Fuel Consumption Gauge

[swiss318is]

Which signals are used for the fuel consumption gauge??

[haledj]

The signal comes from the ecu, where I assume it is calculated from speed, rpm, and pulsewidth.

[swiss318is]

the problem i have.. and thats the reason for this question in this thread,is that sometimes i have a stottering of the engine, when this happens.. the fuel consumption gauge (fcg) goes up to the top.. so, the solution of this problem could be one of the inputs. one of this inputs is not working properly

[haledj]

I would try swapping in a known good ECU

[swiss318is]

the curious thing is ... there is no problem for months and then suddenly it begins.. and disappears for the next half year..

[haledj]

Could it be temperature or humidity related?

[Cobra Jet]

Are you sure it's not your ICV acting up?  The only reason I has is last week my MPG gauge was fluttering (and so was the engine)...  I pulled off the ICV, ran the proper diagnostics based on multiple threads and manuals and it turned out to be an ICV issue.  I cleaned the ICV, lubed it and reinstalled with pretty good success.

Prior to removing and cleaning my ICV, it was not functioning properly - even when doing a KOEO (key on engine off) test... When I would turn the key on, the ICV was not "on", meaning it was not buzzing as it should be when it's "on".  The only way to determine if it's buzzing when on is to touch it w/ your hand, you should feel a buzzing sensation.  If it's not buzzing, get a small hammer and tap the outer casing, this should "wake it up".

I would also do an OHM test on it and see if it's operating within specs - manuals state the ICV should be seeing 20 OHMS...  anything less and it's not operating 100%.

Another quick way to tell if the ICV is malfunctioning is when the car is running at idle, tap the ICV's outer casing with a small hammer - if the idle fluctuates and engine revs either "stick" up or down, the ICV is in need of a cleaning, or in severe instances, replacement.

If the ICV is not operating 100%, you would experience idle stuttering, driving stuttering, high or low idle, throttle or engine flucutaion in RPMs while driving or at idle, etc...  Such fluctuations will be seen on and affect the mpg meter as well...

[swiss318is]

Are you sure it's not your ICV acting up?  The only reason I has is last week my MPG gauge was fluttering (and so was the engine)...  I pulled off the ICV, ran the proper diagnostics based on multiple threads and manuals and it turned out to be an ICV issue.  I cleaned the ICV, lubed it and reinstalled with pretty good success.

Prior to removing and cleaning my ICV, it was not functioning properly - even when doing a KOEO (key on engine off) test... When I would turn the key on, the ICV was not "on", meaning it was not buzzing as it should be when it's "on".  The only way to determine if it's buzzing when on is to touch it w/ your hand, you should feel a buzzing sensation.  If it's not buzzing, get a small hammer and tap the outer casing, this should "wake it up".

I would also do an OHM test on it and see if it's operating within specs - manuals state the ICV should be seeing 20 OHMS...  anything less and it's not operating 100%.

Another quick way to tell if the ICV is malfunctioning is when the car is running at idle, tap the ICV's outer casing with a small hammer - if the idle fluctuates and engine revs either "stick" up or down, the ICV is in need of a cleaning, or in severe instances, replacement.

If the ICV is not operating 100%, you would experience idle stuttering, driving stuttering, high or low idle, throttle or engine flucutaion in RPMs while driving or at idle, etc...  Such fluctuations will be seen on and affect the mpg meter as well...

sounds very interesting... but what is a ICV??

[Cobra Jet]

ICV = Idle Control Valve.



I think this part is located in the same area as on the U.S. M42's.

It's mounted on the back of the engine near the upper intake (close to the firewall).  There is a 90* hose that is connected to one end of the ICV which connects to the upper intake, while the other end of the ICV is connected to another hose which is routed along the underside of the upper intake.

Undo the small 10mm nut that holds the ICV bracket to the intake, then once that is removed, pull the hose off the upper intake and then pull the ICV towards yourself.  

Test the unit using an multi-meter set to OHMS.  Using the multi-meter probes, connect them to the metal prongs coming out of the ICV connector on the bottom of the ICV.  If you see less than 20 OHMS, the ICV is faulty.  I've read online on some sites that the readout should be 20+ OHMS, but most manuals and threads state a minimum of 20 OHMS, anything lower and the unit is not functioning 100%.

When I did the KOEO test on my 318ic over this past weekend, the ICV was not even buzzing when I felt it, meaning it was not operational.  I removed it, did the multi-meter/OHM test and saw that it was below 20 OHMS.  I then soaked the inside of it with carb/brake cleaner, let it dry out completely, then used WD40 to lube the inside of it and after doing that I took a small hammer and tapped the exterior casing all around.  After doing so, I reinstalled it and when doing the KOEO test, the ICV was buzzing again.  The car started right up with no hesitation and when on a test run, the car drove and idled much better than it ever has in the past...  It also solved the stuttering idle while at a stop and my mpg meter did not bounce around anymore (due to a better/steady air flow and the ICV being operational again).

[swiss318is]

ok.. thanks! i didnt know for what ICV stands for.. i will try that as soon as possible..