Ferrari 355 5.2 Plenum Chambers I have had to remove my plenum's as I needed to replace the gaskets as they were leaking slightly. I have done this with the engine in situ. Is there any tricks in putting the Plenums back onto the velocity stacks with the four rubber seals. I am finding it very hard to align the plenum's with the rubber seals to the velocity stacks. Also it is quite difficult to fix the metal collets and jubilee clip to the rubber seals that attach the velocity stacks and plenum chambers. Any suggestions or help much appreciated as this is turning out to be a very difficult job.
There are no tricks, it just takes some experience having to do this a dozen times in order to get good at it and to recognize when the metal collets are not fitted right and start over. Suggestions: 1. Get some steel bolts and toss the factory stainless steel bolts. Thank me later after you drop those bolts and cannot get them out with a magnet. 2. Engine lid off, in case you have to climb into the engine bay 3. Dry fit outside the car and learn to read the gap between the two metal collets when they are perfectly fit around the rubber seal. That is the only way the metal clamp will fit 4. Start with the one closest to the front of the car, then the one closest to the rear of the car, then the two middle ones. 5. I always do it this way: a. rubber pieces on the velocity stacks b. Air plenum over the top in the correct position c. Fit the two metal bands around the rubber piece, observe the proper gap between the ends d. snake the loose clamp around the rubber piece, pull it tight, hand thread in the long bolt, tighten it. e. move to the next one. I was never successful doing this any other way, including pre-installing the clamps outside the car.
Much appreciated for your quick response, you are correct the stainless steel bolts are a nightmare as I found out from experience, I will try your method of doing the front velocity stack and the back velocity stack first.
The bolt swap is a major suggestion. Love that. I dropped one and damn near had a hear attack trying to find it in the mess that is the valley. Visions of tearing it all back apart to find it. Fortunately it materialized. A second set of hands helps tremendously. I fought 1 side taking multiple attempts to get it without pinching the rubber seal somewhere. Then the other side just popped on no drama. Securing all the clamps is just patience.
I found a good way of managing not to loose the stainless steel bolts that secure the collets. Just tie the bolt with a piece of cotton thread and make a loop at the other end and tie this to your wrist. saves a lot of time and effort. This ensures you dont loose them and you know exactly wherte they are when they ping out, saves a lot of time and effort. simply just pull the cotton off when secured.
Aother trick i have learnt is that if you secure the front velocity stack to the plenum chamber and attach collets correctly seated and secure with retaining clip loosely. It is possible to adjust the other three rubbers to ensure they are correctly fitted first and then secure the back velocity stack to the plenum chamber next. In situ this is a long fiddly job but it just takes time to align all the components correctly. To ensure this was completed correctly I ran a smoke test to make sure there were no leaks on completion.
Now that the car has had a major service, cam belts and various related ancillaries. I have developed a problem since putting it all back together where the car will not idle at the correct revs and can drop as low as 500 rpm but is hunting more often than not between 800 and 1000 rpm. Any ideas, I thought it was an air leak but I have checked all connections and smoke tested for leaks. Any ideas or help appreciated.
OK, chances are something has gone wrong with the Throttle Position Sensor when you were trying to re-install the plenum stacks. My suggestion is to check the throttle position sensor connector, and the relative resistance of the three pins for that sensor to see if they are in spec. I have seen one case when the two connectors (3 pin each) for the throttle position sensor and the cam position sensor are swapped. That does not work well, even if it runs.
