Weird flatspot at 4600rpm, can't 'break through' it in 4th Options

[nebreitling]

hi all

i've discovered a weird ignition/fuel system quirk in my '75 2.0, which has probably been going on since i've owned it (3 months) -- just haven't noticed it.

the engine has a flatspot at ~4600rpm -- it feels like the fuel cuts in and out to keep the engine below this speed. now, i can 'break through' it in 1st --> 3rd gear, it just pauses and stumbles a bit at 4600, then moves merrily along toward redline. but in 4th (and 5th, i presume), it feels like i don't have enough power/momentum to 'break through it'.

2 months ago, car had a full tune up, valves adjusted, etc. airpump removed, air injector jets plugged. aside from this quirk, it runs smoothly and strong.

does anyone have suggestions for things to check? (IMG:style_emoticons/default/confused24.gif)

nathan

[airsix]

Unplugging my TPS while the engine is running (won't start w/out it) causes it to run like shit.  idle drops, definitely a little surging and bucking.  are you saying that this is a sign that my TPS is bad or good?

thanks,  nathan

(Somebody with better communicaiton skills than me please feel free to join in and save this)

It is normal for the idle to be poor with the TPS unplugged because the ECU runs a richer mixture at idle and with the TPS unplugged the ECU doesn't know to do this. Unplugging the TPS and idling in the driveway won't tell you anything.

Usually if the TPS is bad then you will get slight surging/bucking when you are cruising down the road at a steady speed (with TPS plugged in). I was saying that at steady speed there should be NO bucking with the TPS unplugged. That's the test - if you have surging/bucking at steady speeds with the TPS PLUGGED IN, and the surging/bucking GOES AWAY when you UNPLUG it, then the TPS is suspect. Note that I am ONLY talking about steady speed where you are not moving the throttle. Witht the TPS unplugged the car will not run well while you are moving the throttle, but should run fine when the throttle is held steady. I hope that makes more sense.

-Ben M.