Vibrating Throttle Body Butterflies

[keybaud]

I thought my journey was nearing its end, but it appears that it was a false horizon.

 

I've just returned from getting the car on the rolling road and Dave at Mekmotorsport noticed a strange behaviour with the throttle body butterflies. They were vibrating and giving off a distinctive chattering sound, as if there was a pulse in the manifold. Unfortunately, this meant that the TPS was being rotated forwards and backwards at idle and steady throttle, so the ECU was adding fuel as it thought the engine was starting to accelerate. Dave desensitized this, but the knock-on effect is that there is now a pause at the start of hard acceleration and double declutching doesn't rev the engine in certain conditions.

 

I am aware of 2 possible causes and I'd be grateful for any input that can help solve this riddle. The causes could be:

 

1. The oversize inleft manifold, which means there is a 2 to 3 mm step around the cylinder head inlet ports.

 

2. The cam profile or timing.

 

3. Something else.

 

The cause may have been present with the other throttle bodies; however, the problem may have been reduced by the fact that the parrallel throttle bodies are in pairs, so a vibration in one butterfly may be damped by the vibration in the other one connected to it, whereas the ITBs are all independent.

 

p.s. I now know why Dave couldn't do the hp losses previously. I thought it was an airlock, and had replaced and bled the clutch fluid, but it now appears to be a problem with the master cylinder seal, as the the hydraulic pressure reduces whilst the clutch is held depressed.

 

Edited by - keybaud on 18 Oct 2012 15:51:46

[Paul Deslandes]

was this a resonance at one particular frequency/revs or broadly across the rev range? Did it happen only at small throttle openings? It must have been pretty severe to make the TPS jump load sites.

[charlie_pank]

I would have thought this problem has already been solved by someone else with the same TBs. How is the TPS secured?

[keybaud]

Quoting Paul Deslandes: 

was this a resonance at one particular frequency/revs or broadly across the rev range? Did it happen only at small throttle openings? It must have been pretty severe to make the TPS jump load sites.

 

It wasn't a resonance, as it did it across the rev range.

 

Quoting charlie_pank: 

I would have thought this problem has already been solved by someone else with the same TBs. How is the TPS secured?

 

The TPS housing wasn't moving, it was the central bar the TPS connects to, which the butterflies also connect to, that was moved by the butterfly vibrating. You could put your fingernail on the butterfly and feel the pulsing.

 

The effect seemed to be much worse on number one cylinder than the others, although number 3 was also noticeable. All 4 cylinders were compression tested and they were all within expected parameters.

 

Edited by - keybaud on 18 Oct 2012 16:07:06

[Paul Deslandes]

yes, point re resonance noted . Daft question I know but are all four butterflies balanced to get the same airflow through each one at idle, if they are I can't immediately see why there'd be more affect from one cylinder over the others.

Can you do a (hot) compression test or, better still, a leakdown test, just to check that you don't have a leaking inlet valve, head gasket problem or something that might potentially cause pulsing in one choke.

[keybaud]

Quoting Paul Deslandes: 

yes, point re resonance noted . Daft question I know but are all four butterflies balanced to get the same airflow through each one at idle, if they are I can't immediately see why there'd be more affect from one cylinder over the others.

Can you do a (hot) compression test or, better still, a leakdown test, just to check that you don't have a leaking inlet valve, head gasket problem or something that might potentially cause pulsing in one choke.

 

The butterflies were balanced, but it was awkward due to the problem on cylinder 1.

 

How do I do I do a hot compression test or leakdown test? The compression test was done with a hot engine, all 4 plugs removed, full throttle and then tester in each cylinder, one at a time, turning over on battery.

 

Is the head port size smaller than the manifold port size a red herring?

 

Edited by - keybaud on 18 Oct 2012 16:33:45

[Paul Deslandes]

That's the right way to do the compression test. Doing it hot ensures that everything is at operating temperature and as sealed as its going to be. Doing it cold can give very misleading results.

 

What pressure readings did you get on each cylinder? Were any of them wildly different from the others? If the compression test was ok, i.e. all four were within a few percent of each other, there's probably no point in doing a leakdown test which is really to help diagnose where any leakage is occurring, e.g. inlet or exhaust valve, piston or head gasket etc.

