13 replies to this topic

[bloke]

Hi there, having owned various SPI Mini's in the past from new, And now currently owning an MPI 2000 Mini I have noticed the throttle response when the ECU goes into idle mode is pretty poor. When you blip the throttle at the traffic lights, the engine slows down slightly then attempts to accelerate.

 

Normal driving is fine and accelerating whilst moving along is perfectly fine too. I'm just wondering if this is consistent with everyone else's MPI Mini? I've checked for various air leaks and replaced any O-rings that I thought maybe faulty. Having a spare set of electronic sensors I replaced them all just in case with absolutely no difference, so I put them all back again, just to keep the new ones in the boxes for when I really need them.

 

As I say, it only happens when it's in its idle mode and warmed up, as you can't tell when its cold due to the revs being high.

 

I had a similar problem with Cooper SPI about 10 years ago, But I suspect that that one may have very well being faulty, as when you would take off from a roundabout you'd nearly be killed by traffic coming at you when the engine would effectively stall. But that's another story.

[brivinci]

How many miles does this motor have on it? Have you replaced the timing chain ever?

 

My SPi had similar issues with the blip. It just didnt respond. If I smashed the throttle from idle, it would actually almost die and backfire through the intake. Now, I am not 100% what caused this or if it will be fixed when i finally fire the rebuild motor up BUT I had excessive timing slack for sure. There are sooooo many junk chains out there. I will only ever buy from Keith Calver as I know he has sourced the very best. The two I got from Swiftune both stretched within 1000 miles. Anyway, I think this could be an issue. You hit the throttle from idle and the lag is the timing getting caught back up. You would not feel it on the move because the pressure on the timing chain would be consistent and maybe not flex as much.

 

Again, not sure but maybe something to think about.

[bloke]

Mileage is fairly heavy at approximately 115,000 miles. I must admit I don't know the condition of timing chain, gearbox and engine were sorted out by the previous owner approximately two years ago. Will definitely have a look. If I have to change it I'll probably go for the quality duplex chain I've seen somewhere, possibly from Keith Calver. He seems like a nice bloke.

 

Thanks for the reply.

[spiguy]

Happened to me recently on my SPi. Press throttle quickly, the engine would drop then rise, and if you opened the throttle very quickly, it could backfire. In my case the cause was one of the vacuum lines. I had replaced the short line from the inlet to the fuel trap. However I did not use the correct Rover pipe, I made my own with vacuum pipe and two elbows. The heat back there had softened the plastic so that it had kinked.

 

The effect of this was that although vacuum was still reaching the MAP sensor in the ECU, the kinked pipe was acting as a restrictor so that the very fast change in vacuum which happens when you blip the throttle, was not reaching the ECU due to this restriction.

[FlyingScot]

Check the throttle cable and the TPS. As it's an MPi the TPS is different but the same principles apply.
When you say you changed all the sensors was this one of them?
Could be you have a noisy TPS and the MEMS is getting big variation in the reading.

FS

[jamesquintin]

Possibly something to do with the temperature sensor. I had an issue on mine where it wouldn't go back down to idle when coming to traffic lights on longish journeys (Like the L2B). I had a secondary issue of the fan kicking in when it shouldn't have. I used the replacement Rover temp sender cable, and its been fine ever since

 

Q

 

[Fast Ivan]

whilst you say you have replaced all the sensors this doesn't mean that they are communicating as they should be with the ecu

one of the many advantages of the code reader is that it not only checks that the sensors are not broken but also that they are working as they should and most importantly that they are actually talking to the ecu and that the ecu is giving the correct outputs.

 

How's the service condition of the car? filters all good, spark plugs gapped ok, valve clearances and so on.

Also make sure all your earths are good.

 

What colour are your plugs? I ask because one of the causes of hesitation like this can be an incorrect air/fuel ratio, which can be caused by a faulty TPS or MAP, as both of these are used to calculate the volume of air entering the inlet.

[bloke]

Okay, after checking the TPS very carefully with the meter both the original and the spare work fine. So I figured that there must be something allowing a air leak into the carburettor.

 

Having a rummage round in the loft I found a spare carburettor that I had ordered from eBay, for one of those ‘just in case’ moments. ;)

 

I stripped this down and gave it a full service and clean (a dam good scrub in the sink)

 

I found some parts left over from a previous carburettor service pack I had in the loft which had a couple of rubber O-ring seals for the butterfly.

 

I have to say this is probably one of the worst carburettors I’ve ever encountered, not only is it badly designed; the tolerances and end float on the butterfly are massive. I had to include several O-rings from a 'pound shop' special box of various size O-rings and a washer to take up the slack. This allowed the butterfly to stay precisely where it is supposed to be. No wonder they jam and warp.

 

With that job done I decided to take the old carburettor out of the car and have a look to see if there was something wrong with it. Most certainly there was something wrong with it, as you can see from the picture below, this does not look quite right.

