Mystery Solved

[Ragtop_Renegade]

I recently had a problem with my 86 4 cyl. The engine had a serious lack of power, seemed to misfire at idle and the exhaust manifold would glow bright orange. I finally found the problem after weeks of messing around by doing what I should have done at day one: a compression test. Engine compression was pretty bad, 115 PSI on cylinders 1 & 4 and only 50 on 2 & 3!!! I pulled the head off and found some pretty intersting stuff. Turns out the engine had been rebuilt - all the pistons and rings were replaced and the cylinders are bored .030 over. As it turns out whoever did the rebuild totally SCREWED UP the head. It was warped .004, had a crack between 2&3, and all the valves had leaks that would put the Titanic to shame. I had the crack pinned and the head shaved flat, replaced the head gasket and bolts, did a complete valve job and the engine is finally running better.
I was always taught that a compression test was the first thing you should do when diagnosing engine problems, but I messed up by not doing one first. I would recommend to anyone who works on cars often to invest in a compression gauge and to USE it.

I am still having problems with my plug wires, this is the 2nd set of brand new AC/Delco Wires in the last 60 days and they are arching up a storm. Anyone recommend a set of high performance wires? The OEM ones are obviously NOT doing it.

[De Fiero 88]

what actually does a compression test do? I might need one done on my fiero. When you start it, it's idled up to about 2 half rpm and then when it's warm it dropps down to 1. THough should it drop down to 0?

[Ragtop_Renegade]

Compression is, by dictionary definition, decreasing the space between molecules, causing the volume of the matter to lower while the mass remains the same.
Good compression is essential for proper engine performance because fuel burns better and therfore releases more energy when compressed.

A compression test is used to check the individual compression of each cylinder. Measurements are taken in Pounds per Square Inch(psi) Just like a tire. Problems are identified when one or more cylinder's compression is less then 75% of the highest reading. For example, after testing the compression on your 2.8L engine you come up with the readings 150, 145, 155, 135, 105, and 140 psi. Our highest reading was 255 psi, so our lowest should be no less then 75% of that, or 116 psi. So it looks like we have found a serious lack of compression on cylinder #5 - why is this? Compression leaks are caused by the following:

1. Piston ring or cylinder wear
2. Valve leaks
3. blown head gasket (usually found when 2 cylinders next to each other have low compression.)

As you can see, all the problems that cause poor compression are realted to the basic mechanical core of the engine. That's why compression test are so important. No matter how many expensive high performance power enhancing super duper whatchamacallits you bolt on an engine, if it has worn rings or bad valves, it's still gonna run like s**t. Before you decide to mod up your engine you should run a compression test to make sure it's mechanically sound, or you might just be wasting time taking all those new parts back off to overhaul the engine later.

Don't worry, there doesn't appear to be anything seriously wrong with your Fiero, a 1000 rpm warm idle is a wee bit high for a 2.8, I like to see 800-900 rpm tops but the slight difference could easily be a minor vacuum hose leak and is not worth a crazed panic just yet.
Think about it... the only time an engine is at 0 rpm, NO revolutions per minute, is when it isn't running.