Lack of shove above 4,000 RPM

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Lack of shove above 4,000 RPM

Postby Owen L » Sun 18.12.2022, 02:51

I'm getting a good response from the car as i rev it through each gear up to around 4,000 RPM. From there the revs build more slowly and the turbo gauge shows a solid 0.4 Bar. I have done hours of reading here to see if people have had a similar symptom and the cure. Here is what i know so far and what I have tested so far.

1. The car idles perfectly - so unlikely to have gross vacuum issues
2. The wastegate rod moves - i haven't pumped it up, just wiggled it
3. I have checked every clamp and pipe from the Air intake right through to the Inlet chamber - nothing loose or fitted badly.
4. The Boost Control Frequency valve (BCFV) from now on known as the Boost solenoid (Turbo shop told me we don't call it that anymore) works when 12V is applied to it.
5. The car does not perform any worse/differently when the Boost Solenoid (BCFV) is unplugged. This leads to me to suspect it is not being told to open by the ECU?

The car does not stutter or hesitate at all during acceleration. It definitely doesn't over boost.

I have ordered the parts need to construct a cable and once that's here and built, i will plug it in and see if the data shows any issues. What should i look for exactly here? I am aware the solenoid needs 4 inputs and no codes to be allowed to open by the ECU sending a signal.

What I'd really like to know is how different a correctly working car behaves when you unplug the Solenoid. Does the car then perform like this (i.e. a lack of urge beyond around 4k)

Anyone got the time/inclination to unplug it and drive round the block to see what difference it makes?
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Re: Lack of shove above 4,000 RPM

Postby Tuga2112 » Mon 19.12.2022, 15:27

im assuming your not hearing any hissing noises or whoosh noises when the needle is on the 0.4 ?
just making sure to rule out the obvious air leak from the system.
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Re: Lack of shove above 4,000 RPM

Postby RonR » Tue 20.12.2022, 19:02

The secondary throttle comes into play at 4700 RPM, could it be a fault in that system? A vacuum, electrical or mechanical fault could mean the throttles aren't doing what they're supposed to. Mine were almost seized when I dismantled the intake recently, I managed to work them free again with plenty of Plus-Gas and wiggling.

Edit: Another thought...
Do you have a Dump Valve fitted? If the dump valve has too weak a spring it could bleed off the turbo pressure at 0.4 bar.
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Re: Lack of shove above 4,000 RPM

Postby Tuga2112 » Tue 20.12.2022, 19:11

RonR wrote:The secondary throttle comes into play at 4700 RPM, could it be a fault in that system? A vacuum, electrical or mechanical fault could mean the throttles aren't doing what they're supposed to. Mine were almost seized when I dismantled the intake recently,


secondary throttle ? have you got any pictures of where this is ? it be funny if i could squeeze a little more power out of my car :D
1991 elan se
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Re: Lack of shove above 4,000 RPM

Postby RonR » Tue 20.12.2022, 19:25

Tuga2112 wrote:secondary throttle ? have you got any pictures of where this is ? it be funny if i could squeeze a little more power out of my car :D


The secondary throttle is in the lower intake manifold, the one hidden down the back of the engine. It's controlled by the ECM electrically, and has a separate vacuum valve and reservoir, also hidden between the engine and firewall.
It's in:
Closed Loop Engine Management Manual section EMJ - 3 - L
Open Loop Engine Management Manual section EMK - 3 - L
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Re: Lack of shove above 4,000 RPM

Postby Owen L » Sat 24.12.2022, 05:37

Tuga2112 wrote:im assuming your not hearing any hissing noises or whoosh noises when the needle is on the 0.4 ?
just making sure to rule out the obvious air leak from the system.


No obvious noises, no. mind you its all starting to happen at that point. I now have ElanScan, so is there anything in the data i can zoom in on to give me more clues? Appreciate your videos, used them just now to locate the plug for the scan. Cheers.
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Re: Lack of shove above 4,000 RPM

Postby Tuga2112 » Sun 01.01.2023, 00:31

Owen L wrote:
Tuga2112 wrote:im assuming your not hearing any hissing noises or whoosh noises when the needle is on the 0.4 ?
just making sure to rule out the obvious air leak from the system.


No obvious noises, no. mind you its all starting to happen at that point. I now have ElanScan, so is there anything in the data i can zoom in on to give me more clues? Appreciate your videos, used them just now to locate the plug for the scan. Cheers.


ive been fortunate enough to never had any major engine issues with any of my cars I read somewhere else in the forum that the turbo wont work properly if the car is not up to temperature. and i can confirm from experience that happens. because my thermostat is stuck open right now. and when i tried to boost. it did cut off and brought up the CEL.

the only other thing i could think was the wastegate wiggle, but you already checked that.
1991 elan se
1991 elan se project
91 MR2 Turbo (import) project
94 Celica GT4 (Import)
94 4Runner
98 Celica SR

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Re: Lack of shove above 4,000 RPM

Postby Owen L » Sun 01.01.2023, 01:26

Tuga2112 wrote:
Owen L wrote:
Tuga2112 wrote:im assuming your not hearing any hissing noises or whoosh noises when the needle is on the 0.4 ?
just making sure to rule out the obvious air leak from the system.


No obvious noises, no. mind you its all starting to happen at that point. I now have ElanScan, so is there anything in the data i can zoom in on to give me more clues? Appreciate your videos, used them just now to locate the plug for the scan. Cheers.


ive been fortunate enough to never had any major engine issues with any of my cars I read somewhere else in the forum that the turbo wont work properly if the car is not up to temperature. and i can confirm from experience that happens. because my thermostat is stuck open right now. and when i tried to boost. it did cut off and brought up the CEL.

the only other thing i could think was the wastegate wiggle, but you already checked that.


i’ve now advanced the base timing and the car is transformed. i remember watching WD and listening to Ant say this was essential to check. So yeah, he was very very right and my car revs way past 4 now with ease and maintains a fair bit of urge whilst doing so. day to day driving, i don’t,rev much past 4, but now,it,isn’t fading out on me as i go to change gears. i may play with the timing farther, but for now i want to clean it and get back to sorting out the 20 other niggles it seems to have.
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Owen L
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