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Engine drops 100 rpm in idle then recovers, what gives

Engine drops 100 rpm in idle then recovers, what gives
C

cuban11182

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CORPUS CHRISTI
Vehicle(s)
84 CJ7: 258, T5, Dana 300, Holley 390, Nutter Bypass.
At first I thought it was the alternator, but it's new and so is the battery. I completely disconnected the alternator and started it and it still does it. The engine idle is 750-800. Of course when it drops down the lights dim etc. The Alternator is a powermaster 90 amp 3 wire.

It's an 84 with AMC 258 i6 / 4.2l and T-5 . No emissions. It has the Team Rush and nutter bypass with all the wiring removed. Currently has a new MC2150 on it.

It's does it both warm and cold. It happens repeatedly, but not while the engine is in gear and running. I purchased the CJ with a bad alternator. I first noticed it after I installed the amp, but the amp is disconnected right now.


https://www.youtube.com/watch?v=yVcTYMNhQno
 
check the EGR valve and look for vacuum leaks?:cool:
 
If the EGR is not working it can do that. believe it or not an EGR is a good thing and makes the engine run better and smoother. A little shot of carbon monoxide is good for combustion. Mine does the same thing yours does and I believe it is because of the lack of an EGR valve. Header does not have EGR tap. If I ever pull the head I am going to see about mounting an bung in the header to connect the EGR back up.:cool:
 
Guess I need to find some vaccum lines then. I have a two port CTO in the intake manifold so I'll have to see if it's ported or manifold vacuum that ties into the EGR.

Thanks again.
 
EGRs also get clogged, keep that in mind.:cool:
 
Reinstalled it, but still no dice. I did see that I have an exhaust leak, so I"m wondering if that may have anything to do with it. In any case I'll drive it like it is and once I swap out the carb and intake manifold see if it rears it's ugly head again.
 
It was hard to tell from the video but, it almost looked like your compressor engaged. If there is a signal wire to the compressor clutch, try unplugging it and repeat the test. Also, if your 2150 has a dashpot check to see if it is collapsing a little bit and allowing the throttle to close.
This link has some good info on the 2150.Motorcraft 2150 2V Carburetor
 
Thanks Bent. At first thats what I though too, but after double checking the compressor wire is disconnected.

AS far as the 2150, I don't have a dash pot on the driver side. Here is a good image.
20140414_061551_zpsgdqp0zfq.webp

If it is the carb it shouldn't be on too much longer. I purchased a Holley 390 so that will go on with a single plane Offy.
 
did you pull a vacuum on the EGR to see if it worked/ has a leak in the diaphragm?
 
Strange. I probably watched the video 10 times. I keep thinking it sounds like it's being slowed down by an additional load placed on the engine and not a throttle reduction. Strange that it won't do it in gear. I wonder if a power steering pump going bad would cause that? Maybe take the PS belt off and test. A lot of work for a long shot though.
 
It's worth a try if the new carb and intake manifold don't work.

The guy that has the intake manifold also has a set of headers with a dual outlet setup. I'm going to need to see the condition and what he wants for them. Plus I'm going to be visiting family in PA, so I'm going to have to make it home with these things as well. LOL
 
Fuel injection time? :cool: just kidding, I never had luck chasing down carb/vacuum related issues.
 
I guess changing out the Carb will rule it out. :rolleyes:
 
So the Offy intake deal fell through. I put an EGR plate instead of the EGR vavle, and it's still doing it. :rolleyes:
 
Are you sure that ALL the manifold bolts are tight?
Clean your PCV valve out.
LG
 
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