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I'm working on a 94 Z26 with the 3100 that has an odd problem. ÂÂÂ It seems to run well but if you take it to 4000 rpm in neutral (or under load) the engine starts to run real bad. ÂÂÂ Under load it backfires a little. ÂÂÂ When you let off of the accelerator it sometimes makes a 'bang' around 2000 rpm.  It's a loud metallic noise.

I haven't been able to pin-point the problem and it's driving me nuts.  It's got new plugs, wires, and fuel filter.

Any ideas?

Seems kinda odd any codes??
almost sounds like a bad lifter,push rod or rocker arm. even a broken or bent valve..
pluged or bad egr valve?? bad cat??  bad or warren out or leaky fuel injector or regulator gowing..
got me stumped
Mr Goodwrench

(Mr Goodwrench @ Jun. 19 2006,22:49)Q
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ESeems kinda odd any codes??
almost sounds like a bad lifter,push rod or rocker arm. even a broken or bent valve..
pluged or bad egr valve?? bad cat??  bad or warren out or leaky fuel injector or regulator gowing..
got me stumped
Mr Goodwrench
Yeah, it's a puzzler.

No codes so that's a bummer.

I'm thinking of pulling the top end and having a look because I'm thinking push rod or lifter.  Never thought about the rocker arm...good idea.

In neutral and park the 3100 is programmed to not go over an RPM that is close to 3500-4000.  You might look into that.

can you get it over 4000 rpm when driving?  Im thinking maybe the park/neutral switch or something else that tells the system its allowed to rev over 4000 rpm.

correct it does have a rev limiter in park an neut.  thinking 3,800 to 4,200 rpms.  it may back-fire a little
but it shouldnt be banging..

Mr Goodwrench

Sounds like a cat plugging up, or breaking apart to me.  Gotten a good whif of the exhaust lately?

(KFLO 93 GT @ Jun. 26 2006,11:30)Q
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ESounds like a cat plugging up, or breaking apart to me.  Gotten a good whif of the exhaust lately?
Yeah, that's what I'm thinking.  Even though it's only a year or so old, it certainly smells like a bad cat.  Phew.

if it only a year old and gone bad check to see if it has any warranty.  most cats have a 1-5 year on them..

Mr Goodwrench