MFI throttle body rebuild

58A - 71E · Post by **58A - 71E** » Thu Sep 20, 2007 3:15 pm

Spent a full day at the weekend tackling MFI issues (dodgy relays, chopped wiring, replacing missing bits, testing solenoids etc) and it now looks like I'm going to be doing a throttle body rebuild

- worn bushes, surgical cleaning (the air intake adjusting screws are having no effect at all) and replacement of all the connecting rods (all worn and not confident of getting correct correlation). Just wondered if anyone here had done this and could give advice/step by step guide?

Done with engine in / out?

How hard is it to disconnect the MFI hard lines from the injectors (potential bent pipes/damaged injectors!) Soak in penetrating fluid, use flaired spanner?

What to clean with to ensure all carbon removed? (40 pipe cleaners and half a can of carb cleaner had no effect when removing the 6 springed screws)

Powder coat or spray paint mag air stacks / TBs?

Bushes - PITA to install?

Came across this on Pelican http://forums.pelicanparts.com/showthread.php?t=279401 but no responses - Alan did you work it out?

Cheers

hot66 · Post by **hot66** » Thu Sep 20, 2007 3:35 pm

James, Mike Bainbridge & JohnM helped me with my throttle body rebuilds as they know a decent place near Preston ( I think) that can sort out the bodies etc .. give Mike a call

Alan @ CanfordClassics · Thu Sep 20, 2007 7:55 pm

Hi James,

Yes, I have done this job quite a few times since then. In fact since then I have also had a jigged made which enables me to overbore the throttle bodies. For example I have just had some E Throttle Bodies turned into S spec for a customers engine.

If the bushes are worn I suggest you contact Mike at MB engineering, he is the chap to speak with, I can do them but do not offer that as a service. I can also help with the throttle arms if you need a set. The original ones are NLA and are actually ally rather than the steel arms which make up the rest of the linkage.

All of this can be taken out and done (if required) with the motor still in the car.

HTH

Alan

58A - 71E · Post by **58A - 71E** » Fri Sep 21, 2007 10:25 am

Thanks chaps, It was Mike Bainbridge that diagnosed the worn bushes

he also noted that my MFI lines into the injectors were stuck on solid on cyls 1,2,3.These are NLA so I have sourced myself a set (just in case they need more than a little persuasion

)
I have bought a set of bushes through local OPC along with all the gaskets and am just looking into what else I will need to do the job / possible problems to look out for to decide if it's something I can do myself.
Mike recommended Supertec Performance in the US to supply the rods, as they are NLA from Porsche as you say Alan, was it the Supertec rods you used?
What is involved to replace the bushes?

Cheers

Alan @ CanfordClassics · Fri Sep 21, 2007 8:33 pm

Yes, I use Supertecs MFI rods. I recently bought 5 or 6 sets

1972_911t · Post by **1972_911t** » Tue Sep 25, 2007 10:46 pm

I got my local machine shop to change the bushes in a set I had they were very resonable on the price. I would have to check but I think it was something like £6 per bush plus £20 to make up an insert so they didnt crush the bodies when pressing them in. Let me know if you want there details. Incidently A customer of Mike's now has these throttles so he may be able to give you an idea on the quality of the work.

Steve

58A - 71E · Post by **58A - 71E** » Wed Sep 26, 2007 9:42 am

Thanks Steve - if you could send me the details that would be great, I'm guessing from some of your resto pics that you are not too far from me in South Yorkshire?

1972_911t · Post by **1972_911t** » Wed Sep 26, 2007 9:52 am

Hi the place in arnetts in doncaster. I live in the dearne valley area so carnt be too far from your.

http://www.arnetts.co.uk/

Steve

johnM · Post by **johnM** » Wed Sep 26, 2007 2:14 pm

Hi

Throttle bodies need to be refurbed correctly, to replace the bushes the butterflies require removing so the shafts can be pulled out. The screws that fix the butterflies can often be difficult to remove sometimes requiring drilling out. There are also two types of screws that locate the butterflies so make sure you get the correct ones, (do not use plated screws). Getting the bushes out can be a little tricky and be careful that you do not damage the magnesium surrounding the bush, this area is very often thin due to the return spring wearing the material away. Also the magnesium casting can often be cracked around the mounting flange and around the cut out for the injector, if this is the case this needs to be repaired with the correct magnesium filler rod and once welded requires post weld heat treatment, failure to do this will result in the welded area cracking again. The area around the butterfly when seated can wear, the worse the bushes the worse the wear in this area will be. If to bad the butterfly will flow too much air when closed and this will result in a fast idle. to rectify this the throttle bodies will need to be bored out and over sized butterflies put in. Once all this is right then you can rebuild the throttle bodies, it is very important that each of the six throttles is set up to flow the same amount of air in its closed position and with the bypass closed, we do this using a flow bench. Failure to do this will mean the engine will run and idle poorly. Unlike carburettors, with MFI the amount of fuel delivered to each cylinder is pre determined and the volume the same across all 6 cylinders, (assuming the pump is calibrated correctly) the amount of air delivered to each cylinder is determined by the butterfly position so if each throttle flows different volumes of air you are in a position were one cylinder can be running rich and the next weak. It is also very important that the throttle links have no wear in them as they will also result in one throttle flowing more air than the next. Hope this helps it really is important to get these right.

58A - 71E · Post by **58A - 71E** » Thu Sep 27, 2007 9:36 am

Many thanks John, thats just the info I was looking for. I reckon I'll take 'em out and have a look how much wear there is / if there are any cracks first - and then decide what to do with them. Knowing my luck it wont be simple

, will post up my findings

Cheers

58A - 71E · Post by **58A - 71E** » Thu Sep 27, 2007 9:38 am

Alan - you have PM Re Supertec's MFI rods

johnM · Post by **johnM** » Thu Sep 27, 2007 1:41 pm

Just a couple of photos showing some typical cracks.

Throttle stop cracked, this throttle was flowing twice the amount of air as the next one.

Repair

This crack had ment that the flange had bowed and could be a source of an air leak.

Repaired

Finished, each throttle set up to flow the same volume of air and new throttle links fitted.

Alan @ CanfordClassics · Tue Oct 02, 2007 10:49 pm

Just to add to this thread, here are some of the products discussed, such as the super tech rods, also in the picture are MFI fuel line supports, RSR style plug connector holders (used on twin plugged motors) and RSR style plug holders.

HTH

Alan

58A - 71E · Post by **58A - 71E** » Wed Oct 03, 2007 9:47 pm

Thanks for all the replies, I should be stripping these down next week so will post some photos of what I find

58A - 71E · Post by **58A - 71E** » Sun Oct 07, 2007 10:35 pm

Just to add to this thread as well:

I had tried to adjust the air intake unsuccessfully a couple of weeks ago

So set about cleaning out the passages that the adjustment screws sit in.

40 pipe cleaners and half a tin of carb cleaner later (just to prove it

)

No effect seen on the synchrometer

but plenty of rubbish on the pipe cleaners.

Advice from Mike Bainbridge and others on here convinced me to remove the TBs

In the end I decided to take the engine out of the car just for ease of access and to allow for the "whilst I'm in there" jobs

First step was easy, remove the air filter and funnels underneath