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Hesitation When on Boost?

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Since i collected my, standard engine wise, S15 from Liverpool docks, it has started, idled, and rev'd perfectly fine. Being as it hasn't been road legal, the only 'test drive' i have managed to do is to the top of my road and back :rotfl:

This is where i noticed, when it comes on boost it begins to hesitate, and splutter, still boosting and revving through the rev range but a definite lack of power. a feeling of being held back if you will.

I put this to the back of my mind as i know of a lot of fresh imports needing a good run to blow out the cobwebs, and my S15 had been sitting for quite a number of weeks at the docks in Japan. it was also low on fuel, which was now pretty old too. maybe it just needed a good run, and a tank of v-power when it was road legal?

i carried on with modifying it as i was waiting to register it, and i fitted a FMIC, apex intake pipe and apexi filter.

I proceeded to clean the engine bay, and as i moved a connector block, it revealed this



The 3 wires to the o2 sensor on the turbo elbow were broken.

Could i have found the problem? would the o2 sensor cause it to run like this?

I repaired the wires, 1 black wires and 2 white.

black to black, obviously, but the two white wires were not marked up. in the past on other cars i have replaced faulty o2 sensors with a universal o2 sensor, and the white wires do not seem to matter where you connect them.

I test drove it again and it hadnt seemed to of made a difference. maybe the o2 sensor is faulty/white wires not wired correctly.

Now today my registration and tax came in the post so it was ready for a real test drive! first destination - Shell for some v-power :thumbs:

i then took it on a long run, with it still displaying the same fault. as it comes on boost it splutters, and hesitates, the power being held back.

throwing up some ideas in my head of what it could be:

- knackered/fouled up spark plugs? (not checked yet)
- now faulty o2 sensor?
- fault mass air flow sensor?

anyone had the same problem?

I intend to spend tomorrow finding out the problem, so all your input would be great
 
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Mine did a similar thing when I had a boost leak, did if definetly do it before the fmic install?
 
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The two white wires didn't matter which way round they were on my old car either, so i doubt it's that.
 
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yeah it definitely did it before....i'm going to replace the fuel filter, if i can get a hold of one today, as it was super low on fuel when i got it, and may have picked up sediment from the tank. the symptoms its showing could be a lack of fuel.

A guy on SXOC said he had a similar problem on his S14 and it turned out to be his coilpacks. i wouldn't have thought a faulty coil pack would be the source of the problem. would a faulty coil pack let the engine behave ok under normal driving, but then behave differently (hesitate etc) under boost?

but i suppose if they are starting the break down when your asking for them to perform at higher revs (when boost comes on) they can't cope, and would give the lack of power.

i also had a similar problem on an old honda civic, and it turned out to be the cat was blocked up. does seem more like a fuel/ignition problem to me though
 
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ben7356

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A problem im having at the moment sounds similiar however mines not there ALL the time and i also know what the problem for mine is :thumbs: my turbo is loose where it meets the manifold and is leaking boost pressure from being out of allignment, it goes away when i put the foot down and the turbo seems to reallign itself. i just need to tighten the bolts which are a mega slut to get to lol dont suppose youve got a boost leak anywhere?
 

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i have just had a similar problem but not when on boost, with mine it was when driving at a constant speed off boost. changed the spark plus, and problem gone....
 
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NIZAN-R

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1-change plugs
2-check for cracks in coil packs
if you find a crack or 2 tape it with good electrical tape and test drive if problem is gone replace the coil pacs
3-feul pump is failing
 
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Thanks for all the input guys. i changed the fuel filter today, and no change. I have ordered some NGK Iridium BKR7EIX plugs that will be here in the morning, so will see if that clears it up.

BUT....i noticed something today...

As you do, you mark up your HT leads/Coil Packs 1-to-4 to not mix them up. I noticed that mine had been marked up

no1. one pink dot
no2. two pink dots
no3. NOTHING
no4. Four pink dots

I will add, the plug cover was missing from the car.

Possibly at the auction house in japan/docks a devious opportunist has swapped his duff coilpack for my nicely working one? it is a possibility i suppose.

Will throw the new plugs in tomorrow, and if that doesnt help i'll source a new coilpack
 
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i ran my car with the o2 sensor unplugged and it ran fine mate,its mainly there to help your fuel consumption under 3k revs,obviously better with one lol
when i first got my car i had this and it was becasue they had put spark plugs in the werent cold enough so just spluttered and felt like it was hitting a brick wall around 3.5k defo sounds igniton related so i would just eliminate things one at a time,plugs are cheap enough to change grade 7 coppers are about £2 each ,then obviously coil packs ,cleaning the maf always helps anyway,fuel filter is also inexpensive
I just gave the car a proper service when i got it ,fuel filter,all the liquids,engine/diff/gearbox/rad then at least you know where your at with it.
Good luck getting it sorted mate,hope its something simple
 

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Your coilpack situation could go one way or another... as you say for #3 not to be marked might have been due to someone swapping a duff one for a working one (in your favour) or the other way round (to your disadvantage).


For an engine to be running correctly across the rev range you need the following:

1. Decent spark (plugs + coilpacks + good earths)
2. Decent fuel (pressure + filter + pump)
3. Decent airflow (no leaks)
4. Decent compression

Unfortunately it's a process of elimination starting with the easiest/cheapest and work your way through it...
 
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Well iv'e just replaced the denso iridium spark plugs with ngk iridium BKR7EIX

test drove it, and the misfire when it hits boost has gone. great? but it still has a definite loss in power. it was boosting to around 0.4bar, now it boosts to around 0.7bar

so to clarify, it goes through the rev range ok now, but when it boosts, there is no increase in power. all noise and no go haha

What does this point to?
 
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Well iv'e just replaced the denso iridium spark plugs with ngk iridium BKR7EIX

test drove it, and the misfire when it hits boost has gone. great? but it still has a definite loss in power. it was boosting to around 0.4bar, now it boosts to around 0.7bar

so to clarify, it goes through the rev range ok now, but when it boosts, there is no increase in power. all noise and no go haha

What does this point to?
I have just cleaned the MAF sensor, and although throttle response seems better, it still is lacking power.
 
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So it's boosting more now but has less power?
It doesn't have less power, but hardly any MORE power. it was misfiring when hitting boost before, obviosuly reducing power, but now the misfire is gone, you hit a wall when it comes on boost, the feeling of being held back. I'm going to investigate boost leaks tomorrow and check the manifold and turbo bolts for security.

any other ideas?

That 'possibly duff' o2 sensor wouldn't cause this type of fault?
 

craig8585

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O2 sensor wouldnt cause that sort of issue. Just unplug it and try again to eliminate it.

I'd check the fault codes in the ECU firstly, then if that gets you nowhere, get it RR'd to have the AFR checked out.
 

LuPix_S15

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Just check the fuel pipes going in to the plenum area and forms the loop which includes the 'damper' or 'pressure regulator' is the correct way round.


It might be nothing but I had symptoms (in hindsight) of 'hitting a wall' with boost when I first collected my 14a and since then, it's been revealed by my mate mechanic after I couldn't get her started that the fuel pipes (one of which has the fuel filter attached) was completely the wrong way round going in to the plenum pipes!! :wack:
 
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0.7bar is not going to be mega fast anyway, you should however have decent pick up in 2nd or 3rd when coming on boost with hardly any lag if your using the revs right.

Maybe you should take a quick video to explain...3rd gear 2500k...foot to the floor.

Are you 100% its stopped missfiring?
 
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