 

I can't remember whether you're using solid lifters or still have the hydraulic cam followers. If one was stuck or lacked oil it would clatter like a good 'un so you should know if its that.

 

I guess the port step could be an issue but I would have thought you might have resonance peaks due to standing waves rather than a broadband effect. And why would it be more pronounced on one cylinder over the other three? Is the step 2-3mm or is that the difference in diameters? Presumably you have equal length trumpets and not the mixed length idea that's been discussed at length (pardon the pun) on here recently. If you remove #1 plug lead does it change, apart from the obvious?

 

You could try removing the trumpets all together and see if it makes any difference. Not sure what this would prove though.

 

Its good that you can reproduce the effect at home rather than having to do it on the rolling road.

 

Paul

[keybaud]

I'm fairly positive the pressure readings were:

 

1. 210

2. 215

3. 215

4. 220

 

It has hydraulic cam followers and I'm not aware of any clattering.

 

The problem was present with and without trumpets (they are all equal length).

 

I've not tried running the engine and removing No 1 plug lead, so I'll try that later.

 

The step is an overlap the whole way round, up to 3mm in places.

[kenny.]

Are these 420H cams that are set up on original timing marks?........or are you on verniers. Just wondering if maybe you are one tooth out, which is maybe giving off this slight vibration.

 

I take it the bloke on the RR knows all about setting the bypass screws etc for each body so we are assuming that the TBs are are not causing this issue and are spot on.

 

As for the "overlap" on head/manifold........I had similar on my last VX 218 Evo until I had them matched. It did make a big difference too.................but I personally can't see that being your issue here.............I stand to be corrected though as that car was on Carbs.

[Paul Deslandes]

Nothing wrong with the pressure readings or the spread. Quite high compared to mine but that may be to do with the cam overlap which is likely to be greater in mine.

 

Goes into thinking out loud mode!

 

You could try putting some plasticine around the step temporarily to smooth it out but I'd be very worried that it might get sucked into the engine. If you only tried it at idle it might be ok as the butterflies are all but closed. If you try it and it goes wrong do not blame me!

 

There's no possibility that you have an air leak at one of the interfaces?

 

One trick to see if one of the cylinders is working less hard than the others, or just differently, is to remove one plug lead at a time, noting the change in idle revs and the sound.

 

do your TBs have bleed/bypass screws? If so and they're not adjusted correctly in relation to the butterflies, that might have an effect

 

Did you get a result from the mapping and power run or did you have to abandon it?

 

[keybaud]

Quoting kenny.: 

Are these 420H cams that are set up on original timing marks?........or are you on verniers. Just wondering if maybe you are one tooth out, which is maybe giving off this slight vibration.

 

I take it the bloke on the RR knows all about setting the bypass screws etc for each body so we are assuming that the TBs are are not causing this issue and are spot on.

 

As for the "overlap" on head/manifold........I had similar on my last VX 218 Evo until I had them matched. It did make a big difference too.................but I personally can't see that being your issue here.............I stand to be corrected though as that car was on Carbs.

 

I am on verniers and the cam timing was done when the car was mapped on the previous throttle bodies. It hasn't been changed since. The cams are a development profile, and I have since found out that they were originally Arnies, but I don't know what the actual profile is and there aren't any markings on them.

[keybaud]

Quoting Paul Deslandes: 

Nothing wrong with the pressure readings or the spread. Quite high compared to mine but that may be to do with the cam overlap which is likely to be greater in mine.

 

Goes into thinking out loud mode!

 

You could try putting some plasticine around the step temporarily to smooth it out but I'd be very worried that it might get sucked into the engine. If you only tried it at idle it might be ok as the butterflies are all but closed. If you try it and it goes wrong do not blame me!

 

There's no possibility that you have an air leak at one of the interfaces?

 

One trick to see if one of the cylinders is working less hard than the others, or just differently, is to remove one plug lead at a time, noting the change in idle revs and the sound.

 

do your TBs have bleed/bypass screws? If so and they're not adjusted correctly in relation to the butterflies, that might have an effect

 

Did you get a result from the mapping and power run or did you have to abandon it?

 

I don't have bleed/bypass screws.

 

I'm not aware of any leaks and holding the palm of my hand over the trumpet causes a low pressure to pull the palm onto the trumpet, but does not cause any hissing noises elsewhere that would indicate a leak.

