As you can see by the pictures I have two cracks in the trunk side header of my 3.4 V6. The cracks have been there for quite some time and although I don't think they go clear through although they may have expanded over time. As far as I can tell there are no cracks in the firewall side header. I have not driven the car in some time because I'm sure the headers would fail the smog inspection.
I think these may be Sprint headers but I don't really know anything about them or what they are made of. They came on the car when I bought it several years ago. Is it possible to do a repair with some kind of high heat JB Weld type stuff or does it need to be welded? I'm afraid to remove it to have it welded and then find that it won't fit correctly upon re-installation.
When metal reaches 2400 °F, it's glowing white-hot. I can't imagine the stuff sticking to white-hot metal; the 2400 °F claim sounds like a load of marketing bollocks.
Exhaust doesn't get that hot, but I'd expect it to unstick and be blown out of the crack.
The JB Weld might work for a short-term half-assed fix if you're absolutely desperate to get the car working right now, but welding is the long-term quality repair.
If you did want to try the JB Weld route, you should drill out the ends of the cracks, so they don't continue to propagate. But I would avoid the JB Weld altogether; any remnants of it may contaminate the weld job.
Mig or Tig welding is the only solution to fixing those cracks in the exhaust. Preventing them in the future involves keeping cold water from dripping on the hot exhaust when the deck lid is opened.
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Very likely have engine problems on top of crack exhaust.
Engines running lean or wrong base timing can cause glowing exhaust and this overheating will make broken headers and even cast manifolds. GM has several TSB for Fiero and other models just for this.
Weld to repair crack line above often won't help for long. More so w/ above issue.
Yes you can, often will, Fail E-test w/ crack exhaust. Worse cracks upstream of O2 sensor can suck air into the pipe and make O2 sensor output bogus data and screw up the ECM even w/o setting any codes. Running too lean or rich can also cause Cat overheating problems and even destroy it.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
On second thought this crack could be the result of a leaking EGR tube. I saw that quite a while back on a V6 Fiero that I was repairing. The manifolds glowed bright red until the tube was replaced. Probably the result of an overly lean mixture
I doubt there are any problems with the motor unless the OP failed to mention that the engine light is on. Let's not forget that the V6 has a blower motor and supporting duct/tubing to blow cool fresh air directly on that area of the engine bay for a reason. Fresh air has a path up and over the inboard header area thanks to the deck lid vents, which should afford it a better cooled environment than the aft location, although I still suspect there's a crack somewhere in the inboard header also.
Exhaust temps from when I actually ran an EGT sensor were around 1600F on the high side under sustained load, but generally 1-1200ish under moderate driving loads.
These are aftermarket headers, in place of stock manifolds that were also known to crack and shear off exhaust bolts, so this is to be expected in my experience with tubular exhaust manifold runners that are relatively short, with little to no provisions made for stress relief from heat expansion. Tubular manifolds have far less capacity for heat absorption and dissipation unlike the cast iron manifolds, so they will get very hot and stressed when pushed, especially in the Fiero, which is why heat wrap on a manifold of this design without expansion joints is a no-no. I warped cast iron manifolds by wrapping them after all the expanding and contracting worked the bolts loose allowing more movement.
This is an easy fix with a MIG welder. Remove the exhaust gasket, torque the manifold directly to the head with appropriate spacing at the exhaust bolt holes, don't forget to loosen the bolts at the "Y" pipe connection to release the tension from removing the gasket, take the car to a trusted muffler shop if you can't weld and I bet they'll tack weld the crack as needed to hold positioning before removing to complete and if possible, repair it on the car if there is room, if not, it's the easiest of the the manifolds to remove.
If you have an extra cylinder head as already mentioned, that would be even better, take it to someone who can weld and they should be able to fix you right up. This is the approach I used to repair my warped exhaust manifold, I cut it between the exhaust ports while bolted to a cylinder head, welded it back together with flanges flush against the head and used shielding instead of heat wrap, along with studs in place of the exhaust bolts and never had another problem with the exhaust, for the remaining 4 yrs I had the car before selling it.
Originally posted by Joseph Upson: This is an easy fix with a MIG welder.
I would say a return to a like-new state; not a long-term fix.
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Originally posted by Joseph Upson: These are aftermarket headers, in place of stock manifolds that were also known to crack and shear off exhaust bolts, so this is to be expected in my experience with tubular exhaust manifold runners that are relatively short, with little to no provisions made for stress relief from heat expansion.
Restoring the manifold back to its stock-style state is likely to result in stock-style reliability. Dismal reliability, in other words.
People assume that there's some underlying engine problem behind cracked manifolds, but I think the factory Fiero exhaust design was just marginal.
This is my Fiero:
I suggest bellows on the stock manifolds, and it looks like bellows could be retrofitted to the Sprint pieces.
Here is the Dorman Jeep 4.0 exhaust manifold:
I guess for OP in California, my main concern about installing bellows would be the smog inspection. Maybe this modification would cause the car to fail smog.
[This message has been edited by pmbrunelle (edited 10-14-2020).]
Restoring the manifold back to its stock-style state is likely to result in stock-style reliability. Dismal reliability, in other words.
People assume that there's some underlying engine problem behind cracked manifolds, but I think the factory Fiero exhaust design was just marginal.
... I guess for OP in California, my main concern about installing bellows would be the smog inspection. Maybe this modification would cause the car to fail smog.
I'm with you all the way, especially with the bellows install which GM FWD crossover pipes have incorporated for a few decades now. Just keep in mind that you are "idealing" in terms of those like you, me and others who can actually perform these modifications ourselves. He was considering JB Weld so modifying the headers to include bellows is quite a jump from that and beyond keeping it simple and functional, considering as manufactured they may have provided several years of proper service before finally having enough. The pics suggest they're about 14 ga steel which is very good for the job it's doing.
I remember seeing that on cars back in the 80's. Not sure how thick that tube wall is but looks very thin. You may weld the cracks and stop the leak, but it will likely crack in another spot. Your long term solution may be to go with a beefier header set up.
Originally posted by Joseph Upson: Just keep in mind that you are "idealing"
Yes, that's right to some extent.
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Originally posted by Joseph Upson: considering as manufactured they may have provided several years of proper service before finally having enough.
Forum member GTDude was a GM dealer mechanic, and he stated he that he did many 2.8 Fiero exhaust manifold replacements (more than on other cars), while the cars were on warranty (3-year warranty?).
So I'm not convinced that a repair without changing anything in the header's design will yield an "acceptable" service life.
Of course this depends on OP's expectations for reliability after the repair.
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Originally posted by Joseph Upson: modifying the headers to include bellows is quite a jump from that
Yes and no... if OP is ready to bring his headers + a head (or RD welding jig) to a local welder/fabricator, it wouldn't be much of a stretch to bring four bellows, and ask the welder to add them in.
[This message has been edited by pmbrunelle (edited 10-14-2020).]
