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2.0T High Pressure Fuel Pump Timed to Exhaust Camshaft
A question for those who maybe know. I'm trying to figure out whether the high pressure fuel pump is timed to the position of the rear drive slot gear on the exhaust camshaft.
Backstory:
I purchased a 2012 Q5 which needed an engine rebuild and found the oil baffle plate floating around the head which ultimately damaged the exhaust camshaft. I was able to source a decent OEM camshaft for around $300 CAD but i guess i managed to miff that one too somehow as it bounced around the teardown table needlessly too long. Essentially, one side of the 4 sliding lobes became chipped on the side where the actuator drives the lobe over. Not being one to immediately spending another $300, I realized that the original camshaft had damage on lobes 3-4, and the newer camshaft on 5-6. So i decided to swap lobes 5-6 and 7--8 seeing as Audi uses the same repeating part number on sets 1-2 and 5-6. Going into this, I knew full well the shaft was splined and the ball and spring might be a bit difficult to reassemble but ultimately found that part very easy to reassemble using the lobe spacer tools out of the timing kit set standard for this engine. I also noticed each sliding lobe has a pilot hole visible when looking down the shaft from the chain sprocket side which appeared inline with 1/4 of the shaft rotation. Everything makes sense, lobes 1-2 fire first, followed by 5-6, then 7-8, and finally 3-4 to complete the rotation firing order of cylinders 1-3-4-2.
Last piece of the puzzle is the slotted drive gear for the vacuum pump which ultimately actuates the high pressure fuel pump. Unlike the lobe assemblies I replaced, I wasn't smart enough to mark the end gear with a metal paint pen. This slotted gear drives the high pressure fuel pump but am wondering if the orientation matters any at all. There is a low fuel pressure sensor and a fuel regulator on the fuel rail which makes me think it does not matter. But, when looking from the back of the camshaft it appears the drive slot is pointed in the same direction as the timing mark on the front of the gear sprocket. I came to this conclusion looking at several pictures online and a video by naptown tuner on youtube where he does a camshaft tray install in which the camshaft does not move but the camera pans from the front to the rear. Pressing the rear drive gear onto the shaft is not the issue but rather the starting position but got me thinking, is there a timing position for this? Is this similar to a diesel fuel injection pump? Obviously i could put it back together and try and run the engine and if it runs rough or doesn't run at all, i would start by replacing the camshaft. But all of that involves new anaerobic sealant, a cleanup job, and another 4 or so hours of work if i could source yet again another OEM camshaft. If it is in fact timed, I'm likely wasting energy on something that will not work as i have no way to be that precise when pressing in.
Somethings to share:
NOTE1: The Chinese knock off camshafts appear to have the pilot holes in the back of the lobe assembly rather than the front, but even all of those have the rear drive slot gear oriented the same way as OEM. I used OEM pictures and video for my confirmation and for my reference.
NOTE2: Pilot holes 1-2 and 7-8 align in eyesight of the valley of the sprocket where as 3-4 and 5-6 align to a peak of the tooth.
Does anyone have experience in rebuilding these camshafts? I realize this may be a bit much for the forum, but really couldn't find any content out there to help me out. Chipped end of sliding lobe Pilot hole for 1-2 Pilot hole for 3-4 Rear drive gear for HPFP. Notice its pointed at 3 o'clock position Notice timing mark pointed at 9 o'clock position.
Yes, the HPFP is pumped by the rearmost lobe on the exhaust cam. That's why when people let the timing get really stretched out, they can start to get fuel pressure issues. The ECM knows the position of the intake cam because it has VVT and so has a cam position sensor present. It has no such awareness of the orientation of the exhaust cam. The ECM controls the pumped volume by controlling the length of the solenoid activation. If it's not timed with the physical pumping action correctly, the wrong fuel volume is processed.
Not sure I follow the o'clocks. The last pic, the timing mark for the chain sprocket is at 11 o'clock. And for the HPFP lobe, the hole is at 10:30, rather than 3 (though there does appear to be some round light colored pin at 3).
Audi likes to just press fit this stuff for cost savings, so there's no orientation keying for reassembly. For example, some have had the issue of the chain sprocket rotating some distance on the cam shaft after an engine failure causing a full stop event.
Best bet would be to review a new OE one in hand, work out the relations of the chain sprocket, four valve lobes, and the HPFP lobe from it. Not sure if a dealership parts department would have one in stock and let you look it over.
Yes. 10:30 is more apparent rather than 9. I realized that after the fact and couldn't figure out how to edit the post. So pumped volume is controlled through the length of the solenoid turning on and off at the HPFP. This has to coincide with the pumping action of the lobe. As the solenoid opens, the pump likely pushes fuel through. I appreciate the input. Dealerships around here are a bust. I'm surprised to learn the ECM knows the volume of fuel pushed through each injector. Is there a PIN on the ECM you can read each number? Or is this total volume in the rail? If the latter, one way i thought i might be able to re-time this lobe then would be to set the camshaft on a cylinder head straight edge or a piece of glass with the timing mark pointed at 10:30. Then counting backwards from the timing mark, not including the timing mark, count the number of teeth until it touches the edge or glass again. What would be that number? 15, 16? Maybe its in-between the two teeth? Not exactly an ideal science i know, but gives me the best shot moving forward. Assuming the circular circumference on the lobe suggests even something relatively close is going to work.
These modern ECMs are using extensive modeled data for decision making. For example, there is no exhaust gas temp sensor, to save costs. The ECM still uses EGT in the operating formulas, but the EGT is a modeled value based on fuel and air mass consumed since start. As originally tabled by measuring an instrumented lab engine. Meaning, 262k miles later, my EGT might not actually be what the model predicts. But they only need it to work correctly for "lifetime", which is 200k km in corporate land. Same with the HPFP. I'm sure there might be some level of adaptation tweaking in the running instance. But in general, the ECM is working from a complex lookup table of rpm, engine load, timing, etc, to determine when to release the solenoid each pump cycle to produce the desired fuel volume to produce the desired fuel pressure, validated by the high pressure rail fuel pressure sensor. If you want to read up on how it operates, it's detailed in SSP 384, pages 38-43. And SSP 401, pages 33-35.
Without an intact camshaft to inspect, it's all guessing. With one in hand, one can just visually confirm the correlation. You might post a "anyone have a CAEB exhaust cam they can look at" thread over at the B8 A4 forum at audizine. I have one, but it's in my engine :-)
The revision chain for the B8.0 CAEB engine exhaust cam is:
06H 109 022 AK > AR > AQ > BD > BG > BJ
So any visuals you find of any of those revs should be considered equivalent.
Posting an update I guess for anyone who might find themselves wanting to rebuild the exhaust camshaft as I did. My Q5 is up and running, so lets call this in the name of research and science I suppose.
The correct position is for the flat edge of the rear lobe to rest evenly on the table and the pilot hole is pointed at the 4:30 position. Moving to the front sprocket, with the timing mark also pointed at the 4:30 position, tooth 7 and 8 counted after the timing mark should both rest evenly on the table. Once these two marks are set, you can proceed to press the rear lobe back in. Below are some pictures.
04-27-2024, 02:42 PM
2.0T High Pressure Fuel Pump Timed to Exhaust Camshaft
