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B230FT backfire under boost

Usually is the intake hose into the turbo from the air filter collapsing. Or you have bad air leak somewhere from the turbo to the intake. Could be spark blow out if you have big turbo and way more boost then stock, fix that with colder plug and tighter plug gap. NGK BPR8ES at .022 to .025 gap.
 
I'm having the same problem. Was it ever figured out?

It probably was a lean condition that sometimes causes a "backfire" at the intake level. Some call it a lean POP! Do you have a wideband installed?

EDIT: Reread the OP's question/description. It's probably what Sbabbs is describing and not what I thought it was...
 
Most common issue would be spark blow out, from looking at this thread and reading it sounds like his .030 plug gap causing the issue. I recently have a similar issue coming up on my wagon where after a period of time my car will start to buck and miss at the onset of boost. I pulled my plugs and they were up to .030, I gapped them back down to .026 and it was back to normal. I had the same issue 4-5k miles ago and the fix was the same thing a new set of plugs gapped correctly and the problem goes away.

Other good advice in this thread from having a WB, not feeding it to LH, along with doing a pressure test.

But the plug gap is the most common issue besides the intake hose collasping just like sbabbs mentioned. Only thing I have to add to that is that the bpr8es plugs might be a little to cold as some locals have had minor issues with it on mild boost (15psi).
 
I don't have any soft intake hoses, no boost leaks, afr's go down to 11-12 before backfiring starts at about 4psi of boost. I installed a boost controller, boost gauge and afr gauge. I had the boost at 12 psi, car was running great, then I turned it up to 14psi, didn't go lean, but it barely did that backfire thing, so I turned down the boost and it just got worse and worse. Now it hits 4psi and backfires/ missfires / bogs. I have a video of it that I'll post soon, and I'll gap the plugs to 0.026 when I get home from school. Thanks for the help!
 
Head gasket leaking fire between cylinders? :grrr:


Start with plug gap then fuel pressure (under load) to make sure fuel pressure raises with boost).
Then look at ignition secondary, measure plug wires, check cap & rotor.
Maybe a new set of standard cheap plugs OEM heat range?
 
I just got a new cap and rotor and plugs from IPD for the turbo models. Replaced intake manifold and throttle body gasket, cleaned throttle body, did a hot compression test with 138-145 psi on all cylinders. I have a coolant leak between back of motor and firewall if that does anything.
 
Could also add to the list of possible failure points: Failing fuel pumps, bad MAF, dying ECU, weak coil.

How did you check for boost leaks?
 
I have a coolant leak between back of motor and firewall if that does anything.

No coolant leak is acceptable, more so if it is coming from between the block & head.
Even more so on a boosted motor!
That's the clue bus stopping and giving away day passes.

Is it rolling coal or is the rear bumper sooty?

Did gapping the plugs cause a change?
 
No coolant leak is acceptable, more so if it is coming from between the block & head.

Is it rolling coal or is the rear bumper sooty?

Did gapping the plugs cause a change?

I don't think that it is rolling coal, doesn't appear to be. I have an open downpipe so the rear bumper isn't sooty. The coolant leak seems to be coming from the heater hoses between the engine and the firewall but I'm not 100% sure. Give me tips to try to pinpoint the leak please. Yes, gapping the plugs caused a change!... for about 10 minutes. I let the car idle and warm up and I was happy when the car ran ok, and pulled hard at 7psi with only a couple misfires. I turned up the boost to 12psi and the car continued to run with only a misfire or two per pull with AFR's around 12. 5 minutes later, the car started to do the same bog/ backfire at 12psi, then 11, then 9, 7, 5, and now it only goes to 4 psi before completely misfiring. I'm racking my brain trying to figure out what the problem is. I really hope it isn't head gasket related. This whole time I only lost about a quart or two of coolant, I know that isn't good, but I also don't feel like it is too bad. Please post some more ideas
 
Sounds like you have a large boost leak, I had something similar and it was the IAC hose was torn under boost, it would whistle over a certian PSI but at lower psi's it would just leak can cause misfires. Next time you pressure test it use a spray bottle with soapy water and spray it on every place there is a connection for pressurized air.
 
The progressive drop in boost where this issue is occurring might point to insufficient fuel supply. Does it happen more with the tank 1/4 full or less than with it 3/4 full or above?
 
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