free hit
counters
Light throttle stumble on 92 SE - Engine/Ancilliaries - The Lotus Forums - Lotus Community Partner #ForTheOwners Jump to content


IGNORED

Light throttle stumble on 92 SE


joakim_adolfson

Recommended Posts

Hi,

I have a 92 2.0 SE which has slight hesitation/stumble when going from 0% throttle.

I have replace the TPS and set to 0,71 volts = 0% throttle.

I remember there was some discussions on this before but I can't find it

I have no reported ErrCodes and the engine does enter closer loop (after a while on idle though).

Have anyone experienced this??

//joakim

Link to comment
Share on other sites


Upgrade today to remove Google ads and support TLF.
  • Replies 22
  • Created
  • Last Reply

Top Posters In This Topic

Yes... Everybody has. It's a problem with the mapping on the GM ecu.. It's a long story.. but basically it boils down to poor throttle mapping. It's most noticeable around 3000rpm.

Modifying esprit's.. now that's fun..

PS... I AM NOT A CERTIFIED MECHANIC.. I Have chosen to help those in need, in the past and must not be construed as being a certified technician.

Link to comment
Share on other sites

I too have lived with this for a while. Although changing the throttle mapping helps a great deal, I dont think its the complete solution. With my car I always notice the problem on very light throttle openings and just picking up from idle. The infamous 3000rpm stumble was never a significant issue on my car.

Read my thread from last year on the topic.

http://www.lotusespritforum.com/forums/ind...p;hl=hesitation

Eventually I worked through all the sensors, changing most, also fuel pressure reg, fuel pump, TPS and fitted an finally an S4s spec chip. Much much better, infact more or less perfect now (maybe not 100% perfect). Biggest improvments came from changing the O2 sensor and then what little stumble remained after this was almost totally removed by the change to S4s chip.

Good luck

Malc

Edited by Malc Holmes
Link to comment
Share on other sites

I have a 92 2.0 SE which has slight hesitation/stumble when going from 0% throttle.

I have the same thing at 0%, too. I also experienced the infamous slight 3000rpm stumble, but haven't had it recently.... it was replaced by an intermittent very large throttle stumble.. sometimes complete stall at 40kph or so.

Over the last 12 months, I've replaced the:

Exhaust (including the removal of the EBPV)

Turbo core

Oxygen sensor (Lotus original)

TPS (and adjusted it with Freescan)

Spark plugs

Plug leads

Injectors (6)

Coil pack

Numerous vacuum lines and valves

Chargecooler pump impeller

Lots of relays/frequency valves...

Charcoal canister (and associated valve)

Fuel Pump

Fuel Pressure Regulator

...but the intermittent large hesitation/stalling persisted.

Last thing I tried was a new ECU (using original SE chip and mounting assemby)

I still get the slight hesitation at 0%, but so far so good with the stalling/hesitation(large and small) at about 3000rpm(40kph?).

Unless someone knows exactly what causes the hesitation at 0%, I would learn to live with it... as you can waste an awful lot of money trying to get rid of it :no

Cheers.

Ian.

Edited by Qavion
Link to comment
Share on other sites

'Unless someone knows exactly what causes the hesitation at 0%, I would learn to live with it... as you can waste an awful lot of money trying to get rid of it'

Got to agree with you there Ian. Seems like you started off with more of an issue than me. By the time I had replaced the O2 sensor and went to S4s chip I think I was becoming hyper sensitive about the small imperfection that remained. I spent 10 years designing and fine tuning automotive electonic systems (before moving into styling to play with clay and felt-tips last year) and the experience probably left me too damn sensitive to anything that was less than perfect.

Malc

Link to comment
Share on other sites

We do know what the stumble is caused by.. and.. since you ask I'll explain as best I can:

The engine runs off of a MAP sensor, but on intitial throttle "tip-in" the map sensor cannot monitor proper fuelling, so there's a "throttle tip-in map" so what happens is that the ecu monitors the amount of throttle applied vs the time it takes to open the throttle (how fast you hit the gas pedal) and assumes a certain amount of airflow and adds fuel accordingly. Unfortunately the computer is wrong about the airflow... ESPECIALLY if you've uprgraded the turbo. So what happens is the engine thinks it's getting "x" amount of air, but really it's getting "x+y" amount of air.. so it only adds enough fuel to compensate for "x" and therefore does not give enough fuel because the air flow is greater than it "thinks" it is getting. If you use a wideband to monitor this, you will see the AFR (Air Fuel Ratio) jump from 14.2-14.7 at nuetral throttle to about a 17 AFR and then (once the throttle tip in map is finished it's cycle it goes to the Manifold Air Pressure fuelling map) it drops to a 10.5-11.0 AFR and dumps too much fuel... hence the "hesitation"

I hope that explains what's going on... btw.. the throttle tip in map only lasts a short time before it switches to Manifold Air Pressure again....

