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2004 i-CTDI low MPG

Ok, I know little of Diesels, I'm in a Petrol, but the O2 sensor on my exhaust went a couple of years ago. Hammered the living daylights out of my economy as the engine registered the faulty sensor and would just fuel within very safe boundaries. This was seeing somewhere between 330 and 360 miles a tank. Since I changed the O2 sensor I'm getting 400-430 a tank. I don't know if Diesels have a similar setup, but you could always get the engine read for possible fault codes on sensors etc (apologies if you've already done this - I skimmed the thread, but didn't read in detail :blush: ).
 
Thanks a lot to John and Dave, we gave tested the MAF yesterday and today and we are getting almost same readings +-2 g/s, so it's not MAF problem.

We also have chacked Turbo & Intercooler. It's clean there and Turbo wasn't changed.

We alsi have checked all air pipes as we had suspicion that somebody could forget the piece of cloth, for example when changing the clutch but no luck again.

So the last option left is injectors. We have to send them for test on Tuesday or Wednesday. Even there is no smoke, we have to illuminate that option.

Thanks Dave for support we are looking for the problem of low mpg and not testing my maths here.

Steve there are no faults, car is checked on diagnostic almost every evening.

Fred, even if I will establish that I'm getting lower mpgs on motorway than in city, how is that going to help?

Ebod. I wish I would have 43 mpg =). I would say 43 is normal if you have combined motorway/city driving with breaking speedlimits on motorway. I used to get same mpgs when speeding 100 miles an hour on motorway + normal city driving. And it's not 17" defo, again from the experience they do not make huge difference maybe up to 3 mpg max.

Anyway the next step established - injectors.
 
I was about to say that my next thought would be injectors especially given the miles the car has done.
It might not be smoking but I dare bet a different set of injectors or a recon on your ones will make a massive difference. Fingers crossed it does.
The only other thing would be a fuel leak when the car is running but I'm hoping that would have been spotted before now.

Freddofrog I wasn't arguing with you, just trying to point out that the mpg is obviously seriously down on what the owner knows these cars can do from her previous ownership experience so how it was calculated doesn't really matter.
 
I really cannot get my head around this one and, so, am watching with interest to see the outcome. I just cannot understand how the car can run well with no apparent symptoms other than the fuel consumption. The only other thing I can suggest in addition to having the injectors checked is to also have the cylinder compressions checked.

I do wonder if this is one of those (thankfully rare) situations where there is not a single major fault but a combination of several minor faults causing the symptom.
 
When was the last time this car spent a day in the hospitality of a good Honda garage. It costs more than your local mechanic, but you get what you pay for with my local Honda. Little jobs I get done locally, but once a year she gets a thorough overhaul with Honda. They know me, know the car, know it's nuances and what to check for in relation to age and mileage. I've heard some dodgy stories of Honda garages, but find yourself a good one and they're more than worth the money in my opinion. And they should give you a nice car for the day while yours is being worked on.

Could be worth a thought. Drop it in for a thorough service and get them to replace the injectors. Could be costly, but I'd be confident it would do the trick and then it would be game on!
 
Some quick calculations I just did, show that with a leaky injector(s) dribbling fuel, then mpg at steady 70 will give better than mpg at steady 30 or 40, more-or-less regardless of choice of gear. Something like a valve timing fault would show marginal mpg differences at any steady speed between 30 and 90 in say 4th or 5th gear. Both kinds of fault give 30-ish mpg over 30 mph, with 30mph or lower giving low-20 mpg.
 
A couple of further thoughts. Is the engine thermostat working OK - not stuck open? What does the ECU believe the engine temperature to be? - needs to be scanned for this one, it's no use relying on the temperature gauge.

Apologies if you've already checked these.
 
