So as usual I'm back with a problem, after I started my car today and about 10 seconds at idle it started making this thumping noise from the exhaust and the boost gauge showed it creeping up out of vac toward the 0 mark when I wasnt even touching the gas peddle and it didnt sound like it was revving...after I revved it once or twice the problem went away completely but I've noticed it happen a few times before....please let it not be an expensive repair again:-(

I dont think it was boosting, i think you had late ignition in the exhaust manifold. there are about 70 different causes...lol

If it doesnt come back then dont worry about it. If you havent done so, do a tune up!

I dont mean it was boosting....just the boost/vac gauge was showing it mysteriously climbing toward 0

It's done it a few times now this is about I guess the 4th or 5th time always right after I start it and always goes away right after I rev once or twice

so I guess I'll change the spark plugs and wires? or...?

I am not sure........sounds kinda like its fuel/ignition related but its hard to tell without seeing it. Since reving it corrects it, Fuel/ign sounds about right. Any black smoke out of the tailpipe when its running like shit?

I am sure your vac gauge is correct, i dont think that is reading wrong.

I wonder if you have lifters collapsing. If two Exhaust lifters are collapsing, then at cold startup will be thier lowest point. Your almost on a dead cylinder and that will cause the cylinder to back up into the intake resulting in a poor vaccum. Reving it would increase oil pressure and raise the lifters to operating preload.

Will it do it if you leave it sit for 5 minutres or only cold?

Edit: lets analyze this in a different angle as well. Ignition timing is directly related to engine vacuum. As ignition advances or goes up, vacuum increases. As ignition retards or decreases, vacuum decreases. When ignition decreases enough, the combustion process is allowed to happen during the exhaust stroke. This could very well cause a poping in the exhaust manifold or the thumping you describe.

what would cause the ignition to retard that much? What sensors affect ignition? crank angle, cam angle, map, coolant temp. What else? Cam timing will affect it. I am willing to bet you have an engine code from this event. Check that out and make sure the CEl bulb works too. See if you can get the computer scanned to see the values of the sensors and make sure they are operating correctly.





Terry

Check your CTS and MAP sensors. Possibly O2 sensor as well. I had horrible low vac and the same "thumping" you described a couple years back and it was due to a faulty CTS and a failing O2 sensor. Fucks with your timing causing a low vac. situation.

EDIT: Damn Terry snuck back in and suggested the same thing. ha.

just replaced the O2 sensor about 2 weeks ago and it definately ran better but obviously that didnt stop the thumping/climbing I do have a CEL that occasionally comes on but goes away after 2 or 3 drives

Thats your key right there......have it scanned and see what it is

Its still in the computer, its just not currently happening so its not throwing the light.

Hmmm..

YouTube.com

Is this what it’s doing???

no that's not what its doing....fantastic cameramanship though ;), when I took that video it wouldnt hold itself at idle so I had to keep it revved via the accelerator, took off the FCD and it ran perfectly and still does other than this problem...

Originally posted by Star Turbo Talon
I wonder if you have lifters collapsing. If two Exhaust lifters are collapsing, then at cold startup will be thier lowest point. Your almost on a dead cylinder and that will cause the cylinder to back up into the intake resulting in a poor vaccum. Reving it would increase oil pressure and raise the lifters to operating preload. Will it do it if you leave it sit for 5 minutres or only cold?

is that a fancy way of saying my engine is about to go byebye?


so I take the car to autozone and have them check the CEL again? that's it?

Eh, thats just speculation at this point. Go after the CEL first.

one more thing I noticed but didnt think of until now....when I first start the car (when its not doing the weird thumping/climbing) the boost/vac gauge needle jumps up and down between 20 vac and 15 vac once every second or so and that too goes away once the car warms up or revs a few times

So heres an update, I went to Autozone to get my CEL checked it still said front and rear O2 sensors were defective I guess I didnt reset the thing good enough last time so I unplugged the battery, CEL went away and seems to have stayed away, I notice that after started when its warm (like starting it to come home from the store or something) the car starts to lose power around 3k RPM unless I go WOT once I reach that RPM (EDIT: In other words when I accelerate nice and easy like 1/2 or 3/4 throttle, so I dont think its fuel cut) ...this is really starting to confuse me but at least its drivable now

The jumping needle indicates a valve issue, which could also be a lifter going bad.

Loosing power can be either lean or rich condition. When you lose power does your vac change?

why would the valve issue stop after I get the car down the street though I dont understand sorry :shrug

I havnt seen any real change in vac when it loses power and my A/F gauge reads normal when it does and like I said it only happens after the car is hot and shut down and then restarted

FYI - Failed/Failing CLT typically reports below freezing temperatures to the ECU, which causes it to continually run a warm up/enrichment program. In situations like this, the car can run better when it's actually cold, but living in Arizona, where we're still seeing temps into the 90* range on a daily basis, the ECU trimming fuel as if the coolant is below freezing can result in rich conditions due to the hotter, less dense intake charge. Run too rich too long and I suspect you can coat your new FHO2S with enough soot that they're ineffective to boot.

Beyond that, the CLT is often the cause of all sorts of random, annoying, bullshit gremlin type problems. They're like $20 at Autozone. You want the one with the two wire connector on it. The one with the single, spade connector is only for the gauge in the cluster and has no other function.

Originally posted by DR1665
FYI - Failed/Failing CLT typically reports below freezing temperatures to the ECU, which causes it to continually run a warm up/enrichment program. In situations like this, the car can run better when it's actually cold, but living in Arizona, where we're still seeing temps into the 90* range on a daily basis, the ECU trimming fuel as if the coolant is below freezing can result in rich conditions due to the hotter, less dense intake charge. Run too rich too long and I suspect you can coat your new FHO2S with enough soot that they're ineffective to boot. Beyond that, the CLT is often the cause of all sorts of random, annoying, bullshit gremlin type problems. They're like $20 at Autozone. You want the one with the two wire connector on it. The one with the single, spade connector is only for the gauge in the cluster and has no other function.

What's a CLT so I know what to ask for? :P

(Nevermind figured it out)

Go back and read what i explained about failing lifters.

so if i was going to repair the valve/lifter problem...how difficult would it be? how much would it cost more importantly?

No way to tell without knowing what the exact problem is.

First thing would be to pull the VC and start it up cold and watch the valves while it acts up. Your looking for one or a couple not moving like the others.

Terry

wouldnt that spray oil all over me? lol

How do you think v-8 rockers are adjusted?

no idea I have a 4 cylinder eclipse :P