I tuned the engine, got some interesting tidbits

[Black Smokin' Diesel]

Since I replaced the head on my 1.6TD I kept the fuel a bit lower than stock TD to make sure everything was ok. I soon found out that 10w30 synthetic oil was way too thin for summer use and would set off the oil buzzer/ligh in the cluster when the engine got hot. So I switched to 15w40 dyno oil and the problem mostly dissapeared except for really hot days and long hillclimbs. I wasn't too happy about using dyno oil with my newly rebuilt K24 and low oil pressure isn't what you want on a turbo engine. So I got my hands on a 1.9TD oilpump (36mm gears instead of 30mm). VW used 30mm pumps until 87 even thought they switched to hydraulic lifters in 86.5. In 88 the TD got a 36mm pump. The 36mm unit provides more flow and pressure. So the pump fixed the oil pressure issue (still using 15w40 though).

For those wondering, these pumps are extremely simple, two gears spin in opposite directions sucking oil from the pan through the pickup tube and pushing it into the engine block. There's a safety valve to prevent excessive pressure. That valve is probably the most common failure. If it goes bad, all the pressure is release through it and none is left for the engine. In other words, the pump part doesn't fail. Unfortunately the valve isn't a replacement item.

Having proper oil pressure, I decided to up fueling on the pump this evening. Turned on the engine, played with the fuel screw until RPMs reached 1800 and used the idle screw to bring it down to 1000. Smoke isn't that bad, there's no thick black crap shooting out my tailpipe when I floor it. The added power is a blast though. Takeoff from a standstill is much better, less feathering with the clutch. RPMs also dropped a bit on the highway, down from 3000 at 110kph to 2800 at 110. There also seems to be more revs available up top. It would run out of fuel at 4000, now it seems like I could get to 4300. I have to play with the max RPM screw on the pump though, just to see what I can gain. Top speed still is the suck at 140kph but I don't really care about top speed, I cruise at 110 all day, everyday. Seems to be the sweet spot for mileage and cruise speed. 100 is too slow for the fastlane and too fast for the other lanes. People have been driving a lot slower lately, most likely due to the gas prices.

For some odd reason, my fuel mileage has been way better lately. I would do 210km with 20l of fuel before (9,52l/100km), now it's up to an average of 250km with 20l with a best of 287km (6,96l/100km). Odd thing is that I haven't change my driving habits. These figures are for mixed city/highway driving, about 50/50.

[nokivasara]

Thereīs something wrong with your tach if it shows less rpm at 110kph now :shock:  
My Passat still gets the exact same mileage (6.1l/100km) now with fuel screw turned in 1 whole lap and more boost compared to bone stock. Thatīs wierd, īcos it sure is a lot stronger now, but thatīs the neat thing with these old diesels...

[Patrick]

Never looked to see if it can be done, but a standard trick (around here anyway) on an old chevy was to shim the spring on that relief valve in the oli pump.  The spring gets fatigued over time...........
Like I say, I haven't looked at the VW pump to see if it's posssible. On the old chevs it's just a matter of pulling a roll pin and adding a washer to the top of the spring, re-install the roll pin.

[pariah]

have you done the advance spring shim removal? i was thinking about it, but not wanting to sacrifice any milage or break into my pump i just paid 900 for a rebuild on....

[Black Smokin' Diesel]

Thereīs something wrong with your tach if it shows less rpm at 110kph now :shock:

Why? I got more power so it takes less RPM to keep it at 110kph. Well it makes sense to me lol

Never looked to see if it can be done, but a standard trick (around here anyway) on an old chevy was to shim the spring on that relief valve in the oli pump.  The spring gets fatigued over time...........
Like I say, I haven't looked at the VW pump to see if it's posssible. On the old chevs it's just a matter of pulling a roll pin and adding a washer to the top of the spring, re-install the roll pin.

Unfortunately you can't do that on the vw pumps. The valve is in a cartridge press fitted into the pump with four tabs holding it on. I don't see how you could remove it :?

have you done the advance spring shim removal? i was thinking about it, but not wanting to sacrifice any milage or break into my pump i just paid 900 for a rebuild on....

Yes I did the shim removal. Gains were somewhat dissapointing but I only had two shims in it (one thick, one thin, I replaced the thick one with another thin one). It made the engine run a bit hotter but not much. Results are different from cars to cars, some people reported a pretty nice gain while others said they lost some power.

[bigblockchev]

BSD it is physically impossible to have different tach readings for a given vehicle speed in the same gear. Everything is hard geared, so many engine rpms will give so many Kmh. Nothing slips once the clutch is engaged so basicly it is a solid gear train from the flywheel through the gearbox , differential , cv joints to the wheels. Unless there were constant clutch slipping before or after the change there is no way a gear train can have different engine speeds at the same road speed. This is not true in automatics where there is always some slippage in the torque converter until it is locked up by the computer. Hope this helps. Cheers Dan

[Vincent Waldon]

Standard or automatic transmission ??

If standard, there's an exact mechanical 1:1 relationship between the engine and the wheels and thus the RPM at any particular speed in any particular gear is a guaranteed constant, unrelated to engine power.

If automatic, there's a viscous torque relationship between the engine and the wheels and I guess I could see how more power (ie torque) could result in lower RPMs at any given speed.

(edit:  Andrew and I seem to have posted roughly the same ideas at the same time...maybe I'm nuts but he's usually right !)

[Black Smokin' Diesel]

I see what you guys mean. So does anyone have an explanation for that drop, I mean I didn't change wheel size, gearing or even tire pressure. Unless my brain is playing games with me (wouldn't be the first time )

[bigblockchev]

Since the tach is driven off the alternator is it possible that there was or is some slippage in the Alt belt or a difference in the pully sizes. Just a thought

[jtanguay]

i have to re-tighten my alternator belt about every month or so... it just keeps getting loose  :x

hard to see a 2000 rpm drop though... look for glazing on the belt, and feel the temperature of the pulley after a trip.  they do get warm, but not hot enough to burn a finger (mine burnt my finger once...)

[bigblockchev]

Jt I think he said that the change was 2800 rpm to 3000 so only 200 rpm diff. I was thinking that in the course of changing oil pumps and such that there was a pully change in there somewhere. Cheers Dan

[con]

@ Black smokin' Diesel, Was it just the fuel screw you adjusted, did you crack open the LDA or modify the boost level at all??

[jtanguay]

Jt I think he said that the change was 2800 rpm to 3000 so only 200 rpm diff. I was thinking that in the course of changing oil pumps and such that there was a pully change in there somewhere. Cheers Dan

typo on my part...  i dont think you can get a pulley that would spin 200 rpm's less.

i would say it is all in your head, or your alt is off somehow.

[Black Smokin' Diesel]

@ Black smokin' Diesel, Was it just the fuel screw you adjusted, did you crack open the LDA or modify the boost level at all??

Didn't play with the LDA this time. I did play with it the last time I upped the fuel but I tuned it down when I replaced the head and didn't reset the LDA. It doesn't smoke a lot, I need to up the fuel more and play with the max RPM screw.