Some Car Troubles

[GeorgeS]

Not motorcycle, but Mechanical, if you have a Chevy. Might be of interest.

I have been battling a power loss, bogging down, problem on my 2003 Chevy Blazer, V6, 4WD. For about the last 4 months. ( has 104,000 miles on it )

It started bogging down, would not go over 30 MPH, about 4 mo ago. Research indicated that CAT, was a prime suspect. So I pulled it out, it looked OK, clean, and could see thru it. So I Replaced it with aftermarket unit, and a new muffler.

Did not fix problem, so it progressed to replaceing fuel pump, fuel injector sypder, a rebuilt distributor, MAF, MAP, Throttle position sensor, idle air control, Plugs, Wires, Rotor, Ignition electronic unit, Ignition Coil, fixed a few small vacuum leaks, replaced gaskets on intake plenum. Eliminated all vacuum hoses, as to being bad.

Ran lots of Sea-Foam thru fuel, and some in oil. AND A NEW COMPUTER, --- NO HELP

 

All NO Help. As the last 3 months progressd, problem got worse, and the Intake Vacuum, would only hit, about 12 inches, and was decreasisng and got down to 5 inches 4 days ago !! What the heck is going on ???

 

--- Last week, I decided to change timeing chain, from supposed expert advisor, did not help at all. !!

 

--- In desperation I pulled the intake plenum again, and pulled the Intake Manifold !!

AH HA, Bad gasket on right side of intake manifold, At least is looked pretty bad, so maby Anti freez getting into cylinder, Replaced with new gasket set. NO HELP !!

 

I did find that the Throttle Position Sensor, Return spring did not work, and new one did. --

 

Also, replaced Crankshaft Position Sensor- No Help

New Distributor also has a new CamShaft position sensor, no help.

 

At this point I am thinking, it looks like will have to be pulling the heads OFF !!! ?? BUT, I ain't buying that as yet.

 

I redo Engine compression test all cylinders, Dry, and with Oil added. Only One cylinder is below 200 lb. compression with oil squirted into plug hole ????

I pull valve cover to look at valve springs for the cylinder with low compression springs, all look OK. ( Only 180 PSI wet, on cylinder #3 )

 

OK, Yesterday I quit working on it, with ONLY 5 INCHES OF VACUUM, AT IDLE OF 600 RPM !!! ????? Engine will now only run to about 800 rpm and die out, NO VACUUM in intake . No leaks, Tried Propane testing, Nothing happened.

 

--------- OK, last nite I'm researching internet, and find reference to something called a """Pre-Cat""" on Chevy's and other vehicals. What the heck is that???? say s I , I know about the CAT, but my Chilton Manuel for Chevy S-10 Says nothing about a Pre - Cat. ????

Then I remember the fat spot, in exhaust header 4 1/2 Dia, 7 inches long. !! Hmmmm ?? Sooooo, this morning I cut a hole in it, and peak in !! Wa La , its Empty, looks like a resonator, Hmmmmmm ??? Clean as a whistle in there !!

 

So I pull out the new CAT, that I installed, 3 months ago---- guess what, The Guts from the Pre - Cat, and completely ( well almost ) plugging up the CAT !!!! Engine No Can Breath !!! Cause Exhaust can't get OUT the rear end ! Ah Ha !!! ( Time for a Beer !! )

 

No Can Make Power !!!!

 

Point in Case------------ If you have a Pre - Cat, on your car or truck, it, can Self Destruct, and dump lots of crap into your main CAT, and plug it up, and pretty soon you are dead in the water.

 

I know, this is a " Boreing Story " !!! But what the hey, nuttin else to talk about, Rideing season is almost over. So now you all know my sad Catalic Converter Story !!!

Sunshine in Seattle tomorrow, Going for ride, as soon as the NEW CAT, is Installed !! In the Old Chevy ---- :whistling:

 

P.S. And in the middle of all of this, the Radiator Started leaking, had to replace that !! ( not related to the main problem )

But noteworthy Ha Ha Also, yesterday the water pump started leaking, but I can Fix that !!!

Edited October 1, 2014 by GeorgeS

[Flyinfool]

WOW

You almost paid for a new engine with all of the parts you tried.

