4.6 L DOHC Help

[Peeker]

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This pic is taken from the passenger side looking across towards the drivers side. There are two ports covered with duct tape. I believe they are vacuum but not sure. Anyone who is running a 4.6 if you could help me out with these. Thanks

[Joecobr]

I have a ‘98 Cobra 4.6 DOHC engine. I have attached some photos on how mine are. One is blocked off and the other is connected to a fuel rail piece with a small diameter, blue tube. They are both pollution stuff mostly eliminated in my case.

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[Peeker]

It looks like the one to the right is the blocked off one. The one coming from the top rear of the intake appears to go into some type of vacuum type diaphragm. If there is any chance you could take a couple more closeups id appreciate it. Thanks

[Joecobr]

Do these help? The diaphragm is rerouted back into the intake manifold with the blue tube. The OEM rubber piece originally had two tubes running from it...one of which is now blocked off with black silicone.

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[Peeker]

I don’t have the diaphragm that it connects to. Where is that diaphragm going to. I was thinking it needed to go to the canister in the back of the chassis with the charcoal vent.

[Mark K]

I have a later model year 4.6 DOHC (2004). On mine, the rear-most fitting supplies vacuum, and the fitting near the throttle body is the intake for the fuel vent charcoal canister.

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[Peeker]

On Joes it appears that the line near the throttle body is capped off. The one coming out of the top rear of the intake appears to go into a diaphragm. I don’t have the diaphragm or at least I haven’t seen it. You are definitely running a different intake than the 96. Not sure if those lines are the same. I bought this as a partial build so it may be in one of the boxes that I haven’t gone thru. I’ve been a bit under the weather so that’s my excuse.

[Joecobr]

The diaphragm is an OEM fuel rail pressure regulator with a vacuum connection to the intake manifold. You appear to have an after market fuel rail with no similar regulator so I would simply block off the intake manifold opening.

[Peeker]

Got another issue for those of you with the 4.6 L DOHC. I’m trying to figure out the O2 sensors. My downstream ones have been dieted out. So I assume there still should be 2. In my harness I only see one and it is coming off the engine harness. I was told there should be one coming off my transmission harness but there is not one there. Can you explain to me or even show me pictures of how yours look. Is there a sensor in each side pipe?

[Joecobr]

My two rear O2 sensors have been dieted out. The two front sensor wires come off the engine harness on the drivers side. The passenger side sensor wires run along the front bottom of the engine to the passenger J-pipe. Hard to get a good pic. Don’t recall if I routed the passenger sensor wire through the engine harness myself.

[Mark K]

For the O2 sensor that you do have, does it still use a connector to attach to the engine harness? Is there an empty connector like it elsewhere on the engine or trans harness that's for the other O2 sensor? I'm hoping that's the case, rather than having that sensor/connector completely dieted out.

[Peeker]

I think I’ve got it figured out. In the harness I received it did not have the connection in the cab that leads to the 2 O2 sensors and oil pressure leads. Luckily the guy I bought the car from saved all the old stuff for the car he pulled the engine from. I found it and am in the process of cleaning it up and making it look like the rest of the wiring. Thanks for your help.

[dpariso]

if it helps here's a pic of my 1997 Lincoln Mark VIII engine with a Cobra intake.
Because I has so many problems getting my ECM to talk to a scanner (OBDII errors) I had a Holley HP ECU installed. Took care of my idle issues and tuned much better.
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[Mark K]

Nice - really clean install of a 4.6 4v. Like the Race Deck, too.

[dpariso]

Thanks! It looks good but... it needs just a little more getty-up. When the Holly HP was installed I had it tuned on the dyno. Everything is stock and put out 305hp at the wheels. I wish it has about 100hp more. I believe 400hp is perfect for our cars. I thinking I have a few options
1. rebuild it
2. add a supercharger
or 3. buy a blueprint crate engine that already has 400hp.

[Alan_C]

I built my car using the 4.6L DOHC from 2004 Mach 1. Stock except for EGR delete and performance tune. Used CAT J-pipes and GAS-N side pipes. 2nd owner had car dynoed at 298 to rear wheels, so in the same range.
For more power, new CAMs will help, but not likely to get close to 400 at rear wheels. For that kind of HP, you are looking at a Coyote or a supercharger. The engine bay was already tight, so fitting a supercharger will be a challenge.
In the manual, Dave Smith suggested that 300 HP made for a perfect street car, but we always want more.
There is a guy on the other forum who changed the CAMs and went with a carb and generated HP around 350 if I remember correctly.