420A: stock compression (test results)

necrotopsy · 06-16-2012, 09:47 PM

my car is at my mechanics. failed fuel injector and a broken spark plug (the piece of metal that curves over the electrode broke off).

He had said in passing that "you got 125 compression across the board, so looks like the engine is fine"

but after looking it up, it looks like stock compression should be 210?
does that make sense?

i seen that 210 was for a "DIY" compression test, so i was wondering if a compression tester that mechanic would have would display a different reading.(i know this isn't likely, but my mechanic, who i trust, acted like 125 was good. but then again maybe he had the wrong information on what it's supposed to be. or maybe he mean 225. really just grasping at straws here.)

misc info:
180k miles on engine
basic bolt on's (cai, full aftermarket exhaust, msd coilpack and plugs)

bryanwheat · 06-16-2012, 09:59 PM

125 psi is very low for a 420a.

Alan11 · 06-16-2012, 10:04 PM

It does not have to be 210, but I believe 125 it is a little low for a 420a.

necrotopsy · 06-16-2012, 10:05 PM

i'll call him up monday and talk to him again. keep my fingers crossed i heard him wrong, or he said the wrong numbers.

bullettdsm · 06-17-2012, 03:07 AM

Figures should be between 175-220, with no more than 15psi between cylinders. The lower service limit is 100psi.

You are getting down there. Might want to start planning now.

MB

My1GLaser · 06-17-2012, 04:02 AM

Was the engine at operating temp or cold when he did it?

Josh97eclipse · 06-17-2012, 08:26 AM

That is real low. I had a 185xxx motor with 210 compression before i swapped my built motor in. As MB said might wanna start planning a rebuild.

necrotopsy · 06-17-2012, 12:09 PM

let me put it this way...
at first i thought i had a broken valve and piston, so i sent it to him to look at it.
if it had in fact been a broken valve and piston, i would have stripped the car and junked it.

i'm driving this car until it wont drive anymore (smaller repairs not withstanding) then stripping it for parts.
i can't afford to do a rebuild.

jayson427 · 06-19-2012, 05:51 PM

i would put some lucus in it and sell it while you can man 125 is defintely low

spadepro22 · 06-19-2012, 06:06 PM

Quote:

Originally Posted by jayson427

i would put some lucus in it and sell it while you can man 125 is defintely low

Why put that on someone else? I think its just wrong. Just my thoughts.

DSMTyson · 06-19-2012, 06:10 PM

Quote:

Originally Posted by jayson427

i would put some lucus in it and sell it while you can man 125 is defintely low

You are obviously a complete douche if you are advising him to cover up the problem and pawn it off on someone else....

Wow dude, just wow

Karma's a bitch.

------------------------------------------------------

Yeah, 125 is really low. Just drive it till it won't run.

jayson427 · 06-19-2012, 06:27 PM

you guys are lame i said lucus so he can actually drive his car longer then a month. did i say hey cover it up and sell it to someone? what he tells someone is not up to me. the lucus was just advice to keep the compression up before he gets so much blow-by and his sensors clog up then he cant get anything for the car. if someone knows what they are doing they could pull the head off and fix the rings or valve seats and have it for a dd. so dont call me a douche

livedsm4g63 · 06-19-2012, 06:51 PM

So the sell it while you can theory doesn't apply as you stated? Hmm interesting.

Drive it till she goes! You can find a donor engine and swap it out if your mechanically inclined.

necrotopsy · 06-19-2012, 07:53 PM

talked to my mechanic.
125 was the correct number he gave me.
125 across all 4.

100 or below is when it gets too low and you start getting misfires and the like.

i'll drive it untill i can't drive it any longer, then part the SOB.
hate this car...

96' Eclipse GS · 06-19-2012, 08:02 PM

The car is not the "silver avenger" as your profile picture is it? I can't remember, by the way even if it is not, I feel for you man...

spadepro22 · 06-19-2012, 08:11 PM

I feel you man. I have low compression and if I cant find a great rebuilt one or someone to rebuild me one Im parting mines and ending this love hate relationship.

grothe3297venge · 06-19-2012, 08:35 PM

i'll drive it untill i can't drive it any longer, then part the SOB.
hate this car...[/QUOTE]

Chuckled when I read this, car is almost 20 years old.. Cant expect it to be perfect, but those low numbers if your giving up, start constructing a part out thread..

necrotopsy · 06-19-2012, 09:33 PM

and yes the car with 125 is the "silver avenger"

glowryder · 06-20-2012, 09:07 AM

Lol. why part it.. its not worth much.. we all know the avenger market is dead.. and the only ppl with money in have everything already.. IMO learn and fix it. or get out of cars.. this is the same crap you faced when you purchased the other boosted venge.. or buy a creat motor for it, swapping in and out os not hard, even you can do it. : P

96' Eclipse GS · 06-20-2012, 10:14 AM

Damn it,

That blows, I wish i lived closer. I would not mind giving a hand on it.

I love that color scheme & body add's!

I would just pull it & find another (2.0L) and get it running again!

Doug99RS · 07-04-2012, 10:30 AM

A day late and a dollar short but I'm sad no one mentioned checking the timing or allowing fuel-soaked piston rings as being a possible cause for consistently low compression numbers across the board. Granted, the mileage, history and such could be just cause for a rebuild but I was under the impression assistance in coming to a diagnosis should take precedent over blindly throwing a repair idea out there.

Timing that is off one tooth may permit the engine to both run and compression to be low. Performance would suffer and if the cam that is out is the intake but you may not get a check engine light (Crank sensor looks at crank, cam sensor looks at exhaust cam only). If it's the exhaust cam that's out or both then you'd probably get a cam/crank correlation fault code.

Anyways, good luck with the fix.

necrotopsy · 07-04-2012, 04:47 PM

i have the car back, and it runs perfectly fine now.
if a cam gear was off a tooth, wouldn't it idle funny? I don't have any idle issues, and has plenty of power still (as much power as can be expected for this engine anyway)

Doug99RS · 07-06-2012, 03:45 AM

If it were off a tooth and running then the idle may or may not be noticeably different. I've had a 4g63 NT off one tooth and thought it was right until the test drive. Lacked power but I was still able to drive it out of the shop. The vacuum was about 3-5 inches low once I got it back in trying to figure out what I had done wrong.

What was the corrective steps (if any) you've taken to get it back on the road and running better?

AlbeUrDemise · 07-11-2012, 09:05 PM

I know I'm new but for the sake of posting and for adding encourgment. I reccomend you learn to do the rebuild yourself, and save your money for parts. Best of luck with whatever descision you make.

necrotopsy · 07-12-2012, 03:50 AM

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.

Doug99RS · 07-12-2012, 09:07 AM

Quote:

Originally Posted by necrotopsy

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.

KC2RPM · 10-25-2012, 07:47 AM

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.

glowryder · 10-25-2012, 09:08 AM

^you do know you are posting in a 420a Forum....?^

necrotopsy · 11-14-2012, 11:29 PM

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.

Doug99RS · 11-15-2012, 06:27 AM

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.