Hard intake backfire!!

I

im4darush

Member
When going into boost, it backfires hard enough to blow all the vac lines off the tree. Does it all the time, no exeption. Just started out of nowhere, ran fine before. any ideas?
 
Do not get into boost. You are running severly lean if it backfires that bad. Check your fuel pump and regulator.
 
im4darush said:
When going into boost, it backfires hard enough to blow all the vac lines off the tree. Does it all the time, no exeption. Just started out of nowhere, ran fine before. any ideas?
Click to expand...

More specs on parts/combo.... at WOT or during moderate acceleration? Stock MAF or LT/SX.... need more info please.:) early on when i first got my car i had a backfire on the highway and then the car idled like crap and felt like there was a massive miss fire. turned out my MAF sensor crapped out ....

ps if it does it EVERY Time..... quit doing it. until you find the problem....especially if you are doing constant WOT blasts - A $100/200 dollar fix could turn into a major headache. HTH
 
I stopped going into the boost after the 2nd occurance. WOT is not required, it will backfire hard as soon as the boost starts coming in.

This is no coinsidence I am sure, but this started happening after I ran the car really low on fuel. Was on the freeway doing about 70 when the car just shut off. Had about 1/16th left in the tank (according to the gauge) and was trying to make it to a gas station. Well the car just shut off and I coasted to the side. Started back up and got me to the gas station. After that, I started having this issue. Probably ran it too low and sucked some crap into sock of the pump. Planning to change the pump asap and see if that was the issue.
 
Sounds like you have a fuel issue. It's a good chance that running it almost dry picked up a load of junk and clogged the filter and/or damaged the fuel pump. I would start with a the cheap stuff. Change the fuel filter and put a fuel pressure gauge on it that you can see while driving. Cruise around gently and see if the pressure drops off as you approach boost, if so that is a sure sign something is wrong. It should rise on a 1:1 ratio as vac drops and boost rises.
Also, Please go easy on it during testing, backfires in the intake is all sorts of bad for lots of parts. :eek:
 
Yes, I agree. I have a walbro and hotwire harness on order. The pump is probably the original, so time for it to go. Will change the filter at the same time, and stay out of the boost until the parts come in. Fuel pressure at idle is 40psi. Gauge is under the hood, so can not verify if it goes up as it should.
 
Installed the walbro and hotwire kit today. Still backfires through the intake like a SOB. Set the fuel pressure to 43 at idle with the vac line off. It seems to run better part throttle and has good power, but if I get into it real hard and the boost gets up there..............POP...blows all the vac lines off the intake. I dont have a FP guage in the cabin (under hood only) so cant see if the fuel pressure goes up 1:1 with the boost. Other ideas and/or advice would be greatly appreciated. Was sure it was the FP but alas.....Im not so lucky.
 
Go to the parts store and by you a decent fuel pressure gauge, one with the extension. Pull the one you have off and screw the new one on and tape it to your windshild.

It wont be the last time you use it I can promise. A couple of good tools to have are...

Good FP gauge
Compression/Leakdown Tester
Known good MAF
Known good Coil and Module
Spare set of Head Gaskets;) J/K on that one

Do you have a scan tool?
 
While you're working on the fuel side....make sure your fuel filter is fresh too.

I've also had a bad coil pack cause this. Bad plug wires can do it and so can the wrong heat range spark plugs....
You can check the coil pack and plug wires out with an ohm meter. Coil pack should be in the range of 11-13K Ohm across each tower set.
 
Yes, I have a scanmaster. Also have an external fuel pump in addition to the walbro in the tank. Makes no difference if I turn it on. Backfires all the time when the boost climbs over 20 psi. Would be strange if it isn't getting enough fuel with a new hotwired walbro as well as an external pump. Are there any other things that can cause the backfire through the intake aside from going lean?
 
Update....

I changed the plugs on the car and it stopped backfiring when accelerating from a stop. Runs very well from a dig. I am not on the track so cant really take it through all the gears. However, I have found that the car still backfires when I downshift into a lower gear at highway speeds. From 55mph as an example, putting my foot into it will bring it into a lower gear and it will backfire if the boost climbs high enough. Is there more load on the motor in this situation??
 
im4darush said:
Update....

I changed the plugs on the car and it stopped backfiring when accelerating from a stop. Runs very well from a dig. I am not on the track so cant really take it through all the gears. However, I have found that the car still backfires when I downshift into a lower gear at highway speeds. From 55mph as an example, putting my foot into it will bring it into a lower gear and it will backfire if the boost climbs high enough. Is there more load on the motor in this situation??
Click to expand...

The plugs might have only been part of the problem. I hope you got the R43's.
What gap did you use?
Have you checked your coil pack and your plug wires with an ohm meter yet?

Most load is on the motor in 3rd at WOT at about 70mph.
 
Hi,
If the MAF is reading 14 g/sec at idle,you have a problem. Also,if it reads zero,and reference voltage is good,watch out.Average is around 4. My car ran like crap,misfiring and subsequently running rich when the MAF went out.
 
meanchicken said:
I've also had a bad coil pack cause this. Bad plug wires can do it and so can the wrong heat range spark plugs....
You can check the coil pack and plug wires out with an ohm meter. Coil pack should be in the range of 11-13K Ohm across each tower set.
Click to expand...

x100! Coil Pack gets my vote.... given your most recent information....
 
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