Chevy & GMC Vans

Failed AGAIN

Before the test:
Replaced all plugs (3&5 were completely crusted over all others were clean).
New AcDelco O2 sensor.
Changed oil (put in 20W50 (the usual) and 1 bottle of No Smoke/No Leak) (Oil PSI is waaaay up there.)
Set timing 2-3* after TDC ( I was having bad pinging/knocking).
Ran 1 whole can of Seafoam thru a vac line.
Put 3 cans of Seafoam in the tank with premium grade gas.
Ran the tank out and refilled with premium gas for the test.
Engine was at normal temp.

25/25 Test
Item / Allowed / Actual
HC / 184 / 205 fail
CO / 2.29 / 0.28
NO / 1195 / 247
CO+CO / 6.0min / 14.6
RPM / 2500 max / 1300

50/15 Test
Item / Allowed / Actual
HC / 188 / 207 fail
CO / 1.69 / 0.36
NO / 1300 / 269
CO+CO / 6.0min / 14.6
RPM / 2500 max / 1327

Ya'lls thoughts ????

is this on the 1990 astro?

for shits and giggles run normal gas cause thats what the engine was bult for and a premium gas actually burns slower not faster so maybe its not buring completetly causing your hc (hydro carbons aka unburnt fuel) to come out the tail pipe.

92astro wrote:is this on the 1990 astro?

Yes

knucklehead wrote:for shits and giggles run normal gas cause thats what the engine was bult for and a premium gas actually burns slower not faster so maybe its not buring completetly causing your hc (hydro carbons aka unburnt fuel) to come out the tail pipe.

Hummmm

I had planned to use the premium fuel with 2 bottles of octane boost and then push the timing to 3-4* btdc.
And then do a re-test.
Theory is to get more fuel burned by early timing and the octane to reduce the pinging/knocking.

When I was viewing the timing, I did not notice spark scatter.

No matter how much it pings/knocks it does not throw a SES.
Sometimes when it is really ping/knocking really bad I can observe black smoke from the exhaust.
Still no SES.

I have previously replaced the knock sensor and the distributor.

But then, I'm not to sure about applying advice from someone who's logged in as "knucklehead"

Water Boy wrote:

knucklehead wrote:But then, I'm not to sure about applying advice from someone who's logged in as "knucklehead"

hahaha very funny. to give my thoery a leg to stand on i am a first year automotive technican (aka mechanic but doesnt is sound better?)

on early vans the cat is mounted slightly too far back so it runs slightly cool. The correct testing procedure is to rev the van up in neutral for about a minute then let it idle for a minute or two then repeat. The idea is to heat the cat up to the temp is should be running at. If you get the cat nice and hot before you go in you should pass.

Another person suggested to run the test in D not OD.

Maybe more heat for the cat huh ? ? ?

But, most people here are missing the point. Like Knucklehead said, HC is a product of unburnt fuel, has little to do with the quality of the cat. Rich would be CO. First thing I would do is, the basics, a correct procedure for a compression test. For one reason or another unburnt fuel is entering the cat. Not a rich mixture.

I just saw the miles, you have a dead engine dude.

good lord 550k+km i think a V8 is about due

mikedamech wrote:I just saw the miles, you have a dead engine dude.

Shuuuuuuuu
Not so loud.
She doesn't know it yet.

I was out delivering water in the van today.

Cobra wrote:good lord 550k+km i think a V8 is about due

When I buy a case of 20W50 I double the value of the van.

I buy gas 3-4 times a week, the pumps stops at $75.00 (75.1799805 Canadian) before the tank is full.
And it has the crappy paint job.
and ......the list can go on.

mikedamech wrote:But, most people here are missing the point. Like Knucklehead said, HC is a product of unburnt fuel, has little to do with the quality of the cat. Rich would be CO. First thing I would do is, the basics, a correct procedure for a compression test. For one reason or another unburnt fuel is entering the cat. Not a rich mixture.

So, there is a difference 'tween raw fuel and unburnt (rich) fuel

Sometimes my mind can't wrap around the simplest theories.

OK, for you visual people....


18,000 miles (28,968.192 Canadian) on 3+5 35,000 (56,327.04 Canadian) on 1,2,4,6


Close up of 3+5