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MG MGF Technical - Is the problem the new cat?


Hi all

Just returned as most of you know from the Riveria trip and I seem to have developed a wierd problem..

To give you the history I replaced the cat about two weeks ago prior to the trip. The honeycomb in my old cat had become loose and was rattling like mad.. I sourced a new cat from Britishcarparts.com.

My old cat came with the car (a japanese import) and had a temp sensor going into it which i subsequently found out is not standard on UK spec cars. The old cat is physically much larger than the replacement which i found strange.

The Symptom:

I noticed a couple of times towards the end of the trip my rev's didnt seen to drop that quickly when changing gear. I.E when i depress the clutch the revs dropped slower than normal and in fact sometimes would go up a couple of hundred before dropping?

At first i thought it was me doing crappy gear changes but i am convinced now that i do have a problem.. The car seems to be idling a little higher to about 11-1200 rpm

The throttle body was replaced last year for a metal 52mm jobby and the cable does not seem to be sticking!

I am wondering if this smaller cat which has now 2500miles under its belt has furred up a little so to speak and is restricting the air flow? My exhaust is noticeably louder with the new cat (motorbuild sport exhaust) which i am sure anyone behind me on the riveria trip will testify! I dont seem to have any power loss and eng temp is normal.

The problem is not constant but seems to occur if you have been pushing the car for a bit.

I am on the RR day saturday and will see if anything shows up on that.

So the question is:

Do you think this after market Cat is likely to be causing the problem or should i be looking elsewhere?

Sorry for being so long winded but a difficult one to explain without the history

STU
Wokingham

S.C. Dickens

Stu

It was a bit long winded wasn't it! I don't think the cat is your problem matey. Sounds like the air valve stepper motor (or according to the manual an Idle air control valve) is dirty and sticking and just needs a clean. Used to happen on my Maestro 2.0i from time to time and accounts for the high idle speed.

Cheers

BPR i
Blue Pocket Rocket

I agree, sounds like the stepper motor to me too. Give it a clean out with Greygate plastic polish (or similar) and see it that helps.

SF
Scarlet Fever

It doesn't sound like a stepper motor fault to me though - the MEMS will keep the revs high momentarily on over-run for emissions purposes. This is also known as a 'soft landing' (I know about this because Tim was having problems with his car when his cam timing was out).

Which makes me wonder about the back pressure that this new cat is generating...?

Stu, do you still have a cat bypass tube? You could try a power run both with and with out the new cat fitted to see how restrictive this aftermarket replacement is...
Rob Bell

I too have fitted recently a new cat from Britsicarparts and I'm pleased with the result : power feels OK, noise is back to an "acceptable" level (with original SP supersports exhaust ;oP that's quite noisy but not as much as with my old empty cat).
My new cat is about the same dimensions as the old one, and it's not noisier (I mean when the ceramic matrix was still intact).
If your had a much larger cat before, then it seems logical to me that it was quiter too...

As Rob, I wouldn't suspect the cat, but something to do with the MEMS.
What about that extra temp sensor that Japanase imports do have : If you just unplug it, what happens ?
Does the MEMS think the cat is cold as it's reading ambient temperature ??

How is your fuel consumption ?
Fabrice

I think the temp sensor is just for the cat overheat light on the dash.
Kingsley

I think your right Kingsley about the temp sensor, i just linked out the connector so the light on the dash stays permanently off.


Thanks all for your input, will check out the stepper motor..

Rob i do still have the cat by-pass tube! I'll bring it along but i think we may be pushed for time. there's alot to do !!

Meeting up with David near his place which means up at 4.30am on a Saturday !!

Its official.... I am mad! the physco is right !!

Looking forward to another interesting day.

STU

S.C. Dickens

I agree with daubts due to catalyst relations.

May be you got *over sensitive* ?
I think mine does the same with sometimes getting back slowly to the idle mode.
I'll keep an eye on it. From memeory it might be as well have happened after hot rides. Have noticed this at my very old standard MGF from 96 and now as well at my newer 99 made with 200 cells metal cat and big throttle body.

A notice beside regarding the stepper motor control. There was a change with the newer ECU in 1998?? and they increased the count of steps per turn of the stepper motor. This makes a difference in principals between older and newer cars.

Regards
Dieter


Dieter K.

>> Rob i do still have the cat by-pass tube! I'll bring it along but i think we may be pushed for time. there's alot to do !! <<

I'll bring my tools, jack and ramps (loads of room in the boot of the ZS!) Can't bring the axle stands though - they are being used elsewhere... ;-)

SF
Scarlet Fever

I can bring some axle stands Andy

Stu
S.C. Dickens

I was meaning to bring Axle stands too.

Stu, Your soft landing problem is probably sensor related. In fear of making a balls up of the explaination I would ask Dave Walker at Emerald tomorrow. An IACV sensor alters the fuelling based on exhaust emissions. It's probably related to that. I'm sure it's a simple thing which can be fixed by a fully ported head with large valve, MTB's and an Emerald ECU ;o) Is that the excuse you were looking for.......
tim woolcott

Stu,

I've also had high idling problems in the past - cured by replacing the temperature coolant sensor - about a tenner and fitted in 30 mins.

Tim,

Is DVA coming to Emerald tomorrow then?

Dave
Dave

LOL

Tim

You mean its that evil darkside again calling !!!

