MySunset350Z

iTrader: (23)

i was having problems with my engine making a clunking noise on warm starts. somone brought up that i should do a compression test.

i just finished getting all the readings and i noticed that i have a 15psi difference in one of the cylinders. i retested 2 times with the same results.

is that normal?

im not sure what the numbering system is on the cylinders but heres what i got.

westpak

iTrader: (19)

Well 185 is standard and minimum is 142 and it says that max difference between cylinders should be 14, so even though your drivers side seems low you are still OK. Did you follow the proper procedure and follow up to verify lower readings per the manual?

Not sure how a compression test would diagnose a clunk though.

westpak

iTrader: (19)

Here is proper procedure from Manual.

JCat

iTrader: (4)

Please explain your problem in more detail.

I noticed a nitrous bottle in your trunk. What size shot are you running?

g356gear

iTrader: (12)

Have you checked your oil for metal. It almost sounds like you may have a main bearing problem. When the engine is hot the oil is thinner...if you pounded a bearing from nitrous use then it would clunk when hot and be quiet when cold. If the motor makes the clunking sound consistently when hot you can disconnect the coil pack from each plug one at a time to see if the knock goes away. That will tell you which cylinder is having a problem. Worth a try.

Sharif@Forged

iTrader: (92)

I wouldnt worry with that one 15psi difference. Might just wanna recheck sometime in the future. I'd say your engine is in decent shape.

MySunset350Z

iTrader: (23)

thx for the info westpak, i did follow those exact procedures. except for disconnecting the fuel pump fuse. forgot about that.

last time i ran nitrous was 7/28/04 and this problem just came up about a month ago. i was running a 125 shot dynoed slightly rich.

a little more backround info. this problem of clunking started happening about a month ago. when the engine does make that sound, the whole car shakes slightly as if something got wedged in the engine. it only happenes when the car is in park and on a warm start. never on a cold start.

as for metal chips. there was some metal on the spark plugs. very very tiny pieces but they were there and you can easily see them.

would i damage the engine if i disconnect the coil pack while the engine is running? can i just disconnect the power clip that connects to the coil pack instead?

thanks for all the help. its very appreciated.

Sharif@Forged

iTrader: (92)

why would you want to disconnect the coil pack while the engine is running? That would not be good...but doubtful it would damage anything.

MySunset350Z

iTrader: (23)

g356gear, you said to try disconnecting each coil pack to c which cylinder is causing problems.

did i misunderstand something?

g356gear

iTrader: (12)

would i damage the engine if i disconnect the coil pack while the engine is running? can i just disconnect the power clip that connects to the coil pack instead?

If you disconnect the clip from the wiring harness to the coil pack when the engine is running then that will stop the ignition spark from going to that cylinder. That piston/rod will just be along for a free ride....no damage done. If there is a bearing problem then the rod will knock when the ignition fires the fuel mixture. If you disconnect the coil and remove the spark you wil get no ignition and no pressure of the piston and rod down on the crank....and no knock. You will be able to tell right away if you connect and disconnect the coil clip and the knocking comes and goes with the firing of the sparkplug. You may get a check engine code but just reset the ecu after the testing.
If you had metal on you sparkplug and it was noticeable to the naked eye then you had a detonation event. That aluminum is from the top of the piston. You may have damaged a ringland or burned a valveseat in that cylinder with the lower compression. That would explain things.

MySunset350Z

iTrader: (23)

thanks for the in depth info. i will try unplugging the clips tomorrow night hopefully.

why do damaged ringland and burned valveseat sound very expensive to fix? lol

g356gear

iTrader: (12)

unfortunately to tell for sure the head has to come off

etx

Hey man, if your ever around Canton or Southfield (where i work) get a hold of me and i'll take a listen to it. What kind of plugs are you using, and what kind of oil? Stock fuel pump?

MySunset350Z

iTrader: (23)

etx, where do you work? when? call me. pm sent.

im using denso 2 step colder plugs. i've been using mobil1 full synthetic for about 15thousand miles. i just switched back to the usual stuff today when i changed my oil. not sure if that helped though. i am using the stock fuel pump.

MySunset350Z

iTrader: (23)

a quick update.

the clunking i've been hearing has died down to maybe 10% of what it used to be at best. i used to feel the car shake with every clunk, but i notice that im having to roll down the windows just so i can listen for it. the car used to shake with every clunk and trip the CEL atleast twice a week. the car doesnt shake anymore and the CEL hasnt been tripped since i got the oil changed back to the non synthetic stuff. (almost 5 days ago)

am i losing it or what? im gonna wait a month and then recheck the compression to see if theres a difference.

what do you guys think?