VW Vortex - Volkswagen Forum banner
  • Mwerks and Fourtitude have rejoined VWVortex. For more info, see this thread.

1 - 11 of 11 Posts

·
Registered
Joined
·
224 Posts
Discussion Starter #1
I just finished putting a JH 1.8 motor in my '84 Jetta. The exhaust is new from the manifold back including the O2 sensor. I run the car for not even five minutes and the back end of the cat turns bright red and sets the undercoating on fire.
I adjusted the mixture, what else would cause this?
 

·
Registered
Joined
·
20,310 Posts
Re: Problem: New Cat turns red hot!! (SoloIIRacer)

Do you still have the heat shield in place?
 

·
Registered
Joined
·
10,608 Posts
Re: Problem: New Cat turns red hot!! (millerwj)

Mixture can do that. I've it happen. Do a very thorough check for vacuum leaks before adjusting your mixture and well you're at check your ignition timing.
 

·
Registered
Joined
·
224 Posts
Discussion Starter #4
Re: Problem: New Cat turns red hot!! (SoloIIRacer)

Heat shields all in place.
Is this caused by a too lean or too rich mixture?
I would think a vacuum leak would cause a lean mixture, correct?
 

·
Registered
Joined
·
14,303 Posts
Re: Problem: New Cat turns red hot!! (SoloIIRacer)

If the CAT is getting really hot, then the CO value is too high which means the fuel mixture is too rich. Also incorrect ignition timing can cause problems. Recommend you check both of these items. Regards, WWR.
 

·
Registered
Joined
·
224 Posts
Discussion Starter #6
Re: Problem: New Cat turns red hot!! (WackyWabbitRacer)

It's fixed.
Mixture was leaning out due to too much draw thru the injector air shroud connection on the head. I disconnected and plugged it and the problem went away. The timing is still off I know, but that will be fixed shortly as well.
Thanks for all the help.
 

·
Registered
Joined
·
14,303 Posts
Re: Problem: New Cat turns red hot!! (SoloIIRacer)

Jeff, sorry I gave you some wrong information about the fuel mixture. Guess I had a brain fart or didn't have enough coffee yesterday. I should have remembered that high EGT readings on the race car mean a lean mixture and that a red-hot CAT is caused by lean mixture. It happens with old age!!!

Again apology for the wrong poop! Keep the CAT cool, WWR. http://****************.com/smile/emthup.gif
 

·
Registered
Joined
·
224 Posts
Discussion Starter #8
Re: Problem: New Cat turns red hot!! (WackyWabbitRacer)

Hey WWR, no problem.
Well, I thought it was fixed, but it happened again last night after I timed
it correctly. I'll be getting a fuel pressure gauge set-up soon, that should help me diagnose this problem.
 

·
Registered
Joined
·
10,608 Posts
Re: Problem: New Cat turns red hot!! (SoloIIRacer)

In my case, the problem was caused by a vacuum leak, a cracked vacuum line, to the knock sensor control unit, this threw out the mixture and timing.
 

·
Registered
Joined
·
224 Posts
Discussion Starter #11
Re: Problem: New Cat turns red hot!! (eurotrashrabbit)

quote:[HR][/HR]checkO2 sensor
[HR][/HR]​
O2 is new, see start of thread.
Does anybody know where the '84 air shrouded injector feed hose is supposed to draw vacuum from? The Bentley isn't much help here.
 
1 - 11 of 11 Posts
Top