided that we will not use them. This is because those would only work up to 350-400hp, and our aim is a lot more. Only solution was to modify our original injectors to the maximum output. This modification is something that is not done on garage floor, so we turned in to professionals. Company named Rengaspalvelu Karjalainen took the challenge happily. After they did their magic we ended up with injectors that were capable of 110% more fuel flow than the originals! This is more than twice the amount of the original injectors. We were extremely happy about this because now these injectors should be able to produce power up to 600hp.
First test day!
We headed to local race track 11.4 to make some baseline software developing. Unfortunately the test day was ruined by faulty fuel control valve at the HPP. The car did run fine for while, but then started to mess around. High pressure is very strictly controlled by ECU and it doesn’t allow much tolerance to it. Because of this faulty fuel valve, high pressure did bounce up and down irregularly. This causes the engine to shut down immediately when the pressure got of the chart. So the test day was ruined but the next day we got a new valve that fixed the problem.
Next day the car was running with out shutting down all the time. There still was some problem that restricts the power from high rpm range. For some reason the software limits the fuel flow just when magic is starting to happen. When the boost kicks in the fuel flow gets restricted. This is probably some safety limit that is trying to save the motor. We are working with the best MB software specialist in Finland, so we are very confident that the problem will be solved very soon. This kind of problems are new to even him, because none of his customers has ever wanted this radical changes to their software. MB engineers have hidden these safety values to the software and now we just need to find them and get those erased.
Of course we couldn’t sit waiting for the solution, so we figured a way around the safety limit. We did fool the boost pressure sensor in a way so it sees the pressure to be at 1bar. Even tough there is about 3bar in the system. With this simple mod and some adjustments to the software we were finally able to see some of the potential of this engine. With this system we were able to get 530hp from the engine on the dyno! Now we would need to find the problem on the software so we could get the software working with the boost pressure sensor. I am pretty sure that there is great potential to get closer to 600hp level. Testing will show if the high pressure pump is big enough for that target.
Ps. We still have those new injectors for 350-400hp if anyone would be interested.