[Guest divey]

As I was reading through your story, I had your problem solved only because I went through something similar albeit with an older model Chev. I had a 1975 Impala that always ran like a top until one day we were heading out on holidays (when else do things go wrong) and I lost power and couldn't get much over 30 mph. Stopped on the roadside, turned it off, started up again and it ran fine. Same thing happened a few more times along the trip and a couple mechanics who looked at it were also suggesting some expensive fixes.

 

When I got back home, I took it into my local mechanic. He put it on the hoist, took a large flat head screwdriver out of his tool chest and commenced to knock out the screen that was inside the end of the tail pipe. Started the car back up and a bucket full of rust came flying out the end of the tailpipe. The screen (allegedly put in there by the manufacturer to prevent critters from crawling inside) was blocking rust bits and gunk from inside the muffler and tail pipe assembly thereby preventing the engine from exhausting properly. Problem solved.

 

All the resident experts who were hanging around the shop that day immediately went out and did the same thing to their vehicles! I don't see those screens in the newer vehicles but many of the older vehicles had them in. Doug

[Eck]

I read your story and your right.............its time for a beer.....

[djh3]

I have to laugh a little. I read about 4 lines or so down. shortly after the replacing CAT muffler etc I'm thinking "this sounds an awful lot like a collapsed inner exhaust pipe" I had this happen on me when I worked in a garage early in my automotive career. I was kind of struggling at stuff to look at. My boss walks over, nonchalantly asked a couple questions and said remove the tail pipe here and then here and see if it runs better. The cross over pipe was double walled and had collapsed inside. Live and learn. Bet next time you pick right up on it.

[Condor]

I scanned through your story, and might have missed it George, but did you replace the Mass Flow Sensor. They're very touchy, and can be damaged very easily.

1998 Suburban w/Vortec V8. 200,000 miles.

[jakester]

Great story, just think of all the parts you do not have to replace for a long time now. thanks for sharing.

Bill

[djh3]

Condor:

so it progressed to replaceing fuel pump, fuel injector sypder, a rebuilt distributor, MAF, MAP, Throttle position sensor, idle air control

About 5 line down

[Condor]

Condor:

About 5 line down

 

Thanks Dion. That's what happens with TMI. My brain starts to reject..... I also don't like to read things twice... I'm surprised George is having so much trouble locating the problem. He's a pretty savey guy....

 

[cowpuc]

Thanks Dion. That's what happens with TMI. My brain starts to reject..... I also don't like to read things twice... I'm surprised George is having so much trouble locating the problem. He's a pretty savey guy....

 

 

And also TENACIOUS

Our buddy George dont take no lip from NO machine NO HOW!!!

Glad ya figured it out my friend and THANKS for sharing!!

Puc

[ricksbike]

For everyone out there,after wrenching for 45 years,any time I had a power problem I would have someone rev the engine while I held my hand over exhaust(with glove) to see if I had good flow,if questionable I would drop exhaust at manifolds and test drive.They also make a back-pressure test kit that screws into o2 sensor hole,over 4-5 lbs of back pressure you have a problem.

[BlueSky]

I had a cat checked at Midas on time. They drilled a hole in the exhaust pipe in front of the cat and checked the pressure with a gauge. Then they brazed the hole up. They didn't charge much for the service either as I remember.

[MikeWa]

George.

That is a classic plugged cat story. I have seen it many times. There are several ways to check for this. Engine vacuum is a big one. Also exhaust back pressure. Drill a small hole and test with your vacuum or fuel pump gauge. Yes most vacuum gauges also have a small pressure scale. Then braze it over or use a sheet metal screw to plug it. Sometimes just removing the O2 sensor will relieve enough pressure to let the engine run better.

Glad you found it and got it whipped.

 

Mike

[GeorgeS]

I scanned through your story, and might have missed it George, but did you replace the Mass Flow Sensor. They're very touchy, and can be damaged very easily.

1998 Suburban w/Vortec V8. 200,000 miles.

 

Yes next thing after the first new CAT

[djh3]

Also some of you old farts might remember the old trick of shoving a potato up the tail pipe of a car. Then they didn't run so s#it hot either. Long before the days of cat converters.