Modifying esprit's.. now that's fun..

PS... I AM NOT A CERTIFIED MECHANIC.. I Have chosen to help those in need, in the past and must not be construed as being a certified technician.

Link to comment
Share on other sites

Hmm,

yep I do have the 0% hesitation, not the 3k stumble (using GT3 chip 10).

I wonder though why it seems only to be happening on certain cars??

To me it is clear what you say and I agree that this is probaly the cause but I do wonder why?

From where does the engine gets its extra air or is it that the engine does not get fuel quickly enough?

To me it could be either the MAP, the TPS or fuelpressure perhaps as these are the only sources for adding more fuel?

If any of these components are slow (not the TPS) I guess you could get this effect.

I hardly think Lotus or GM designed a system without ironing out these faults from the factory as it can't be seen as satisfactory.

I would guess that it could possibly be solved by opening up the TPS and thus fooling the system that it already has some throttle opening (I have already pushed the envelope here I think without getting more than 0% throttle 0,71 V) this would add extra fuel when idling but would also possibly cause the idle to be a little higher.

Any more ideas?

:-)

Link to comment
Share on other sites

Joakim... I think you missed the point of Mark's message...

"but on intitial throttle "tip-in" the map sensor cannot monitor proper fuelling,..."

There is not enough data available to the ECM to analyse, therefore it guesses the fuel/air ratio (based, presumably, on experimentation in the GM/Delco workshops). This is a common practice in fuel control in the absence of reliable sensor data (even on Boeing jets).

But please feel free to re-invent the wheel :lol:

Cheers.

Ian

Link to comment
Share on other sites

I noticed a big improvement in pick up from idle after changing to the S4s chip. 3K stumble seems to be a bit more pronounced than it was with the standard SE chip however :lol:

Keith

Calypso red '92 Esprit SE Hi-wing

Calypso red '87 Excel SE

Blue '07 BMW X3 2.0TD SE

Link to comment
Share on other sites

Joakim... I think you missed the point of Mark's message...

"but on intitial throttle "tip-in" the map sensor cannot monitor proper fuelling,..."

There is not enough data available to the ECM to analyse, therefore it guesses the fuel/air ratio (based, presumably, on experimentation in the GM/Delco workshops). This is a common practice in fuel control in the absence of reliable sensor data (even on Boeing jets).

But please feel free to re-invent the wheel :lol:

Cheers.

Ian

haha, sure, yes I did understand that, what Im trying to say is that somewhere on the line these two systems will have to swap, basically going from tps -> map. If the mapsensor isn't matched to what the tps gives you will feel when they do move over. I guess this is what is happening. What Im trying to understand is why that is??, This was sorted by Lotus when the cars were new so obviously there is a fault or slightly malfunctioning part somewhere, the map isn't faulty here as the map will not change over time while sensors and engine condition do.

This is my point!

:-)

Link to comment
Share on other sites

I think the reason it's more prominant with some cars is the different turbo's. If you put a better flowing turbo on (like the WC Engineering turbo on Aerobats car) then you're getting even more air than the computer thinks you are.

There's a few other factors as well (and this is why I'm a huge fan of MAF as opposed to MAP based ecu's)

1. If you're exhaust is modified, you will change the back pressure on the turbo which will effect the turbo's performance (and make it more efficient) which will cause more air to enter the plenum on initial tip-in

2. Valve adjustment will effect the amount of air coming into the plenum as well

3. Any number of other factors that the computer can't monitor like a dirty fuel filter or a bad fuel pressure regulator, piston ring wear etc..

Modifying esprit's.. now that's fun..

PS... I AM NOT A CERTIFIED MECHANIC.. I Have chosen to help those in need, in the past and must not be construed as being a certified technician.

