MAP fluctuations from long intake plumbing (4A-GZE)

[mullett]

I had my car tuned the other day for the first time with the EMS (DualSport), and it drives like a pig. The guy who tuned it said it was very hard to get a smooth tune, because the MAP was jumping all over the place, from -kpa to positive boost pressure, on anything other than WOT. I watched it, he's right, it jumps a lot, and of course because the fuel map is MAP based, that dumps in far more fuel than it needs. The best (and only) was I can think of to overcome this is to move the TB to just ahead of the intake. If anyone's got any suggestions about this (Ben Wilson ) I'd be well keen to hear them, or if someone else has found a way to solve this problem in the past. Oh...and kinda OT, but what spring pressure suits a BOV being used on a supercharger?

Cheers, RM.

[TurboRA28]

My mates 4agze had the same problem. He moved the throttle body and its a bit improvement.

Cheers
Joel

[bansheebuzz]

try a restriction in the vacume line to the map sensor

[jonra23]

Try putting an inline fuel filter in your MAP line, have used it on the OLD motec systems that had trim pots for tuning and it does help with erratic MAP readings.

As the BOV is only to dump over boost when running throttle body after supercharger set it a couple PSI above your calculated max boost numbers.

regards
jon

[Hen]

I had an ECU tuned to run my basically stock 4AGZE and I've never experienced problems like this. It drives fine (idle's a challenge, but that's a different story).

The only thing I can think of is that my MAP line to the computer comes off a factory vacuum restrictor thingy on the manifold.

Hen

[slide86]

what was the story with the guy running 2 throttle bodies on his GZE setup?

one before the s/c in factory location and another of the same size on the inlet manifold. apparently it made a big difference to drivability and idling.

i was thinking of trying this on mine. as i have a complete custom inlet and piping setup

[Skein]

what was the story with the guy running 2 throttle bodies on his GZE setup?

one before the s/c in factory location and another of the same size on the inlet manifold. apparently it made a big difference to drivability and idling.

i was thinking of trying this on mine. as i have a complete custom inlet and piping setup

That was GZE86, red/orange sprinter from Victoria which featured on the cover of Zoom magazine. I can't remember the exact details of the article, but he was, like you said, running two throttle bodies.

If I can find the magazine I'll dig up the details.

[Ben Wilson]

mullett - I never had any problems with fluctuations, perhaps my big plenum smoothed them out? Try the paper fuel filter, it works nicely on multi throttle body cars.

For the spring, I got the spring turbosmart make for the job, it's a fair bit softer than the factory one.

what was the story with the guy running 2 throttle bodies on his GZE setup?

I tried it, they were a bastard to get in sync and getting the idle right sucked.. I gave up and went to single TB and BOV instead (still not 100% perfect, but it was better).

[nick.parker]

In 'real life' even with a plenum any engine will have SOME crank angle based manifold pressure variation...there has to be! The flow into the engine is not smooth!
On my car (4AGZE with 4AGE bigport inlet manifold) I had an approx +/-10kPa variation within each revolution of the engine at light loads. It had a subtle but annoying effect as the car would gently and slowly surge faster then slower under constant RPM/Throttle conditions due to the 'beat' frequency created. The cause was "aliasing" of the MAP signal (My home made / custom ECU). Google for 'sampling theory' - if you sample a sinusoid too slowly it can look like a different frequency sinuisoid or even a DC level.)

The problem in the car is that a given MAP level / waveform needs to represent one 'LOAD' but its not just one constant value.

If you don't have a restrictive MAP hose, or a clever ECU (e.g. angle based MAP sampling) then your ECU will have some HACK e.g. Heavy lowpass filtering of the MAP signal - leading to potentially bad throttle response (hesitation), or it might take the minimum of every X MAP sensor sampled values etc.

Mullet, I reckon use a restrictor or maybe a small inline volume (lathe a custom mini cylinder to go into the map line and make it as small as possible such that it solves your problem...actually maybe just get a longer map hose..

Regards, Nick

[takai]

I think a longer hose wont solve the issue, but a small chamber for reverberation would, as would dampening the signal. Thats what the mini chamber and mini fuel filter do for you.

[nick.parker]

Try blowing through 1 foot then 3 feet of vacuum line! The longer hose will damplen the signal dues to more volume and its restrictive.

[mullett]

It's ok, I'm half-way though moving my TB anyways That being said, maybe I will try this, just see if it works with a little restrictor or a chamber. Ben W: Just out of curiosity, just how soft IS the spring they suppled you?

Cheers, RM.

[Ben Wilson]

Not as soft as I expected, but still a fair bit softer than a standard spring.

[Enchanter]

Try blowing through 1 foot then 3 feet of vacuum line! The longer hose will damplen the signal dues to more volume and its restrictive.

I do remember someone tested a very long map hose vs a much shorter one for a MS ecu and there seemed to be no noticable difference.

Im very interested in the outcome here as my 2jzge will have itbs furthur down the track and I know I am going to have similar problems.

[oldcorollas]

to dampen signals, you use a restrictor (MIG welding tips work well and come in sizes from 0.6 to? 1.2? 1.5?) and a carby fuel filter...

you can put the restrictor before (takes longer to change the pressure in the filter) or after (so the filter acts like a spring, but the restrictor reduces the effect)...
think of it like a resistor capacitor setup...

i'd start with just a filter and then restrict the line from the manifold (initially just by squeezing/clamping the tube until it makes a difference ) until it's good...