1996 4.0 can your torque down the intake manifold without taking anything off the motor and what is the torque values and sequence for this?Could it be possible if the bolts are loose to make the motor missfire?I keep getting a missfire on #2 cylinder and I canged plug wires check compresson and it doesn`t miss all the time and it takes sometime driving before it throws a code.

 

What code does it throw?

The tightening sequence is, looking from the front:

3 5 7 2
Front of engine
1 6 8 4

The torque steps are 6, 11, 16, 18 ft-lbs. I usually check each bolt twice before going on the the next step.

This is important when you install a manifold, you don't want to tighten any particular part down much more than the other, where you can distort either the manifold or the new gasket. If you think you have one or more bolts loose, you should just tighten it, as most of the manifold has been clamped down already. But it's going to be hard to get to the ones on the driver's side, as they are obstructed by the upper intake.

If you suspect a leak, you can try spraying around joints the with carb cleaner trick, to see if the engine runs any differently. If the bolts have been loose for a long time, you may need to actually replace the gaskets.

 

The carb cleaner method does not often work. The computer will compensate for any changes and you will likely not notice a change in RPM. Now if you have a friend watch with a scantool while you do this, you will see a sudden drop in the STFT when you spray the leak.

A smoke machine is a worthwhile test, it is more thorough than the carb cleaner method. Most shops will charge about $80 to smoke test, but it will find all the leaks, not just the worst or most obvious one.

I would recommend replacing the gaskets if there is an intake leak, they harden and shrink with age.

 

Gee, the spaces I put into my illustration got removed. Let me try again:

3 5 7 2
Front of engine ->
1 6 8 4

 

Thanks for the info guys.the only code it throws every now and then is a missfire on #2 cylinder.Could a loose manifold bolt do this?

 

Yes a loose bolt could do that. Be careful about leak induced misfires, if ignored, they can do damage to the valves due to an extreme lean condition on that cylinder.

Check the condition of the plug on that cylinder, see what story it can tell you.

 

unplug the O2 sensor at it's connector reached thru the hump hole. stops the PCM from readjusting for troubleshooting spray.

then use the carb cleaner or i like to use propane/butane out of unlit torch with flex hose. the propane/b is heavier than air so stays in place.

http://www.aa1car.com/library/vacleak.htm


can also be a weaky partially plugged or carboned over injector nozzle.

guy is a weird grease head but does show propane tank with hose adaptation

http://www.youtube.com/watch?v=9CPqbaSgcok&NR=1

 

Well when I changed the plugs out they all were burning good and they all looked the same.I`m going to try anf tighten the intake bolts and see what that does if that doesn`t work I thry the propane method.Thanks again for your help.

 

disconnecting the O2 sensor does not correct for the intake spray, the computer is compensating for RPM. If the spray causing an increase in RPM, the computer will adjust very rapidly, more quickly than you can detect the change. You need to have an assitant look for changes int he STFT when the area around the leak is being sprayed.


I have said it many times, the spray method is almost worthless, first off, you have to be able to access the are where the leak is occurring. On an Aerostar, this is almost impossible. If the area was accessible, you would be able to find the leak without using a spray or propane. Secondly, the method is dangerous, you are taking a flammable gas and spraying around many sources or ignition. I do in fact know of someone who has been burnt badly doing just that.

A 1996 has full OBD-II diagnostics at your disposal. This means you have long term and short term fuel trims which can help you find a problem. If it were my van, I would pull the intake, and inspect all the vacuum lines while they are out of the vehicle. You really can't check them all with the intake manifold still in there. If your valve covers are leaking, I'd pull those too, and pull the lower intake. Then you can do all the gaskets. and inspect the seals around the injectors which can also leak and are more likely to leak than the intake gasket anyway. I did this on my '94 recently and found 4 leaks, not just one, and none of them were around the upper intake gasket. Two were in the lower gaskets. The lower gasket leaks were undetectable to the spray method because the leaks were drawing from the crankcase.

 

Propane vacuum leak testing is an approved ASE troubleshooting method. i've had good luck with it for years on old carb'd systems, OBDI, OBDII and CAN systems troubleshooting for vacuum leaks, for correct stoichiometric mix and checking O2 sensor operation.

The propane fed to a vacuum leak into a cylinder brings the stoichiometric mix back up correct proportions for a no miss operation. one listens for the miss to quit and the engine to run smoothly. The Aero OBDII system is slow and does not quickly adjust to rpm changes, one can usually see and hear an increase in rpm also. I use a 6ft long flex hose with 3/8" ID. The amount of propane needed is small.

of course, none of the tests do anything for a vac. leak mix that only occurs from on the road vibration which occurs often in the Ford V6s with the high top heavy long runner vertical plenum and poor gasket design.