1MAX2NV

iTrader: (5)

What's the procedure? I just need to check the compression on one cylinder since that's the only one that seems to run lean on. Here are the pics of spark plug from cylinder number 4.

http://public.fotki.com/1max2nv/1max2nv/engine/

subs1000w

pull all plugs, screw in compression tester, open the throttle all the way and turn the engine over 3-5 times

Bags

iTrader: (3)

Man I hope the tip of the plug broke off AFTER you removed it..

and it's white..


Just disconnect EVERY coil pack, Plug the tested into the cylinder you wanna test and crank it 7 TIMES.

Then read the result and your done

Bags

iTrader: (3)

Do you need to open the throttle ?

I have not heard that and that is not the way I have been doing it.. man I hope I have been doing it correct

subs1000w

i read somwhere that you could get a lower reading with the throttle closed

teejnut

iTrader: (8)

I heard that you should open the throttle for a better reading as well...

wow... did that tip break off in the engine?

iansw

iTrader: (7)

I pulled a plug out of a 91 300zx TT my buddy bought with only 26k miles on it.

The guy who owned it before had the turbos turned up from the stock 9PSI to 18PSI with no other modifications except exhaust.

Strangely the engine survived the abuse and after replacing the plug runs fine. The Turbos are blowing out oil into the exhaust because the seals are blown however.....he's doing an Turbo rebuild now.....

(Moral of the Story - sometimes a good deal isn't really a good deal)

IanS

1MAX2NV

iTrader: (5)

It didn't break off. It melted off. I don't know how I ran lean in just that one cylinder. It might have happened previously from a nitrous run I did. I'm going to double check the fuel delievery to that one cylinder and see if I can pinpoint the cause.

Bags

iTrader: (3)

HOLY SHIET!


Which clyinder BTW?

nismology

iTrader: (8)

#4 from the first post...

1MAX2NV

iTrader: (5)

Number 4. Anyway, I replaced the spark plug tonight but I didn't drive the car yet. I'll do the compression test tomorrow after I go buy the gauge.

nick

iTrader: (10)

make sure the engine is at operating temperature before doing compression test, if not the results won't be accurate.

Nick.

ejj

iTrader: (5)

FWIW, I've gotten the same readings with a warm engine, cold engine, open throttle and closed throttle.

I don't think it makes a whole lot of difference.

Stephen Max

iTrader: (59)

I've gotten slightly higher readings with the throttle open, and engine temp didn't seem to make any difference.

You really want to check all your cylinders, since variation between cylinders is important, too.

My last check I did I got 197 low and 205 high, the other four were right at 200. A little high, but not bad for 140,000 miles.

1MAX2NV

iTrader: (5)

If I do get good compression reading, would it be worth it to get a leak down test done by a shop? I know a leak down test can pin point where the cylinder is loosing compression but what test can I do to see if my piston surface is still good.

Stephen Max

iTrader: (59)

If you are looking for detonation damage, then the only thing I can think of (other than a teardown) is to use a borescope (also known as a boroscope) to look at the piston surface.

http://www.tooldesk.com/shop/borescope1.wml

But if your compression is good, why worry about?

MardiGrasMax

iTrader: (14)

Warm the car to normal temp, leave it running at idle, pull the fuel pump fuse while its running to get all fuel pressure out of the fuel system (very important to prevent wash down which will result in low readings), pull all plugs, throttle open, crank till the reading stops climbing, 10-15 for me. What I discribed is the short version of the FSM procedure, thats how I do it.

nick

iTrader: (10)

this is the only way to do it right !

Nick

1MAX2NV

iTrader: (5)

I don't want to sound lazy...okay...I am. Do I have to pull all the plugs? Can I just pull the one I want to test and just disconnect the coil packs for the rest?

Stephen Max

iTrader: (59)

Yes, you can do that. But if you get a number that is marginal, like 160 psi or so, you're going to wonder if that is due to damage to that particular cylinder or are all your cylinders low? If you get 185 or above I guess you can stop.

But really, it only takes about 30 minutes to do them all, and you should be monitoring cylinder compression and spark plugs pretty frequently anyway to keep track of the overall health of your engine.

1MAX2NV

iTrader: (5)

That's true...I'll just do all of them. I put some 1 step colder plugs in there last night but I should change them out for 2 step colder while I'm at it. Thanx of the advice everyone and I hope that one cylinder survived.

Jeff92se

iTrader: (82)

http://www.cybrrpartspro.com/Chilton...61CH03_26.HTML

1MAX2NV

iTrader: (5)

Looks like I did some damage to cylinder number 4.

205 205 205
190 180 190

I found out why it ran lean. It was the short nitrous test run I did. There was a small spec of something that blocked the fuel jet for cylinder number 4. I was getting at the most 50% fuel to that cylinder due to the blockage.

iansw

iTrader: (7)

I think you're OK man - that's not a horrible reading.

Still well within spec.

IanS

Stephen Max

iTrader: (59)

Yeah, it's definitely not worth doing an engine swap over. Unless you want to, of course.

1MAX2NV

iTrader: (5)

I learned a hard lesson. I'm going to start chaning my fuel filter every 20K miles. I don't believe I have a fuel solenoid filter so I'm going to add one.

MardiGrasMax

iTrader: (14)

I bet if you put some mile on the motor the reading will pick up a bit. Wear back in, if thats possible