Stumble at very low revs SORTED

[DAVES_GT3]

Hi Guys

Been battling with this stumble ever since i had the car.

If its revved from stationary either warm or cold the revs dip before they pick up. if the revs are held at 1500 rpm then revved it doesnt happen.

obviously causing me a problem when pulling away as it makes the car hesitate. you have to rev it up before you can think about dropping the clutch or it will just kangaroo on me.

unsure if this is related but i get a big stumble too at about 2000 rpm when there is load on the engine. i know what most people will say "stop driving like a bitch and give it some throttle" but there are sometimes when you cant i.e: at night in a quiet street.

so your in second at 2000 rpm and you give it some go go juice and it falls flat on its face. you have to gradually pick the revs up otherwise you look like your a learner driver!

i know i need to replace the engine mountings which wont be helping the situation at the moment but i need to get to the bottom of this one as its doing my head in. its as if there is a hole in the intake manifold, that sort of thing.

two things to note

1) big improvment when the ecu is reset (gets worse as the ecu learns its parameters)

2) free scan shows no problem

items ive changed and checked

new IAC valve and set correctly (i know this can cause a problem if not reset correctly)

new TPS and set correctly

k&n air filter and no blockages in the intake hose

new spark plugs (ngk originals with correct gap setting)

new magnecor kv85 ignition leads

no cracks in the coil pack

no leaks on map/vacume plumming

checked for a blockage in exhaust system/cat with a back pressure gauge

no leakes on intake manifold

new fuel filter

new plenum gasket and cleaned butterflys

removed each ignition lead while engine running to note drop in revvs ( goes to 950 rpm with any lead disconnected)

ignition not being retarded

i know freescan is showing all is ok but could it be fouled injectors for instance? or would that give me another problem and show on freescan?

any ideas? help apreciated.

cheers dave

Edited September 25, 2005 by DAVES_GT3

[alan]

1) big improvment when the ecu is reset (gets worse as the ecu learns its parameters)

2) free scan shows no problem

It sounds as if the default parameters are OK, but its getting some duff data from one of the sensors which is either causing the ignition timing to be set wrong or the mixture wrong.

Possible things to check are the knock sensor (assuming it has one - not checked) - see below for an explanation of how they work

http://www.wellsmfgcorp.com/counterpoints/..._v4_i4_2000.pdf

Or the lambda sensor

http://www.picotech.com/auto/lambda_sensor.html

Its more likely to be the knock sensor as its difficult for the ECU to tell if anything is wrong with this sensor so it can end up gradually advancing the timing too much.

Hope that helps

Alan

[DAVES_GT3]

It sounds as if the default parameters are OK, but its getting some duff data from one of the sensors which is either causing the ignition timing to be set wrong or the mixture wrong.

Possible things to check are the knock sensor (assuming it has one - not checked)

Edited September 19, 2005 by DAVES_GT3

[x6gas]

What chip you running Dave?

[s4simon]

Dave, have you read the burst in the Lotus MPFI Manual on 'Hesitation and stumble'. There's a couple of pages on what and how to check for the problem.

[DAVES_GT3]

Dave, have you read the burst in the Lotus MPFI Manual on 'Hesitation and stumble'.  There's a couple of pages on what and how to check for the problem.

<{POST_SNAPBACK}>

chip # 11 ian but had the problem from day 1

yer ive read that simon. quite lengthy and probably a bit too involved for me.

understood most of it but not all

dave

[CarlC]

... just thought of one thing which i never said, fuel mpg is absolutly crap. i get about 250 miles if im very lucky out of a 50 quid tank

<{POST_SNAPBACK}>

Now you've got me worried.

I actually ran out of juice about 1 mile from home a couple of weeks ago. I thought my fuel gauge was faultly. So I dropped in

[DAVES_GT3]

  Now you've got me worried.

I actually ran out of juice about 1 mile from home a couple of weeks ago. I thought my fuel gauge was faultly. So I dropped in

[DAVES_GT3]

SORTED!!!!

While i had the boot out the other day i took the fly wheel sensor out to check that over. There was a load of oil and crap over it that was obviously blocking it from sensing anything. Has definately cleared the revvs dipping before they progress. Well happy.

had to wait a day or so after resetting the ecu just incase it came back as it is usually ok for the first few miles after resetting the ecu.

Dave

[s4simon]

'Fly Wheel Sensor' ??

Didn't know I had one - how did you find that ?

[DAVES_GT3]

'Fly Wheel Sensor'  ??

Didn't know I had one - how did you find that ?

<{POST_SNAPBACK}>

It sits on top of the fly wheel. If yur in the boot looking at the engine its just to the right but further down from the charge cooler. i.e: by the green oil/air separator. looks like a rear abs sensor if you have ever had the pleasure of taking one out. but a hell of a lot easier!!! made it and easier job though with the boot out but could still be done with it in.

probably worth checking as its bound to get crap stuck to it over time

dave

[Paul C]

So your crap fuel economy sounds fairly good to me!  Can anyone else confirm this?

<{POST_SNAPBACK}>

My fuel light / guage is typically rubbish!

