12 replies to this topic

[spiguy]

Hi folks,

 

For the last couple of days the car has started doing something odd. Unless I am very gentle indeed when I press the accelerator, the engine hesitates before the revs increase. Doesn't matter where I do this - ie if idling and I blip it, and not even a very sudden blip, it does it. If I build the revs up to say 2k and then blip further, it does it. I think I can feel it slightly when driving too.

 

I have disconnected the O2 sensor, still did it. I have recently replaced dizzy cap, rotor arm and leads - it didn't start doing it in co-incedence with these changes, they were changed a couple of weeks ago. I have checked the vac lines, all appear to be good and the car drives and pulls well, and idles normally at 750 rpm.

 

Cheers

Craig

 

 

[FlyingScot]

TPS is likely candidate mate as it is sending perhaps the wrong position to MEMS relative to the physical flap in the SPi body.
The track on it can get "noisy" with wear.
Stick you multimeter on it and look for a smooth progression of voltage with on or pull the plug and check ohms between centre wiper and outer with it off.


Should be easy to rule out.

FS

Edited by FlyingScot, 19 March 2015 - 03:10 PM.

[spiguy]

Thanks FS, I will be doing that while I try to track this down. Thing is I already replaced the TPS with a 'new to me' one that I got off ChrisG, because the original one had a noisy output, this one was clean as a whistle when I replaced it a month or two back. Suppose it could have been on it's way out too mind you! 

 

I still have this nagging suspicion that there is some kind of vacuum leak on this car, but I can't find anything! Just seems a little underpowered to me.

 

Bloody minis!

 

Actually thats a point, I meant to ask you about this. Do you think it would be possible for someone to have been messing around with my throttle body, such that the position of the flap relative to the TPS position is now wrong?  for example if the flap was a little more open, then it would draw a little more air than it should for the fuelling that the ECU will give based on TPS output? I know that at idle this would be controlled out, and in theory should be controlled out whenever the ECU is using the O2 output to alter the fuel, but I am sure I read that the ECU stops including the O2 sensor a fair bit before wide open throttle. The reason I wonder is that as I said above, the car feels a touch underpowered to me, but I have noticed that there is a point on the throttle that I am better being 'less on the pedal' than 'more on the pedal' if you see what I mean. Like I am accelerating, and if I push a little more, the acceleration tails off a little, then if I back off it comes back on a little.

 

I wondered if this could be the point at which the ECU just goes by the map and ignores the O2 sensor, and as such could indicate that my car pulls a little too much air of normal?

Edited by carlukemini, 19 March 2015 - 03:48 PM.

[FlyingScot]

Worth checking but unlikely Lightning has struck twice..

It could have been messed around with in several ways or maybe just basic things like fuel pressure (filter been changed?) injector clogging, the list goes on....
At idle MEMS will also control the timing to maintain the motor running as this reacts quicker than the stepper, then depending on the sensors including the lamda uses values from one of the stored table values as you put your foot down.
AFAIK as the ECU senses the throttle position reaching towards full open it ignores lamba and just adjusts the injector pulses but it may be the motor revs it uses for this. I better have a read of my green book....

I have a full set of spares including a few full SPi bodies and ECUs if we need to start swapping things to elliminate the issue.

FS

[FlyingScot]

And of course a diagnostic setup..

[spiguy]

Thanks FS. Appreciate it. I have been wondering about the fuel filter. I have a new one to swap out hopefully on Saturday.

[FlyingScot]

It's always worth doing, the system relies on the basics including whether the injector is spraying correctly and it always amazes me in comparison to other FI cars how few times it (the injector) gets changed or ultrasonically cleaned.
Big advantage is since Japanese the filter will probably come off without breaking the pipe...

FS

[spiguy]

Found the cause of this... It was the short vacuum line from the manifold to the fuel trap. I had made a new one up as the old one was split, and had used plastic vacuum line and rubber elbows from minispares. Seems the plastic isn't up to the temperature back there, as it had softened to the point that although vacuum was getting through, the pipe had folded over a bit making the hole so small that it would have restricted sudden changes in vacuum. Gentle throttle changes and hence slow changes in vacuum not a problem, but sudden ones were not being seen by the ECU.

 

Changed it for a proper one and the problem has gone away. Lesson learned?  It's always the bl**dy vacuum lines on an SPi!!

[FlyingScot]

Aargh, don't use anything but genuine parts. Vacuum elbow are the devils spawn and only for non fuel injection cars.
The number of bodged "vacuum" pipes I have seen and problems they have caused...

Hold you head in shame Mr Carluke Mini I thought better of you

Glad you got it sorted Craig

FS

Edited by FlyingScot, 19 March 2015 - 10:26 PM.
Spelling on an iPad

[spiguy]

Ha ha... yeah I know, I'm not proud of this failure! I just ordered a full set of proper ones today so that I have a spare set too!

[brivinci]

I actually did away with my OEM vac lines. My go-to mini guy had sourced the perfect, thick walled silicone tubing. Does away with the elbows and worries.

Nice to hear you got it sorted though.

[spiguy]

Hmm. I actually bought some samco silicone tubing to do just this, but when I tried it I got a similar sort of hesitation to what I had described above,so went back to hard vac line and it was fine again. Now I think about it, I bet it was just the short one even then, I probably just disturbed it a bit when fitting the silicon - I initially just fitted silicon on the long run from the trap.

[brivinci]

I have a full set of brand new OEM lines just in case but the these silicone lines seem really nice. They are very thick walled to prevent any vacuum collapsing. There are no elbows so they are a little long then stock to make up smooth bends. The only one that I didnt replace was the one that goes from the back of the throttle body to under the airbox. Not sure why actually:-)