hiflexaust

Hi there 993 TT Boffins.....I need some help!
I super sprint my car and also do tarmac rallies with it and on my last track day I noticed a hesitation at around 4000-5000 rpm. It then pushed thru and accelerated just as hard as usual. I have taken it to my tuner and I am told I need to fit an "interceptor" to allow manual adjustment of the boost to solve this problem? Others whose opinions I have sought have suggested fuel pump issues and breathing issues. The car is fully serviced with only 22,000km's and has new I/C hoses and new everything else. The car had a $6000 service before these dyno pulls. feel free to mention anything you like about the dyno sheets but please, if you can, be productive. Thanks in advance.

Full Boost

Grant,

Sorry to hear this.. and Richard has no answer?

I have to say by looking at it that it is an electrical issue - seems too consistant for anything else (noting your boost settings)

As for a MBC - i will let the experts elaborate?

See you on Sunday?

Jean

Grant,

I am a bit confused as to why your tuner thinks you need to go with a fixed boost controller? If I understand it correctly, you felt a hesitation while on WOT..This is not uncommon on our cars that are being tracked, it typically suggests that you need to change spark plugs, check the plug wires and distributor or in your case take a look at your MAF maybe.

As to fuel, the only reason it would do this is if you are having fuel supply issues at full boost or a dirty fuel filter (unlikely since it is limited to a certain RPM). Fuel supply: Have your tuner do a test on flow pressure, simple to do, simply needs to plug a gauge into the fuel rail, or alternatively the fuel pump ot know if it is an issue with the pump or FPR or what.

I would not jump to conclusions, namely if the car has been running well so far, why would it suddenly go into uncontrolled overboost that I am guessing your tuner is trying to correct?

These dyno charts don't mean much to be honest, boost seems to be holding stable, the Hp hickup that you see must be due to something else as mentioned earlier.

I might be missing sth obvious, but this is my quick opinion

TB993tt

Is the engine 100% stock ?

If yes then see Jean's analysis. I had similar problem which a new MAF solved. The hesitation at around peak torque is (or was on mine) too much overboost leading to the ECU cutting the spark momentarily - this is much easier to do on a modified engine since the boost control function (wastegate control) is not super fast and the engine can be made to severely overboost if one plays with the throttle in a certain way - a stock engine should be far away from hitting this limiter so it would point to a component failing....

Edit
Actually I am a little confused, the top dyno sheet shows curves at different boost levels, is this a fixed boost level via a controller ? if yes then the problem you have is more simple to explain (however you mentioned your tuner NOW suggests a fixed boost interceptor solution so I don't know what boost control you are running)

hiflexaust

Hi Simon......PRT suggested the "Interceptor"........yep, you will see me Sunday and I will be there early to help park cars like last year.

Hi Jean.....Was hoping you would buy into this one. Car has new plugs, leads and distributor......but not MAF......will go there first! I also do not understand the manual boost control suggestion.....Im ok with the concept but not as a band-aid to side step a problem........thanks for your help so far but you might not yet be off the hook......will let you know how it pans out.

Hi Toby......I was also hoping you would help me out! I have read and re-read a lot of your posts over the last few days as you have dealt with boost quite a bit. The engine is a 993 TT S spec engine which is standard all but for a FVD Motronic unit. It dynoed on another dyno at around 395 HP at the wheels which would have given around 430 or so at the crank allowing for all the normal inconsistencies. Now we seem to have 317 max at the wheels and the hesitation you can see on the charts. The different curves on the top sheet are because the tuner fitted a makeshift manual boost controller and played with it to see what happened......keep the advice flowing please

TB993tt

Grant

OK, I understand the different boost levels on the dyno sheet now...

So you have been running it with FVD ECU for a while with zero problems until recently is that correct ? (BTW is it 450PS base model ? )

The FVD ECU is more than likely the culprit maybe in conjunction with an iffy MAF (I had a similar problem on my last engine set up which the MAF appeared to solve)
The way these agressively tuned ECUs work is to bring the torque on quite abruptly by aggressively ramping up the boost (presumably by advancing timing) which under certain conditions can cause too much boost which in turn trips the ingnition cut out and gives you that stutter. Once the boost drops the engine will continue so it is momentary.

The "certain conditions" in my experience (based on the fact that yours was NOT doing it before and it is a new condition) are:

MAF going bad (happened to me)

Atmospheric conditions changed so that parameters go out of range at peak torque. eg if it is colder and the air has more mass then the poor boost control of the ECU may give that little bit too much air mass triggering the cut out (with warmer air the same overboost level will not reach the critical air mass level hence no cut out)

Any use ?

Felix

It would be real useful to see a boost curve under those track load conditions.

Consider changing the N75 (frequency) valve as they seem to get lazy as they age and may allow an overboost that the ECU pulls the timing for in order to protect the engine. The part number is 993 605 119 00

Steve Weiner-Rennsport Systems

I'd love to know what grade fuels you used during the dyno sessions as well as ambient temperatures.

malcolmd

Hey Grant,
Not much to offer here other than sympathy. It seems like we are all having trouble lately (Simon, you and me). I'll be reading your posts with interest. My engine is due to go back in next week. My tech is in Thailand on holidays slowing things down. Patience, patience, patience....
Hope you get to the bottom of this quickly. I replaced my MAF a year or so back. You might want to bring it in from the US, as the local cost was about twice the US price....

Malcolm

hiflexaust

Toby, I have written to FVD with these dyno sheets and they are adamant that it is a mechanical problem, either fuel or something else. The unit is a 450ps base unit. I do not claim any of the dyno figures to be accurate in terms of how much HP the car is putting out but if all done on the same dyno then the numbers should at least provide a constant. I am checking now to see when the MAf was done as I have a sneaking suspicion it was not that long ago.

Phelix...thanks for your help and I dont have any way of doing the boost load on the track. Will look at the frequency valve in this round of problem solving.

Steve....thanks to you too and the car runs 98 RON pump fuel as it is what we run in Super Sprints and about the best you can get locally.

hiflexaust

Hi Malcolm, Thanks for the sympathy but in comparison to your issues, none needed. My problem is a small niggling one that does not have major repurcussions as I drive according to it and only use the car every other month. Write me a mail and tell me how yours is going and what you've done and blah blah blah. Simon and I are at the PCNSW concourse this Sunday and mine is in for wash and polish Race Car section. Madly cleaning and polishing now but we have gale force winds at present and Im fighting a losing battle!