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Discussion Starter #1
I had never noticed this before but when I floor the gas the boost gauge pegs all the way to the right (S4s chip) but as the rpm rises boost drops back to the 3/4 mark somtimes 2/3 mark. Am I out of my mind or is this normal and I just never noticed it before? There is no loss of power that my butt can tell and still pulls very hard. However, if boost is dropping off should the car be even faster than it is now? Or is this caused by the higher rpm and engine is drawing more air?

In the past once I see that the boost is pegged out, I then take my eyes off the boost gauge and to the tach.

I have had turbo cars before and have never seen this happen.

Thanks in advance gurus!

:facepalm:bow::popcorn::panic:
 

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Cal H
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Touch test the Chargecooler right after a good spirited run. The pump might have failed and is limiting you to .65 bar like a regular turbo car or if you have a BOV it might have loosened up and spring is not holding it shut.

Cal H
 

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a hot chargecooler will reduce power, but not boost.

If the engine coolant is too hot or too cold, then boost will be restricted. Also if the engine goes too lean, then boost will be restricted.

A plugged exhaust, leaking intake, bad spark can all reduce boost just by reducing flow through the engine.
 

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Cal H
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In the SE and S4 when the engine is allowed to make more power until
the ChargeCooler heat soaks. The continuous power level is based on
mechanical wastegate pressure, and the temporary high power is a result of
an ECU-allowed overboost condition that can exist as long as certain
sensor-monitored engine parameters stay within set limits... like fuel
pressure, engine temperature, and ChargeCooler temperature.

The Esprit SE, S4 and S4s also use the ECU to monitor gear selection
(difference between engine rpm and ABS wheel speed sensor rpm) and then
limit maximum boost in the lower gears in order to protect the transaxle.
Some of the aftermarket chips, like the High Torque chip, remove those boost
limits and permit full boost in all gears. That's why the car feels so
strong despite not making more peak power.

That is the way it was explained to me
 

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I had never noticed this before but when I floor the gas the boost gauge pegs all the way to the right (S4s chip) but as the rpm rises boost drops back to the 3/4 mark somtimes 2/3 mark. Am I out of my mind or is this normal and I just never noticed it before? There is no loss of power that my butt can tell and still pulls very hard. However, if boost is dropping off should the car be even faster than it is now? Or is this caused by the higher rpm and engine is drawing more

:facepalm:bow::popcorn::panic:
an accurate boost gauge shouldn't stay pegged all the way to,the right as you would be over boosting.
Normally if you spike the boost under full throttle, the ECU will modulate the wastegate capsule to maintain max boost at about 1.0 ATM for the S4S chip. The stock chip allows temporary excursions to about 0.85..
So yes if your gauge pegs all the way to the right you SHOULD see boost reduced to the 1.0 mark and then hold there under full throttle till it's time to shift.
As Travis said, the ECU allows boost based on engine temp, not intake air temp. Hot intake air will cause a reduction in horsepower.

Randy
 

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Cal H
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With the S4s chip the peak boost is like 1 bar or a little over like 1.1. With a heat soaked chargecooler it will most likely drop to .65 bar or there about. Chargecoolers are put on our 4 cyl cars to maintain the peak boost set by the ECU for a longer period of time. Same HP numbers, just that it tries to keep the air cool enough to *maintain* that boost (and therefore HP) for a longer period before the MAT (mass Air Temp) gets to the point where detonation occurs and lowers the boost (bypasses it to the atmosphere instead of the intake manifold). So, the chargecooler is mainly there for boost-time-duration reasons, not to increase HP... just to maintain it for longer.

Also if you have a BOV check to see that it is not opening up as the spring loosens up
 

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The Esprit SE, S4 and S4s also use the ECU to monitor gear selection (difference between engine rpm and ABS wheel speed sensor rpm) and then limit maximum boost in the lower gears in order to protect the transaxle. Some of the aftermarket chips, like the High Torque chip, remove those boost limits and permit full boost in all gears.
There no gear related boost control in the 4 cylinder cars, there is in the V8's though.

