reduced boost?

[C.Giles.T]

Any ideas? I took my s4s out today (after it eventually started) only to discover poor exceleration, everthing seemed normal until I floored it in 3rd, the boost gauge wouldnt read more than about .5, .6 bar which Im sure is not normal and although the turbo seemed to kick in there was nothing like the kick I usually get, also, the cars a bit "stutery" at lower revs and has been fir a couple of weeks. Could this be anything to do with the electrics as it has been cold and wet for the last week?
Cheers

[C.Giles.T]

.....and just to add, i've had no engine warning lights!

[cnh1990]

Is the coolant temp below 82c. If it is it will limit the boost. Sometimes when there is a dramatic change in weather I reset my ECU. Also check to see if the EBPV in between the cat and muffler is opening up after engine warm up.

Calvin

[lotusguy]

C.Giles.T said:

Any ideas? I took my s4s out today (after it eventually started) only to discover poor exceleration, everthing seemed normal until I floored it in 3rd, the boost gauge wouldnt read more than about .5, .6 bar which Im sure is not normal and although the turbo seemed to kick in there was nothing like the kick I usually get, also, the cars a bit "stutery" at lower revs and has been fir a couple of weeks. Could this be anything to do with the electrics as it has been cold and wet for the last week? Cheers

Hi,

As Calvin suggested, check to see that no exhaust flow issues exist. Also, check the condition of the plugs, remove the intake trunking and check for excessive oil at the turbo. Also, check to see that the chargecooler is cool to the touch after a spirited drive. If the chargecooler impellor has failed (not uncommon), the chargecooler will feel warm and the ECU will automatically limit the available boost. Hope this helps. Happy Motoring! Jim'85TE

[d didit]

I had the same problem. But mine was due to a poor connection at the Secondary Fuel Injector circuit. Do the ALDL thing and check if code 26 comes on. If it does, the ECM knows a circuit is unstable and it doesn't let the wastegate actuator funtion to allow increased boost due to a possible lean mixture if the secondaries don't function.

Cheers,
Dindo

[andecorp]

I get that if it sits in the garage for a few days or if I drive it through traffic. All it needs is for the pedal to be floored a few times in every gear. By the third time I do that, I have full boost. And I always have full boost after that until it gets driven in traffic again or it sits too long.

[cnh1990]

Andecorp,
I hope you cat matrix is not breaking down and pluging up the muffler. The muffler has a couple of perf pipes and the holes can get cloged up the the cat breaks down. I have rammed my matrix out of the cat so it is just a hollow can.
Calvin

[C.Giles.T]

Cheers guys, its booked in now for a service, got to wait 2 weeks but i'll let you know whats up with the poor girl!

[andecorp]

cnh1990 said:

Andecorp, I hope you cat matrix is not breaking down and pluging up the muffler. The muffler has a couple of perf pipes and the holes can get cloged up the the cat breaks down. I have rammed my matrix out of the cat so it is just a hollow can. Calvin

Thanks Calvin. Actually, I have stainless sports exhaust systems on both cars, without the cats.
What I worte earlier, is how I 'fix' the boost 'problems' on both cars.

[Kev@carnoisseur]

Bloody hell!! mine does the same thing!!! Ive booked mine up for a complete s/s sytem and doing away with the cat, getting a hybrid T3 with 360 bearing and moddified compressor wheel and aftermarket boost gauge and hopefully gettting it re-mapped at 1bar of boost.
That should sort it!

[igreenrover]

Hi

Did you guys ever get to the bottom of this?

My 89 SE is behaving in EXACTLY the same way! Sometimes it's great, but if I get stuck in traffic then I after I get reduced boost at about .4 or .5 bar (gauge).

Next time I go out it might be fine again...

Temperature on the Gauge moves between about 90 and 100 in traffic, but could the ECM water temp sensor be reading low, especially at higher temp??

Gareth

[danny tattersall]

Strangely enough mine does something similar. If I take it easy and let it warm up to over 82 degrees I will get some much boost that it goes off the end of the gauge (fitted with high torque chip). However, once it has boosted this high it will only allow 0.5 to 0.6 bar boost until it has been left for a while. The chargecooler is running fine and there are no check engine lights, although I occasionally get one related to the oxygen sensor under certain conditions. This resets itself after about a minute of coming on. It never comes on at initial start, rather it comes on when you have been on a short journey, shut down and get back in after an hour or so. It will light up after a couple of minutes driving and then reset. Bizarre but it could be related. Possibly a suspect oxygen sensor even though it was replaced a few years ago?

[dictys]

danny tattersall said:

However, once it has boosted this high it will only allow 0.5 to 0.6 bar boost until it has been left for a while.

I'm sure this is the ECM thinking that it has too much overboost and then regulating the boost until it reckons everything is ok. Someone has explained this before try search the forum using keyword overboost.

Rgds
Dictys 89 SE

[MikeyRide]

danny tattersall said:

Bizarre but it could be related. Possibly a suspect oxygen sensor even though it was replaced a few years ago?

I'm not sure if it's related to your boost problem but I've seen O2 sensors fail in frustrating ways. The light doesn't come on at start because the sensor is ignored at that point.

I could swear that Marcus said your experience is not unusual for a chipped car. You really need to have Freescan connected and logging to see what the ECM is reading from the sensors. That should tell you why you're not getting full boost.

[cnh1990]

You will not get full boost unless the coolant temp is at or over 82. Also if the boosted air temp is too hot you will not get full boost, one istance is the chargecooler is heat soaked as when idling in traffic. After you start moving and chargecooler temp cool a bit then you will have elevated boost. Also very hot ambient temps may cause lowered boost conditions from the air temp sensor on the intake plenum.
Calvin

[danny tattersall]

Thanks for the advice guys. I too think that my car has a problem with overboosting and then the ECU limiting it. I just can not understand why it boosts so high though. I even tried lengthening the wastegate rod but this does not help much either. I had it so long that the wastegate was slightly open all the time and I was still getting too much boost. I have freescan but have never run it whilst driving the car. May be worth a try but who knows what sensors should be reading what figures? Not me for sure!

[oharedm]

May I suggest you read the following:

ALL ABOUT BOOST

www.lotusespritworld.co.uk/EMaintenance/boost.html

and

USER GUIDE TO FREESCAN

www.lotusespritworld.co.uk/EMaintenance/freescan.html

It is an ongoing project so any suggestions for improvements most welcome.

I will happily receive Freescan logs for diagnosis.