33 MPG! Graph look ok? - Injectors under load. - Alfa Romeo Forum
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(Post Link) post #1 of 5 Old 20-01-15 Thread Starter
Status: Trying to improve mpg.....
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33 MPG! Graph look ok? - Injectors under load.

Following on from the this thread: http://www.alfaowner.com/Forum/alfa-...injectors.html

Does the graph below highlight anything wrong? I thought Injector one was a little out of tolerance before I ran the graph but now I have no idea whats going on. The graph was taken running at 90 degrees on a very slow traffic laden motorway commute. The section where the graph flat lines is where I accelerated hard:


Thanks Guys.

Last edited by seismic22; 20-01-15 at 17:49.
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(Post Link) post #2 of 5 Old 20-01-15 Thread Starter
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Evening bump.......just done a brim to brim check on my 80mile 50-60mph 90% dual carriageway/motorway commute and it works out at 33mpg!!!!


Runs at 90 degrees
Just changed oil filter, air filter, fuel filter, Bosch MAF, intake boot,and thermostat on the weekend.

Few weeks back cleaned MAP sensor and EGR.

Tyres pumped right up.

That leaves injectors right?
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if this helps it was a nugget from tribesman regarding injector correction values regarding something in my thread but related to your graph
Injection correction values are only calculated up to around 35mm/inj... Diagnostics show the latest value calculated at lower load, but ECU does not correct the injection at full load...
so basically it looks like as the graph flatlines around 1/3 way across its more than likely that the total fuel injection quantity has passed above the 35mg/I threshold and is substituting values based on just prior.
I tend to think of these values as a balancing function, each injector will inject more or less mg/I than its theoretical ideal based on the acceleration of the crank/piston.
it thinks its too fast it thinks its injecting too much and will reduce accelerates too slow and will inject more ,always trying for a smooth 4 piston strokes also so also balancing across the 4 injectors to achieve a steady smooth rotation of the crank.
so Im still convinced the injectors will sort of mirror each other to some degree, you may have one worse injector (3 or 4 under load) but the opposite injector apposes it to keep smooth so looks like 2 are bad.
yet towards the end of the graph cylinder 1 appears to be the worst.
I have the description of the values here post 194
I would repeat when warm again and just do idle speed 30 secs and then increase to 2000rpm 30 sec and back to idle slowly.

you've tried injector cleaner , I would also be sure to clean the injector plugs with electrical contact cleaner and work the plugs in and out a bit to be sure of a good contact.
then repeat the above idle and 2000rev log see if anything changed.

also bear in mind there is a known weakness In the injector plug/harness for Vauxhalls and seen a few on here in the last few years looking for info on them but I don't remember many posting up any before and after values just issues then issues gone sort of thing.
search for injector number 3 plug and theres a repair kit to solder in.
Diesel - 1.9 JTDm (2) - Autolusso New Alfa Romeo Parts

also bear in mind there could be an underlying mechanical issue affecting the cylinders also like compression rings, valves , leaky swirl flaps leaky egr could all give symtoms the ecu will think is injector variation.

and try a reset leanrned values if it has it, or maybe an ecu reset might help especially after you've done a lot of cleaning of sensors.

also what are values of maf ? a quick log of maf mg/I and boost pressure mbar under a bit of load 3rd or 4th full throttle for second or 2 (due to road conditions and weather)

id like to try to pinpoint stuff before I stuck a 95 injector on it.

that mpg sounds low but the injectors would need to be pumping it in to do it alone does it smoke much ? it would be very rich if dumping in too much fuel , which those values don't look like that bad .
what mpg were you getting before the cold weather, I usually lose around 8-10mpg this sort of weather on winter diesel.

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(Post Link) post #4 of 5 Old 20-01-15 Thread Starter
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Thanks for the great post, will have to read over that a couple of times! Will look at maf values but i5 is brand new.

No smoke whatsoever!

Running brilliant, plenty of power!

Just blanked the EGR with a spare ten minutes tonight and its now running even better.

MPG is still bad though??????

Long story short, I might have got a lot of oil in the cat over the weekend (see URGENT plumes of smoke thread), even though power is good could a partially blocked cat cause bad mpg?
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(sorry for stealing your thread)

What about injectors on 8v JTD? In FES it only shows class 1 or 3. I have strong vibrations in neutral and around idle-1300 rpm. No such thing at acceleration.

Thing is it can be, DMF, pressure plate, release bearing, injectors, clogged inlet, off the normal clearance of the valves (in manual says they must be checked every 80.000 km) ... but I cannot afford to buy something and realize that it`s not that thing that causes the problem. Especially DMF and injectors.
I know that this cannot be done on forum, but honesty it is more cheaper for me to change whole engine then doing all this ...
Vibrations are coming from the top of the engine, under the engine cover. Some mechanic say it is DMF but I know a topic on the forum that a guy have the similar problem and ended up with injector problem. My fuel consumption is normal, have a black smoke on strong acceleration.

So is there some "rule" that says if your car is doing this it must be this or something like this, so I can pinpoint right cause of the problem or ..?
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graph , injectors , load , mpg

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