With the S4s chip the peak boost is like 1 bar or a little over like 1.1.
The S4S maximum boost is 1 bar.
 

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Cal H
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There no gear related boost control in the 4 cylinder cars, there is in the V8's though.
In a way as gear selection is determined by speed and the VSS function as stated in the service manual for the 4 cyl cars "This information is used by the ECM to control the a/c and radiator fans under certain conditions (see EMH.2 - H) and the boost control solenoid valve"

The S4S maximum boost is 1 bar.
That is the correct figure for the stock Lotus S4s.
This person has an S4 with what he tells us is an S4s chip. I don't know of many that actually bought their S4s memcal from a Lotus dealer so I usually assume that they have acquired the chip through secondary market sources. Depending on the chip I have seen peak boosts up into 1.1-1.2 range. Each of the chips have their own advantages and quirks. That is why I say " 1 bar or a little over". Many people also refer to "about" when talking about re chipped cars. Over a decade ago when our cars was more line with the fastest road cars I was like a little kid "oh you have a new chip, let me try, oh please let me try" and I would be swapping and testing. So that is why I know about the different chips. These days with improved modern sport sedans and other cars being as fast or quicker my days of performance mods have slowed. I am resigned to driving a vintage/collector car as both car and driver age gracefully. Oh except for my last performance project mod that will make my SE much quicker. rotfl

Cal H
 

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Discussion Starter #10
Hey Guys,

Thanks for the input and info.

- There is no whistling or any leaks that I can hear. Then again at that rpm all I hear is the engine.

- Yes I have a BOV but even removed, the boost still varies. Ater 6k rpm boost drops back but on the way up it is at full boost.

- Chargecooler is only warm to the touch and yes I have also heard that if intake air temp is too hot the computer would limit boost, but that is what I have read/heard.

- When I say S4s chip I mean it is an aftermarket chip with S4s specs.

- Will freescan pick up info if the CEL did not come on? Anyone in Socal willing to help a brotha out?

- Had a bad cat a few months back and turbo would not spool, punched it out and car boosted well.

Like I mentioned on the way up the rpm band I get full boost, just once up in the higher rpm range that boost limits back a bit but varies. Might the ECU like Travis said....
 

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Yes, the ecu knows engine speed and vehicle speed but there is no calculation of the gear in the code.

The maximum MAP the ecu can detect is 2.07 bar, any pressure higher than this and the ecu is not aware of it. The stock S4S 'Boost Limit Set' (aka KWGMAPH) scalar is set to 2.06 bar because of this.

Regarding seeing any higher pressures, if these are from Freescan then the readings are erroneously high with that s/w.

Freescan will give live data without the CEL being illuminated.
 

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- Will freescan pick up info if the CEL did not come on? Anyone in Socal willing to help a brotha out?

- Had a bad cat a few months back and turbo would not spool, punched it out and car boosted well.

Like I mentioned on the way up the rpm band I get full boost, just once up in the higher rpm range that boost limits back a bit but varies. Might the ECU like Travis said....
Yes you can use freescan to log data as the car is running and then email that to me to look for clues. You don't have to have a check engine code.

But based on your last statement, it sounds to me like the ecu is limiting boost after the initial full boost, for a while anyways, which is exactly what mine was doing when it was running lean due to low fuel pressure with boost. In my case, fixed with a new pump.

If you can borrow freescan and a cable, then log some data starting withe the engine cold, let it warm up to 80C water temp while only idling. Then drive it and try to replicate the issue.
 

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Cal H
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Hey Guys,

After 6k rpm boost drops back but on the way up it is at full boost.
Wish I could see what you mean and the time it takes to do that. It almost sound normal as peak boost and sustained boost are 2 different things.

