B230FT backfire under boost

[paulcurran]

My street driver is a 93 240 2.4 with a 94 940 turbo motor & T5. It has oversized pistons, RSI stage 1 cam & adj. gear with 2 deg. advance, Lostartof chips, 15 lbs. boost on 15g. Ran pretty well first 2000 miles, now it has started to cut out under boost, will actually backfire if the throttle is opened quickly. It started just occasionally doing this, now it's almost undrivable. No ck engine light, drives smoothly down the road. If you keep your foot in it now it will stop accelerating & buck until you lift, worse in higher gears under load.
Any ideas? I was thinking throttle switch, but runs well off boost. I don't have a wideband yet, sure feels like it's leaning out though. If the prepump quit would it act like this? Doesn't matter how much fuel is in the tank. Can cruise at 80 mph but can't pass from any speed.

[olov]

blowout? plug type and gap?

[paulcurran]

NGK BP7 something? Forgot, will have to go pull 1.

[Magnum TE]

pressurize the IC plumbing from turbo outlet to throttle body and see if there's a leak.

Got a wideband?
What do the plugs show?

[mrjaybeeze]

lean ? same behaviour as an old volvo with not enough choke when cold....?

YS Jaybee

[PEGASUS 6]

good luck guy, seems like a lot of blind tuning imo w/o a wideband

[Juggernot]

Does sound like a boost leak though.

[B_licious]

check your maf sensor

[B_licious]

also check your fuel pressure regulater pressure and return pressure

[Juggernot]

Also, is the hose between the MAF and the turbo collapsing? Mine had a hole that I couldnt see at one point that gave me similar problems.

[Dicktater]

Originally Posted by Juggernot

Also, is the hose between the MAF and the turbo collapsing? Mine had a hole that I couldnt see at one point that gave me similar problems.

This gave me major headaches! When I would mash the gas it would fall flat on it's face,let off the throttle and it would take off. The really bad thing that would also happen when it did this is the engine would suck one of the three front engine seals sideways and cause a major oil leak. This happened twice before I found a soft turbo intake hose.

I did get plenty of practice changing front seals....

[Jerd]

Get a wideband. Problem solved.

[Karl Buchka]

Originally Posted by PEGASUS 6

good luck guy, seems like a lot of blind tuning imo w/o a wideband

Originally Posted by Jerd

Get a wideband. Problem solved.

lolwat

[paulcurran]

Thanks for the input. The plugs are NGK BPR7ES .030 gap. I ordered an AEM wideband, are there any threads on wiring these? The intake hose going into the intercooler looks real soft, try to find a replacement & see what happens. Paul

[ElBertoPolvo]

hmm...mine still does this.....if i cut the engine off then back on sometimes it will go away.
yes, the consensus is that a wideband will work wonders for diagnosis....but i am thinking my intank pump is pooping out.

good luck......

[Magnum TE]

Originally Posted by Magnum TE

pressurize the IC plumbing from turbo outlet to throttle body and see if there's a leak.

Do you have a boost leak, do not pass go do not collect 200$ pressurize the intake plumbing before you do anything else, this is a STAGE ZERO maintenance item.

Originally Posted by paulcurran

Thanks for the input. The plugs are NGK BPR7ES .030 gap. I ordered an AEM wideband, are there any threads on wiring these? The intake hose going into the intercooler looks real soft, try to find a replacement & see what happens. Paul

Pull the plugs, what do they look like? White? Dark? You need to tighten up your plug gap a bit, stock is .028 for testing purposes go to a .026 just to be sure that you're not blowing it out. (later you can go back to a .028)

Follow the install instructions for the AEM, it's simple enough to not need a thread. At this point you don't need to know what's coming out of the engine. You need to know if un-metered air is going in, or already metered air is leaking out.

...has oversized pistons, & bucks until you lift

My wife's got oversized pistons as well and she doesn't stop bucking until I let off, I don't see the problem here. (she insisted that I wrote that)

[monkecmonkedo]

I just installed an AEM wideband in my +T (92 245) today. Piece of cake, just follow the instructions for the most part. For the power and ground, I just used my existing gauge power and ground. I took all four wires out of the sheath to make them more flexible (I just coiled the extra wire up and zip tied it). I'm using the Nernst output (0-1V) for my O2 readings, so I ran the white wire (analog out) through the firewall, put a spade connector and insulator on it and hooked it up to the O2 sensor input terminal. There are no splices, the wire runs directly from the gauge to the O2 sensor. I've heard the Nerst output doesn't work well for others, but I hooked up this way and it works perfectly (LH2.4). YMMV. Be sure to set the pot on the back of the gauge to P4 for Nernst output if you're going to use one O2 sensor. I'll be using the serial out (blue wire) for data logging in the near future so I coiled the wire up in an easy to reach spot for later.

The toughest thing to do was to pass the wire with the six wide connector for the wideband O2 sensor through the firewall. I used the rubber plug near the exhaust manifold (there is a big wire bundle passing through it and there are two smaller areas that are open). Just cut as "x" in one of the open spots with a razor blade to allow the wire to pass through. It is a bit tricky to get the six wire white connector through. For an easier install, you can pull the wires out of the connector, they'll pass through much easier. Just be really sure that you mark down which wire goes where in the connector.

Hope this helps. If you have trouble, I can post some pics in a few days.

[Magnum TE]

David, I'm glad you had success using the Narrow Band output off the AEM for LH. You are the exception to the rule, I would not recommend anyone using the simulated output for LH's O2 reading, it just adds one more variable to the equation. I used my AEM (I use an innovate LC1 now) I just had it stand alone, and not interface with any of the Volvo's systems.

If possible you should ground the O2 sensor to the ECU ground at the passenger footwell, this will help ensure a accurate reading by limiting ground faults.

Still the OP needs to confirm that he hasn't got any leaks, and that his MAF to turbo intake hose isn't collapsing.

[1983Turbo242]

Originally Posted by Magnum TE

David, I'm glad you had success using the Narrow Band output off the AEM for LH. You are the exception to the rule, I would not recommend anyone using the simulated output for LH's O2 reading, it just adds one more variable to the equation. I used my AEM (I use an innovate LC1 now) I just had it stand alone, and not interface with any of the Volvo's systems.

If possible you should ground the O2 sensor to the ECU ground at the passenger footwell, this will help ensure a accurate reading by limiting ground faults.

Still the OP needs to confirm that he hasn't got any leaks, and that his MAF to turbo intake hose isn't collapsing.

I don't quite get why everyone hates the Nernst simulator on the AEM widebands. Mine works great with L.H. 2.2 For the most part L.H. is too dumb to know it is not getting a true narrow band signal.

Check fuel flow. If it is doing it almost all the time I would be suspicious of a fuel supply problem. When was the last time you changed your fuel filter?

[superveggie12]

I'm having the same problem. Was it ever figured out?

[sbabbs]

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.

[poulrais]

Originally Posted by superveggie12

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...

[sbabbs]

Yeah what exactly is it doing? FAlling on it's face or popping and jerking?

[shoestring]

Just because no one has said it, I'd also look at valve springs.

[thelostartof]

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).