Scooby_iky

Hi all I have a bugeye sti import, I have gotten the car mapped by andy carr some while ago and before the remap I had issues with 02 sensors so I've changed it before the remap. At around 4000-4500rpm I'm getting some hesitation when I'm at full throttle and while I'm just cruising. It feels like it's activating launch control then after about 4500rpm it goes back to normal. Mods on car are tomei turbo, tomei inlet pipe, tomei 3 inch straight through exhaust system and 3 inch downpipe, 2.1 stroker, hdi fmic, gt spec headers, 3 port boost solenoid, in-wing induction kit, sti pink injectors, launch control and overun. Power in region of 380bhp no print out as it was road mapped running mafless but still in place as I was told to leave it in, When i disconnect the maf engine light comes on. Been remapped with carberry software. I recently took off the coilpacks and put another second hand set in, New plugs pfr7b gapped to .5 the previous plugs where pretty bad and they where pfr6b. Car drives and feels better but still doing the same thing. Andy carr looked at it again and tried it with and without launch control and still doing same, but he don't know what it could be and haven't experienced this before, and Andy carr did say it's not the mapping and not coilpacks or plugs. But could either be,
1- Injectors.
2- cam sensor
3- camshaft pulley

The car will probaby need stripping down and see what the problem is.
Its weird because it happens while im cruising normally and its real annoying as i cant really drive the car. Has anyone had this before? Any help please as stripping the engine down isn't particularly cheap, thank you

hedgecutter

iTrader: (5)

I had a "miss" on a blob wagon at 3500rpm, hunted it for months, turned out it was poor injector spray pattern, felt like a new car after cleaning. Specialist mapper had previously told me it was unlikely to be injectors....but they will be in **** state by 70k miles

Scooby_iky

Cheers mate, I'll be taking the injectors out and getting them flow tested and cleaned and i can get a set of service kit with new seals and filter for the injectors so might aswel do that while they out. Hopefully that will do the trick.

Linksfahrer

I had a hesitation issue that threw up O2 codes , it turned out to be a intermittent movement on intake tumbler motor / plug,
the fault was found by Plymouth engine tuners and they carried out a TGV delete. Its still a good idea anyhow to do your injector flow test though,

Scooby_iky

Just an update with the hesitation and I know it's been fair few months since I last posted about this continuous problem. Well I finally got the reason for the hesitation and to help anyone else with a similar problem so you can look for the same thing. Right so after looking into the injectors, turbo, cam sensors, crank sensor, spark plug change and coil pack change. Also to add the car has been back and fourth to garages. Done many diagnostics on it and still no luck. So I eventually gave up. So I bought a exhaust bung for my exhaust system as I've got a tomei titanium system which is loud while the silencers in the car has quietened down dramatically, while driving I've been hearing a very weird sound coming from my engine area, so I've rev the car up to then notice it's got an exhaust leak. So off to garage and I've put it on ramp and what I noticed is the lower up pipe gasket is completely shat itself, and half the gaskets gone missing. Then the mechanic then noticed I got 2 cracks on my headers (gt spec and 3 bolt up pipe). So gone in the new gaskets and headers beens welded. All seems fine, boosts much better than before and no more hesitation. Spool is really noticeable and the sound of the exhaust is Miles better. Hope this helps anyone else with the same issue

Linksfahrer

Hi Iky , well it’s good to see you found your solution, and for others thanks for posting this one.

It prompted me to do a Failure Mode and Effect analysis. FMEA.

!Geek alarm!

So I have simplified it for general digestion.

Exhaust / Boost leakages will start occur first in a turbo system at highest boost level , but these will be masked to some extent by the turbo compensating (simply spinning to higher speeds) which it does while the waste gate remains closed, and which it will until the ECU sees sufficient boost for any given power circumstance that the mapping requires. Any acceleration hesitation experienced during a previously well behaved system can be notoriously difficult to find and in your case Iky was .

I have to say though on a Turbo system that exhaust leakages are the first thing to look for, this is especially the case for any car that goes to the mapper for a re-mapping which will likely mean increasing boost as well as timing changes in the search for more power are being applied. As soon as this is done then the engine will create more heat and heat causes expansion of metal, the cooling system is placed under more stress and all manner of pipes , sensors, electrical connections are also more likely to fail.

After adding a new down pipe / uppipe / and a full exhaust system , (Re-mapping is also typically carried out to make the best of these mods / or on a higher flow system becomes essential anyway to correct air fuel ratios under boost conditions ) .

The following seal/ gaskets are disturbed and will need replacement.
you need access to the turbo :-

Intercooler (IC) to blow off valve (BOV) paper gasket.

Turbo to IC flex pipe (inspect / reseat seal or replace jubilee clips as needed).

Turbo gasket to downpipe / uppipe.

Uppipe gasket to Headers.

Most downpipe exhaust changes will require you to jiggle for space so invariably the uppipe also has to come off, “alert” or was at least loosened without a gasket change !!

Equally any turbo change may require the uppipe to be completely disconnected. So then replace both uppipe gaskets.

So the same applies for header gaskets to the cylinder head if the turbo assembly and or new Decat or new tuners uppipe are really difficult to jiggle into position , you might need to loosen these bolts as well. My personal experience is that the exhaust header to cylinder head gaskets can be re-used (if the headers are not dismounted) but a Subaru workshop would not do this. Personally I throw away the gaskets provided by aftermarket exhaust supplier and use the original Subaru ones.

Any Turbo removal / loosen top end of uppipe always replace both gaskets.

Why ? Because you need to let the uppipe seat without stress onto the header. To do so you also need to jiggle the bolts for on the connection of uppipe to header exhaust. Note: The original uppipe designer saw that a flexible joint was required to allow for expansion/ contraction. Most aftermarket uppipes don’t have this feature so you need to be very precise in alignment and use all available wiggles to get proper alignment before re torquing.

This bit you won’t find in any manual:
Iky this for you.. or the previous owner of the (Tomei ?) uppipe / exhaust fit.


And for when the downpipes attached to the turbo are reconnected to the rest of exhaust system and potentially applicable to any joints along its entire length that still need to swim into position.

These are best loosely hand tight reassembled (yes untorqued).

Warm the engine , let it run for 10 minutes ! just at idle !, this allows the piping to expand slightly , seating into position. And in the first couple of minutes it allows you to listen / feel for the leak positions.

Then allow all joints to cool down to touch ( if you can’t touch it for more than a couple of seconds its still >60deg C so wait a while !
before final torquing the bolts.

Allowing this cycle will help prevent expansion stress transfer into the headers (originals are cast iron and do not flex can crack if unequally torqued ) / (aftermarket are welded flanges that potentially crack at the weld joint ) and helps prevent potential gasket / bolt fails at the uppipe.

Following your torque up restart the engine and check for leaks .

Any that leaks that do occur might show a system misalignment and a twist in system, do not over torque to stop as this causes abnormal bolt loading.

Better to go back a few steps and find out why and fix it now , than to develop a leak / shear a bolt later.


Enginetuner daily reality...
finding and fixing…

1. Boost system leakages.
2. Radcooling / overheating.
3. Exhaust system leaks.
4. Managing the punters disappointment, when his pride and joy does not meet his power expectation.

Michal

My problem is arround 4500-5500 little low power there and boost little going up and down