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Discussion Starter #1
Hi guys,

I'm new to the forum and own a 91 Spider with 68,000 miles. I have had the car about two years and it has performed well. It has a minor problem in that it surges when accellerating; as if you were gently pressing and slightly releasing the throttle. The problem is less noticable when the engine is warm, but still there. It occurs at all throttle positions. I don't know where to begin to look; is it fuel-related or ignition-related? Any ideas would help; I am ready to start replacing components. At this mileage, should I replace the O2 sensor? Anything else? I am afraid that the dreaded previous owner did not care for the car very well.

Thanks much,

John
91 Spider
68 Triumph TR6R
 

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More than likely you are experiencing problems due to vacuum leaks in the intake hoses. They can develop small cracks that are hard to see but can let in umetered air as they flex under engine torque.

The technical term for this is False Air Leaks - they are false because they occur after the Air Flow Meter and therefore the engine ECU cannot adjust for the additional air.

Joe
 

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Hi John -

Don't start placing any major components just yet...chances are this is a simple fix, and with minimal effort you'll have it sorted out.

Have you done a search on the forum for similar problems as yours? JoeCab raised a good point - checking all vacuum/engine connections. Check all the hoses for tiny cracks, take a screw driver and make sure all the clamps and connections are still tight -

But why stop there - chances are if you go around the car and check every hose connection, and wire connection, and ground - your problem might go away.

Other than that, you might start with the simple things - plugs, wires, rotor - stuff that needs to be done anyway. I know that might not fix the problem - but at least you'll be able to rule them out (and then you'll have a tuned up car).

And yes, replace the 02 sensor - it is overdue.

Has the "Check Engine" light come on recently? And clarify for me - if you were to hold the accelerator down at a specific point in it's travel, does the engine cut off for a second? Also, when the car isn't in gear and you press the accelerator, what happens?
 

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Discussion Starter #4
Thanks for the quick response, guys. After spending four hours reading this forum last night, I am planning to check all the hoses, connections, and wires on the engine. Yesterday I replaced the plugs and stock air filter element. I will replace the O2 sensor as I now realize that it is due. I also have a new fuel filter that I have not yet installed, and that may be the culprit.
To clarify the surging: in neutral the car revs freely and crisply, but when accelerating under moderate load (like climbing a hill), the engine surges every two seconds or so, as if you were continually depressing and releasing the accelerator a small amount every couple of seconds. It does not cut out or mis-fire. Depressing the accelerator further brings continued surges and no increase in pickup, although the engine sounds like its working harder as it should. Cresting the hill, the car accelerates properly under less of a load. At cruise, the surging seems to disappear.
I have never seen the "Check Engine" light come on.

Thanks again, I appreciate the help,

John
 

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John -

After reading your latest post, and I may be jumping the gun, but I wonder if this is a slipping clutch...what you described above sounds like the engine is performing fine (at cruising speed on the highway, or out of gear, in the driveway revving the engine), and that as you are climbing a hill or under load, the engine still continues to rev while the car doesn't respond to that increase in engine speed - and therefore the car surges, as if accelerating or decelerating.

But I could totally be misinterpretting what you've written - but from what you've said, the clutch might be another possibility.

Frankly, don't do anything drastic to the car until others have chimed in (and I hope they do).

All the things you mentioned doing: checking electrical connections/grounds, replacing fuel filter, plugs, filters, checking hoses, O2 Sensor - these are all things you should be doing on the car anyway.

Do a search here and elsewhere on slipping clutches - it might be that you clutch, as it fails, isn't slipping smoothly - but is catching and releasing, catching and releasing.

I had this happen to me on an old motorcycle...and it was the clutch.
 

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John

Another thing to check ... sometimes the throttle linkages get old and the throttle behaves like it sticking. A way to check is to let it idle warm in neutral and then gently step on the throttle. If it accelerates smoothly up to 3000 rpm and then back down, all is OK and forget I said anything.
Regards

Simon
 
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