Hi all, I am from Romania and I am having the same problems with my 2007 i-CTDi Honda Accord. I bought mine in May this year. At that time the car had an average fuel consumption (highway/town) between 9-10L/100km and smoking heavily. Testing the car with the HDS, no errors were found, only showed a big correction (-2.4) on the 4th injector. Changed the injector and cleaned the other three (now the correction on the all injectors are between -0.1 and +0.1). The smoking was gone but the consumption was almost the same. I was to my local Honda Dealer and they didn’t know anymore what to do. Then a friend of mine suggested me to go to a Honda Dealer in Hungary in a town called Debrecen. There they said the problem is the valve from the fuel common rail. After changing it, the fuel consumption dropped with approximately 1L/100km. In my opinion this can be less. So I am stuck again. I am considering to put in new thermostat, new engine temperature sensor and new MAF, maybe new MAP, dough the MAF and MAP were cleaned and no errors were showed on HDS and the parameters are in the permitted limits. The onboard computer shows the average fuel consumption with approximately 1.2L less than what I calculate after a full tank. I presume that should be the correct consumption.

Maybe my experience helps, or maybe you have new suggestions to my problem.
 
Hi Baxy, welcome to the club.

The only valve on the fuel rail (at the left end, as you look under the bonnet) is the fuel over-pressure relief valve. In the event that this does operate, whether correctly or in error, the fuel vented is returned to the fuel tank. So I can't see how this might affect the fuel consumption?

It's a difficult problem to understand, have you tried the obvious things like sticking brakes?
 
How the Honda mechanics showed me the valve is in the right side how you look under the bonnet. And because the valve is not replaceable i had to replace the entire fuel rail. They discovered this problem by looking with the HDS at the pressure in the fuel rail after the engine is stopped. The pressure in the fuel rail must not drop very fast (there are some limits), at my old one was dropping very fast. Everyone I said that after changing the fuel rail the fuel consumption was less then before, are not believing it. In my case, believe it or not, it did.

The sticking brakes was eliminated at the Honda Dealer like the other obvious things: MAP cleaned, MAF cleaned, new oil (MOTUL 0W30), new OEM fuel filter, new OEM air filter.
 
We have seen that our common rail is leaking as well but also thought that this should not affect fuel consumption. Anyway you don't have to replace the rail you can just put the valve on that, so that is something we will consider to do next.

In the meantime we have realised that we have 2 good Accord injectors lying around in the garage, so today we have took 2 mine and replaced by 2 good ones. The car is working much quitter it's a fact but I'm not sure about consumption.

Just to reply all the suggestions

It's not thermostat - it was checked.

Could be a timing chain - but it makes no noise. But we have decided to change that but after we will check all four injectors as it's really hard to take them off and you need to get them off to change the chain. Especially it's only €100 (I'm not talking about the labour as that will be done in our garage). Just to note that on my first Accord we had to replace the chain at 125K miles as that started to make noise, so just to be aware when you pass that mileage. Honda manual doesn't suggest you change the chain but if it starts to make noise you really need to change that.

There is no way I'm bringing my car to Honda dealer! I would not trust them even my bicycle. The only thing they can do properly is to charge you!

Anyway I' will keep you posted
 
My last fill up was 57L and did 682km, that means 8.35L/100km, 60% town driving, 40% country roads at max 120km/h
The onboard computer showed an average of 7.2L/100Km
 
baxy said:
My last fill up was 57L and did 682km, that means 8.35L/100km, 60% town driving, 40% country roads at max 120km/h
The onboard computer showed an average of 7.2L/100Km
Click to expand...

That is arround 30 MPG, ours is around 27-29. What milleage is on your car?

Does yours have a slight vibration on engine?
 
My car has 150k km.
About the vibration, I didn't drive other Accords before to see the difference. But in comparison to other diesels i drove, the Accord has less vibrations.
Can you be more specific about this vibrations ?
 
Is it possible that either the MAP or MAF have gone out of spec i.e. giving incorrect electircal output relative to pressure (MAP) or airflow (MAF) .......but only at particular pressure or airflow ?
If this was the case, then the poor mpg would only be experienced either above, or below, certain rpm and load conditions (hence my suggestion to experiment mpg at certain speeds)
 
If it's not an injector or sensor issue, then since both cars are second or third-hand etc, then maybe someone has done work on the car previously and not put things back properly. For example, on a partuclar make of French diesel from the 80s/90s, it was not unusual for people to replace the head gasket, and put the timing belt back one tooth out. I don't know the timing chain on the Accord diesel, so I don't know how easy that mistake would be, or how rough the enigne would run if it was a tooth out.

