Backfire at low rpm

I have been having some backfires at low rpm. Usually in 3rd, 4th and 5th gears. Generally under 2000rpm.

I am running a Novi 1000 with about 4-5psi of boost. Fuel pressure is about 43psi. I am using Motorcraft AGSP 32c plugs. I have Edelbrock Performer 5.0 heads machined with the "O" ring groove.

I had this problem when i was running my GSS (ball drive) blower. Its like i let off of the throttle a little then get back in it, it has a backfire or two. I am running an FMU and a bypass valve. They are both irrelavent cause it did this befor.

Any suggestions?

Thanks...........:( :confused:

what is your fmu calibrated at? when you stab the throttle you may be getting a fuel spike. Do you see any boost this low?

Sounds like it's way rich, and then igniting some of that unburnt fuel when it's still in the header.

Does it backfire through the exhaust or the intake?

I had a problem with lean poping through the intake and I fixed it with a couple more pounds of fuel pressure.

I'll bet good money there is an e-cam involved too. :)

what kind of timing, and have you tried backing the fp off some?

Okay, the FMU is calibrated for 30lbhr injectors. Or atleast supposed to be. I had the backfiring befor i started using it though.

I cant tell if the backfiring is through the intake or exhaust. How can i tell. I kinda think its thru the intake cause its kinda quiet.


Yes, i am running an E-cam. I am currently running 8* timing. I have also ran 10* too. No change.

I havent reduced fuel pressure cause i really dont think i have enough fuel as it is. But i can try.


Anything else?


Thank You

Take it down 1# at a time. If you hear it ping, step it back up. Check your 02's. They could be fouled. Check to make sure there are no major exhuast leaks at the headers to head gasket. And check for unmetered air.

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Originally posted by UNTCHBL
Take it down 1# at a time. If you hear it ping, step it back up. Check your 02's. They could be fouled. Check to make sure there are no major exhuast leaks at the headers to head gasket. And check for unmetered air.

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okay...I am gonna go take it for a drive. Will report back in a few

cool.

If it back fires through the intake its usually lean.

if it's through the exhaust it's usually rich :)

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if it's through the exhaust it's usually rich

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ive had this happen, sounds like a gunshot, had the kids running around by my house screaming for help. lol. same with the lean one thru the intake, not a pleasent sound.

Okay gentlemen. Back from the test run. I think you'll be surprised with the results.


I backed the fuel pressure down to 40psi. It still backfired. I then took it down to 33psi. It STILL backfired.

I just read some new replies to this post and maybe i didnt describe the sound very good. Its not a LOUD backfire. More like a cough or something.

Anyway, i was going down the road with regular or normal driving. I was in 5th gear doing about 65. My tach was just under 2000. I decided to hit wide open throttle real quick. It coughed or backfired quite a bit. When i hit the throttle, i pushed .5 to 1 psi of boost.

Explain that? Why would the mothertrucker cough & stuff like that?

:eek: :confused: :eek: :confused: :eek: :confused: :eek: :confused: :eek:

I dont get it:(

ur firing order right?

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Originally posted by green93notch
ur firing order right?

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I am almost positive. It runs too strong not to be. But i'll check anyway.



**when i aint at low rpm anyway**:D

ignition? do you have any? MSD? Accel? is ur C&L clocked right? cause i know C&Ls have to get air into the sampling tube to get 'metered' air, thats what my problem was when i had it. i got tired of it and just bought my 80 mm pro-m for 240 bucks :D

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Originally posted by 5.02GO
I am almost positive. It runs too strong not to be. But i'll check anyway.



**when i aint at low rpm anyway**:D

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Firing order checked and okay.

13726548......

Umm....Any chance in the spark being blown out. If so, why not under heavy acceleration? Just wondering. I gapped those plugs at around .032 (32 thousands)


Anyone else got any ideas? Its quite embarrasing when you have a car like this and you can really get in its azz at low rpm. You gotta ease into the throttle just a little then let it rip.

do you have a bypass valve?

this might sound crazy but it fixed my bucking problem at low RPMs (if thats kinda what you're getting) did you cut the oil return line hose? or do you have it so it goes below the oil pan then back up to the pan? (looks like a U shape) if so, cut that just way its a streight shot into the pan, my oil was backing up into the SCer and causing my car to buck some, blew the seal also out 2 times....

Yes, i do have an msd system. 6btm with boost retard as a matter of fact. However, i have unhooked it and am using stock ignition.

And i do have a C&L 73. When you say "clocked" do you mean that is straight up? It is pretty much is straight up. But does have a slight angle.

Yes, i do have a bypass valve. A bosche.


thank you.

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Originally posted by green93notch
this might sound crazy but it fixed my bucking problem at low RPMs (if thats kinda what you're getting) did you cut the oil return line hose? or do you have it so it goes below the oil pan then back up to the pan? (looks like a U shape) if so, cut that just way its a streight shot into the pan, my oil was backing up into the SCer and causing my car to buck some, blew the seal also out 2 times....

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Uhh, i ran my return line from the blower to the side of the oil pan. Just like what the instructions show.

This problem is quite annoying aint it.

try to turn ur mass air meter from 12 to 3 or some where between there, im just trying to give you different ideas to help..my novi kit didnt come with directions and i called paxon to send some, they didnt so i had to print them from online but when your black is fadding out, its hard to see...