 

 

 

After stripping it down I found that the pressed bearing had not been pressed in at all during manufacture, and it had crushed the rubber O-ring against the spring hanger.

 

 

The O-ring seal was visibly damaged and was crumbling, letting presumably a lot of air in the at the wrong place.

 

 

Here is the carburettor all refurbished and ready to put in.

 

 

Anyway the old one will be a job for another day to repair, with the new carburettor installed and the idle air control procedure performed I started up the engine and everything feels very nice and smooth.

 

The true test will be tomorrow when I go for a bit of a spin in the car and see what it is like when it’s warmed up.

 

Will keep you all posted, and thanks for the replies too. Cheers.

[FlyingScot]

Throttle body...

FS

[brivinci]

Thats VERY interesting. I have never really looked at the throttle body in any amount of detail. I might just have to now. I cant wait to hear how it all goes on the drive. If nothing else, I'm sure you sorted an problem that, if not now, would have caused MASSIVE issues and scratching of head later.

[bloke]

Fair doo's, I seemed to get the word carburettor in my head probably because I was pinching parts from the carburettor service kit, most definitely a throttle body.

 

Testing it this morning and it feels lovely, acceleration is nice and smooth and the pedal feel is much better. Still not as crisp as a carburettor based Mini, but now pretty close. Will probably change the vacuum pipes between the IACV and the smaller pipe just in front of it just for piece of mind, with something a bit better than the cheapy rubber hoses that are in there at the moment.

 

Thanks all, and happy Mini'ing..

[bloke]

Possibly something to do with the temperature sensor. I had an issue on mine where it wouldn't go back down to idle when coming to traffic lights on longish journeys (Like the L2B). I had a secondary issue of the fan kicking in when it shouldn't have. I used the replacement Rover temp sender cable, and its been fine ever since

 

Q

 

 

Sorry, for some reason your two quotes did not turn up until this morning. Very strange. Thanks for the reply, I managed to find a few brand-new temperature sensors at Castle Coombe last year, so that was one of the first sensors I changed just in case.

 

whilst you say you have replaced all the sensors this doesn't mean that they are communicating as they should be with the ecu

one of the many advantages of the code reader is that it not only checks that the sensors are not broken but also that they are working as they should and most importantly that they are actually talking to the ecu and that the ecu is giving the correct outputs.

 

How's the service condition of the car? filters all good, spark plugs gapped ok, valve clearances and so on.

Also make sure all your earths are good.

 

What colour are your plugs? I ask because one of the causes of hesitation like this can be an incorrect air/fuel ratio, which can be caused by a faulty TPS or MAP, as both of these are used to calculate the volume of air entering the inlet.

 

That was the strange thing, the code reader seemed to indicate everything was perfectly fine, but the update on it isn't fast enough to register when you blip the throttle. Service of the car is as good as I can get it is far as I know plugs, oil and oil filter all new, plugs gapped to the right setting, and I did valve clearances last week. Also just changed the expansion tank, for a new aluminium one, so had the excuse to clean up the ground point behind there as well.

 

Need to take the Mini out for a long run to see how the plugs look, but from memory the old plugs looked fairly textbook.

 

Thanks for the replies. All the best from Bloke.

Edited by bloke, 03 July 2015 - 10:08 AM.

[bloke]

So, it's been a few days; and I ended up ripping out most of the tubes in the engine bay, as they'd all perished to a certain extent. The low pressure stuff to the clutch bell housing, and the timing chain housing had holes in it, however this doesn't make any difference to the overall compression, I just wanted to tidy it up, so I fitted some blue silicon hoses.

 

What I did find though, was yet another airleak where the servo was fitted on the manifold. What I did with this was plug the hole, as this connection is a bit of a mess anyway, removed the metal piping system, and fitted more silicon pipes instead of the rusting metal tubes.

 

Rover insisted on installing an anti-stall device, consisting of a restricted tube (on the metal tube system) going from the low pressure to the high-pressure side on the manifold, since I've now technically removed this metal piping with the restrictor in it, I had to come up with an alternative. The restrictor only comes into action when you take your foot off the accelerator and the butterfly goes back to it's rest position closing off the air. This causes the car to almost stall until the IACV allows more air through. The solution was to drill a pinhole in the butterfly. I opted for a fractionally smaller hole than Rover designed, to allow the revs to drop slightly quicker, and the result is a fantastic car to drive again.

 

Whilst I was in there, I plumbed in a vacuum gauge, and mounted it next to the bonnet release in a little podule. This should help me spot any further vacuum leaks if they ever happen again.

 

Plus all that silicon piping instead of rusty metal tubing is quite nice to see. :)

 

One final note, the carbon canister pipe that connects to the solenoid operated valve had a perished o-ring on the end of the solenoid operated valve part itself, so the canister was effectively venting fumes into the engine bay. I just connected a longer tube to the connection, taking out the plastic part that seems to have been badly designed.

[jamesmpi]

Come on that must be worth a photo of your engine bay to show off your handy work?!?