Strange Acceleration

[Ian C]

It's not a TT ECU you've got in there by accident is it? That does strange things at exactly that rpm

[Benjy]

My NA 6 felt as if it had an extra push at around 4500rpm. I had a double decat, 3" cat back, HKS plugs and an HKS induction kit.

[Guest Roger NE]

It's not a TT ECU you've got in there by accident is it?

 

No it's definitely an N/A one

 

My NA 6 felt as if it had an extra push at around 4500rpm

 

Yes that's when the ACIS system switches from a twin intake to a single one, that's why you sometimes get a power burst

 

But this is MUCH more dramatic than that . . . as I say it's like 30% extra power !

[Graham1984]

No it's definitely an N/A one

 

 

 

Yes that's when the ACIS system switches from a twin intake to a single one, that's why you sometimes get a power burst

 

But this is MUCH more dramatic than that . . . as I say it's like 30% extra power !

 

You do realise stating NA and 30% power boost will have people mimicking your set up....... the rest of them will say now it's only slightly more powerful than a Fiat Cinquento

[Guest Roger NE]

Yes but it's not 30% EXTRA power . . . it's obviously LESS power until you hit 3750 rpm!

 

Now that the sun has stopped shining I've just checked the Ignition Timing with a strobe . . . and it's spot on.

 

So that's ruled that possibility out.

 

I'd welcome any other suggestions as to what could be causing this.

[Graham1984]

Well now that the sun has stopped shining I've just checked the Ignition Timing with a strobe . . . and it's spot on !

 

So that's ruled that possibility out.

 

I'd welcome any other suggestions as to what could be causing this.

 

 

Is just enjoy it not an option

[Guest Roger NE]

Is just enjoy it not an option

 

NO ! Because I'd rather the power was there below 3750 rpm too . . . and obviously something isn't right, or else this wouldn't happen.

 

(if I wanted sudden power increases I'd have a turbocharged engine - it's one of the many reasons I don't like them!)

 

Does anyone know at what RPM the Fuel Pump ECU starts giving full power to the fuel pump? (if it's at 3750 rpm this would be a big clue)

[Guest Roger NE]

Does nobody have any idea about this?

 

Where are all the techies?!

 

The best way I can describe what happens is like if you've ever had faulty HT leads that are breaking down . . . you're accelearating hard, but only on 4 cylinders . . . suddenly the 2 faulty leads start working and INSTANTLY the car surges forward with 30% extra power.

 

That's what this is like . . . but it's obviously not an HT fault as it ALWAYS happens at exactly 3750 rpm

 

I say always . . . actually it only happens at WOT, not at half throttle . . . that must be a clue too.

Edited July 19, 2014 by Roger NE (see edit history)

[LOGIE]

When you say your using the correct ecu ie 2JZ-GE are you using a manual one? Or possibly an auto one? Just a thought.

[Guest Roger NE]

No its definitely a Manual ECU - the engine was from a Manual Mk4 Supra, and I bought it with its ECU and all ancillaries (and having had to suss out all the wiring to do this transplant there were obviously none of the Auto connectors)

[Josh42]

The auto ECU could also be used to control a manual car, just not the other way around.

[Guest Roger NE]

One other thing I have just thought of to mention . . .

 

The speed signal that the ECU gets from my Mk3 dashboard is MUCH slower than it would get from a Mk4.

 

However, I don't think the ECU actually uses this signal for much on a Manual car . . . perhaps power steering (but I'm using my Mk3's PAS controller, which is separate) . . . the speed limiter of course . . . and perhaps spoiler control (which again I don't have).

 

I didn't bother connecting the wire at all originally, but it threw up a Fault Code as it wasn't receiving anything - connecting the wire from the Mk3 dash seems to keep it happy.

 

But as I say, I can't see how this can be related, as it's not speed dependent - the sudden surge happens at 3750 rpm in ANY gear at WOT.

Edited July 19, 2014 by Roger NE (see edit history)

[stevie_b]

However, I don't think the ECU actually uses this signal for much on a Manual car . . . perhaps power steering (but I'm using my Mk3's PAS controller, which is separate) . . . the speed limiter of course . . . and perhaps spoiler control (which again I don't have).

 

I didn't bother connecting the wire at all originally, but it threw up a Fault Code as it wasn't receiving anything - connecting the wire from the Mk3 dash seems to keep it happy.

 

But as I say, I can't see how this can be related, as it's not speed dependent - the sudden surge happens at 3750 rpm in ANY gear at WOT.

Correct AFAIK: the mk4 only uses the speed signal for speed limiting, and controlling ancilliaries like power steering. Like you say, as your problem is rpm-dependent, it seems doubly unlikely that its anything to do with the speed signal.

 

I don't drive mine much, but the next time I do I'll do the tests you describe. I'm pretty sure I won't feel any surge though: I've never noticed it before.

[Guest Roger NE]

That would be good Steve, thank you (or anyone else that could do this too)

 

Even if you notice the SLIGHTEST change at 3750 rpm, it will tell me that SOMETHING changes at those revs on these engines . . .

 

Then I can continue trying to suss out what it is on MY setup that is exaggerating the problem.

 

I seem to be ruling more and more things out . . . but not coming up with any new ideas as to what could be causing this!

Edited July 21, 2014 by Roger NE (see edit history)

[Guest Roger NE]

So has this really baffled all the Supra Experts out there?!

[Guest Roger NE]

Disappointed that nobody has any ideas about this - have I really baffled all the experts on here?

 

Someone suggested putting it on a Dyno . . . but that would only tell me what I already know - it wouldn't tell me what's causing it!