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Originally posted by green93notch
try to turn ur mass air meter from 12 to 3 or some where between there, im just trying to give you different ideas to help..my novi kit didnt come with directions and i called paxon to send some, they didnt so i had to print them from online but when your black is fadding out, its hard to see...

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That sucks. They tend to have a bad habit of NOT sending stuff they are supposed to. And still dont when they say they will.

do you have a a/f guage?

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Originally posted by green93notch
do you have a a/f guage?

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Rich/lean gauge?

Yes. It mainly stays on the lean side. In fact, it hardly moves. It moves very slow. It NEVER goes higher than the middle of the guage. Even with the FMU hooked up. Something is going on with my motor.

To show you what i am talking about, here is a pic.



http://www.nordskogperformance.net/i...el/m7009lg.jpg

im running out of ideas :(

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Originally posted by green93notch
im running out of ideas :(

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LOL!! ME TOO!!

I just found some info at Pro-M's site. That somewhat describes my problem. It almost sounds like my regulator sucks. Pressure does change when i unhook the vacuum hose.


Here's a link. And I CERTAINLY APPERICIATE your HELP in the matter.

http://pro-flow.com/tech%20info/t-car.html#fuel

Click on "fuel system".

Thanks again for your help. This problem is tough. However, its probobly a simple fix like everything else. Just figuring it out.

thank you

yea it sounds like your problem, are you going to swap out the FPR??

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Here's a link. And I CERTAINLY APPERICIATE your HELP in the matter.

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Thanks again for your help. This problem is tough. However, its probobly a simple fix like everything else. Just figuring it out.

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you're welcome :)

i had the exact same problem with my car

my problem was the C&L-how much space do you have form the mass air to the supercharger

C&L's like about 8 inches of space to work right

also did yours come with the electronics or did you have to use the stock electronics on the new meter-had bad feeling about that

i could never get my C&L to work right so i traded a friend for his granateli-and it solved all of my problems

but that was me

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Originally posted by apv-stang
i had the exact same problem with my car

my problem was the C&L-how much space do you have form the mass air to the supercharger

C&L's like about 8 inches of space to work right

also did yours come with the electronics or did you have to use the stock electronics on the new meter-had bad feeling about that

i could never get my C&L to work right so i traded a friend for his granateli-and it solved all of my problems

but that was me

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I am using the inlet tube that paxton sent with the kit for the mass air sensor.

My C&L did not come with electronics. I reused the stock electronics off of the stock sensor. I purchased a sample tube from summit for 30lb injectors.

I have heard of people having trouble with C&L's I'll keep that in mind.

Thank you

Sorry to jump in so late on this one but the last post I read said that you are using the Paxton supplied tubing for your mass air meter. Does this mean your meter is pretty much sitting right next to the head unit of the blower? My car ran like yours does when my 73mm C&L was next to the head unit. I threw on a powerpipe and it fixed the problem. BTW I did put the stock meter on before I used the powerpipe to make sure that was the problem. But like everybody else, this is what fixed my problem, not sure if it will fix yours. ;)

Chris

Ditto. Not to make you spend money but my C&L wouldn't idle till i put my meter in the fender and clock'd it so to speak.

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Originally posted by Chris_H
Sorry to jump in so late on this one but the last post I read said that you are using the Paxton supplied tubing for your mass air meter. Does this mean your meter is pretty much sitting right next to the head unit of the blower? My car ran like yours does when my 73mm C&L was next to the head unit. I threw on a powerpipe and it fixed the problem. BTW I did put the stock meter on before I used the powerpipe to make sure that was the problem. But like everybody else, this is what fixed my problem, not sure if it will fix yours. ;)

Chris

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Yes chris, the meter is sitting RIGHT beside the head unit. I am using the black filter cover that covers the filter to prevent fan wash.

Maybe i need to purchase a pro-m meter.

Uhh, that power pipe. Does it put the mass air meter thru that 3 or 4" hole in the fender. I cant go thru the hole where the STOCK air filter was. I have my MSD box mounter inside there.


I am greatful that you all are helping this matter.

This is a quote from pro-m's website. I think its interesting. I am gonna try it this weekend. Here goes........




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If you have a turbo or a super-charged system the crankcase vent tube must be enlarged (5/8 " to ¾ ") and plumbed between the mass air flow sensor and the inlet of the super charger/turbo.

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Thanks.....:confused:

You can make the C&L work it just takes a little patience. Try clocking the flowtube to the inside most egde of the stock paxton pipe. i just run breathers. i don't run pcv. everybody will have thier own take on this subject. Mine is that oil causes detonation. Check out Morpheus.com

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Originally posted by regattacoupe
You can make the C&L work it just takes a little patience. Try clocking the flowtube to the inside most egde of the stock paxton pipe. i just run breathers. i don't run pcv. everybody will have thier own take on this subject. Mine is that oil causes detonation. Check out Morpheus.com

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I will........


Thanks for the help:D

I have fixed the backfiring.

I took the mass air meter apart and discovered that one of the "elements" was black. It was covered with oil from the K&N air filter that i had on it. I took some alchohal and cleaned them both. There was only one element that had fluid on it. It was the one in the back (with the black electronic installed upright).

The backfires are GONE. The car runs sooo good now. It even sounds better.

I ALSO WANT TO THANK EVERYONE FOR THERE TIPS AND SUGGESTIONS!!!:cool:

I still have a bug or two. But believe i will be able to work them out tomorrow.

Heres a pic of what i saw. You can hardly see it, but its darker than the other element.


http://www.hunt101.com/img/070076.JPG