5 replies to this topic

[minimowta]

When they brought out the SPi and MPi I thought "Great, no more fiddling with points and topping up the carb pot" Everything was fine until about 6 months ago when a missfire developed. I found this excellent forum with loads of other people having the same problem and have been trying to sort it out ever since!

The car is a bog standard 2000(X) 1.3 MPi with 58k on the clock.

I have checked for air leaks and had all the sensors and cables checked and replaced when neccessary...... every time we find something I think that's got to be it but..... it isn't. Iv'e still got the problem.

I recently took the filter box of and, with the engine running, put my hand over the intake. It nearly sucked the skin off my hand but kept running (if a little laboured) Should it have stalled do you think?

The garage has changed the plugs and adjusted the throttle pot and checked the fuel pressure. They now think that the problem is most likely mechanical and think that as the mileage is so low there is a build up of carbon on the valves which is literally soaking up the fuel that should be going into the engine. This is very plausible as it does feel like fuel starvation. When I put my foot down hard it runs fine, the problem is on light load, 30mph, in traffic when I am gently on and off the throttle - it's jumping and bucking something awful!

Some other info.... There is a constant smell of oil when I'm driving but no signs of an oil leak or oil on the drive. I have checked the compression and all cylinders are the same so I think the head gasket is OK.

The garage do say that they cannot gurantee a de-coke will solve the problem but I really think they have a good point but don't want to take the top off until I'm a bit more sure.

So.. my question is (at last I hear you say!) As well as, should the engine have stalled when I put my hand over the intake? Has anyone else solved this problem with a de-coke? Sorry that's two questions!

Any help and advise would be greatfully received!

Cheers

[miniman retford]

I bought my W reg MPI 18 months ago which had done 8000 miles & have now done 19000 & have had a similar problem at exactly 2k revs not as bad as yours sounds but just a slight hesitation, Suppose i have just got used to it & dont find it a problem now!

[dmdangermouse]

I have the exact same problem mate!

Seems like all SPi/MPi's do

When I took my '99 to a garage they had it for about a month testing sensors, they thought it could be the ECU so they sent it off to be tested but came back fine.

I never had the bill for it haha

Let us know if you get to the bottom of your problem

[elvisthepizzaman]

It sounds like an issue with the map sensor signal. 2K and light throttle causes a lot of rocking and if the wiring harness is not clipped to the throttle body it stresses the contact pins on the sensor. over time the contacts get cruddy from arcing and the ecu will start getting intermittent signal. If the map signal cuts out then the ecu will shut the engine off. I would suggest you wiggle the wiring harness behind the throttle body that goes to the map sensor and see if you can get it to misfire. if so, then take the connector and map sensor off and clean the contacts with some light sand paper and also try to clean the contacts on the connector as well.

another idea to reduce the bucking would be to change the rubber joints to poly joints

Edited by elvisthepizzaman, 07 April 2009 - 04:23 PM.

[minicooper1.3i]

I'll have to go with Elvis on this one. Engine rock from worn top steady bushes can really bugger up the wiring to the MAP sensor which will cause this kind of a problem. I had the same thing myself and it only came to light when it was plugged into a diagnostic machie and the tester happened to notice the fault when he revved the engine hard, causing it to rock. As the engine revved it would be ok (ie making connection) bu when he let off it would appear (break in wire reappeared).

If it is a wiring fault then they can be repaired, or replacing the engine loom with a new / 2nd hand one is only about a half hour job.

by the way, when you did the compression check, did you take all the plugs out together, or one at a time before replacing it? Because if you did it one at a time, and there's a leak between cylinders, all you'll do is compress two cylinders at once and not get an accurate reading. Just thought I'd mention it.

[minimowta]

Thanks for your input guys.

All the sensors have been checked on the garage diagnostic machine. The water sensor and plug were replaced. We had a good look at the MAP sensor and plug, gave it a good tug - all seemed well. The top engine mount has been replaced recently.

When checking the compression I took all the plugs out. Good point about pressurising two cyls at once! I took them all out at same time more by luck than judgement to limit the time my helper (wife) was cranking the engine! There are non of the tell tale signs of cross contamination - mayo in the rad!

I had another poke about last night. Checked all the tubes and all seemed to be OK. I checked the nuts on the maniolds and found a flat or two of tightening up possible...... didn't seem to make much difference.

Do you think the engine should have stalled when I put my hand over the air intake? It seems air is getting in somewhere!

What do you think about the oiley smell? - I checked the pipes from the crankcase breather to the air inlet.... all seemed Ok

Is the idea that the carbon on the back of the valves could soak up the fuel before it gets in the cylinder a reasonable one?

Cheers