Link to comment
Share on other sites

I think the reason it's more prominant with some cars is the different turbo's.

what can I say, I'm very happy for all the responses but please read my initial txt.

I will clarify myself a little more.

1. I have a 2.0 (italian version), this means not possible to do a s4s update!

2. I have no problem with the 3k stumble!

3. I have an off idle stumble, of more to say off throttle hesitation. Instantly when I press the throttle the engine dies very briefly before it picks up revs. It does not matter if it idles or is running full tilt, the artifact is the same.This has nothing to do with turbos backpressure and sorts believe me.

4. I have upgrade the memcal but effect was the same

5. I have changes the O2 sensor = same effect

6. I have changed the TPS and reset it to 0,71 V = same effect, maybe a little less pronounced

So please lets restart this discussion from the beginning then :-), since I still need to find out why it's behaving a little wierd.

Mvh

joakim

Link to comment
Share on other sites

Hi Joakim,

What you are experiencing is not uncommon, but it actually does not appear on all cars ...

Dont worry, there is a solution.

1. please reset your ECU when your engine is warmed up ! (disconnect battery for a couple minutes)

2. reconnect and go for a short run.

3. Is your hestitation still the same, or is it bigger or is it smaller ???

Please report !

Cheers

Marcus

Marcus

Link to comment
Share on other sites

Malc,

Please dont get me wrong, but I tried it this way, because its quite a complex scenario and I wanted to make it more easy for you and me ...

For example, if it is better just after the resetting, then you had a "running a bit lean problem" -> i.e. try a new O2-sensor

Cheers

Marcus

Marcus

Link to comment
Share on other sites

Marcus... The problem (from what it sounds) is almost certainly a "lean" problem. My question (as I certainly don't know all the inns and outs of this ECM) is.. is the car in open loop or closed loop during the throttle tip-in map? I would have assumed it to be open-loop operation because of the fact that the problem never seems to correct itself.

Modifying esprit's.. now that's fun..

PS... I AM NOT A CERTIFIED MECHANIC.. I Have chosen to help those in need, in the past and must not be construed as being a certified technician.

Link to comment
Share on other sites

Might be worthwhile checking and resetting the pintle in the IAC. It has a step which could be out. At idle the ECU is constantly monitoring and adjusting it with reference to the TPS, RPM, battery voltage, coolant temp, oxygen sensor etc. Also at idle the engine fires every other stroke, which on a four cylinder doesn't auger well for smoothness off idle.

DanR

Link to comment
Share on other sites

Well mine desepeard with few upgrades but not sure wich one since I did them all @ the same time,

it was never there when I used to drive unless I was looking for it arround 3krpm moving the throtle back and forth

to get some flame out of the exhaust :dizzy: but barely noticable,

I like my map sensor readings from as close as posible to the throtle body buterflies on my cars so I tapped

the runners,

installed msd coils 8224 not 100% sure on part # and denso iridium plugs,

also did cut up & install some universal wires I think they were taylors

that did it for me

o one more thing I banged the fuel pressure regulator a little to alter the pressure litlle bit

so all thees were done @ the same time

good luck

Link to comment
Share on other sites

Hi Joakim,

What you are experiencing is not uncommon, but it actually does not appear on all cars ...

Dont worry, there is a solution.

1. please reset your ECU when your engine is warmed up ! (disconnect battery for a couple minutes)

2. reconnect and go for a short run.

3. Is your hestitation still the same, or is it bigger or is it smaller ???

Please report !

Cheers

Marcus

Ill give it a try tonight, thx..

Link to comment
Share on other sites

  • 2 weeks later...

Hej,

I have now tried to reset the ECU while hot and it just made things worse.

The funny thing was that resetting it while cold with the new TPS setting at 0,71V and some running made things better (before hot reset), it still stumbled but a little less.. In other words a little confused.

However it does seem to be a little better before going close loop so maybe it is the lambda anyway (I did change lambda before without it making any difference though)

Link to comment
Share on other sites

What's you're fuel pressure at?

Modifying esprit's.. now that's fun..

PS... I AM NOT A CERTIFIED MECHANIC.. I Have chosen to help those in need, in the past and must not be construed as being a certified technician.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.




×
×
  • Create New...