As well as that issue, if the water pump was failing, then the engine would run hotter, and that will affect efficiency. You could compare fan cut-in at idle with a similar car.
 
baxy said:
...Honda mechanics showed me the valve is in the right side how you look under the bonnet...
Click to expand...
At the right hand end of the fuel rail, as you look at it from a standing position at the bonnet, is the fuel rail pressure sensor... this electronic sensor informs the ECU of the actual rail pressure and has an electrical connector. A while back I replaced the fuel rail on my car, complete with relief valve and sensor, it's an easy job.

You can check if the relief valve is leaking by removing the return pipe to the fuel tank, plugging it, then running a tube from the relief valve outlet into a suitable container - a bit like an injector leak-off test. Be aware that the fuel pressures are extremely high!
 
Sorry, my bad... Jon you are right, in my case the pressure sensor was the problem, i thought is like a valve.
 
baxy said:
My car has 150k km.
About the vibration, I didn't drive other Accords before to see the difference. But in comparison to other diesels i drove, the Accord has less vibrations.
Can you be more specific about this vibrations ?
Click to expand...

Well it's like the whole car is shaking a little bit and you can feel it everywhere inside and outside of the car. It's something similar like you shake when you are freezing cold =)
If that is the case I think we have the same problem and it is a timing chain.

Anyway we got the chain ordered and will get it changed on Saturday. I've heard from lots of people that chain give lots of trouble, so just to be on the safe side it's better to replace that anyway. And we really believe that it could cause increase in fuel consumption + it will also explain the vibration. So after chain replacement vibration should be gone.

By the way thank you very much for pointing out about the injector correction readings, we did not realised we can do that as well, so today we are removing all 4 injectors + we have 2 left from our friends car, so will select 4 the best ones by correction readings and install them and then I will drive a bit to see how is the consumption like.

My feeling is that we are close to the solution of the problem - Injectors, Chain, Valve

By the way in relation to the valve on the rail - Jon_G that's exactly how we tested that. The thing about this one is - it's really hard to understand how this can affect the consumption BUT if sensor on the rail is faulty and makes too high pressure in the rail + leaking injector, those two factors can cause higher fuel consumption. That is probably what happened to baxy. He fixed injectors than rail and then felt the difference in consumption.

MAF & MAP. Usually if MAP is faulty would show fault on diagnostic but it does not, so do not think that it's the one. MAF - we have compared readings and it doesn't seem to be faulty as well. So we don't think it's a problem. But if injectors, chain and rail will not help we might have to go back to them.

Anyway thanks everybody for the support as it's important not to feel alone. The car will not be sold in any occasion, as we decided we have to find what is causing the problem.
 
I am not experiencing that kind of vibrations. I read somewhere that also the flywheel can give vibrations that you describe and the injectors vibrations are not regulate from what I know. But, since cold weather is here I observed every morning I start the engine a fine ticking. It is audible until the engine gets warm and only outside the car. Every time I start the engine in the morning I let it at idle for about 2-3 minutes. After I take my daughter at the kindergarten (aprox. 1 km), and then the sound of that fine ticking is almost gone. Maybe the timing chain, maybe valves ? Can this affect fuel consumption ?
Glad that my experience with the injector correction helped. But in my case this only fixed the heavily smoking, not the fuel consumption.
 
Have you ever changed the gearbox oil in it? It can help with fuel comsumption although it won't get back your mssing 30mpg B) Also you'd be advised to change alot more than just the chain, as once you get in there you may find guides, tensioners and so forth need doing :eek:

Can't say I've had many bad experiences with the main dealer I use, but the I'm in a petrol, so they're alot less troublesome :)
 
In case it helps a bit more, to be getting such a severe reduction in mpg on that diesel engine, either
1. the combustion efficiency would reduce from 40% to 20%,
2. or if the combustion efficiency is 40% then it would be due to fuel "loss" of over 1 litre per hour (leaking injectors etc),
3. or if the combustion efficiency is 40% then it would be due to an increased friction loss somewhere in the engine or transmission, from typical 5 HP loss to a 25 HP loss (which is a huge extra loss). I think you can rule something like this out.

A valve timing problem might cause a combustion efficiency issue of that order, but, if an inlet valve is bent (or not sealing properly) on one cylinder, in effect it's only running properly on 3 cylinders.

Over the four cylinders a reduced compression in one cylinder represents both an overall loss in combustion efficency, as well as an increase in friction loss (due to pumping loss in a cylinder not doing any work) i.e. a combination of points 1 and 3 above.

