Buck at steady speed
 

I have a 74 2.0 914 with a problem. While cruising at a steady speed, any speed any gear, I get a very slight buck. Its just like a split second cut out of the engine. Anyone had this problem before?? I appreciate any help.

Alex

I had the same problem once and it turned out to be the throttle position switch.

If you are running d-jet fuel injection I would agree that it could be your throttle switch. A simple test (from How to Modify Bosch Fuel Injection) is to turn the ignition on (do not start the engine)and go to the engine compartment and slowly open the throttle switch by hand. As you do this you will hear the injectors firing (clicking). From a closed position to wide open throttle, you should hear 20 evenly spaced clicks. The key phrase is "evenly spaced". If they are not spaced evenly, then try adjusting the throttle switch (Pelican Parts has a tech article on this). If that does not work, then you may remove the switch, and open it (take the plastic cover off) and clean the printed circuit board with a very fine sand paper and spray it with some type of electronic switch cleaner. If this works, please understand that it is usually a temporary fix and the switch should be replaced with a new one. I had a brand new switch do this to me and after I opened it up, I discovered tiny copper shavings were causing the switch to short. I cleaned it and its been running flawlessly ever since.

Best regards

Alex

I had the same problem on my '73 2.0. I assumed it was a throttle switch, but I decided to change the plugs and pulg wires first. Problem solved.

A different test for the TPS: Unplug it. The car should run without it. Idle may be a bit odd, and acceleration will suck most fearsomely, but steady-state running should not be affected. If your stumble goes away, the TPS is almost certainly the problem.

Then you can open it up and look to see if the traces on the circuitboard have been worn away or not.

I'm not sure that the "evenly spaced" test will catch this problem. But then, I don't like the "How to Tune and Modify" book very much anyway. I far prefer Probst's "Bosch FI and Engine Management".

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

I agree with DD. The "evenly spaced" test doesn't make sense. If the switch is misadjusted and/or your throttle stop is misadjusted, you'll get fewer than 20 clicks, but there's no accurate way to judge if they are even or not.

The disconnection test is the standard method for evaluating this problem.

Brad Anders

Thank you all for your replies. I have heard that it is commonly the throttle switch but haven't done the test yet. I'll do the disconnect test, that makes sense to me. I'll let you know the test results http://www.pelicanparts.com/ultimate/smile.gif
Thanks Again
Alex

Hello

Not to forged the other possibilitys.
Vacuum leak or missreding NTC lean out or faten to much.

Grüsse

Yep. Throttle switch is my problem. I dissconnected it and the can doesn't buck a single bit. I will order one tomorrow. Thank you all for the advice.

Alex