Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Replacing the plastic throttle body.

Didn’t know if to post this or not but it might just be of interest to other Duratec owners.

The Druratec is a cracking engine but it is blessed with a Micky Mouse plastic throttle body. I had a bit of a niggle with my original TB on my first car. It took me ages to track down the cause of a slight rev hang. The engine revs would fall away annoyingly slowly when I took my foot off the throttle. Eventually I discovered it was the plastic butterfly valve flap inside the plastic body leaking air. The butterfly valves are manually sealed from new so I suspect a bit arbitrary from car to car. I resealed mine and it was much better and the normally nonadjustable engine idle speed dropped too. There was another annoying characteristic, I could make the butterfly valve leak just by tightening the filter hose clip and distorting the body, I could hear the idle speed change as I tightened it.

For my newly acquired Duratec I spotted a ‘proper’ all metal TB advertised in the US. It was quite cheap so didn’t expect too much but it has turned out to be brilliant and nicely made. The die cast metal version appears to be a direct one to one copy of the original Ford plastic injection moulded version.



I took the precaution of sealing it before I installed it, here is a little video of how to seal a TB should anybody be interested.

I originally installed the new TB with the stock air filter and the difference was both noticeable and subtle. The idle speed instantly dropped from a 1000rpm to just under 900. It’s probably just psychological but it does feel sharper and nicer to drive now.

So now I’ve removed the standard Focus filter box arrangement and able to securely fit a nice big K&N filter directly on top without the risk of distorting the body.



Happy days

Well done

Very good job Roger.

When I swapped my old Zetec Silvertop engine to my new 2L Blacktop engine the one downside was having to use the newer plastic throttle body which has a very poor inlet tract and also has a butterfly system which initially gives a very slow throttle response to make a Ford Focus more "comfortable" to drive in traffic.

The old aluminium throttle body is not a direct replacement but I'm currently studying ways to do exactly what you've done.

Where did you get your throttle body from, I wonder if they do a Ford Focus Zetec replacement as well?

I don’t know but worth contacting the ebay seller in my link above to see if they know of anything suitable? There does appear to be more available in the US. Hadn’t realised the Zetec had one too. I think Ford gave up on plastic around 2007. The inlet tract is good on the Duratec but the sealing is a bit iffy and given that they appear to be made from glass loaded nylon it’s hard to imagine how they would even achieve a precision seal across the operating temp range. No surprise they can feel a bit ‘soggy’ to drive.

Interesting.

I was wondering about the sealing of the throttle body after watching the video. I used to assume you wanted some air getting around for the engine to run but now I assume you want it 100% sealed and at idle it is just the Idle Air Control Valve system allowing air in to keep the engine running, so would the sealing be why your Idle dropped by 100rpm or something else caused by replacing the throttle body?

I was also a bit confused by the sealing using something that makes a gasket on the butterfly but leaves reside from the butterfly on the inside of the throttle body which I didn't see him clean off. I would think you want a nice smooth surface to the throttle body to allow the air to flow in as quick as possible. But if he did scrape it off would the butterfly still make a seal?

Anyway glad you car is going better now.

My understanding is that with an Idle Control Valve the TB butterfly plate should be fully sealed to allow the ECU to regulate the flow using the ICV. If there is any leakage I guess the regulation will be compromised and the idle speed increases. I bet there is quite a tolerance on this or the ECU would complain.

I think the sealant is a hard gap filler rather than a gasket and it does leave a rough step. Probably the benefit of filling gaps outweighs any disruption to the air flow.

Below is pic of the underside of my original TB (it’s done around 5k miles). You can see how the manufacturer's sealant has been ‘liberally’ applied.

I think you're absolutely right Roger.

My old Silvertop Zetec had an aluminium throttle body which also had a small 2.5mm hole in the butterfly to assist the idle airflow but when I came to fit the new Blacktop engine it had a plastic throttle body with the same black lumpy sealant on the butterfly.

Being keen to promote the cleanest possible airflow, I of course cleaned up the butterfly whilst scratching my head as to why they would put this horribly gunky stuff on to an already thick butterfly.

Only then did I see a small sticker warning the installer NOT to remove the sealant otherwise running problems might occur.

As I have said several times on this forum "We Live and Learn" (I think I'll have that put on my gravestone).

However as luck would have it, That sealant is only really needed with the OEM ECU which as calibrated to open the Idle air valve assuming no air is getting past the butterfly. If some air was getting past the butterfly, it would cock up the OEM calibration.

As I'm using the Omex ECU, we do it slightly differently and indeed I have drilled a 2.5mm hole in the butterfly to work in conjunction with the Idle air valve.

On normal temperature tick-over, the IAV is hardly open and is used more for cold start tick-over or as a sort of anti-stall valve.

This is similar to what you would do with ITB's where there is an idle adjust screw on the butterflies to crack them open slightly for tick-over.

Ah, the joys of clever modern engines.

Thanks Rob 👍👍


Stefan