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Technical => Engine Tech => Topic started by: SR71blackbird on March 07, 2012, 03:00:06 PM

Title: LOUD Backfiring
Post by: SR71blackbird on March 07, 2012, 03:00:06 PM
So whenever the engine is winding down after revving, cruising or getting into the gas, it back fires A LOT. The higher i rev it up, the louder the backfire fir is and most of the time there is multiple backfire when winding down. It is REALLY loud. my car runs rich during those^^^ times too. Could that be the reason?
Title: LOUD Backfiring
Post by: ZondaC12 on March 07, 2012, 03:47:08 PM
LOL give me your car NOW so I can go cruising around town scaring the  out of everyone.
 
I already do that in the summer with my '38 Buick by flipping the ignition off and back on, but I'd love to be able to do it in a thundercat. Yes you have a severe rich condition most likely. Maybe also valves sticking open...but more likely injectors not closing.
Title: LOUD Backfiring
Post by: SR71blackbird on March 07, 2012, 05:26:15 PM
lol how loud it is backfiring, it would DEFINITELY scare someone! You know what, im thinking it might be one of my valves sticking open then! When i start my car up, a puff a blue smoke comes out. Ive been told it is a valve stem seal. I am hearing chatter from the valve train. And now this! Im thinking the shop i had build my cylinder head had a bunch of monkeys working on it!
Title: LOUD Backfiring
Post by: jangus on March 07, 2012, 07:19:01 PM
Quote from: SR71blackbird;383287
lol how loud it is backfiring, it would DEFINITELY scare someone! You know what, im thinking it might be one of my valves sticking open then! When i start my car up, a puff a blue smoke comes out. Ive been told it is a valve stem seal. I am hearing chatter from the valve train. And now this! Im thinking the shop i had build my cylinder head had a bunch of monkeys working on it!

 
That's why I do my own work. I have one local shop I trust for my general machine work, and one guy I trust who does my valves and valve seat profiles. I just give them the specs I want to see, and do all the assembly work and parts sourcing myself.
Title: LOUD Backfiring
Post by: SR71blackbird on March 07, 2012, 07:47:47 PM
So do you think that my problem is because of the valve stem seal not being put in right so its is letting oil by and making the valve stick?
Im sending a different head off to boport to get it fixed up and i'll be selling my current head soon.
Title: LOUD Backfiring
Post by: jangus on March 07, 2012, 08:09:49 PM
Does your vacuum/boost gauge bounce around at idle? A sticky valve will play heck with your vacuum reading. Sticking valves can be caused by burnt oil residue between the guide and stem (which can be caused by bad seals, but not usually), improper valve guide to stem clearance, or a bent valve stem. If you're running super rich when you close the throttle, try and figure out why. I know I'd much rather fix that issue and replace the valve stem seals than needlessly buy another head.
Title: LOUD Backfiring
Post by: SR71blackbird on March 07, 2012, 08:35:47 PM
OMG ALOT!!!! its vibrates really badly until 2000rpm.  so that's the problem...... The guy that build my head is going to get an hear full!! Thank you for the help Jangus. I appreciate it.
Title: LOUD Backfiring
Post by: TOM Renzo on March 07, 2012, 09:03:29 PM
Sounds like you HLA'S may be to tight. But you said it makes valve train noise . So that is not the issue unless one is real tight. I have seen countless engines with loose guides run perfectly. Just start any Porsche and watch the blue smoke come from the exhaust. And they all do it. Their guides and seals are designed very loose. They do that for a reason. But if your engine is not smooth until 2 grand you have other issues than valve seals. The 2.3 Ford seals are basically pretty good and it takes a lot to mess them up. Unless one is missing. Also if you have a cam bigger than 470 Lift the retainers must be modified or the guides cut down. I dont know what the lift is on the 2.5 BO-PORT CAM??  But a compression test or leak down will set you free.

Also Bo-port cams are reduced base circle cams. So shimming is critical. Was it done correctly???

Also the 2.5 needs the guides reduced. I think nything bigger than the 1.9 needs guides reduced. Was it dun???
Title: LOUD Backfiring
Post by: jangus on March 07, 2012, 09:14:22 PM
Quote from: SR71blackbird;383308
OMG ALOT!!!! its vibrates really badly until 2000rpm.  so that's the problem...... The guy that build my head is going to get an hear full!! Thank you for the help Jangus. I appreciate it.

 
Hold on. Before you go tearing someone a new one, you need to start checking things over. Tom did hit on a very good point on the HLA clearance. You should check it. Also, if you have a weak valvespring or two, that could cause havoc also. Now, combine a weak spring with HLA problems, and you've got a major headache. The point I'm trying to make is: Start checking things first. As for the valve guide clearance issue, it could be a problem if it's to tight. If it is, when they get hot they'll start to grab the valvestem and cause the valve to hang open.
Title: LOUD Backfiring
Post by: TOM Renzo on March 07, 2012, 09:43:05 PM
The 2.5 would need double springs at the least. BO would not recommend a stock spring. Stock springs are JUNK and cant even tolerate a stock cam. I have changed many valve springs on the 2.3 even in daily drivers. The springs SUCK. As far as a tight guide it is very possible. But then the motor would not smoke. Just saying. But everything is a possibility if the clearances are UN KNOWN. When building an engine a build sheet is mandatory.
Title: LOUD Backfiring
Post by: jangus on March 07, 2012, 10:23:36 PM
Couldn't agree more on the build sheet Tom. Without knowing what the clearances were, it could possibly have a tight guide on one valve, and loose one on another. Depends on how much pride the machinist had in his work.
Title: LOUD Backfiring
Post by: TOM Renzo on March 08, 2012, 05:39:31 AM
True very true. I think at this point a leak down or compression test might be in order. I would also check the HLA clearance just for giggles.
Title: LOUD Backfiring
Post by: Chuck W on March 08, 2012, 07:22:09 AM
OR...it still could be a tuning issue.  I know you kind of half-assed attached that O2 ground wire (the orange one that's supposed to attach to the turbo), and you're still running stock engine management with a bunch of mods done to the car.
Title: LOUD Backfiring
Post by: SR71blackbird on March 08, 2012, 11:48:55 AM
Well i have a full boport roller assembly. i have the springs down below. Bo said they would work with my setup. I guess it would make sense if it was the HLA's because they are wider then stock ones. I gave the shop a build sheet. The guy that built it has built 3 2.3 circle track winning cars so he has worked with 2.3's before. I did a compression check 2 weeks ago and 3 of my cylinders had 130 and one had 125.
Chuck, I got a good ground on that wire about 2 weeks ago thanks to Toms help. So that shouldnt be the problem. However i do have a pigger back tuner that comes with a computer, tune, filter and wiring in my garage that might be going in soon.
http://www.bo-port.com/index.php?act=viewProd&productId=37
Title: LOUD Backfiring
Post by: beast50 on March 11, 2012, 08:42:53 AM
I had a valve guide installed pen 15eyed that caused backfiring occasionally.  Ended up being an intake valve and it finally stuck, not once but twice.  Mangled the pushrod both times and the last time it stuck in the head/guide.  Ferrara valves are not cheap!