Loss of power

Thank you for that I will check this morning, I replaced the front calipers while it was on a SORN so I may have done something amiss.

Stalker wrote:

It passed its MOT recently but was told it needed new plugs and coil packs whatever they are.  The engine did not seem to misfire or sound rough so I have no leads.

 

I go back to what Mr Stalker wrote in his first post.  Clearly, at some point a technician looked at this car and said that it needs plugs and coils.  

We don't know the reason for that diagnosis, and indeed we don't know if it was a well-founded one, but IMO it is worth starting there.  

Myself, I can in theory see how weak coils and/or compromised plugs could cause these symptoms.  Now, it is completely correct that the usual failure mode means that one or more cylinders stops firing, and that this is very evident to the driver -- on a 4-cylinder engine, the loss of a cylinder will make the thing feel like a paint shaker at idle, if it idles at all.  But it is just possible that heat soak is affecting weakened ignition components just enough that spark is sufficient at idle/no-load but fails at higher engine loads (when more fuel is present in the chamber).  In any case, the MOT man said the ignition system needed titivation, so I would start with that.  

The cat clogging issue -- the most obvious alternative diagnosis -- seems to be ruled out or at least made unlikely by previous work.  Binding front brakes also seems to me somewhat improbable, given that 1) they were renovated and 2) if they were really binding that badly they would do so consistently, and also would tend to give steering effects and (especially after 10 miles to the office) a rather notable stink.

So I'd say, spend a little bit on the coils & plugs and see if that does it.  You could even install these new parts at home if you were so inclined -- we can help if you need guidance with the job.

Hi Motacilla,
Thank you for your comprehensive response to my question. The car idles perfectly happily and I can rev the engine hard without any sign of a misfire. I fitted new front calipers a few months ago, the air filter is clean and I also blew my air line through it, the brakes are not binding when I jack it up and spin them. A new cat was fitted at the time of the MOT and the new section has what looks like two cat cylinders so a blocked exhaust is unlikely. The chap who organised everything for me is a body specialist with F1 but has a team of individuals who sort the other tasks. A new idea came to light today which concerns fuel. The vehicle has been on a SORN for several months so done no mileage other than two and fro to the test station so it is possible that the E10 fuel has degraded and I should now use E5. I need to speak to the "organiser" but he is somewhat elusive when the F1 season is in full swing.
All that said plugs and coils are still top of the list but when I removed the cover I was unable to remove any of the connectors and was unsure how much force to use.
Than you again for your thoughts, I will persevere.

Hi Motacilla,
I am afraid it is me again, I have just taken the Jimny for a drive to the next village which is 5 miles away. No level ground all up and down hills and I drove it as as hard as I could and it drove perfectly until I reached the last and steepest hill one mile from home and crawled up the hill home in first gear. If I tried to change up or accelerate the engine began to rev much higher. The engine sounded rough but was not "coughing" to suggest a misfire but it sounded as I remember my land rover when the exhaust was rusting and what I describe as "blowing" , exhaust gases were clear and no black smoke. No warning lights on the dash.
I was smiling until a mile from home but that soon changed when I was crawling up hill in first gear.
The search goes on!

Hello Stalker, sorry to hear about your disappointing drive. You have ruled out brake binding definitively, though, so that's progress.

Stale fuel I would say is a red herring; petrol can get a lot staler than that before it causes problems, and water contamination would stop you dead typically.

Based on what you've written, with the usual caveats about diagnosis at distance, my money is still on an ignition problem.

IMO there's no reason to pull the coils/plugs for a visual inspection. The failure point will not necessarily be obvious to the naked eye.

I think the replacement of the ignition parts would be very cheaply and easily done at most any garage, if you brought the parts along. If you order the parts from our host here you will be certain of having the right bits. Good luck.


Edit: Cars hate being SORN'd, and sometimes they will "act out" upon being put back on the road.  You may find more than one problem, or that you fix one thing only to have another thing fail soon after.  Your best tool here is patience: you will get there in the end.

Many thanks again Motscilla, apparently the "fixer" is back according to a relation so I will ask tomorrow what reason he had for mentioning new plugs and coils, as you say that is still top of the list of differential diagnoses.

I have lots of other Jimny questions but do not wish to appear geeky so first things first.

Again many thanks