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hesitation under acceleration

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I think something bad is going on with my engine, can anyone suggest what it might be?

The car starts fine, runs fine, but sometimes if I floor it from like 60mph it accelerates but judders/misses?/hesitates, it doesn't seem good, so I go off the power. I thought maybe I had something in the fuel system so I used some redX injector cleaner, its had 4 treatments on full tanks, I thought it was cured cause I didn't get any problems for a week or 2 but it seems just when I forget about it, it happens again. I don't thrash the car all the time.

I cleaned the Maf sensor too, hard to do much else. I figured it could be electrical or fuel related, pump on the way out, coil packs, leads etc. I did the paperclip thing on the diag port & its 55 - no malfunction.

Any ideas?? im going to have to take it to a garage I guess but it would be good to have ideas of what it is most likely to be before I take it.
 
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S15AK

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I had a similar issue it would only happen at high speed when I needed to get on the power. I went through, plugs, maf, cas etc even a new engine loom. Turned out my engine valve springs was on the way out. You can uprated Valve Spring & Retainer Kits from various manafactures.

But you would need a to confirm it, get it on a rolling road mate.
 
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Is it when it's hot or cold? And does it only do it at 60? Cool packs sounds like the most obvious from other similar threads on here
 
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It's happened most when I'm going to work, start off at 30-40mph, it gets up to temperature right before I have to go up the slip road to the dual carriageway (I have separate oil & water gauges) then depending on what position the traffic is on the road I might decide I have to accelerate hard to join the road & sometimes it just gives lumpy hesitant acceleration, it doesn't happen every time I drive it. I went out today & had no issues.

i said 60 mph because of course I would never speed...... lol.
 
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CMR

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Plugs would be the first port of call for any type of missing or hesitation
 

S15_SAM

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I would guess at Coilpacks too. 2 friends with S15's have had missfires under load and Coilpacks have fixed it.

Other likely suspect would be boost leak.

Get some new plugs (Ngk bcpr7es are cheap and quality, gapped to 0.7mm) and try that but it won't fix it unless your old ones are cracked.
 
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The plugs are about 2 years old, NGK iridium. If it was a boost leak, wouldn't it be there all the time? Yesterday & today I've had no problem with the car, drives normal, accelerates properly etc.

Update - Everything is normal Im going downhill at 30mph, foot off the accelerator pedal & the exhaust starts popping/banging about 5 times.

It does pop & bang in general, like one time when changing gear or off the power as the revs drop etc, but never more than once. Is this pointing even more at bad ignition? spark plugs/coil packs?
 
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walbro fuel pump, cat back exhaust, blitz filter, fmic, boost controller, running at 280bhp.
 

CMR

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Sounds like the exhaust is leaking somewhere near the turbo and pulling in air
 
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Intermittently broken? Afterwards the car had no problems, the fault comes & goes & Seems to happen on full load & minimum load. I have more normal running days with no incident than days that I get the acceleration problem & this is the first time I've seen this banging thing, 5 pop/bangs each a second apart with zero acceleration, I thought it could be unburnt fuel dumping into the exhaust, maybe meaning an ignition fault in a cylinder.
 
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Are you recirculating the BOV....How many miles on those Iridiums Personally I would get rid of them, Ive had nothing but problems with them..I only use Platinums these days..
Have you checked for boost leaks..Could also be your O2 sensor..
 
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No its got a BOv. The plugs are just under 2 years old, do you have the part number for the platinum plugs? Would a boost leak not be giving me a consistent problem? I drove it again today & its totally fine again. Is it worth just replacing the o2 sensor anyway just cause of the age?
 
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I'm using the NGK PFR7B's...a cooler plug..If you have run a rich tune at some stage then yes that will kill an O2 sensor..Is it more noticeable under load/boost... I also know temp sensors can play up as well...It's tricky because its intermittent...Coil packs can also be very intermittent
 
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Sounds like the same issue I have with mine. Runs fine until I floor it, and then it'll sometimes miss and hesitate (but not always). Cleaned MAF, done paperclip check and code 55 too. Might be worth checking coil packs since it does seem to be a known thing.
 
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So you can easily test a coil pack for a fault even if its intermittent? I take it that if it was the o2 sensor I would have more consistant problems?

The mechanic I go to doesn't like it when I tell him I have an intermittent problem, especially electrical, my a pillar boost gauge randomly goes to the bottom, then to the top & then back down to the bottom & that's it until I turn the ignition off & back on, he says until it stops working he wont be able to figure out what it is.
 
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