Can the spark plugs make a marked difference to economy for 5zfe

[Woodchip Lurker Find all posts View Profile Close Woodchip]

I recently had some work done on my 98 prado and ended up with an exchange engine from a later model Hilux. Fuel economy is now really bad compared to standard bad. I noticed on the heads they rebuilt before the whole engine needed replacing that there are single electrode spark plugs installed. Will this alone be able to cause a 30% reduction in fuel efficiency?

[williade Avid PP Poster! Find all posts View Profile Close williade]

Twin ground sparks are recommended for the 5VZ-FE because of the way the ignition system works. Because there are 3 coil packs and 6 cylinders, each coil pack drives 2 spark plugs. For this reason the spark plug will fire at the top of the compression stroke as well as the top of the exhaust stroke. It does nothing useful when it fires on the exhaust stroke but it means the spark plugs fire twice as often as they do most other 4-stroke engines. This will lead to accelerated wearing of the electrodes so twin ground spark plugs are recommended to get better life out of the spark plugs.

Single ground spark plugs are unlikely to lead to bad fuel economy unless they aren't firing at all or miss firing intermittently and if they were you would be able to hear it. It would sound very rough at idle.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

I doubt it very much, myn in my 97 grande V6 wernt platinum tipped or any thing special just a basic spark plug, Put new genuine in myn when I had the gass fitted up to it and certainly looked no different ?? Have you checked/cleaned the map sensor wire ?? I believe this can make a difference (I doubt 30% but) Are all the sensors conected properly ? (i imagine you would have engine light on if not) I know the lux would have different gearing to the prado but wouldnt be your problem unless you changed diffs/gearbox may be different but no mention you changed any of that. May have some thing to do with cold start eg maybe a sensor not detecting temp or some thing so running rich ?? Again Im clutching at straws here just to give you things to think about, is it blowing any different or more or less smoke out the rear end ?? idling higher ?? Im just guesing here..............

[williade Avid PP Poster! Find all posts View Profile Close williade]

What electricals were changed over? If the Hilux has a hot wire MAF sensor and it was plugged into the same loom of the previous mechanical MAF (or VAF) then the ECU would get incorrect readings as the older VAF sensor uses a different pin out to the newer hot wire MAF.

If you used the ECU from the Hilux, it may need input from an oxygen sensor. Later model 90 series Prados had oxygen senors where older models (like yours) used a fuel map table.

If either of the above is applicable I wouldn't be at all surprised to see a 30% increase in fuel consumption.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Hi Declan you sure about the series two having an oxygen sensor ?? My mate had an 02 GXL V6 3.4 an it didnt have one, only reason I know that is I was under his one day looking at it as they put one in my old 97 when they put the LPG on it, he had LPG as well and was checking out his set up, only reason I know he didnt have one....Regards steve

http://www.pradopoint.com/archive/in.../t-16891.html?

Regards Steve

[williade Avid PP Poster! Find all posts View Profile Close williade]

You're right Steve. My reference was the Haynes Manual.

O2 sensors weren't present on series II 90 series in Australia.
http://www.toyodiy.com/parts/p_G_200...PNKQ_8401.html

But were on models sold in Europe.
http://www.toyodiy.com/parts/p_E_200...PNKW_8401.html

Well never mind about the O2 sensor if you're in Australia, Woodchip.

[Woodchip Lurker Find all posts View Profile Close Woodchip]

The only thing they changed was the engine and all the electrics and peripheral bits were the same and left untouched. I cleaned the MAF sensor with the right cleaner but that made little difference. I will give a new air cleaner a run and see what that does for it. They are not that good on fuel to start with but they are very good as a 4 wheel drive so the sacrifice is only in running costs. It is just a bit of an annoyance that after 6 grand for an exchange engine that it guzzles more fuel. I might have to get it dynotuned but in Townsville I might be hard pressed to find one that can do 4 wheel drives. It does smell a bit more fumy than the old motor at idle but that just might be paranoia. The power is still the same and it idles smoothly.Will change the fuel filter too as it is the only thing I did not do on the major overhaul I gave the car. (it did not get here in time while I had things apart and after reading the other post realised it is still in the box.

