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Compression test results

Babaganoosh

Babaganoosh

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From my understanding everything is in good condition, and not one dropped at all.

Here is my question, the number 8 was shooting fuel out of the spark plug hole. What does that mean? #8 was the only one to do this.

Thanks.

32465680156_large.jpg
 
Yep, all looks good to me. I can't say about the #8 cylinder fuel issue but IIRC that is the shortest runner and also the plug that usually fouls before any other cylinder.
 
I can't thank you enough, you went above and beyond to help me out.

Huge kudos. :thumb:



Now to trace down the problem of my plugs looking like its running rich and surging while driving I think its time to send my quadrajet off to SMI or jet performance.
 
What brand of plugs do you run? I have tried MANY different plugs in my time and have found that the NGK V-power plugs work the best and i've been using them ever since without any issues.

I'm guessing that obviously your compression gauge worked versus the "loaner" one(s) that turned out to be crap?
 
Nothing but AC delco plugs (R45TS) sense the engine was put in 18 years ago. I ended up walking down the street to a buddy's house and grabbing a virtually bran new one to borrow.
 
Humor me and go buy a set of NGK V-power plugs and run them and tell me what you think. I'll bet you never want to run a different plug again.
 
I just looked at the v power ngk plugs. What makes them so special? I see the grooved tip, but doesn't seem to be a big deal. I use NGK in my dirtbikes, standard and iridium.
 
just for record... those numbers are a little borderline... the 135 to 155 difference is a fair amount over a 10% difference...

she'll run tho...
 
By the readings I got what would you guys say the condition of the engine is?
 
a vacuum test would be better to go off of

my engine was 7 cylinders @ 145 and 1 @ 150
bought it, drove it home, drove it around some
the motor was junk within 2 months
 
What do you mean by a vacuum test?

Can't remember exactly what it was when I tuned the idle mixture screws, but it was far into the green on the gauge.
 
Honestly
I've never done it myself
but what I've read, it should paint you a better picture of how things are sealing and wearing in the engine. A compression test is part A and vacuum test is part B. I've only done it once, my cousin and I, checked my 100k mile s10 and it was great. See how much vacuum the engine pulls and how well it holds it I think was the basics for the test.
sorry, that's all I know
 
Really the only thing a vacuum test will tell you is if the valves are seating properly. The problem with doing a vacuum test is that if anyone has installed a non factory cam (performance cam) the vacuum reading starts to drop as the cam gets wilder. A stock cam will allow an engine to produce usually between 17-21 inches of vacuum. If the reading keeps jumping all over the place then that says the valves aren't seating correctly and there is issues with the heads.

A compression test and a cylinder leak down test will tell you ALOT about the engine with the leak down test giving the most info.
 
Sounds like a leak down test is next in order. For some reason I think my engine was pulling 20 inches of vacuum. :dunno:
 
Are you having some issue that makes you think there is something wrong with the engine? Those numbers you posted don't give any indication of a problem as far as i'm concerned unless there's something else you aren't telling us.
 
Well it is having a drive ability issue, everything will be going awesome then random it will start surging. to the point of rpm dropping to around 200 and barely running or not at all in the middle of traffic. Last time I drove it, I had to power brake at stop lights to keep it running.

My spark plugs are very black like the engine is running rich and I believe the carburetor is in ok condition. The quadrajet is running .073 main jets and .050 metering rods. I also put on a bran new fuel pump so we can rule that out. As well as I'm having a hard time passing emissions because of the engine running rich. To avoid anymore fees I dumped rubbing alcohol in the tank to pass. :doah:

The compression test was a piece of mind to get a idea of what shape the engine was in. I thought maybe it had low compression which was making it not combusting the proper amount of fuel.
 
I would start by looking at the choke to make sure it either isn't sticking or somehow coming on when it shouldn't. Next I would check fuel pressure, a carb doesn't like more than about 6-7 psi otherwise it can hold the needle and seat open and flood the carb. Also, keep in mind that once a spark plug fuel fouls it will NEVER fire correctly again.
 
I have tried driving with the choke unplugged and plugged in (electrical) But if my memory serves me correct the choke can still function without haveing +12v.

I thought maybe the fuel pressure could be messed up so I warrantied out my pump, granted that's not a proper test but it could have ruled one out. I need to find a way to test it's receiving the correct psi.

Once It started doing this I changed the plugs out and they very quickly went back to the recent condition of being black.
 
I would physically wire the choke open so there is NO CHANCE of it closing at all. If this doesn't work then i'll bet there is something wrong with the carb itself (plugged passage or something along those lines). Did this start doing this all of a sudden?
 
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