engine raps on when cold start

[licketysplitbob]

when starting my 3100 V6 i hear what sounds like noisey lifters rapping for a short period untill engine warms up. it then runs extremely quiet. have changed oil, belt in good condition. noise does not sound as tho its belt tensioner. has 70k miles was well cared for.

[86TATpi]

What weight oil are you using? And what's the temp like where you live.

[richtazz]

if it's not a harsh metallic sound, it's probably just lifter clatter, which is normal in 3100's. If the noise is harsh, it could be piston slap, which is a bad thing.

[licketysplitbob]

thanks for your replies..im not sure what weight oil was in the engine as i just purchased it used from a private seller whose mother in law owned and serviced at pontiac dealer alltho i have since changed to quaker state 10w30 and still makes noise. i live in Massachusetts and the temp was 40 degrees (car sitting outside all night) when i started it. i did hear the noise slightly less after it had sit about 3hrs and restarted it.
the noise is not harsh but sounds like mild knocks/taps as if you rapped the handle of a hammer on a wood table and goes away shortly when beginning to warm.
would synthetic oil like mobil1 stop this?

[carnutcass]

The injectors are fairly noisy on my wife's 3.4 Pontiac Montana when you start it up in colder weather. I'd bet that what you're hearing. Check your oil often to make sure you aren't burning any. Also, look at your old oil next time you change it to make sure you don't have unusually large amounts of metal shavings, indicating excessive wear. My bet is on the injectors though.

Careful with switching to synthetic oil if your engine has some miles on it. Some people have problems with leaks after switching to synthetic oil.

[licketysplitbob]

if its the injectors making the noise is there any way of correcting this such as using fuel injector cleaner? will it get worse and cause more problems?

[DoberManJT]

IF you use any fuel system cleaners that are added while filling up your tank keep on thing in mind - DO NOT do this without changing or having a fairly new fuel filter. If your fuel filter is grimy and clogged putting in a "fuel cleaner" will travel from the tank through the filter, loosen all that old crap, than carry it into the rest of the fuel delivery system. So technically one of those five-or-six dollar fuel cleaners could cause some serious clogging. Change the fuel filter if you think it's never been done, and with a new filter installed use a pour-in cleaner and it'll work great. Take it from someone who learned the hard way...

[DoberManJT]

Oh, and in regards to your oil question - I also have the 3100, 5W-30 is the recommended oil weight, going by the manual, whereas the GT and GTP are recommended as using 10W-30. I switched to Mobil 1 synthetic oil at 30k and have had no leaks since, and that was 34k miles ago.

[licketysplitbob]

good point-i will change the fuel filter first...where exactly is the filter located and is it fairly easy to change-ive learned alot about how things work but always have local mechanic do it.

[carnutcass]

You didn't mention what year your car is so I'll assume it's '97-'03. Your fuel filter is beneath the vehicle, slightly in front of the rear wheel on the left side of the car. Make sure you depressurize the system before you start wrenching.

To depressurize the system I remove the fuel pump fuse and crank the engine. Someone on the board mentioned once that you shouldn't do this.......however, I've always done it this way, never had a problem, and have seen this procedure in print in several of my previous car's service manuals.....including my '96 Bonneville. I'll check the GM service manual tonight to see what procedure they recommend.

[licketysplitbob]

my gp is a '96, is the fuel pump mounted in the same area?

[carnutcass]

Hate to admit it.......but I don't know. I'd bet it is though. My '96 Bonneville had it in the same basic location, except it was on the passenger side.