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Exhaust glowing red at idle

Discussion in 'Technical Q&A' started by Consejero, Aug 4, 2008.

  1. Consejero

    Consejero Karting

    Mar 15, 2004
    68
    Dallas, Texas
    Full Name:
    James R. Consejero
    What the he** ! I can't figure this out. My car was running fine, then one day I noticed the exhaust was getting hotter and hotter...I mean it's glowing red! I started it today and let it idle for about 5 minutes, a leaf fell on it and it immediatly caught fire. I don't know what's going on. It's not the fuel, I don't think. What else could it be? Vacuum leak? somebody help! could my timing be off somehow? I'm so frustruated about it. I'm afraid to drive the car. Also, I think I have an exhaust leak or due to the same problem it sounds like crap. I'm at my wits end....help a brother out somebody! I'll try anything, If I can't figure this out I'm going to drop the engine and I really don't want to do that.
     
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  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Welcome back, JR!

    Although the discussion on this is also in the other thread, the standard reasons for a red hot exhaust somewhat depend on where it is getting red hot.

    Much as you say, if the exhaust is getting red hot at the headers, both headers, it is likely that the mixture is too lean, either from a significant vacuum leak like a leaky hose going into the plenum (and there are a few, one more in a Mondial) or the K-jet is set too lean for summer blend or ethanol gas that the K-jet does not recognize. It is unlikely ignition timing, as your Digiplex usually either runs well or quits with a single side ignition failure (more on this later). Cam timing can do it, but is also unlikely if both sides are equally hot which would suggest both belts slipped - unlikely. If just one header is hot, well then maybe. Although I have not heard, a leak in your air injection might do it if only one side.

    IF the exhaust is getting red hot in the cat, it could be due to a clog. I believe yours is a two cat car. Single cat car overheats can also be from the dreaded single bank ignition failure (of which I had three, before I tossed the Marelli ignition).

    If your ignition fails on one side, the engine will run on one side. The dead side will be pumping unburned air/fuel that will ignite as it meets hot exhaust from the good side. In single cat cars, this happens just before and in the cat. In other cars it occurs where the exhaust mixes. Mine used to light up the entire engine compartment from how bright my single cat got.

    So, after you verify you have spark on both sides, I would go through a methodical check of the air/fuel delivery system starting after the fuel distributer looking for air leaks or crapped out/disconnected hoses. Also, where is it getting hot - both sides? Headers or afterwards?

    Let us know and we'll figure it out.

    Good luck!
     
  4. Consejero

    Consejero Karting

    Mar 15, 2004
    68
    Dallas, Texas
    Full Name:
    James R. Consejero
    Thanks bro! I'm in remission, go figure right? ok more info, well it was running fine before so I don't think it's the cams unless I slipped a tooth on the belt which is probably unlikely. I think it's just the rear side headers, meaning the ones closest to the rear bumper. I took the Cat's off a while back and replaced them with test pipes so it's not the cats. How severe do you think the vacuum leak would have to be to make this happen? I've looked at all the hoses and can't find anything visually but I'll try it with propane this weekend.

    I think it's just one side but it's hard to see since I cover the pipes with exhaust wrap. It's definately the headers though. I'm interested in what you said about it running on one side only. It also sounds horrible, it sounds like there's an exhaust leak but now I'm thinking that it may be because it's only running on one side.

    I'm ready to pull the engine but if I can avoid it I'll be a happy camper.

    Thanks to everyone for the well wishes. Anyone wanting to follow along on my personal progress check out www.caringbridge.org/jrconsejero My wife started it but then she left me and well I'll ***** about that on a different site but can't blame her. Anyhoot. It's great to be back. I'll follow up on this after I do some trouble shooting
     
  5. jon s

    jon s Formula Junior

    Mar 9, 2005
    509
    pocasset ma
    Full Name:
    jon shoukimas MD
    i burned three valves on my 81 gtsi (cats long gone) when the digiplex failed. it retarded the ignition on failure rather than quitting altogether. so it can happen. bad news either way. don't run the car for any length of time until you find out what the problem is - the fried valves ended up costing a lot. regards, jon s.
     
  6. smg2

    smg2 F1 World Champ
    Sponsor

    Apr 1, 2004
    11,730
    Dumpster Fire #31
    Full Name:
    SMG
    JR, good to see you on again.

    sounds lean, no cats and a hot exhaust. is the air injection still in place? if it's leaking air into the exhaust it'll 'afterburn' and spike temps, but it gets worse if the timing is severely retarded and the bank has gone lean. swap ecu's to see if the problem switches to the front bank.
     
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  8. Consejero

    Consejero Karting

    Mar 15, 2004
    68
    Dallas, Texas
    Full Name:
    James R. Consejero
    No, the air injection system was replaced by 8 stainless steel plugs. I do have an open hole in the exhaust but I removed everything including the EGR valve. No air Pump, no air manifold, no exhaust air injectors, no EGR, no Cats either,no ...spaghetti pipes. I kept everything, I just removed the emissions since I hardly drive it. I did of course leave the Air Recirculation device in place from the valve covers, air box and back down to the crank site.
     
  9. Consejero

    Consejero Karting

    Mar 15, 2004
    68
    Dallas, Texas
    Full Name:
    James R. Consejero
    I really think it's the digiplexes...I'll try it out this weekend, I think they may work occassionally but cuts out. I think I'm only running on one digiplex.
     
  10. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    If that is so, then you are only running on one bank of 4 cylinders - a bit dangerous.
    Check that you have spark at the coil wires on both sides, then go from there.
     
  11. Consejero

    Consejero Karting

    Mar 15, 2004
    68
    Dallas, Texas
    Full Name:
    James R. Consejero
    sure enough neither was working... I think they do work intermitantly. I have the schematics but I'm curious what would cause them to work sometimes and not others. I think I'm going to have to finally break down and buy that digital ignition I've been wanting for sometime.
     
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