is this a clogged cat?

[ed hess]

so mad mike brings his typhoon over cuz he has audible knock at 4 psi of boost.
Ok so one vac leak. fix that and road test, swapped 2 bar sensor, coil.
no change.
he had allready done plugs, wires, cap, rotor, fuel filter, pcv ok.
fp was ok and went up with boost.
So i wonder about clogged exhaust. vac gauge on mity vac drops with the slightest throttle movement, and needle flutters like mad when rpms go up to 2500, moving slowly.
Fo the heck of it i put my hand in front of the exhast pipe. doesnt feel like much flow. I compare it to my sy, yep not as much flow.
Bring rpms up to 2500 with my hand near exhaust pipe, and it feels like its pulsating.

Any thoughts from others who experienced a clogged cat?

ed

 

[smeagol]

needle flutters like mad when rpms go up to 2500

hand near exhaust pipe, and it feels like its pulsating


You know what i'm going to say, i won't say it.

 

[ed hess]

brian its not my truck. but i am trying to help out mike. So if its a cat please say it. Or whatever your thinking.

ed

 

[Jimmy]

It's the cat.

 

[Daron]

I'll say it....

 

[ed hess]

ok
So mike when you read this here are the answers to the possible cause of the problem:

1 brian knows but he aint sayin.

2 jimmy says its the cat, but maybe he's just playing with us since brian wouldnt say.

3 daron, posted some kinda cartoon picture that has the word ignition in it. This makes about as much sense as brian tellin ya to go fish.

so mike there ya have it, go fix your truck with that. Btw no charge for my time.

gotta love it

ed

btw anyone wanna give mike a straight up sincere thought. (hopefully jimmy was doing this)

 

[CLONE]

btw anyone wanna give mike a straight up sincere thought. (hopefully jimmy was doing this)

Ignition problem.

 

[smeagol]

Syty rule #1 If you see your tach flutter, you have an ignition problem

(most likely plug wire)

Syty rule #2 If you think you can do anything on the truck in a 1/2 hour, you are on crack. Dedicate the evening or a weekend to the job.

 

[ed hess]

brain
I didnt say tach flutter. The vacuum gauge on the mity vac had flutter!


ed

 

[Mad Mike]

Brian, What Ed is saying is the mity vac was fluttering and the exhuast pulsates almost like a igintion miss. I just changed the the plugs, wires cap and rotor and there was absolutely no improvement or change. The truck is completely stock except for ATR exhaust. With even the slightest throttle you can hear audible knock. Can you look at a diacom file for me? Maybe something will jump out at ya. Thanks.

 

[ed hess]

brain
yeah like mike said, besides that at idle it didnt have hardly any flow against your hand compared to mine.

ed

 

[smeagol]

Sorry, when you quoted needle & rpm in the same sentence, I assumed you meant tach.

I don't think it is cat related, regardless.

Fluttering of any type still leads me to say ignition issues though.

 

[ed hess]

hmm

wonder why the amount of flow at his tailpipe is so radically less than my truck?

ed

 

[Mad Mike]

To update. Rechecked the sitting of prom in ECM, rechecked timing and pulled off the cap and rotor and it still looks brand new. Only igintion part I did not change was the ignition module.

 

[ed hess]

screw it mike, pull of the cat and take a look. knock at 4psi and no flow out the exhaust. Or goover to meineke ask them to pull it and give you an estimate. If its clamped on they may check it for a nominal fee.

ed

 

[Blake]

Stole this from another site. I'm looking for more info for you guys.
clip-->
But, how do you know when you have a problem? Lets look at some readings you will likely see if there is a problem.

The gauge needle fluctuates from 15-20in./Hg rapidly at idle.
This would indicate a sticking valve or ignition miss.

The gauge reading is low but steady and reads between 15-20in./Hg
Indicates a late ignition or valve timing, low compression, stuck throttle or a vacuum leak.

The needle fluctuates as the RPMs increase.
Weak valve springs, worn valve stem guides, or leaking headgasket.
A clogged catalytic converter may also cause this condition.

Gradual drop of vacuum at idle.
Choked muffler or obstruction in exhaust system.
A choked muffler will exhibit a slow vacuum decrease to ZERO at idle.

Vacuum gauge needle drifts.
Minor intake leak of the manifold or bad fuel injector O-rings.

The needle stays steady but then drops regularly and recovers only to repeat.
Burnt valves or improper valve clearance adjustment. The needle will drop when the defective valve operates.

The needle vibrates excessively at idle but steadies out as the engine RPM is increased.
This would indicate worn valve guides.
<-- end clip

More stuff:
http://www.iwemalpg.com/Vacuum_gauge.htm
http://www.ifsja.org/tech/motors/vacuum.shtml
Blake

 

[ed hess]

>>>The needle fluctuates as the RPMs increase.
>>>Weak valve springs, worn valve stem guides, or leaking headgasket.
>>>A clogged catalytic converter may also cause this condition.

the vac gauge needle was rock steady at idle and began fluctuating as the rpms were grdaully raised.

 

[smeagol]

Does the truck feel normal when it drives & accelerates?

Have you tried another EGR valve?

Did plugs look normal when swapped?

Has anything you've done yet produce *any* change, for better or worse?

 

[Blake]

Look at some of those other sites I posted. They have more in depth analysis of vac readings vs. throttle changes,engine warm,engine cold,cranking with ign disabled, etc.
This is just a single tool though. Sometimes you have to do compression leakdown tests and such to narrow it down without having to tear everything apart. Of course your cost of tools starts to increas also :-?
Added some more plagerism:

d. testing for blocked exhaust

idle speed reading slowly dropping toward zero indicates exhaust restriction.
excessive backpressure in exhaust then indicated by reading not increasing quickly to about 16 in Hg when engine speed slowly increased to 2000 rpm.
backpressure also indicated by reading not dropping as quickly when throttle quickly released and remaining 5 inHg higher or more than normal.
disconnect exhaust manifold from engine and retest. If problem disappears exhaust system is blocked.
to locate restriction reconnect exhaust system one unit at a time testing after each until problem reappears.
Blake

 

[Mad Mike]

Does the truck feel normal when it drives & accelerates?
Yes and no, yes drives and accelerates fine except I can hear and see (diacom) knock.

Have you tried another EGR valve?
no

Did plugs look normal when swapped?
yes

Has anything you've done yet produce *any* change, for better or worse?

Nothing better or worse - no change at all