vh41 fuel consumption

[DORIFUTO_The Future]

Howdy peoples,

I have just bought myself a JDM 1993 Nissan Cima powered by a VH41DE. Now seeing as these weren't sold over here in AUS it is very hard to find information on them!

I have some information that I have found via trawling this forum and the rest of the web which states that I should get somewhere around the 10-12 litres per 100km or in the terms you guys use 23.5 miles per gallon.

This is great info but unfortunately I am not getting anywhere near that level of fuel consumption. So far I have been getting somewhere around the likes of 15-18 litres per 100km ( 13.5-14.5 mpg)..... ridiculous I know!

So seeing as the engine was used in the q45 I thought I might ask you guys if you have ever had any problems with diablocal fuel consumption and if there are any fixes.

If there are any known tweaks for fuel consumption then it would be great to hear them as well!

Any information would be greatly appreciated.

Regards,Kodie Graham.

ps: I have changed the air filter and cleaned the afm exterior (need to pull it apart and clean the sensor) and have run through some fuel injector cleaner.

[Q45tech]

Remember highway fuel consumption is based on absolutely steady rpm, level roads, no ac or other extra drag. Extremely slow acceleration and never above even 3,000 rpm...............90% of driving should be 1500>2300 rpm.

Agressive high rpms and frequent accelration can easily double or triple the fuel consumption.

Unfortunately the earlier than 1997 Cima was not impted to US or anywhere else so little reference. City was about 13>17 mpg after the engine was warmed to operating temp.

Check that thermostat is newish [less than 4 years old] to speed up warm up and to get to normal consumption.

Find a Nissan Consult I or II or III to see stored parmeters in ecu to find the answer!

[DORIFUTO_The Future]

The car is always started and allowed to sit till it has reached operating temp before being driving (missus thinks im a nupty for it but I just do it out of habit now) so temp shouldnt be an issue really.The consumption that I have listed is 100% highway driving on flat roads with 1 or 2 hills but even with the car on cruise control at 110kph the engine doesnt see more than 2300rpms even when climbing the hills.

As far as I can see the only difference between the 3 vh41 models is just manifold designs that allowed peak torque to be reached at a lower rpm so I dont know why the consumption would be that bad.

Forgive my ingorance but where does one obtain a nissan consult?

[Q45tech]

Every Nissan dealership was required to purchase at least 1 most have 2-3 for use by technicans [the earliest ones cost $4,000 US each, later one are all intergrated into a Panasonic lap top with accesories they cost $8,000.

Search around for a Nissan OBDI adapter to serial or USB cable then find software...............which will emulate about 1/2 of what Consult does.

Normally one looks at MAF voltage vs injector open time in milliseconds to calculate how much fuel per squirt is flowing4 squirts per rev x 2,000 = 8,000 squirts per minute or how much fuel per mile/minute.

Anything above 1.6 milliseconds is too much cruise fuel. WOT high [4,000>7,000] rpm is ~ 10.5<9.5 msec.

The dead time on an injector is the first 0.7 ms so mass only flow in the next 0.9 [for 1.6 msec].

So 0.1 msec is about ~ 1% so easy to calculate 10% would be an extra 0.9 ms.

The only thing besides a fuel leak that can increase injection time is TPS error, MAF error, or coolant temperature error signal.

[DORIFUTO_The Future]

Sounds like a plan, only thing is I dont know where to plug it in? I have a earlier model vh41 from a cima (going into my 240z) on my garage floor so I had a look at the ECU and I cant seem to find any ports at all.

[DORIFUTO_The Future]

I have no idea how you thought the thread was about an engine swap! I have a spare vh41 that I am sticking into my 240z that is sitting on the garage floor and as it was easier to look at the ecu sitting on the desk in comparision to going to the car I used that as a reference to try and find the consult port you spoke of..........

In short the thread is about MY CARS fuel consumption...... not the engine nor an engine swap.

[Q451990]

I just reopened this thread and merged your explanation into it.

The Consult port on your car should be near the fuse box... it's not on the ECU itself.

Heath

[Q451990]

Here's a picture of the Consult plug

[Q45tech]

Be sure to TEST fuel pressure at idle and WOT 34>43 psi as a failure in regulator or its vacuum line can create a 13% error [which should be corrected by O2/adaptive trim [+- 20% AF] so you look at ecu stored adaptive trim with Consult.

But then again 13% is only a few MPG [3 at most].