I am just really waiting to see how kingsleys settles down then will be in touch with dva to go for the fully monty. Be nice to see 200 horses eh!

But most importantly its my day to day car so its gota stay reliable...

Dave..

Will look into that but dont think i will have time till tomorrow anyway.... it doesnt seem to happen all the time and as Dieter mentioned it seems worse after a hot run..


Tim

I've gota borrow axles stands so if you have some at home can you bring yours save me going over me mates tonight?

STU




S.C. Dickens

Mine will be in use for some of the day but I reckon there should be a bit of free time to use them to change the cat. So you're off the hook
tim woolcott

Stu/Tim,

I'll bung my stands in the boot.

Dave
Dave

nice one Dave

stu
stu

HMMM.......

Interesting day at Emerald yesterday,

This new CAT is giving me a power loss of nearly 8 bhp over the old one. Its coming off the car today!!!!!

So if you are thinking of buyin a new cat, don't get one from britishcarparts.com

Go for and original MG or one of the high flow ones form Moss. b&G etc etc....

STU
Wokingham
S.C. Dickens

Good to know you found the solution, Stu.

This is quite strange... there are several possible explanations:
- all MGF cats provided by Britishcarparts are not suitable for the F, but I haven't found mine to cause a power loss at all. My F drives like it always used to before my old car failed.
- the one you got is faulty, so maybe you could get it replaced FOC
- your F beeing a Japanese import requires a different cat ?
Fabrice

Hi Fabrice

Yea very strange...

I removed it this morning and put my old cat back on after first removing all the broken ceramics inside and imediately noticed the difference. Even with half the guts removed the old cat is much quieter and the car has its spark back!!

Incidently mines a VVC is yours the same? I am just wondering if the higher power of the VVC sees the restriction where the mpi doesnt! Who knows???

Stu
Wokingham
S.C. Dickens

Hi,

very strange this aftermarket cat differences.
Stu, any chance of looking by visible inspection for the ceramics *mesh* size of the bad one ?

Got pix of a standard MGR and a 200 cells metal catalyst at this site. Scroll down to the bottom.
http://www.mgfcar.de/catalyst/index.htm

Regards
Dieter
Dieter K.

Hi Dieter

I'll try to take some close ups of the internals of it today and forward them over..

The main difference externally is it is physically much smaller? but as my old cat was a jap import with the temperature sensor mounting bush, i dont know how the physical size relates to the normal one..

I'll forward measurements too!

Stu
S.C. Dickens

Dieter

You have mail

Stu
S.C. Dickens

Thank You !
http://www.mgfcar.de/catalyst/index.html
I put the pix on the bottom to the document.

IMO you are right. The US made thingy is much smaller and *flow restrictive*. Not sure, I think the other letter rows starting with E... relate to EC-approval numbers of the catalyst body.
Notice, only the body with included ceramics gets type approved, So it's a 'universal' part, just equipped with fitting flanges.

Regards
Dieter
Dieter K.

So There we go be warned !

Although it must be said the cat did do its job and I only really noticed the difference in the high rev range 6+, but a 7-8bhp drop in power was a big shock on the RR day..

The exhaust did sound a little louder than normal too!

I intend to have a word with Dave Walker at Emerald to see if is possible to pop over and put the car through another power run next week just to check to see if the peak power has returned so we know for definate that was the problem..

I bought the cat from Britishcarparts.com and will be advising them once i have comfirmed all with another RR power run.

It would have been interesting to put this cat on a MPI to see if the lower power engine recieved the same loss..

Cheers all

Stu


S.C. Dickens

>>It would have been interesting to put this cat on a MPI to see if the lower power engine recieved the same loss..<<

No chance! ;o) ;o)

I need all the speed I've got to maintain my car's insatiable appetite for road cones...
Rob Bell

>>http://www.mgfcar.de/catalyst/index.html<<

I just had a look at the pix - it appears that the cat has a very abrupt increase in diameter from the exhaust pipe to the body of the catalyst. This is a very poor feature as it plays havock with airflow. Probably the reason why this cat performed so badly on the RR Stu. The standard cat is a surprisingly good design - and is probably one of the reasons why we failed to find any performance advantage in removing it in favour for a bypass pipe.
Rob Bell

Rob

Yea i'm pretty annoyed with britishcarparts.com, they are selling it as a standard cat for the mgf and its clearly not (easy with hindsight!) its was alot cheaper than the normal MG one but there is no mention of it affecting the power of the vehicle... Thats why i am going to speak to Dave Walker and see if he can squeeze me in on the RR next week to see if all is back to normal then take both printouts with the cat back to the supplier! refund please!!!

STU
S.C. Dickens

Stu,
My F is an mpi, so I don't rev it as high as a VVC...

I've had a look at you pictures, and the cat I got from britishcarparts.com is not the same as yours !
It's hard to say if it's a lot larger, or to compare the size of the cells. Mine doesn't have the "embossed dots", is more polished and the lenghts of tube between the body and the flanges are shorter than yours. And, it's about the same size as my old one.

To comment about the power, only a R-R session could tell the truth, as a difference of few bhp somewhere in the rev-range is not that noticeable...

Good luck and keep us posted,

Fabrice
Fabrice

This thread was discussed between 08/05/2003 and 20/05/2003

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