aggravation

I'm trying to find anything that could cause my high idle. I've removed the intake twice and checked all the obvious stuff now I'm trying to think outside the box a bit to find what is probably a small air leak based on my current symptoms. This morning starting a cold car, 54 degree's in the garage, the A/F ratio is lean around 17, the idle started out at 1400 rpm for about 20 seconds then dropped to 400 rpm where it wanted to stay and the engine sounds like it will stall. I give it some throttle and the A/F moves down to 15 and the idle comes up but letting off the throttle it returns to 400 rpm and17 A/F.

Do that a few times then it suddenly seems to get some assistance, enrichment maybe? The idle sits at 1200 and the A/F sits at 15.7 and from there it warms up and the idle will run around 800 sometimes drop below 800 to 675 but usually it is at 800.

I'm wondering if the O rings on the bottom of the injectors can pass false air into the system. They don't look too small but they press into place relatively easily with minimal lube. Visually they don't look like they are leaving any gap but maybe just a small amount through each could cause this...

For those that haven't been keeping track I have tried:
*intake removed and reinstalled
*MAF rebuilt
*O2 sensor replaced (at least twice)
*New ISV
*loaner LH
*loaner EZK
*loaner MAF
*all vacuum lines checked/replaced
*pressurized intake-results not clear
*intake removed and reinstalled again
*various cuss words throughout the process followed by prayers and then voodoo rituals

worf928

In answer to the question in the title of the thread: YES..

If you suspect false air, then you should look for an intake leak (duh!) and there are at least two ways to do it:
- beg, borrow, or steal a smoke machine and fill up the intake tract and see where it smokes
- pressurize the intake (see WSM) to 5 or so PSI with a grown-from-home-depot adapter and using soapy water sprayed on stuff, look for bubbles.

There is also the "spray something flammable around and see if the idle changes method."

Bill Ball

The correct o-rings are rather chubby and exert a good deal of resistance going in or coming out unless lubed well. In fact, with the correct o-rings it is quite possible for a section to get hung on the top of the manifold opening, even with lube. That can cause a measurable leak. We found such on George Suennen's car. You have to be very careful to observe that the whole o-ring goes well into the hole when installing the rails. It can hang anywhere, including on the inner side facing away from you, and that can be difficult to spot.

The Ford o-rings are real small. If you had the Ford o-rings still on the injectors, I would expect the leak to be monstrous. I'm suggesting that even with the correct o-rings there can be an air leak if one got pinched going in. I've seen these o-rings hang up a number of times as I've installed the injectors. Pull it back out, more lube (silicone grease works best for me - Sil Glyde or Super Lube) [CORRECTION: SuprLube is PTFE based and probably better- see later comment by Larry928gts regarding silicone and O2 sensors], try again. Also, I've seen these o-rings get hard and brittle if they are old.

Dave has a good suggestion there. Spray some carb cleaner or WD-40 around the injector bases and see what happens.

aggravation

Thanks Bill and Dave.
The O rings on the 42 lb injectors are the ones I took off the 30lb injectors that came on the car from the previous owners installation.
They were a lot bigger than the ones that came on the new 42 lb injectors. Bill, from your description I'm not sure they are big enough though so I'm going to go look really hard at them right now to see if anything looks out of place.

To determine if there is an air leak I was thinking of using a MAPP gas torch and let some flow toward the injectors and other suspect areas.
I've read that some people have success using Propane gas this way and I have the MAPP cylinders instead of Propane because that's what I use for brazing in my day job. It burns a little hotter than Propane but I think just letting some filter in through an air leak to be added to the A/F mix wouldn't be a problem in small quantities.
Anyone have an opinion on that theory before I commit to it?

worf928

Well, I don't like fire. You'll need to have the car idling while you're swinging the torch around and listening to changes in idle.

On an S4-style intake, I've had good experience with pressurizing the intake with a gizmo I made that looks a lot like what's in the WSM. You get a standard quick-connect air hose adapter, a 3" (or is it 3.5"? I forget) to 1.5" rubber reducer, and a PVC elbow fitting. You have to have regulated compressed air. Pressurize to 5 to 7 PSI and then with a spray bottle of soapy water you spray mating surfaces, injector o-rings etc, and look for bubbles. This method works well for any places to which you can get your eyes or an inspection mirror. For deep-in-the-dark locations you'd have to revert to the flammable method or a smoke machine.

Here's a picture of the gizmo on my twin-screw.

Larry928GTS

You definitely want some kind of lube on the "O" rings when installing, otherwise they can roll out of position or get pinched much more easily. Don't use silicone grease on there though, unless it's specifically labeled as being safe for the O2 sensor. Silicone fumes getting into the intake can kill the O2 sensor pretty quickly, and is why there are "sensor safe" statements on some sealants.

Back when I had my injectors cleaned by Crusin' Performance, I asked about what to use for lubricating the "O" rings when installing the injectors, and was told that a little bit of automatic transmission fluid is what they use.

Craig, have you checked to make sure your idle switch is working correctly? The best way to check it is with an ohm meter at the plug of the LH computer.

aggravation

Oops, another thing I should have put on my list.
I put in a new idle switch the first time I pulled the intake when the new ISV went in and it shows in the SharkTuner that it is working correctly.

I used NAPA Sil-Glyde to lube the O rings, it does contain silicone. Do you think this might have harmed the O2 sensor?

Bill Ball

Hmmm.. Yes, that is a general caution with O2 sensors. Good point. I haven't had problem with it, as the grease doesn't outgas like silicone sealants, but I suppose Teflon grease (Finish Line - synthetic bike bearing grease available at REI) would be better. Others have used Vaseline and that may be fine, but I avoid petroleum-based lubes on rubber. Oh, wait a minute...SuperLube that I mentioned is Teflon, not silicone.

worf928

I use a glycerine-based lube.

But, you could probably use motor oil too even though it is petroleum-based; I would think that it will hardly cause the o-rings to deteriorate more quickly given all the motor oil that the S4 928 intake ingests as a matter of course...

Bill Ball

These o-rings could be oil resistant. You'd certainly expect the breather hoses to be oil-resitant, but they don't act like they are. The front passenger cam cover breather hose turns to mush over time.

ROG100

I thought you had to use a different size O ring when fitting Ford Injectors. One that had a small enough inside diameter to fit the injector and still maintain the correct outside diameter.
FWIW I do sell the correct size O rings for $20 including shipping. Rings are Viton

Fogey1

Maybe a little off topic, but ...

Rather than a combustible like propane or MAPP or carb cleaner or ether, has anyone ever tried using oxygen?

It's not exactly combustible like the others, so it'd be a little safer. but it should change any combustion process into which it's introduced.

Will
curious minds ...

aggravation

I don't know that it would do anything other than lean the mixture out.
As far as a leak detection tool you need something that would change the rpm's when you are introducing the gas into the system so you know what spot is leaking while you are leaning over the engine instead of trying to watch for changes on an Air/Fuel mixture gauge. I guess if you had an A/F gauge under the hood it would work....

mark kibort

just spray brake cleaner around where you think there is a leak, idle will go up when you have a substantial leak. (or carb cleaner)

Tim Murphy

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.