- Chargecooler is only warm to the touch
The chargecooler is supposed to feel like cold metal, not warm. Too bad you do not have known working car similar to yours to A/B the cars so you can easily tell the difference. The cold feeling of a properly working chargecooler is in stark contrast to you heat you feel when you lift up the engine cover. You got the original pump or electric?

When I say S4s chip I mean it is an aftermarket chip with S4s specs.
You buy it yourself or did it come with the car? The high torque chip does make a bit more peak boost than a regular S4s but settles down after a bit.

- Will freescan pick up info if the CEL did not come on? Anyone in Socal willing to help a brotha out?
Won't pick up an error code but you can monitor performance. Sorry can't help with SoCal but you can drive the car to MN and have Tim take a look at it but Travis is only 1/2 the way.

- Had a bad cat a few months back and turbo would not spool, punched it out and car boosted well.
Did the matrix break down? As in did pieces fall out of the cat? After punching out the cat you did remove the muffler and see if cat pieces are rattling around up there?

Hope we are not chasing ghosts and your car is working like it is supposed to. LOL. You must pal around with buddies that have Esprit's or at least know someone in SoCal that has a similar car or are you a lone wolf? Local Lotus club? If no local Lotus club. Join Lotus Limited and they have a list of people and locations where to seek to help. I think they might even list technical ability and type of car they can help on. It's been a while since I was in Limited but Atwell can tell you more.

Cal H
 

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Discussion Starter #14
Yes you can use freescan to log data as the car is running and then email that to me to look for clues. You don't have to have a check engine code.

But based on your last statement, it sounds to me like the ecu is limiting boost after the initial full boost, for a while anyways, which is exactly what mine was doing when it was running lean due to low fuel pressure with boost. In my case, fixed with a new pump.

If you can borrow freescan and a cable, then log some data starting withe the engine cold, let it warm up to 80C water temp while only idling. Then drive it and try to replicate the issue.
Thanks for the help Travis! If the computer is backing off on the boost due to low fuel pressure then that is a nice feature. Keeps my engine from blowing up in a million pcs.
 

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Discussion Starter #15
The chargecooler is supposed to feel like cold metal, not warm. Too bad you do not have known working car similar to yours to A/B the cars so you can easily tell the difference. The cold feeling of a properly working chargecooler is in stark contrast to you heat you feel when you lift up the engine cover. You got the original pump or electric?

You buy it yourself or did it come with the car? The high torque chip does make a bit more peak boost than a regular S4s but settles down after a bit.


Won't pick up an error code but you can monitor performance. Sorry can't help with SoCal but you can drive the car to MN and have Tim take a look at it but Travis is only 1/2 the way.

Did the matrix break down? As in did pieces fall out of the cat? After punching out the cat you did remove the muffler and see if cat pieces are rattling around up there?

Hope we are not chasing ghosts and your car is working like it is supposed to. LOL. You must pal around with buddies that have Esprit's or at least know someone in SoCal that has a similar car or are you a lone wolf? Local Lotus club? If no local Lotus club. Join Lotus Limited and they have a list of people and locations where to seek to help. I think they might even list technical ability and type of car they can help on. It's been a while since I was in Limited but Atwell can tell you more.

Cal H
Thanks Cal.

- I have had a Vortech Supercharge S2000 and the air to water intercooler is the same. Warm but but not hot to the touch. I have never seen a charge cooler where it is cold after running the engine. I have seen where the cooler is hot so that tells me it is not working. Even working at full capacity I have never seen any of these cold. I may wrong but I have to respectfully disagree. I have the OEM mechanical pump.

- The chip was something I purchased after owning the car.

- LOL! Will be sending the findings to Travis.

- Yes the internals fell apart and brand new exhaust system installed same day.

- The guys I know in socal have V8's but have not met any locals with 4 bangers (yet).

Thanks for the educating a NOOB. I am still learning the secrets of this car. Nothing is normal for this thing but it sure is sexy...
 

