# HPFP Drive Ratio



## nate0031 (Oct 24, 2014)

Bit of an off the wall question, but I can't find an answer searching. Does anyone know what the drive ratio is between the crank and high pressure fuel pump? For instance, does the HPFP run at crank speed? 2/3 crank speed? etc. 

Thanks!


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## Aussie (Sep 16, 2012)

nate0031 said:


> Bit of an off the wall question, but I can't find an answer searching. Does anyone know what the drive ratio is between the crank and high pressure fuel pump? For instance, does the HPFP run at crank speed? 2/3 crank speed? etc.
> 
> Thanks!


I may be wrong, but I thought the fuel pump was electric?


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## nate0031 (Oct 24, 2014)

Well, probably. Granted, most of my experience is with TDI's, but I feel it pretty safe to assume the Cruze diesel has an electric low pressure/lift pump to feed fuel to the high pressure fuel pump, which is driven by the timing belt. On the common rail TDI's, which use the CP4.1 instead of the CP1H (god I wish they used the CP1H as well), they have three pumps. One electric low pressure in tank lift pump at ~8 PSI, one electric transfer pump at ~70 PSI, then the HPFP at 26,100 PSI.

I'm pretty sure the Cruze diesels have an electric in tank pump, but I'm not sure if you have the intermediate pump. Many CP3 pumps had a positive displacement gear pump built into the HPFP, and ergo needed no transfer pump, and in some cases not even a lift pump was used. I'm not sure if the CP1H also has that gear pump or not. It could also be application specific.


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## nate0031 (Oct 24, 2014)

Specifically, I'm curious about drive ratio because I want to know when fuel pulses are delivered to the rail. The CR TDI uses a single piston CP4.1. The pump is driven 1:1 to the crankshaft, and the pump camshaft has two lobes separated by 180°. As such, you get two fuel pulses to the rail per engine RPM, and these coincide with the two cylinders that fire per rev. Every 180° of crank rotation you have a cylinder in the power-stroke, and the high pressure fuel pump sending fuel to the rail.

In the Cruze, you have a 4 cylinder engine, and a 3 cylinder HPFP. Your HPFP sends a fuel pulse every 120° of it's rotation, but you still only have a power-stroke every 180° of crank rotation. So I'm wondering if they run the HPFP at 2/3rd's crank speed, to slow down fuel pulses to coincide with the engines 180° firing events. It's either that, or it's run at crank speed and they use an accumulator to hold fuel till the next firing event, in which case pump timing is almost completely irrelevant.


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## karter59 (Feb 14, 2014)

I just looked up the parts. The crank sprocket has 26 teeth, the cam sprocket has 52 and the HPFP has 48 teeth. I saw your post on the TDI forum under 2micron's pump install. There is no need for an accumulator as such, the fuel rail acts as one. There is a pressure relief valve on the end of the rail which sends excess pressure back to the tank on both of these vehicles. I know that all of the manufactures have these pumps timed in some fashion, but for what exact purpose I don't know. The pressure fluctuations in the rail would appear to be of no consequence.
I was out in 2micron's car last Sunday. It engine runs just like stock, except for some additional gear whine from the gear pump on the back of the HPFP.


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## nate0031 (Oct 24, 2014)

Thank you. Good info. Wish I could go take a ride in his car, lol. I've got his kits on the CJAA I'm putting in my Audi, so if the CP4.1 ever tanks, I'll be putting a CP3 in for sure. It was said that the rail didn't accumulate enough pressure to make the CP4.2 worth it, as the second stroke was 90° out from a firing event, and the rail just bled that fuel back to tank. Hence my curiosity. Glad that isn't an issue here. Interesting that Chevy didn't time the pump to firing events, also lending credence to that being negligible.


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