General 100hp mpg drop?

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General 100hp mpg drop?

Yup. Slightly larger than the new ones as they have eroded through use, but nothing worth worrying about.

Checked primary coil resistance and all are about 1 ohm.

Any other ideas?
 
The plug colour looks ok, the gaps look enormous, but that could just be the photo.

Three seem to have rust around the threads, which might suggest water in the bores. Are you losing any coolant?

the gaps look larger than they actually are. they are about 1.1mm.
stock gap is 1mm.

no real coolant loss. just a small amount over a long period of time like most cars.
its more of a blownish tinge. would have to be pretty substantial to cause rusting on the threads. you would see evidence of the plugs being "washed".
its nothing i would personally worry about tbh, looks pretty normal for plugs installed dry.
 
Be sure to fit the plugs to the correct tightening torque. Doing it by "feel" often has them not tight enough leading to problems. Over tightening is (pretty obviously) very expensive if a plug snaps off.
 
New plugs made no difference.

Have tried another lambda sensor and it doesn't really seemed to have made any difference, but need to use it a bit more to really see.

Really running out of ideas now!?!?

Car runs and performs well. No smoke, no real oil or coolant use. Fully revs out without hesitation. Well looked after service wise. MES readings all look fine from what I can tell.

Any other suggestions?
 
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go for a run out. Try not to use the brakes for the last few hundred yards. Test the temperature of the discs. See if on is hotter than the rest.

They can seem fine when tested cold. But expand slightly and drag slightly when hot.
 
I rode a 60 bhp bike 100 miles on motorway. When I arrived the rear disc was blue and so hot the black painted centre had lost all its paint leaving no sign it had ever been painted. The brake caliper had seized. Fuel consumption was not measurably different.

Mk2 Punto Abarth had to stop every time I used the brakes because a front disc was binding. Had to hit it with a block of wood to free it off and avoid using the brakes. New caliper needed but again fuel consumption did not really change maybe 1 or 2 mpg.
 
I rode a 60 bhp bike 100 miles on motorway. When I arrived the rear disc was blue and so hot the black painted centre had lost all its paint leaving no sign it had ever been painted. The brake caliper had seized. Fuel consumption was not measurably different.

Mk2 Punto Abarth had to stop every time I used the brakes because a front disc was binding. Had to hit it with a block of wood to free it off and avoid using the brakes. New caliper needed but again fuel consumption did not really change maybe 1 or 2 mpg.

depends on you driving.


if like me you are light on the throttle and coast as much as possible averaging over 60 mpg then one mild front dragging slightly is around 4 mpg.
 
As mentioned, I have checked over the brakes and nothing is binding.
The rears have been overhauled recently anyway (New discs, pads, sliders and seals).

I am really at a loss. Perhaps after a week with the new lambda things may improve as the ecu adjusts!?

Randomly after fitting the new lambda and testing it worked, I disconnected the battery for about an hour. When I reconnected, it came up saying the car needed a service!?!? It had given up telling me about it ages ago and I have had the battery off a few times since. Not sure why it has decided to come up again now?
 
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Well the replacement lambda kept throwing up an engine warning light due to the heater resistance reading.

Replaced with a brand new Bosch sensor and that fault has gone away.
Disconnecting and reconnecting the battery this time has got rid of the service warning!?!?

Anyway, have used it for a few days with a mixture of short journeys and a run and it is currently reading 43mpg average.

Seems slightly better, I'm not sure if the ecu adjusts itself more over time?
 
Drove up to Scotland and got an average of around 43-45mpg.
That doesn't seem that great to me on a real long run?

No idea what could be making the mpg so crappy? :(
 
I almost never get that much mpg from the 100HP. It's a 16V engine that makes its power well up the rev range. The trade off for that power is less efficiency at "normal" revs.

TBH, I would be happy with 43 to 45mpg at motorway speeds.
 
45 is reasonably good for a old petrol engine I get that sort of mpg from my 2017 fiat tipo 1.4 16v

My turbo starlet does about that mpg!!!

For comparison, my cinquecento sporting does about 45mpg just running around doing short journeys.
That is the definition of old and knackered.

The 100hp has managed about 50mpg+ on a good run in the past.. it used to do 47-48 mpg on a run generally then one day it started doing just over 40mpg on a good run and a bit higher of you are really careful driving.

Something has changed. But without randomly changing stuff, I just don't know what it could be!?!?
 
It could be the pre-cat O2 sensor. If the ECU thinks the mixture is weak it will add more fuel. You won't smell it in the exhaust as the cat burns it away.

A slight missfire (as could be caused by a failing coil) has a similar effect. The unused oxygen causes the ECU to enrich the air fuel mixture. That soots up the sensor and the plugs aggravating the problem.
 
It could be the pre-cat O2 sensor. If the ECU thinks the mixture is weak it will add more fuel. You won't smell it in the exhaust as the cat burns it away.

A slight missfire (as could be caused by a failing coil) has a similar effect. The unused oxygen causes the ECU to enrich the air fuel mixture. That soots up the sensor and the plugs aggravating the problem.

I replaced the o2 sensor with a new genuine Bosch sensor and it made no difference.
Could be a coil, it's not going to be cheap to replace them though! Could be 1 going bad or all 4 :confused:
 
Sorry I forgot that you'd changed the O2 sensor. I cant remember if you are using MES to read the ECU codes and parameters, but it would be a good idea to get a datalog scan while the car is driving.
Coils can be tested for resistance. Agree simply swapping them out for new is not a great idea.
 
Sorry I forgot that you'd changed the O2 sensor. I cant remember if you are using MES to read the ECU codes and parameters, but it would be a good idea to get a datalog scan while the car is driving.
Coils can be tested for resistance. Agree simply swapping them out for new is not a great idea.

i have the free version of MES. i had a look and posted static readings on here and no one replied, so i assume there was nothing obvious there!?

any suggestions on what to look for whilst driving? i have measured the resistance on the coils and they were all the same and about what i would expect for a coil. this was cold though, so i could check them again when hot as that is when a coil is most likely to cause an issue.
 
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