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Old 03 Sep 2019, 12:17 AM   #1 (permalink)
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Angry high than normal fuel consumption

Hi

I have a strange issue.
First before anyone tells me to get the car tuned it is tuned and the issue is not related. (read on scoobynet it needs tuned)

The car is a Impreza Turbo 2000 MY00 with TD05, Cobra exhaust with sports cat, 3 port electronic boost controller, RCM 340lph fuel pump, Samco intercooler pipes, Green Cotton Air Filter, remapped by Bob Rawle 303bhp / 284lb torque.

A few weeks after the remap the car started to misfire which turned out to be worn out coil pack and HT Leads, I replaced all of them with Genuine parts and the misfire was still there but very mild during cold start and went away when warmed up, I then discovered that HT lead no4 was faulty as the rubber boot was too far down the lead and was causing it not to clip on to the spark plug, as I couldn't adjust the boot I cut off 5mm which made the misfire milder I also decided to clean the air filter but ended up damaging it so that got replaced, along with better HT leads from Magnecor and that has stopped the misfire completely and as the MAF was over 12 months old I replaced it and reset the ECU.

However my fuel consumption has increased, when data logging my A/F correction % (standard JECS ECU) is showing that its going maximum values in both positive and negative also my MAF voltage is constantly change from 0 to 2.5v on idle both cold and warm did the same with the old MAF.

Before I replaced anything the data logs showed 0 A/F Correction % in all conditions cold/warm and on boost when engine is full up to temp. Now its all over.

Any help is appreciated.
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Last edited by alunian; 03 Sep 2019 at 12:20 AM. Reason: more details
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Old 03 Sep 2019, 01:01 PM   #2 (permalink)
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Re: high than normal fuel consumption

updated. Just tried spraying carb cleaner on all the hoses around the manifold and the joints for the air filter pipe work while the engine is running to see if it made any difference which it didn't.

I then used Romraider to watch the A/F correction % and MAF volts and it now varys between 0 to 1.5v (cant log or view g/s on my ECU). Whilst parked up and engine up to temp and rev'd up to 3000rpm the A/F correction % stayed within -/+5% until I let off then it when to 15% lean which is correct as the injectors are cut off and then it returns to normal.

Does anyone know if this is the ECU relearning?

Also can a misfire damage a spark plug to cause the fuel consumption to get worse. I read that a misfire can increase consumption but I don't understand how as the fuel is not getting burnt?
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Last edited by alunian; 03 Sep 2019 at 01:03 PM. Reason: readings
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Old 03 Sep 2019, 08:44 PM   #3 (permalink)
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Re: high than normal fuel consumption

Poor consumption wouldnt be down to old plugs, as you now have no misfire I dont think the plugs are an issues,
The off throttle lean is right,
I believe you are running the standard ECU? If so can you get the ID off the case, there are a few ecu`s for the 99/00`s some better than others,
What have been your ambient temps, if it has been during the heat waves we have had then you will use more fuel, less dense air means the car has to work harder,

What is the voltage of the Maf with the ignition on but no engine running?

If its maxing out the injectors then you want to be having a chat with Bob, have you got any old logs from when it was just mapped or similar?
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Old 04 Sep 2019, 02:00 PM   #4 (permalink)
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Re: high than normal fuel consumption

Quote:
Originally Posted by bugeye_bob View Post
Poor consumption wouldnt be down to old plugs, as you now have no misfire I dont think the plugs are an issues,
The off throttle lean is right,
I believe you are running the standard ECU? If so can you get the ID off the case, there are a few ecu`s for the 99/00`s some better than others,
What have been your ambient temps, if it has been during the heat waves we have had then you will use more fuel, less dense air means the car has to work harder,

What is the voltage of the Maf with the ignition on but no engine running?

If its maxing out the injectors then you want to be having a chat with Bob, have you got any old logs from when it was just mapped or similar?

ECU ID:
Y7
226II AE802
AI8-000 D3L 0411

No idea on ambient temps other than it was warm, I wouldnt call it a heat wave though.

