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stock compression (test results)

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Doug99RS:

Valve cover gasket was replaced. Coilpack was replaced. One spark plug. that's it.
i dont think the coil pack that was on it was bad, it was an MSD coil less than a year old.
I think it was bad gas. I've been running 93 octane for about 2 weeks now, havent had a single issue with it.

but it's also been 105* temps here with very high humidity, i figured it would be safer to run a little higher octane since the intake temps will be so high.


EDIT**
i don't mean to say a mostly stock n/t needs 93 octane. it doesn't. but i was running 93 because i think i had a tank of watered down gas, so i wanted to even it out.

If the manufacturer programmed the engine computer to run off of 87 then the only reason to increase octane is in the event of spark knock/pinging. The modern fuel, regardless of octane, is just about equal from any given source. Now, some people may claim Chevron vs BP etc etc bu Chevron 87 vs Chevron 93 is going to be the same QUALITY gasoline regardless of octane.

Octane is not an indication of the quality but rather a rating on the gas' rate of burn. 87 octane will ignite and complete it's combustion quicker than 93. In the case of forced induction, nitrous and high compression the engine needs a higher octane rating because all of those mechanical conditions will have a tendency to ignite ANY fuel quicker than say a normal compression motor. To combat this issue the octane rating used in those engines is increased to slow the burn back down. Additionally, the computer is TUNED to the octane rating that is to be used in the vehicle.

When you increase octane ratings on a car that requires a lower rating, provided you're not trying to get rid of spark knock, then you cause the computer to have to modify it's fuel/spark strategy. You can increase carbon deposits due to improper burn and may even affect emissions and fuel economy.

Water is a totally different factor here. Water in any fuel is going to cause performance issues and simply upping the octane isn't going to do anything. Think of it more like... I dumped sand in to my gas tank so I'm going to up octane and that will make things better. It doesn't. If you suspect you have water in the tank then you need something like "Heat" or another additive that the vendor claims will help rid a fuel system of water.

If you only replaced one spark plug then you need to take a step back and re-evaluate your diagnostic and repair techniques. Plugs and wires should be replaced in sets of 4 unless the plug has say... 1,000 miles on it or something. Even then if you need to replace only one then you probably have a plug that has failed because of ANOTHER failure. I.E. Plug one is fouled because injector one is leaking fuel or valve stem seals for cylinder 1 are pouring oil in to the intake ports. Additionally, when contamination is present on the outside of the spark plug then it probably has contaminated the plug wire as well. Corrosion, oil, or carbon tracks are all examples of situations that cause damage to BOTH components. Replacing only one can lead to a repeat failure with near identical symptoms.
 
It sounds like the shop did a compression test on a cold engine. I have 125-130 compression on a cold engine with my 4g63 and when its warm its usually 173-185.
 
if anyone is interested...

i had got the car back, and a week later i got more knock, no power, misfiring. took it back to the mechanic, they couldn't find anything wrong. they drove it 30 miles or so (a few a day over 5 days) and couldn't get it to do the problem again. I got the car back, hasn't had any issues since (with this). 8k miles later (1200 mile trip to WI and back included)


And on the 93 Octane:
the reason i was using 93 instead of 87 for a bit was because 93 is more stable. the period for ignition is wider, less chance for pre-detonation and misfiring. That's all.
 
Just to clarify, the characteristics you mentioned regarding the fuel work both ways. In forced induction/high compression motors the higher octane i needed for those very reasons. In a motor designed for 87 octane the 93 octane will translate in to burn times that are too long, ignition/management systems that haveto work harder to completely burn the fuel off and increase emissions.

Like on the 5.2L Ram motor with a blown intake belly pan, it would spark knock with the 87 octane it was designed to run on. Increase to 93 and the knock went away. But there was still carbon on the piston tops and there was still a vacuum leak. The fuel simply masked the symptoms rather than fix the true problem.

You're right in your description of the fuel characteristics but there are some more details that needed to be pointed out so people don't jump on the high test bandwagon.
 
oh yeah, i was aware that 93 would just mask the problem (if it did anything at all). But at that point it was $0.30 extra for gas OR several hundred dollars in motor repair. LOL.


i went back to 87 shortly after that. No issues.
 
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