[KICKSHOT]

Low vacuum as you mentioned is the key to let you know that air is not flowing thru the engine. After all take away the fuel and spark and an engine is just one big air pump when it rotates. To add to what was said here. Drill a small hole in front of any thing that can plug up, cat, pre cat, muffler whatever. Then insert a sports needle gauge. (The kind you use to check air pressure in sports balls. Bought mine at wal mart.) Have some one start the vehicle and rev the engine. I say any thing over 1 psi is bad and 4-5 partial plugged 10 to max reading is really plugged. Just don't leave it in the hot exhaust too long because it's not made for that. If the exhaust is not plugged put a sheet metal screw in it and go on. I have diagnosed many a plugged cat this way.

kickshot

[GeorgeS]

Well first thing I did, was fuel filter.

Then pulled out the CAT ( the big one ) 4 months ago, it was NOT plugged at that point, But I put in a new one anyway !!

 

Key to all this, is that, at that point, I had no idea there was a Small PRE - CAT, in that fat spot in the pipe, 12 inches in front of the big main CAT. !!!

 

At that time I assume it was about 50 percent plugged. And as testing , and work progressed, the darn thing was getting more plugged, and dumped it guts into the NEW Cat, that I had installed.

 

This thing is the perfect Set Up, to make life miserable !!!! As I worked, nothing seemed to make any sence, cause I had already replaced the CAT. SO, I was looking for something else,

 

I figured it out just in time, before pulling the heads, was almost to that point.

 

-- Boy, did I get led " Down the Merry Path " as the old saying goes.

 

However, been driving it around for a few days, and---- Darn the thing sure is running great, now if I do say so myself !!! Good for another 100 K Ha Ha, with lots of new parts , just hope the Tranny holds up till the 200 K mark.

[Kirby]

Well I guess I'm no mechanic, but I did stay at a Holiday Inn Express once.

[Condor]

However, been driving it around for a few days, and---- Darn the thing sure is running great, now if I do say so myself !!! Good for another 100 K Ha Ha, with lots of new parts , just hope the Tranny holds up till the 200 K mark.

 

Glad to see you wrestled that critter into submission George....

[GeorgeS]

Low vacuum as you mentioned is the key to let you know that air is not flowing thru the engine. After all take away the fuel and spark and an engine is just one big air pump when it rotates. To add to what was said here. Drill a small hole in front of any thing that can plug up, cat, pre cat, muffler whatever. Then insert a sports needle gauge. (The kind you use to check air pressure in sports balls. Bought mine at wal mart.) Have some one start the vehicle and rev the engine. I say any thing over 1 psi is bad and 4-5 partial plugged 10 to max reading is really plugged. Just don't leave it in the hot exhaust too long because it's not made for that. If the exhaust is not plugged put a sheet metal screw in it and go on. I have diagnosed many a plugged cat this way.

kickshot

 

Good advice!! I almost ordered one of those exhaust back pressure gauges. Local store did not have one in stock. Again, the kicker in all this is " Who Knew " that Chevy Blazer, V6's have " TWO Cats " ??? I had checked my Chiltons manuel it said nothing about this ?? Does anybody know if any other car companies are doing this ??

[KICKSHOT]

Fords have more than one cat on some of their models. Some vehicles have three. One behind each head and a third in the pipe before the muffler. Here is a tip I guess I should have added to my first post. Drill your first hole in the exhaust pipe as close to the exhaust manifold as possible and check for a restriction. If you have two manifolds then you will do this on each side. If you have high pressure there work your way back until you have low pressure and you have found the restriction. Hope this helps some one in the future. But let me assure you that plugged cats have led many a mechanic in circles too. When I was younger and less experienced I had my share of problems diagnosing them. So the path you took was a good learning experience that you will never forget!

kickshot

[MikeWa]

Good advice!! I almost ordered one of those exhaust back pressure gauges. Local store did not have one in stock. Again, the kicker in all this is " Who Knew " that Chevy Blazer, V6's have " TWO Cats " ??? I had checked my Chiltons manuel it said nothing about this ?? Does anybody know if any other car companies are doing this ??

 

Most cars have more than one cat now days.

 

Mike