The Injectors are running at 80% at WOT.

I'll get back with the MAF volts later.

I do have some old logs from just after the remap. Which data would you like me to post/look at?
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Old 04 Sep 2019, 02:14 PM   #5 (permalink)
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Re: high than normal fuel consumption

MAF voltage with key in ON position 1.02v
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Old 07 Sep 2019, 04:18 PM   #6 (permalink)
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Re: high than normal fuel consumption

Im guessing I have a vacuum leak or a stuck thermostat.

Been thinking I may have damaged a the hard pipe that runs along the driver side of the engine when I was fitting the HT Leads as the Magnecor ones are thicker than standard and I had to pull the hard pipe slightly to make the gap wider to get it to clip in place on the side of the engine. Also when driving casually and steadily increasing rpm up to around 2200 I can here a wheezing noise but it coming from the passenger side, not sure if there is a pipe on that side as there is a lot of wires cabled tied together next to the battery and windshield bottle.

As for the thermostat I was thinking back to when I had a 96 Nissan Almera and when the thermostat got stuck the fuel consumption doubled.
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Last edited by alunian; 07 Sep 2019 at 04:23 PM. Reason: more details
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Old 08 Sep 2019, 02:26 PM   #7 (permalink)
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Re: high than normal fuel consumption

I think I found the problem, went out to do some new data logs first from cold start to warm then second WOT, when I started the WOT as soon as I hit around 6000rpm a loud air suction noise could be heard so I pulled over and found the throttle body to intercooler pipe had come loose, not sure if that was causing the A/F correction to be out and my fuel consumption to increase.

Also found that the small filter that is attached to the middle pipe on the charcoal canister had also started to come out of the pipe, the clip isn't strong enough to hold it in place so I am going to try a cable tie until I can get a new clip.
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Old 09 Sep 2019, 12:03 PM   #8 (permalink)
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Re: high than normal fuel consumption

The IC to TB pipe would cause issues,
I was also going to ask what the IAM was like when you log.
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Old 10 Sep 2019, 01:50 AM   #9 (permalink)
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Re: high than normal fuel consumption

Quote:
Originally Posted by bugeye_bob View Post
The IC to TB pipe would cause issues,
I was also going to ask what the IAM was like when you log.

You just did, I will try and post the results later today.
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Old 10 Sep 2019, 11:25 AM   #10 (permalink)
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Re: high than normal fuel consumption

I dont have the option to record Ignition Advance Multiplier, I've got Ignition Total Timing degrees. For some reason Romraider stopped recording during the WOT run so I will have to make another log for that. Im going to see if I can upload the log for the Cold start.
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Old 10 Sep 2019, 11:34 AM   #11 (permalink)
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Re: high than normal fuel consumption

Here is my log from cold start before the IC to TB pipe came loose, on google drive
Click on the download button at the top right of the screen as it will make it easier to view/navigate.
Cold Log
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Last edited by alunian; 10 Sep 2019 at 11:48 AM. Reason: advice
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Old 11 Sep 2019, 12:20 PM   #12 (permalink)
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Re: high than normal fuel consumption

It sounds like its back firing only when driving and you let the revs drop to idle after accelerating.
It doesn't do it when parked and rev'd, there is no back firing when keeping the revs steady and accelerating either gently or WOT.
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Old 11 Sep 2019, 10:20 PM   #13 (permalink)
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Re: high than normal fuel consumption

Here is my log for WOT, use the download button at the top right to make it easier to read.
WOT log

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Old 17 Sep 2019, 03:28 PM   #14 (permalink)
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Re: high than normal fuel consumption

I am now hearing what sounds like a liquid running along the near side from the front to the rear of the car when driving and when gradually increasing rpm from idle to 2200rpm it sounds like liquid spitting/seeping. I can't see any traces of a leak on the ground.

I've got it booked in for a Pre-MOT on Monday morning I've told the MOT center I may have a vacuum or fuel like. I will update this thread if they find anything.
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