Plugged Cat?
Thread Starter
Instructor
Joined: Nov 2012
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From: Grand Island - Nebraska
Plugged Cat?
Would a plugged Catylytic converter cause a start up problem? I have been trying to figure out what is keeping the car from starting. I changesd the FPR. I know I have a mis- matched injector and seem to have what appears to be a "rich" smelling exhaust with blackish smoke to go with it. I just noticed that it appears to be leaking at the cat as well. I am going to change the fuel filter tomorrow as well. The injectors are next. But the car ran as of a week ago before I changed the waterpump. I was very careful to not soak the OPti. Going to remove and test the ICM too. Fuel pump is priming at the turn of the key, at least I can hear it running anyway. If the fuel filter is also bad, starving the motor, could the ECM be telling the injectors to increase fuel output to cure a "lean" condition? Could the MAP sensor be involved as well? Thanks Forum!
Thread Starter
Instructor
Joined: Nov 2012
Posts: 242
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From: Grand Island - Nebraska
Thread Starter
Instructor
Joined: Nov 2012
Posts: 242
Likes: 4
From: Grand Island - Nebraska
Gotcha! Thanks! Up on the jacks she goes. I disconnected the IFC to see if the no start condition acted the same as with it connected and it obviously did not start, but differed in the respect that it tries to fire up and belches a little bit of the blackish smoke. Could a plugged cat simply cause it not to finish the start up sequence due to the exhaust not being able to escape?
Race Director
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From: Rolla Missouri
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Drifting
Joined: Aug 2013
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From: Everett Washington
if i were you id check the cat just to be sure, you just never know. when mine was carbed i got the black smoke left and right from the fuel/air mixture being way out in lala land. are they original injectors? have you checked your fuel pressure?
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Thread Starter
Instructor
Joined: Nov 2012
Posts: 242
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From: Grand Island - Nebraska
I had a bad float in my 75 and it was black smoking too. The injectors are original and the previous owner had replaced one of the injectors with a non-factory one which I only recently discovered when I was ohming them. 8 of them ohm out at 14 and the odd one ohms out at 18! It has been running for the last 2 years like that without detriment. I think I will drop the cat out and see what happens. If I am going to bother to do that, perhaps someone out there might know where I can get a set of test pipes for my race car? I really hate to go over the same old ground, but... has anyone ever had an opti exhibit this type of symptom. Seems to me if it is getting spark at all it would not be the opti. Then again, this is my first C4, I do not know squat on this motor it would seem.
Team Owner
Joined: Aug 2004
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From: Park City Utah
RollaMO-LT4 "gets it".
No. A plugged catalytic converter would manifest itself first, at WOT. At start up, there is virtually no exhaust flow, so a clogged cat isn't what is causing it to not start.
You're (the OP) WAY over thinking this. When it doesn't start, what is missing; spark or fuel?
No. A plugged catalytic converter would manifest itself first, at WOT. At start up, there is virtually no exhaust flow, so a clogged cat isn't what is causing it to not start.
You're (the OP) WAY over thinking this. When it doesn't start, what is missing; spark or fuel?
Last edited by Tom400CFI; Oct 17, 2013 at 12:05 AM.
Race Director
Joined: Oct 2005
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From: Rolla Missouri
2021 C4 of the Year - Unmodified Finalist
St. Jude Donor '10 thru '25
Would a plugged Catylytic converter cause a start up problem? I have been trying to figure out what is keeping the car from starting. I changesd the FPR. I know I have a mis- matched injector and seem to have what appears to be a "rich" smelling exhaust with blackish smoke to go with it.
I just noticed that it appears to be leaking at the cat as well.
You should have 2 cats very close to the exit of the exhaust manifolds (one on each side).
Some people think that big muffler looking thing in the center is the cat.
It is not, that is the resonator.
Thread Starter
Instructor
Joined: Nov 2012
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From: Grand Island - Nebraska
That is much more likely to be part of your "start up" issue.
Ok, now I have to ask just what part of your exhaust system are you calling the "cat"?
You should have 2 cats very close to the exit of the exhaust manifolds (one on each side).
Some people think that big muffler looking thing in the center is the cat.
It is not, that is the resonator.
Ok, now I have to ask just what part of your exhaust system are you calling the "cat"?
You should have 2 cats very close to the exit of the exhaust manifolds (one on each side).
Some people think that big muffler looking thing in the center is the cat.
It is not, that is the resonator.
Melting Slicks
Joined: Jul 2005
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While I guess a horribly clogged cat could theoretically cause the car not to start - the odds of that happening are frighteningly small. As John Marker stated - the way to test is to check for a clogged cat is to check the pressure in the exhaust pipe before the cat. BUT ... When you see hoof prints - think Horses - not Zebras. Start with real simple stuff - do you have a spark at the coil - how about at the plugs? Is the PCM telling the injectors to fire (check with noid lights - or pull the injectors and see if fuel is squirting out of them during cranking). Do you have adequate fuel pressure ??? Did you try a (Small) shot of starting fluid ??? Start with the basics and go from there.
And BTW - the fact that one injector is a few ohms higher or lower than the other injectors is not proof that there is a problem - particularly if the injector that reads differently is a replacement. Some coil designs can use more or less current than others designs, but achieve the same flow.
And BTW - the fact that one injector is a few ohms higher or lower than the other injectors is not proof that there is a problem - particularly if the injector that reads differently is a replacement. Some coil designs can use more or less current than others designs, but achieve the same flow.
Team Owner
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From: Athens AL
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Best way to test is with the pressure gauge in the O2 bung.
The mismatched injector combo probably has more to do with the startup issue than anything else, but if you are getting black smoke out the back, then you are probably dumping so much carbon into the cat that it'll plug up soon enough.
I've had a clogged up cat before and the biggest symptom I noticed was a lack of performance from midrange on up.
The mismatched injector combo probably has more to do with the startup issue than anything else, but if you are getting black smoke out the back, then you are probably dumping so much carbon into the cat that it'll plug up soon enough.
I've had a clogged up cat before and the biggest symptom I noticed was a lack of performance from midrange on up.
Burning Brakes
Joined: May 2013
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From: Valrico Florida
I just had a plugged cat in my 85. Started up and idled great but you could hear the engine loading up with air and the engine would not rev past 1500-2K RPM, and it was very much blocked, not just a little. Whole honeycomb was busted and lodged at the exit.
Melting Slicks
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From: Palmdale CA