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Cal H
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Chargecooler might not have anything to do with your current problem. But during the MN summer like 90F after a good run it feels just like cold metal. I got a new toy an IR temp gun that I use to set tire pressure. I will point it my chargecooler when I get my car is running. The touch test does not tell what temp the chargecooler box is only what you feel through your hand. The mechanical pump is does not last long. I recommend you check the impeller at 25K mile intervals. Mine was a little round wheel at 25K miles/10 years from new. If one blade shears it will take most of them out through impeller rotation in the chamber. At over 30K it is for sure gone. Lunch time I have to go meet another SE owner and discuss my planned mods for my car.
Good Luck

Cal H
 

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Discussion Starter #17
Chargecooler might not have anything to do with your current problem. But during the MN summer like 90F after a good run it feels just like cold metal. I got a new toy an IR temp gun that I use to set tire pressure. I will point it my chargecooler when I get my car is running. The touch test does not tell what temp the chargecooler box is only what you feel through your hand. The mechanical pump is does not last long. I recommend you check the impeller at 25K mile intervals. Mine was a little round wheel at 25K miles/10 years from new. If one blade shears it will take most of them out through impeller rotation in the chamber. At over 30K it is for sure gone. Lunch time I have to go meet another SE owner and discuss my planned mods for my car.
Good Luck

Cal H
Thanks Cal. Maybe my definition of warm vs your definition of cold maybe the same?

Warm = I can put my hand on the chargecooler and leave it there without fear of burning myself.

Cold = before I start the car.

I just can't see how the cooler can be cold like cold metal. Coolant is shared through the same system as the engine. In my S2k I had an electric pump with a serparate radiator/coioling system and that doesn't feel cold like cold metal either. In this case the charge cooler sits right on top of the engine the ambient heat from the engine would be enough to make it warm.

With that said I will check on the impeller this weekend. Went through records and it doesn't look like it was ever replaced.

Duc
 

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Discussion Starter #18
Travis,

Where did you find your fuel pump? My local parts houses (Pep Boys, Kragen) doesn't even have the Esprit in their system. Is there a cross reference or should I just go straight JAE?
 

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Thanks for the help Travis! If the computer is backing off on the boost due to low fuel pressure then that is a nice feature. Keeps my engine from blowing up in a million pcs.
IF it is going lean, then that can still do damage by driving it. So you'll want to verify and fix the issue asap.

The data from freescan can give you clues to whether the ECU thinks you are going lean, and some pointers. But you'll need so other tools to verify. For instance the signal from a failing O2 sensor may cause the ECU to think it is going lean, when it is not, it could be running very rich. Which can be confusing if you only pay attention to the sensor and not the other symptoms.

1)First step, borrow freescan cable, log data.
2)check fuel pressure. even better if you can follow the procedure in the Lotus EMH manual.
3)verify wastegate adjustment, since an out of spec wastegate can cause the boost to spike can cause the ECU to limit boost.

I wold remove the BOV if possible, during troubleshooting.

If possible try to verify boost with another gauge.
 

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Discussion Starter #20
IF it is going lean, then that can still do damage by driving it. So you'll want to verify and fix the issue asap.

The data from freescan can give you clues to whether the ECU thinks you are going lean, and some pointers. But you'll need so other tools to verify. For instance the signal from a failing O2 sensor may cause the ECU to think it is going lean, when it is not, it could be running very rich. Which can be confusing if you only pay attention to the sensor and not the other symptoms.

1)First step, borrow freescan cable, log data.
2)check fuel pressure. even better if you can follow the procedure in the Lotus EMH manual.
3)verify wastegate adjustment, since an out of spec wastegate can cause the boost to spike can cause the ECU to limit boost.

I wold remove the BOV if possible, during troubleshooting.

If possible try to verify boost with another gauge.
:bow::bow:
 
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