So as well as considering valve timing, maybe its worth doing a compression test on each cylinder (Alan "H Peasauce" mentioned this previously)
 
Natasha, does whomever is doing the diagnostics have access to an oscilloscope? If so there's a potentially revealing test that can be done. This is to scope the crank and cam sensors simultaneously - that'll clearly show up any problems with the timing chain.

If that vibration is present when the car is stationary it sounds to me like a dmf problem.
 
Just quick update as I had really long day.

We started 9am trying to take other 2 injectors out. Finished only at 3 pm as one of them broke. Anyway it was the worst one by computer readings, so we had to change it anyway.

Now the conclusion is that consumption did not change =(

So will let you know on Saturday how we will get on with the chain.
 
H Peasource said:
Natasha, does whomever is doing the diagnostics have access to an oscilloscope? If so there's a potentially revealing test that can be done. This is to scope the crank and cam sensors simultaneously - that'll clearly show up any problems with the timing chain.

If that vibration is present when the car is stationary it sounds to me like a dmf problem.
Click to expand...
Oscilloscope is a very neat idea :)

Vibration could be due to a dmf problem, so it could be a timing chain issue and a dmf issue (dmf on its own couldn't cause such a huge reduction in mpg).

But after looking at the chain (either with oscilloscope or visually) if that's not it, then compression test on each cyliner.
 
Has the coolant temp sensors been checked for correct functionality?

On my last car my consumption took a nose dive.. after a lot of messing about we found the coolant sensor was dead and the engine was always running very rich (choke). Replacing that saw my mpg return...

Possibly the same here?
 
Sorry for asking, what is dmf?

Coolant temp sensor is ok. We checked that when we compared MAF readings.

I'm also not sure what you can check with oscilloscope, as we do not have one, unless it's built into our diagnostic. Anyway it's not so hard to change the chain on Accord, so it's better to change that anyway and that will be done tomorrow, so hopefully that will solve an issue.

But in the meantime I'm looking for a new or second hand fuel pressure sensor for rail as that has to be sorted as well.
 
Natasha said:
Sorry for asking, what is dmf?

Coolant temp sensor is ok. We checked that when we compared MAF readings.

I'm also not sure what you can check with oscilloscope, as we do not have one, unless it's built into our diagnostic. Anyway it's not so hard to change the chain on Accord, so it's better to change that anyway and that will be done tomorrow, so hopefully that will solve an issue.

But in the meantime I'm looking for a new or second hand fuel pressure sensor for rail as that has to be sorted as well.
Click to expand...
DMF = Dual Mass Flywheel... rather than the conventional single piece flywheel there are 2 component parts linked by a complex springing arrangement in order to reduce the shock-loading from the individual engine power pulses, and therefore make life easier for the transmission. Unfortunately, this springing arrangement can wear excessively, causing vibration.

Some multimeters have an oscilloscope function, but usually only a single channel. You would be able to see the individual pulses coming from the camshaft or crankshaft sensors using an oscilloscope. If you knew the correct positional relationship for these 2 sensors, then with a dual-channel oscilloscope then you would be able to check whether this relationship between the pulses was still correct... it would obviously change if the timing chain jumped a sprocket tooth, or stretched excessively.

I do actually have a spare fuel rail, complete with over-pressure relief valve and pressure sensor. I know it's OK because I swapped it for a complete secondhand replacement about 6 months ago when I suffered a P0088 DTC fuel rail over-pressure fault, but this didn't cure the problem - I eventually discovered that the fault was actually the electrical pressure control valve (M-Prop valve) in the fuel pump sticking (freed it off and she's still runing well). PM me if you think you might want it, but I'd want to sell the whole rail, not just the sensor.

Good luck with the timing chain swap - despite what you say I understand it's a fair bit of work. Are you changing the oil pump chain as well?
 
One other thought occurred to me re the vibration. I think the balancer shaft drive is from the chain so if the chain is stretched this could throw out the synchronisation between balancer shaft and crankshaft causing the vibration.

That said I too don't believe that the vibration is the cause of the fuel consumption issue. It could contribute a bit but not that much. I'm still struggling with why this engine is not producing a huge smokescreen.
 
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