[williade Avid PP Poster! Find all posts View Profile Close williade]

If the new engine is healthy, i.e. good compression, cam/crack angle sensors working, not burning oil/coolant and seals and bearings in good order (all things which would have more serious symptoms than high fuel consumption) and the all major electronics having been carried over from the old engine, the only thing I can think of that would lead to that big of an increase in fuel consumption is bad injectors.

Matt - mr4x4 was getting poor economy from his 4.0L 120 V6 (different engine yes) and he says replacing the injectors and fuel filter reduced fuel consumption by nearly 2L/100km.

http://www.pradopoint.com/entry.php?...ss-in-the-shed..

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

The 5VZ-FE out of the Hilux is different to the VZ-FE out of the Prado, the Hilux version, has less power (122kw), and slightly more torque (about 15nm more), the mapping and electronic engine controls are different because of this too, so you computer is getting missleading information, hence the increased fuel consumption, you may need to source out a new computer from the hilux.
However I am puzzled why the mechanic did not know this, actually just looking at you location says it all, with the experience I have had with mechanics up in NQLD, I can see why he had no idea.

[williade Avid PP Poster! Find all posts View Profile Close williade]

Croozza: is the engine block itself any different? I would have thought the difference in power and torque would come from different exhaust and induction system because of a different engine bay layout. If you took the electronics, exhaust and induction systems from a Prado combined with a Hilux block, wont you essentially have a Prado engine?

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Croozza: is the engine block itself any different? I would have thought the difference in power and torque would come from different exhaust and induction system because of a different engine bay layout. If you took the electronics, exhaust and induction systems from a Prado combined with a Hilux block, wont you essentially have a Prado engine?

Block and heads are the same, but the cams are different. It also has a different Computer and MAF sensor. There are also some other little differences, but they should not have any effect.
It is also imperitive, that twin ground electrode spark plugs are used, if you use Iridium ones, you can use the quad ground electrode.

[williade Avid PP Poster! Find all posts View Profile Close williade]

Block and heads are the same, but the cams are different. It also has a different Computer and MAF sensor. There are also some other little differences, but they should not have any effect.
It is also imperitive, that twin ground electrode spark plugs are used, if you use Iridium ones, you can use the quad ground electrode.

So is the valve timing and cam profile different?

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

So is the valve timing and cam profile different?

Yep, thats how they got the extra torque, but less power, they had to change the fuel mapping in the process to, otherwise it would overfuel, the MAF sensor is different also because of this, you will notice there are two part numbers for the MAF sensor, one for the Prado, the other for the Hilux. The Hilux MAF is the cheaper one too, (1/2 the price of the Prado one, damn it!), all electrical connections should be the same though.

[Woodchip Lurker Find all posts View Profile Close Woodchip]

Been a while since I checked this post.
So what you are saying crooza is that the engine I have in the car out of a Hilux needs to have a different computer and a different MAF. The Mechanic was from Newcastle and seemed to know his stuff but if the motors are different then maybe not.
what would need to be changed to make it ecenomical. I am thinking of getting rid of it because of its thirst but love the car in all other aspects. I was going to buy a new Prado Maf but if it will make no difference then I wont.

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

Yes get a computer for the Hilux and change the MAF for the hilux one. You can get remanufactured ones for too, much cheaper than brand new Toyota ones, I recently got one for my Prado, (remember the Prado one is twise the price of the Hilux one), for $500, so the Hilux one is around the $250 mark. Toyota want over $1000 and $600 for both of them.
Give the motor a good service too, change the std plugs for Iridium ones (4 prong ground electrodes instead of the twin ground electrodes), dont forget to get the throttle position sensor cleaned as well. After I did all this, I went on holidays to Sydney, so the drive from Brisbane to Sydney (through the centre of Sydney and over the Harbour Bridge cause the kids wanted to go over it), in a fully loaded car for 2 adults and 3 kids, and a little drive to the outer western suburbs (just over 1000k's), I only used 116 ltrs of fuel, I drove at the speed limit all the time and was not afraid to overtake, and give it some beans when needed.
I dont know why Toyota did not give the motor a different code (like 5VZ-FE2, instead of calling it the same 5VZ-FE), because everyone just goes off the 5VZ-FE and think they are the same motor.