If i fill the car up, i can still corner hard enough for the fuel light to come on

(i actually enjoy this!). The light starts to flicker when the needle is shaking

somewhere between 1/4 and 1/2 a tank full. When the needle i bouncing at

between empty and 1/3 of a tank, the light tends to stay lit longer, and at this

point i can get between

[Daniel]

Dave

I've got exactly the same problem with my S4

I test drove 5 cars before I bought mine and they ALL had the same problem.....the one I bought to a lesser extent than the others.

Thanks for the thread anyway, I'll be giving the flywheel sensor a lookyloo ASAP......now

How do I reset the ECU.....disconnect the battery for an hour?

[DAVES_GT3]

Dave

I've got exactly the same problem with my S4

I test drove 5 cars before I bought mine and they ALL had the same problem.....the one I bought to a lesser extent than the others.

Thanks for the thread anyway, I'll be giving the flywheel sensor a lookyloo ASAP......now

How do I reset the ECU.....disconnect the battery for an hour?

<{POST_SNAPBACK}>

yes but for about 5 mins will do the trick.

be careful when resetting the ecu. its straight forward providing you follow the standard procedure.

do u have freescan? not essential

what to do

-make sure the engine is cold and has not been started for at least 3 hours

-disconnect the battery

-wait 5 mins

-reconnect battery

-reset IAC value via freescan if you have it, if not dont worry

-turn aircon thermostat on and fans to at least second switch possition

-turn ignition on (second possition) i.e: dash lights on

-depress accelerator two or three times slowly

-start the car and let it run for 4-5 mins approx idle

-turn air con off and run for a further 2 mins or so

-drive off steady and keep below 3000 rpm for 5 mile or so

-then take it up to 5000 rpm. this is giving the ecu chance to learn its parameters

-then give it WOT

There are different views on this but you may find your boost may be higher than what you had before or lower for the first few miles but this is just the ecu relearning the boost curve.

you should find it will feel a lot smoother.

i personally would reccomend resetting at least 4 times a year. every season change. lets the IAC get in the possition it should be so you dont get any stalling.

stalling is what you will probably get if you dont follow this procedure as the IAC will be in an incorrect position. especially if you try and reset with a warm engine. ive been there done that!

hope this helps

dave

[CarlC]

yes but for about 5 mins will do the trick.

be careful when resetting the ecu. its straight forward providing you follow the standard procedure.

do u have freescan? not essential

what to do. . .

<{POST_SNAPBACK}>

Dave,

Thanks for the reset refresher.

Ill redo mine with this technique next weekend.

I would mention that it has taken about 30 miles or so since my last reset and its only just starting to give me max boost back.

On the bvack of this thread, would it it be a good idea to list out the positions of a few other key sensors and get them cleaned up ?

[DAVES_GT3]

Dave,

Thanks for the reset refresher.

Ill redo mine with this technique next weekend.

I would mention that it has taken about 30 miles or so since my last reset and its only just starting to give me max boost back.

On the bvack of this thread, would it it be a good idea to list out the positions of a few other key sensors and get them cleaned up ?

<{POST_SNAPBACK}>

in what way do you mean carl?

dave

[CarlC]

in what way do you mean carl?

dave

<{POST_SNAPBACK}>

There are obviously plenty of other ECU senors. I wouldnt have thought to check on the state of any of them until you mentioned this problem. Ill check mine next chance I get.

While im at it with the boot floor out I wondered if it was worth checking out any of the others, clean them up etc just in case.

[DAVES_GT3]

There are obviously plenty of other ECU senors. I wouldnt have thought to check on the state of any of them until you mentioned this problem. Ill check mine next chance I get.

While im at it with the boot floor out I wondered if it was worth checking out any of the others, clean them up etc just in case.

<{POST_SNAPBACK}>

oh i take your point now.

only ones i can think of would be the port on the IAC valve, wouldnt try and clean the IAC its self though.

knock sensor, this is underneath the butterflys but i wouldnt think that would need cleang as such. could be tested though to see if it is opperating correctly if you have an ossciloscope (scope).

definately one for cleaning is the tps as that is only a carbon track (potentiometer) that can get very dirty very easily and cause all sorts of idle/acceloration problems and false readings.

soak it in isopropanol (pure alcohol) or nail varnish if your a lady boy!!! turn it a few times by hand to get it inside the tps and on to the track to clean it.

then drench in in wd40 and wack it back on. think most peoples will be dirty even if they dont know it. simple job and costless. its worth doing!!!

dont forget to set it correctly afterwards so you can get the correct voltage readings to give WOT.

should read 0.45v - 0.7v at idle

think it gives code 22 if its not set correct.

should give 4.5v i think at WOT

worth checking all your vaccum MAP plumbing while your at it if you have the boot out. plastic T junctions and rubber elbows are crap. always splitting. also you could check the fuel breather hose coming off the charcoal canister as it can be got at really easly with the boot out. a bitch if it isnt!!

could check the air intake hose incase its being crushed. the one from the air filter housing to the turbo inlet. best to take the jubilee of the turbo and have a good look down it as they can collapse internally.

other than that i cant think of any others.

dave