if the cat is pluged then it will affect the car whenever it is running.if the car will run and rev until warmed up then it is not the cat. since it will run good until warmed up then i would start looking at sensors. a good starting point would be the fuel sys, mainly the o2 sensors. they only other thing i have to say is good luck.

 

i agree this very same thing happened to me, u can take it to a muffler shop and they can test the pressure in the cat while its running should be less than 2 lbs, if its higher than than that its plugged...good luck

 

I highly doubt it's the cat. pull the O2 sensor, and that would relieve some of the back pressure if the cat is plugged.

more likely the timing is way off... otherwise it's running way lean.

 

Seen this before. If you had open headers you would see pretty blue flames from your exhaust.

 

Could someone please elaborate on the issue of :
'lean' causes very high exhaust gas temps.
How could 'excess air' combustion cause high EGTs.
I just don't believe it.
Exception, going from 9:1 to 14.7:1, maybe higher EGTs.
Perhaps this 'myth' came from some guy who works
on airplanes / aircooled Beettles / some other engine with inadaquate exhaust valves,,, and gets around
the problem by running 9:1 AF ratio.
(excess air, leaner than 14.7:1)

 

Silver84, you are correct...

"This ratio is called stoichiometric, meaning that there is a perfect mixture of air and fuel to insure complete combustion. This also happens to be the perfect mixture to get the highest temperature of combustion, and therefore the highest exhaust gas temperature (EGT). "

BUT, as you indicated in your post, take the case of an engine under load. You want more like 12.5:1 to make the best power in a typical gasoline engine. Say under load you're running "LEANer than you should" at 14.7:1 (stoichiometric), you will have extremely hot exhaust gasses, and probably glowing headers, maybe even melted piston crowns.

Those of us pointing to a lean AF ratio are assuming the engine was recently under load. Also, he mentioned it was hard starting when hot which sounds typical of an extremely lean AF ratio.

Now, another topic, how do we get a gasoline engine to survive at WOT and 14.7:1 AF ratio so we're getting the most out of every molecule of gasoline? Hmmm....water injection....don't hear much about it here.

 

Atok, I must be missing something basic.
Lets assume that gasoline octane rating, is not the issue, also, spark timing can be adjusted to whatever
is thought 'best'.
Note, Flame speed is highest at 14.7:1.
.........................
I just don't get how you can have max power
at 13:1 (or so), and not max heat (which would imply
high EGTs).

 

Yes, at 14.7:1 I think theoretically you would make best power. BUT it's not possible to run WOT at 14.7:1 on gasoline. The mixture would detonate and destroy the engine. So from what I've read, 12.5:1 seems to be the best AF ratio for max power (cooler/slower flame). I guess what's happening is you get the highest cylinder pressures without detonation at 12.5:1. 14.7:1 would give higher cylinder pressure but would detonate killing the power and engine components.

 

i disagree with the timing and motor being lean....i had this same situation with my 87....i thought timing off, ....tried to reset it, duh, the comp will do that on its own, no?, so i couldnt figure out wtf was up, until i opened the hood one evening, and seen my pipes just glowing......i though ha, i found u....so i took it to a muffler shop, they pressure tested it, (for free)it was holding 22 pnds of pressure, should be like 2 pnds.....my pre cats, fell apart on the inside, and was A: clogging my left bank, and B: blew all that **** from the left pre cat into my main cat at the middle of the exhaust....so i replaced the final cat, and went to my buddies shop, put the car in the air, and removed the pre cats.... the left one had only a piece of brick in it about the size of my fist which was totaly blocking the left side when running, futher more while it was running i could hear that crap rattling around in there and thought it was a heat shield.....hence all the crap in the main cat...now i have replaced the pre cats with 2 pipes welded in, a new final cat.....and car runs fine.....a tad louder but runs great....as far as mixture, the timing would have to be way way of, to run lean enough for red pipes...and i cant see how it would even run with it off that much to begin with...does the car run like its bogged down, and sound like a jet takin off?...tell tale sign of a plugged cat or pre cat.....loss of power after warmed up, another sign.....my money is on the cats.....just my humble opinion....been there done that....good luck.....

 

"Take out he O2 to relieve back pressure"??? Thats gotta be the most backyard mechanic thing ive ever heard, not to mention a good way to burn things...

Sounds like plugged cats..

Why would his timing be off??? Did the dist just lossen up on its own??? Also as far as it being lean, his engine would be toast by now if it was that lean. Its hard to even get an engine like this to intentionally go THAT lean.

Plugged cats dude.

 

 

I agree that if the engine is running too lean that the pipes will turn red. But it will continue to run with a lean condition until there is damage to the engine. From what I understand an engines peak performance is at the ragged edge of running too lean. If the cats are on their way out the car will run until the cats get hot and cause lots of backpressure causing the pipes to turn red and stalling from too much backpressure. I had a problem with my ’89. It would run find until up to temp. Then the performance would fall off. I bought a y-pipe that had the pre-cats gutted from a forum member, put it on and problem solved. I caught the problem before the pre-cats broke up and clogged the main cat. Hope this helps.

 

Check the timing.

 

Start the car then place your hand in back of the muffler, what do you feel? I would bet its a clogged cat. The stock 84 has a single cat unless of course it has been modified.

 

THE CAR HAS NEW CAT AND MUFFLERS & O2 SENOR, BUT AFTER ABOUT A HALF HOUR OF RUNNING IT WILL JUST STOP ,WILL STILL START BUT I HAVE TO PLAY WITH THE GAS , AND WHEN FIRST STARTED IT HAS A BOG , I THINK ITS THE TIMMING BUT WHEN I TIMED IT IT DID NOT WANT TO STAY RUNNING , PLEASE HELP , AT THE END OF MY ROPE , IT MAY BE 4 SALE SOON, DONT WANT THAT ,BUT IAM GETTING MARRIED IN JULY '05 CAN'T KEEP PISSING MONEY AWAY ON THIS CAR

 

Actually I was thinking the car was running rich and now may need new cats.

 

On the 86, a bad 02 that results in a lean condition sets a code. Don't know about the 84 though.

Jake