Rpms hanging no matter where fuel and idle screws are set, MTDI AHU

[Whitbread]

Hello all, after my 1.6 catastrophically let go, I built an 2.0L mtdi ahu out of parts laying around to go in it's place. My 81 caddy is a nothing more than a beater shop truck so it's nothing crazy, I just want it to run and drive half way normally. Anyway, the pump is the 1.6td pump with a 10mm TDI camplate and head assembly, a DI fulcrum lever so I didn't have to cut and weld anything, and the high speed governor spring is shimmed from when the pump was on the 1.6. I had a local pump shop measure and set the k and ks distances and run it on a bench to make sure it pumped some fuel. I'm still using the IDI governor assembly and throttle shaft.

Now on the engine, no matter where I set the fuel and idle screws, when you rev it the rpms want to hang at what sounds like 2500-3000. With fuel screw only a few threads from falling out and the idle screw maxed out, response is very sluggish and rpms will hang with anything more than a tiny blip. With fuel screw all the way in so it sets the idle, a tiny blip and it will take off and hang at the same rpm.

Does this setup need a stiffer idle governor spring? Any PN for springs if so? Thanks!

Also, what are people running for base timing on ~17.5:1CR Mtdi setups? I have it at about 1.1mm and throttle response is very snappy and it fires up in what sounds like 1 or 2 compression strokes. I have yet to drive it though as the hanging rpm things isn't very safe!

[theman53]

I would start with the easy things. Is the cable bound up at all? If not index the shaft differently, one spline at a time and if it makes it worse or no change go the other way. Seems on here that some have timed the mtdi pumps anywhere from 1.1-1.6mm with good results. Libby thinks it is because the different length delivery valves. Interestingly enough all that he tested with the timing light were about at 12 degrees btdc that ran good and had different mm values.

[Whitbread]

I would start with the easy things. Is the cable bound up at all? If not index the shaft differently, one spline at a time and if it makes it worse or no change go the other way. Seems on here that some have timed the mtdi pumps anywhere from 1.1-1.6mm with good results. Libby thinks it is because the different length delivery valves. Interestingly enough all that he tested with the timing light were about at 12 degrees btdc that ran good and had different mm values.

I appreciate the input! The throttle cable moves nice and free, its actually not even hooked up right now while I'm playing with this. I've yet to even try driving it.

I'll try reindexing the shaft tonight and let you know what happens.

Thanks for the timing info!

[Whitbread]

I tried 2 splines either way on the throttle lever from where the pump was set from the pump shop and moved fuel screw way in/way out and idle screw way in/way out to get it to idle at each position. Still hangs when you rev it almost identically in all positions. I can get it to idle all day long, but as soon as you give it some gas, the rpms take off and hang steady at ~3K. I'm almost ready to scrounge up an ahu ecu and harness and put the electronic pump back on this thing.

Is the idle governor spring not stiff enough to push the fulcrum lever back to idle? I'm familiar with the basics of mechanical VE operation, but diagnosing behavior of a mechanical frankenstein is not my specialty.

Here's a video to demonstrate
https://www.youtube.com/watch?v=5l_cdYKD1lU

[theman53]

weird.

Is the boost line connected from the turbo? If so, try disconnecting. If not you could try the other fulcrum assembly or the springs like you're thinking.

[Whitbread]

weird.

Is the boost line connected from the turbo? If so, try disconnecting. If not you could try the other fulcrum assembly or the springs like you're thinking.

No boost line hooked to the aneroid. The fulcrum lever in it now is from a DI VE pump, either a land rover or an LT, don't remember which. Got it from a buddy who's done a handful of mtdi pumps. It has the longer pivot to ball center distance built in so I didn't have to cut and weld the stock 1.6 one.

I'm all for trying a different idle spring, but does anyone have any suggestions of a bosch PN or some random spring from McMaster carr?

[Whitbread]

I took the top off the pump to make sure nothing was sticky, everything is silky smooth as it should be. Here's what I'm seeing. Does anyone see something I don't?

[Whitbread]

For anyone who cares, I stretched out the idle spring and it runs fine now; no more hanging at ~3000rpm. So my suspicions about the spring not being strong enough to push back the governor were correct.

I tried reindexing the throttle lever to the shaft and it's definitely the happiest where it came from the pump shop lining up with the first lines at 11 and 5 o'clock. With the fueling screw turned in as far as I can to still maintain any idle screw use, it feels a little flat above 3000-3500rpm, but at least it's driveable now with a good hit of low end tq. I can deal with fine tuning later.

[theman53]

Great. Now we know.

If it happens again then you know to get a slightly stiffer spring. I feel like an idiot as this topic came up before and I didn't remember until right now that this was a fix.

[vanbcguy]

I took the top off the pump to make sure nothing was sticky, everything is silky smooth as it should be. Here's what I'm seeing. Does anyone see something I don't?

The black cap that's up against the governor cage is supposed to be up against the idle spring... not sure if that's just the way it's sitting in the photo or what?

Hope you're feeling better!!

[Whitbread]

The black cap that's up against the governor cage is supposed to be up against the idle spring... not sure if that's just the way it's sitting in the photo or what?

Hope you're feeling better!!

Was just the way things were sitting. It was against the spring.


I ended up having to order an 02M kit and some other stuff from england for customers so I had a LR300tdi pump thrown in the crate for free and put it on the rabbit. With some creative machining, it's on and running. I timed it at .060" and it runs pretty good, my motor is only about 17:1 CR so it hazes a bit when it's cold, but that's to be expected. For just pp520s, no porting, stage 3 colt cam, no IC, mk3 tdi KO3 at 19psi, and open exhaust, it scoots along very well.

[vanbcguy]

Yeah those pumps seem to do pretty good. Mine has responded very well to a gov mod too. I've got a Colt Stage 2 and a GTB1756VK, big AWIC but stock compression. Goes up to 5500+ with a smile on it's face.

PS timing wise I'm at about 1.45 on the EGR version of the 300TDI pump. I have a light with a pulse adapter, that comes out to about 12 degrees BTDC for the actual injection event. I think there are two versions of the 300 pump, I'm guessing you have the other one based on your timing numbers.

[Whitbread]

What's the number on your pump?  I'll look at mine tonight. 1.45 mm is .057", so .060" is damn near the same thing.

[vanbcguy]

Ah didn't clue in that you were in inches rather than mm for some reason.

My pump is 0 460 414 099.

[Whitbread]

Eh, I'm a machinist in america, so we're stuck in inches. I much prefer mm, but all my measuring tools and equipment are the evil system.