can the wrong size fuel injector O ring cause false air leak?
11-17-2008, 09:06 PM
#16
Under the Lift
Lifetime Rennlist
Member
Lifetime Rennlist
Member
The one instance I am aware of, reported to me by Brian (Iceman), where the small Ford o-rings were left on, the car would barely run and there were huge sucking noises at idle easily traced to the injectors.
Last edited by Bill Ball; 11-18-2008 at 12:07 AM.
11-17-2008, 10:16 PM
#17
Burning Brakes
Thread Starter
Join Date: Sep 2006
Location: Myrtle Beach, South Carolina
Posts: 1,203
Likes: 0
Received 0 Likes
on
0 Posts
Craig,
I'm pretty sure you would have a bunch of fuel spraying out of the injector sealing area while under boost if the o-ring was too small. Since you haven't mentioned a strong fuel smell it would appear to me that you have a good seal at the injector. This would also be true for a manifold leak, in ther area of the injector, to atmosphere under the same condition.
I'm pretty sure you would have a bunch of fuel spraying out of the injector sealing area while under boost if the o-ring was too small. Since you haven't mentioned a strong fuel smell it would appear to me that you have a good seal at the injector. This would also be true for a manifold leak, in ther area of the injector, to atmosphere under the same condition.
I should have realized that would be too easy. I guess I was hoping the leak was somehow one way, as in a strong vacuum could open a small leak past each of the injector O rings but positive pressure caused the rings to push up and out where they are supported by their surroundings...
There is visible lube around the back side of the O rings I can see with a flashlight and mirror though, so if it was sucking air in you would think that lube would have been sucked into the mix also...
I'm waiting on the refurbished LH to arrive and then I'll try John Speakes recommended SharkTuning procedure again, it didn't work with my old MAF and LH but I've sealed a few minor leak spots since then so with that in mind and with the rebuilt LH and MAF maybe it will be within the range of SharkTuner control now....
The other area that is a likely suspect is the cowl under the MAF, it can produce surging that seems to be the results of large gulps of false air if I don't get the MAF and other tubing strapped down just right so maybe it is also letting a small steady amount in as well. I guess it can't hurt to try some more pressure testing while I wait on the new LH.
11-18-2008, 02:08 AM
#19
Race Director
Yes Sharky ran....but BARELY..... the stock Ford O rings are around 14mm and Porsche requires at least a 16mm O ring....all of mine (the right ones) measure between 16.4-5mm or so...... and they are VERY snug... Bill and I just pulled them all out today during the intake removal...
11-18-2008, 08:02 AM
#20
Burning Brakes
Thread Starter
Join Date: Sep 2006
Location: Myrtle Beach, South Carolina
Posts: 1,203
Likes: 0
Received 0 Likes
on
0 Posts
11-18-2008, 01:14 PM
#21
Race Director
11-18-2008, 01:20 PM
#22
Burning Brakes
Thread Starter
Join Date: Sep 2006
Location: Myrtle Beach, South Carolina
Posts: 1,203
Likes: 0
Received 0 Likes
on
0 Posts
I'm going by the vacuum boost gauge in the console branched off the fuel regulator vacuum line and routed through the firewall down by the CE panel. I haven't checked it closer to the source but I'd bet it's over 20.
11-18-2008, 10:48 PM
#23
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,407
Received 1,587 Likes
on
1,036 Posts
The reading may depend on the location from where the vacuum is drawn and any restrictions (or not) relative to the stock intake tract. To be totally certain if your vacuum reading is indicative of a problem, I wouldn't use stock S4 vacuum readings as a comparison to your Murph'd car. You'd want readings from a Murph'd car taken from the same location you take yours with both measured at roughly the same engine speed.
