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post #1 of (permalink) Old 09-13-2000, 09:04 AM
Robert87yj
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MPI whistle--How loud is yours?

I've been driving the Jeep back and forth to work now for a day and a half with its fresh 4.2 w/ 4.0head and MPI.
The MPI didn't whistle loud at first, but after driving it to work and back and then back to work, It has began to whistle pretty loud. It's kind of got me concerned. How loud are other people's MPI systems whistling? I can clearly hear mine over the engine and radio.

I wonder if the whistling might have something to do with the PVC pipe I rigged to use in place of the flexible air tube. Maybe the airflow needs to be disturbed somewhere along the line to keep it from whistling? I don't know. Maybe I shoud re-torque the intake/ exaust manifold bolts while I'm at it.[img]/wwwthreads_images/icons/crazy.gif[/img]




Robert87yj[img]/wwwthreads_images/icons/tongue.gif[/img]
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post #2 of (permalink) Old 09-13-2000, 10:38 AM
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Re: MPI whistle--How loud is yours?

Definetly recheck all your torques, mine dosn't whistle. My set up is the same as yours. I would start looking for intake leaks.

good luck, let us know what you find.

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post #3 of (permalink) Old 09-13-2000, 10:56 AM
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Re: MPI whistle--How loud is yours?

I agree with JFRALPH. Mine is set up the same as yours as well and is very quiet (I have never heard even a faint whistle).

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post #4 of (permalink) Old 09-13-2000, 11:09 AM
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Re: MPI whistle--How loud is yours?

Sorry boys, but I disagree. Mine used to whistle too. Have you ever blown across the top of a coke bottle? The same thing is going on here. I was going to get fancy with engineering terms, but who really cares? I am about 99% sure your not dealing with a leaking intake manifold. Mine used to get a little worse under full throttle, but I havenít heard it for a while. I was thinking of making a different air intake with a smooth bend and a tube that was bent back from the air filter, but since I just rock crawl, I havenít gotten to it yet. Maybe Iíll do it while I do the 4.0 head. My short-term plan was to get a few of those fittings and play with the shape a little. Iím not sure you want to cut it down too much though. I think the opening should be in the laminar flow section of the tube. I also thought of a little bump to trip the boundary layer in front of the tube would work, but I think just changing the shape of the tip would be enough.

Pete <font color=yellow>83CJ7</font color=yellow>, <font color=blue>96YZ250</font color=blue>
post #5 of (permalink) Old 09-13-2000, 01:13 PM
Robert87yj
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Re: MPI whistle--How loud is yours?

Thanks for all of the ideas so far...

I was thinking that it would be good if I wrote up a better description of the situation under which it does whistle, so here it goes:

It starts to whistle after about 2-3 minutes after the engine is started. The whistle increaces in pitch with the rpm's. My engine RPM's haven't slowed down yet so every time I let it idle the RPM's go up. It whistles the most when not in gear while idling, and at a higher pitch b/c of the high RPM's. It doesn't whislte much at all in gear, but it does when it is in gear and I don't have my foot on the pedal. It also whistles a little in 5th gear when I have my foot on the pedal, but not as much as when I don't have my foot on it.

the flex tube that came with the kit was torn up so I replaced it with a pvc pipe and used soem rubber joints with pipe clamps to hold everything together to the aluminum pieces included with the kit. The pvc pipe is just a 45 degree bend, not a elbow. It has a nice gradual curve instead of a sharp turn like an elbow would. I used 2" pipe to join the bend to a coupler. I did leave in the rubber 90 degree bend that comes off the intake manifold that came with the kit. If I had a digital camera I'd take a picture of the whole thing to show.

Because the whistle changes pitch with the increace in rpm's makes sense to me, but why it doesn't whistle while in gear with my foot on the pedal does not.[img]/wwwthreads_images/icons/crazy.gif[/img].

My thought is to take the air filter off of the tube and connect it more directly to the intake manifold with on of the rubber cupler joints I have been using for the intake tube. So far that is my only idea besides putting a cut piece of pvc in the tube, paralell to the airflow, to split the airflow in two. My thinking here is to disrupt the airflow enough to stop the whistle.[img]/wwwthreads_images/icons/tongue.gif[/img] I have also thought to do the entire pipe with 2"pvc and get rid of all of the stuff that came with the kit except for the aluminum piece that the filter attaches to. What do ya'll think.

Robert87yj[img]/wwwthreads_images/icons/tongue.gif[/img]
4.2 w/<font color=blue>(4.0 head & MPI)</font color=blue>
Process of a moonguy after beer
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post #6 of (permalink) Old 09-13-2000, 05:09 PM
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Re: MPI whistle--How loud is yours?

Robert, I have the MPI on my 86CJ7 and it started to whistle about 3 -4 days after the install. Mine was an intake manifold leak. The fasteners on
both the front and rear of the manifold had lossened. Tightened same and the whistling stopped.

Gary
post #7 of (permalink) Old 09-13-2000, 06:49 PM
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Re: MPI whistle--How loud is yours?

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post #8 of (permalink) Old 09-14-2000, 10:46 AM
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Re: MPI whistle--How loud is yours?

I have a 89 4.0L engine with Mopar MPI setup in a 82 CJ. This required an adapter for the throttle body to the older (Renix) intake manifold. Mine whistled at idle and was caused by a leak between the manifold and adapter. After that was cured my whistle now occurs at a very narrow range (about 55-60 mph)at highway speed. I read somewhere that this whistle is normal and is more noticable because of the open air filter (Turbo City). Can any one confirm that this IS normal?
Thanks,
GM

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post #9 of (permalink) Old 09-14-2000, 11:55 AM
Robert87yj
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Re: MPI whistle--How loud is yours?

Gary,
This weekend I plan to go over all the bolts on the intake manifold and check the torque. Mine didn't do that the first few trips that I made...maybe this is the problem. I'm pretty sure that it is somewhere in the intake system. Just have to narrow it down[img]/wwwthreads_images/icons/tongue.gif[/img]

Thanks,

Robert87yj[img]/wwwthreads_images/icons/tongue.gif[/img]
4.2 w/<font color=blue>(4.0 head & MPI)</font color=blue>
Process of a moonguy after beer
[img]/wwwthreads_images/icons/mad.gif[/img] [img]/wwwthreads_images/icons/frown.gif[/img] [img]/wwwthreads_images/icons/crazy.gif[/img] [img]/wwwthreads_images/icons/wink.gif[/img] [img]/wwwthreads_images/icons/smile.gif[/img] [img]/wwwthreads_images/icons/blush.gif[/img]
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