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Surging engine at 2500 rpms similar to a rev limiter

1K views 9 replies 5 participants last post by  Butcher 
#1 ·
[video]http://vid151.photobucket.com/albums/s152/cybrdweeb/IMG_4371_zpskpazgmzb.mp4[/video]

Hello - I have an 84 1/2 Cabby that had starting problems - sometimes it would fire right up and sometimes would just crank and crank and not start. Then when it would start and increase rpms it would get to 2500 and start surging just like a rev limiter does.

I found a pinhole leak in the fuel return line from the fuel distributor so I put a new one. It fired up, ran great and did not surge so I thought great- it's fixed.

I went out and tried again later and to my dismay it is surging again at 2500 rpms.

I'm at a loss as to what is causing this.

Any ideas?
 
#2 ·
Leaking injectors?

So I checked for vacuum leaks by spraying starting fluid on the hoses and none found.

I then sprayed the injectors at the head and the engine stumbled and misfired. Just the opposite of what expected- I thought the engine would rev up if there was a leak.

I'm guessing the injector O rings are bad but would that cause surging?
 
#3 ·
Check cam/crank timing and ignition timing.
What does your dwell/duty cycle meter tell you the system is doing?

You own a CIS car, you need to master these things, there are very few pros left to turn to.
 
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#8 ·
The idle switch is not working.

There is a huge emissions issue on decel. If you shut off the injectors, the emissions are reduced. Usually the injectors are cut out around 1.5-2.0k. That is why when you raise the engine speed that high, the injectors will stop flowing fuel.

So somewhere the idle switch is not working somewhere. As in the wiring is shorted, switch NFG, or maybe even the module. Check the ETM and follow the tract.
 
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