Questions tagged [terminology]

For questions about words, phrases and definitions that are specific to maintenance and repair of motor vehicles.

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11
votes
1answer
3k views

What exactly are fuel trims?

What is meant by the term "fuel trim"? Why are they so important in diagnosing engine operation issues? How do short-term fuel trims differ from long-term fuel trims?
20
votes
3answers
10k views

What is valve float and how does it impact engines?

The Wikipedia entry is hard to grok: Valve float is an adverse condition which can occur at high engine speeds when the poppet valves in an internal combustion engine valvetrain do not properly ...
18
votes
3answers
174k views

What exactly is a “burnt valve” and what causes it?

I've come across this term a couple of times in the context of diagnosing engine-related issues, but don't know what it refers to. Here is an example from an automotive forum I frequent: I gotta ...
11
votes
4answers
55k views

What are the “1” and “2” or “L” gears used for on an automatic?

In a car with an automatic transmission, we are normally greeted by the acronym PRNDL, or in some cases (older cars) PRND21. I know that the L, 1, or 2 will cause the transmission to stay in a (L)...
10
votes
3answers
5k views

What exactly is a jackshaft?

The Wikipedia entry for the Ford Cologne 4.0L SOHC describes the use of a "jackshaft": It uses a jackshaft in place of a camshaft to drive a timing chain to each cylinder head. Three timing chains ...
3
votes
1answer
855 views

Shortblock vs Longblock

What is the difference between a shortblock and a longblock? Both terms are used to refer to the engine, but what's the difference between them?