Altitude clatter from N/A

[sgnimj96]

I'm told there is no remedy for injector clatter at high altitudes.
Nevertheless, I keep wondering on it. Driving across the sierra Madre
is a long time to listen to that rattle at high revs.
Was thinking maybe it's worth adding a shim to the IP advance spring
to reduce the dynamic advance. I do think the diesel here in mexico is a little
thicker than the US refined ulsd, so I may have more dynamic advance down here.

My question is, will higher cetane (from additive) help reduce the clatter at high altitudes?
Seems like somebody would have some data on this.

[Fatmobile]

I think octane speeds up the burn and cetane slows it down.

I might have that backwards though.

Putting an extra shim in might work.
Especially when it's running at higher RPMs.

I had to put one in a knocky rabbit. It did quite the noise down when I reved it.

[sgnimj96]

I searched around and found that yes, higher cetane (in general) is needed for colder climates or high altitudes.
Diesel here says 45 on the pumps. Diesel #1 used in really cold areas is 50+ cetane.

I think reducing my dynamic advance will be worth doing. This is a real downside to not having a turbo,
but I sure like the reliability out here in the badlands.
Acapulco is close to here, that city is really, really messed up right now.

[Fatmobile]

So you live in Mexico?
Or are you just visiting.
I heard the hurricane really hit hard, left a lot of people in a bad situation.

I wonder if adding some gas to the diesel would get rid of the knock.
You'd have to add lubricity too, like 2-stroke oil.

[sgnimj96]

I have a little house just north of Ixtapa that i try to visit, check on, at least once a year.

These folks seem to know most about what's happened in Acapulco
https://www.tripadvisor.com/ShowTopic-g ... Coast.html

I wouldn't play with mixing gas into diesel down here. Sometimes pockets of gasoline form in the tank and can send
a high concentration through the system. I've got some cetane booster and
I guess a funny thing to do would be to stop and add a shim to the advance spring everytime I cross the country
then remove it

[Fatmobile]

Well good thing they put the timing piston cover in the front where it's easy to get to.

[sgnimj96]

Well, I never messed with timing. Just added cetane booster and carried on.
I don't know how much it helped. Mexican Diesel says it's 45 cetane at the pump,
but I also think the fuel down there is a little thicker, less refined.
The cold weather also seems to be a factor, maybe making the fuel thicker.

It's wierd how when I get back to FL the injectors always quiet back down,
Even in Texas the cold starts have more rattle, thing sounds like an early
Powerstroke, but without the power.

Sucks not having a turbo, not just for less noise. It's unreal how many trucks are travelling across Mexico
from west-coast ports carrying Chinese goods. Lots of slow moving double trailers
which are stressful to pass with 50hp, and always having to back off when I see the black smoke
so I'm not just wasting fuel.


Now that I'm back, i'll try reducing the fuel internal pressure and see what that does.
My diy fuel pressure adapter gauge may be a little off and the pressure is set too high.
Cold start knob never seems to make a difference in sound, but does help it start.
I do like having a lot of dynamic advance.

[Fatmobile]

I bet mexican diesel has more wax than even our summer diesel has up here.
Might cause more advance.
Hagar would have loved it ha.

Yep, time to turbo it.

[sgnimj96]

I put in a slightly stiffer advance spring, but still got no difference
in clatter when the cold-start is pulled.
So I reduced the internal fuel pressure by quite a bit (like 50%) and THAT
made a big difference. I could hear a clear difference in the sound with the cold start
pulled and actually see white smoke after a cold startup if I don't use the
cold start cable. Took it for a test drive and it ran great without all that advance.
Perhaps all the discussions about more fuel pressure and more timing advance
were overkill that doesn't help at all after a point.

My injectors are set to the normal ~2Kpsi and the timing is .90 so it's kinda
of weird that I would get too much advance using normal internal pressure specs.

I guess over the years, the advance spring gets weaker and the the internal
pressure should be lower to compensate (which kinda it kinda does on it's own).
Perhaps the vw engineers knew this and it actually works out fine.
Only thing is fuel pressure being too low may not cool the pump enough.

So I ended up increasing the fuel pressure a little, but only to ~35psi at 1000rmp
I can still detect a slight sound difference when I pull the CS while its running

Basically, I lowered the internal fuel pressure a little and put in a slightly stiffer
advance spring. I'm thinking I could still add a shim to the advance spring as
experiment for mountain driving at 6K altitude with mexican diesel.

Speaking of mountains and IP mod's that aren't necessary, I don't do the governor mod because
when going down a steep mountain in gear, governor needs to be cutting back the
fuel to slow the decent. I want the injectors getting no fuel when I downshift to slow down.
IDI engines already aren't good at engine braking because nothing restricts the air
so if the governor isn't cutting off the fuel with no throttle,
it's not slowing down and all you have is the hydraulic brakes.
The parking brake is near useless to slow the car down going downhill (I tried),
and if the regular brakes fail, that's all there is - and engine braking.

[Fatmobile]

I think the governor mod just connects the accelerator lever more tightly to that vertical lever inside (forgot the name, ha).
When I take my foot off the peddle it slows down just like normal.

There used to be a little spring there that would give way when the peddle is stepped on.
But that doesn't keep the fuel from backing off when the peddle is released.

[sgnimj96]

On a previous IP I put a spacer on the governor spring like the mod said,
but I don't think it helps any. The 1.6 idi can easily use more
fuel than the engine can get air for. It's not like I'm racing it.

With downhill engine braking (like I said, IDI is the worst) I find most of the speed reduction
happens when I engage the clutch from idle. Once the engine
revs up, it doesn't slow the car down much. Seemed like pushing the clutch
repeatedly letting it out into a low gear from idle had the most
effect. The engine speed needs to drop down
quickly before dumping it back into the lowest gear possible.
I hear some heavy loaded trucks doing this too ,going down steep grades.

I didn't really push it, testing engine braking, just wanted to get a feel for what I would
do in a downhill brake failure emergency.
I asked a classic-vw mechanic about that and he said the parking
brakes are just too small to handle it. So that kinda sucks, my parking
brake seems to be adjusted properly.