 

I did get a result from the mapping and it was slightly up on power compared to the parrallel 45mm TBs, although the curve was higher in some places and lower in others. As the clutch was slipping, only readings at the wheel were taken, but this was the same as last time. Previously it was 168 hp at the wheel without a filter, whereas this time it was 172 hp at the wheel with a sausage filter fitted.

 

Edited by - keybaud on 18 Oct 2012 17:55:20

[Paul Deslandes]

apart from the plasticine idea and the pulling the plug lead test I'm all out of ideas at the moment. Pity you can't refit the old setup and see if the same problem is still there, albeit reduced in magnitude. Or can you?

[keybaud]

Quoting Paul Deslandes: 

apart from the plasticine idea and the pulling the plug lead test I'm all out of ideas at the moment. Pity you can't refit the old setup and see if the same problem is still there, albeit reduced in magnitude. Or can you?

 

I could, but the mapping would be out.

[Paul Deslandes]

if you don't have a copy of the old map to reload into the ECU it might not matter so long as it idled. If its 'head and block' related rather than induction system it should still set up the same vibrating air column, assuming that's what it is.

[Bio]

I run the SBD 225 kit on taper throttle bodies and have always had a slight 'clacking ' noise from the induction at idle that can be stopped by resting your finger on normaly number one butterfly.

This was not the case when running the throttle kit on a standard engine with standard cams.

The noise can be reduced or altered by changing the airflow to each throttle although when balanced the clacking comes back.

The car was mapped by the two Steves with no problems and has now done about 7500 miles.

I have also noticed this clacking noise from a tuned Duratec.

I suspect the noise is pulsing in the induction that also causes the butterfly to vibrate .

Hope this helps....Try also talking to SBD.

 

John

John

[andy couchman]

Simon, is it worth trying a stronger throttle return spring?

 

Andy

[keybaud]

I emailed Jenvey about the problem and they said that it could be the spindle bearing. To test for this, they said to open the throttle and then see if the spindle moved up and down within the bearing, which it did. So, I now know what the problem is and Jenvey will fix it if I post the throttle body back to them. If I send the set on the manifold, they'll re-balance them as well.

 

Hurrah!

[keybaud]

I sent the TBs off to Jenvey for a service, as fluttering can be caused by worn bearings and there was some play. The service isn't cheap, but they've replaced the bearings, the springs, the butterflies and fitted a new master throttle linkage The new throttle linakge design resolves some issues with the old one when it was used on individual throttle bodies. A picture of their new shiny status can be found here.

 

For those that are interested, I looked at replacing the manifold with one more suited to the current cylinder head ports. I spoke to Jenvey and SBD and it would need to be modified from any of the standard ones, but the cost of maching on top of the manifold made it excesively expensive. Steve at SBD confirmed that as the engine had been mapped with the manifold step, it should be fine to use until I needed to upgrade.

 

Steve also mentioned that he's been working on a new solution for the C20XE based on what they've done with the Duratec. He'll be at Autosport International in January with this on display. I'll certainly be there having a look, but I may need to send the wife off somewhere else...

 

Edited by - keybaud on 15 Nov 2012 19:27:32

[keybaud]

OK, serviced TBs fitted and car taken for a spin. No more fluttering and the gear change is noticeably less clunky now that the clutch master cylinder seals have been replaced. The only problem I have is that the fueling appears to be all to pot, as it's backfiring and popping & wheezing all over the place. I'm hoping it's something simple like the throttle position sensor being replaced in a slightly different position to when it was removed, but I'm preparing myself for the fact that the fuel mix is now totally different with the non-fluttering butterflies...

 

Edited by - keybaud on 18 Nov 2012 21:11:53

[Paul Deslandes]

not hard to adjust the throttle pot. Get engine up to working temperature. Slacken the pot and turn to minimum, i.e. the ECU is looking at site 0, normally TPS body fully clockwise (note: body not spindle). Adjust idle revs to what you last had when it was mapped. Now adjust the TPS using the software or voltmeter to correct value. If your ECU was an MBE it would probably be 360mV but I guess Omex is different. If you can see the TPS index map the pot setting at idle should be just below (~10mV) the voltage where it transitions from site 0 to site 1. Tighten pot and away you go.

 

Good to know that the vibrating butterflies was easily fixed and not something sinister.