[Guest Roger NE]

Could any N/A owner please at least check whether they notice ANY kind of change at 3750 rpm when at full throttle?

 

I'd appreciate it . . . along with any suggestions about what on earth could be causing this problem.

[Kendo11]

Could any N/A owner please at least check whether they notice ANY kind of change at 3750 rpm when at full throttle?

 

I'd appreciate it . . . along with any suggestions about what on earth could be causing this problem.

YES.

 

I have no technical idea about what may be causing this, I always assumed and think I read that it was normal for it to have a small surge (not 30%) when you get near to 4000rpm.

 

I would say that mine is fine in lower revs, so it's not like it's 'missing' power lower down, but yes I have also definitely noticed a small surge at the higher revs.

 

Sorry I have no technical answer for you though.

[Shane]

Disappointed that nobody has any ideas about this - have I really baffled all the experts on here?

 

Someone suggested putting it on a Dyno . . . but that would only tell me what I already know - it wouldn't tell me what's causing it!

Yes, but what it would provide is a plot to compare with other NAs. Are you sure you are not simply feeling the power band of the engine, maybe with the mk3 being that much heavier than the mk4 it is more noticeable as the power output at lower revs below your peak power band starts is a little below what you are used to?

[mattdavies]

does your engine by any chance have aftermarket cams ?

[Guest Roger NE]

The engine is totally stock, with stock ECU. It is fitted in my Mk3 Supra, but using all the Mk4 ancillaries, MAP sensor etc to make the engine run.

 

Obviously the power gradually increases with ANY engine as you get higher up the rev band . . .

 

But what I am talking about is a FAULT. So at the risk of repeating myself . . .

 

At exactly 3750rpm when accelerating at full throttle, there is an INSTANT big increase in power. It is just as if two of the HT leads have broken down, so you are running on just 4 cylinders.

 

Then it's as if they suddenly fix themselves and you are running on 6 cylinders - so a big increase in power - instantly. As if someone has just flicked a switch.

 

I've had faulty HT leads on various cars in the past, so this is what it feels like. However, that would be fairly random, at different times and revs etc. This happens EVERY TIME at 3750 rpm if you are at full throttle, regardless of what gear you are in.

 

So the fault is obviously not the INCREASE in power, but the lack of it until you reach 3750 rpm. (there is no sign of a misfire, if you didn't suddenly get the extra power you wouldn't realise there was something wrong).

 

But this DOESN'T happen if you accelerate at half throttle - there is no noticeable change at 3750 rpm

[Chris Wilson]

Have you disabled the plenum volume flap and checked if this situation changes?

[Shane]

The engine is totally stock, with stock ECU. It is fitted in my Mk3 Supra, but using all the Mk4 ancillaries, MAP sensor etc to make the engine run.

 

Obviously the power gradually increases with ANY engine as you get higher up the rev band . . .

 

But what I am talking about is a FAULT. So at the risk of repeating myself . . .

 

At exactly 3750rpm when accelerating at full throttle, there is an INSTANT big increase in power. It is just as if two of the HT leads have broken down, so you are running on just 4 cylinders.

 

Then it's as if they suddenly fix themselves and you are running on 6 cylinders - so a big increase in power - instantly. As if someone has just flicked a switch.

 

I've had faulty HT leads on various cars in the past, so this is what it feels like. However, that would be fairly random, at different times and revs etc. This happens EVERY TIME at 3750 rpm if you are at full throttle, regardless of what gear you are in.

 

So the fault is obviously not the INCREASE in power, but the lack of it until you reach 3750 rpm. (there is no sign of a misfire, if you didn't suddenly get the extra power you wouldn't realise there was something wrong).

 

But this DOESN'T happen if you accelerate at half throttle - there is no noticeable change at 3750 rpm

I am sure most of us have experienced wanked out plug leads at one time or another, but you are saying it sounds and runs fine at lower revs, but is somehow producing less power than you consider it should be. Stick a video up so we can get a better idea maybe. Try monitoring the fuel pressure while this happens to rule that out.

[jagman]

Bypass the fuel pump control module , it is signalled from the ecu to up the fuel pump speed , but its a bit vague on when this happens in the manual

[Guest Roger NE]

Thanks for the replies and suggestions chaps . . .

 

Have you disabled the plenum volume flap and checked if this situation changes?

 

Yes - as posted earlier I have tried disabling the ACIS - either making the flap permanently open or permanently closed doesn't affect this big change at 3750 rpm

 

but is somehow producing less power than you consider it should be

 

It's not that I THINK it should be producing more power at low revs - it's the fact that it SUDDENLY produces LOTS more power, just like flicking a switch, at exactly 3750 rpm

 

Bypass the fuel pump control module , it is signalled from the ecu to up the fuel pump speed , but its a bit vague on when this happens in the manual

 

Having eliminated other things, this is the one thing I have already thought it might be . . . whether there is a lack of fuel until the ECU perhaps suddenly runs the pump at full power. If that happens at 3750 rpm, then that would explain it. Do you think if that's the case it could cause this effect? (ie if I had fuel starvation until the pump suddenly switches to full power)

 

The fact that it happens at WOT, but not at half throttle I'm thinking would tie in with this.

 

What I thought I would do as a test is run a wire from the Fuel Pump Feed (which is on the check connector under the bonnet) to inside the car . . . connect it to a meter and get my g/f to see if it suddenly changes at the prescribed point, ie at 3750 rpm.

Edited July 25, 2014 by Roger NE (see edit history)