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Discussion Starter · #1 ·
Hey Guys,

I've just finished "tuning" my GQ 2.8

I've increased the main fuel on my rd28 as far as i can go. Gave it one full rotation and had to adjust the idler tension screw all the way to the end of the threaded rod to get it to idle back at 500rpm (my preferred idle).

I have also adjusted the boost compensator 6 clicks of the cog clockwise and set boost to about 12psi using a manual boost controller (had to wind it down a bit as it was hitting 14psi when first installed) I found the EGTs were lower at 14psi but it felt like the mixture was too lean and it was overboosting without much fuel in air. I have a 3" Mandrel Bent Exhaust, Auto Meter gauges, EGR is blocked and EGT probe is about 40mm back from the turbo, mounted in the dump pipe.

The results I have experienced from doing these few cheap mods are truly amazing. The down low power is 100 times better. I can take off at lights now without that sluggish feeling, dont have to ride the clutch and dont have to accelerate anywhere near as hard to get up to speed. The turbo starts spooling up at about 1400revs and hits 12 psi by about 2500revs. The power is much more noticable across the entire rev range. When on and off boost its noticably better. I barely have to hit 2500 revs before changing gears, therefore im not wringing its neck all the time - so hopefully better fuel economy. Its literally about 150% nicer to drive.

I should also mention I have no black smoke at all coming from the exhaust.

Originally i thought the EGTs are going to be through the roof, as a full turn of the fuel screw is far from conservative, but it seems even with the fuel wound up this far the highest temp i have reached is about 500 degrees Celsius, and that was flooring it up a hill trying to reach the highest temp i could.

I get the following EGTs -

Crusing at 100kms (5th) - 280-300 degrees
Crusing at 80kms (4th) - 200-220 degrees
Climbing a long hill (4th) - 320-370 degrees
Putting my foot down flat out up a hill on a hot day with aircon running - 450-500 degrees
Taking off at the lights - Gets up to about 350-370 degrees when accelerating hard, then as soon as i reach cruising speed it comes back down to the 200-250 degrees.

The only reason i reached 500 degrees is because i was testing its capabilities. With the way it drives now, i just dont need to work it that hard anymore, so the max temps ill experience in every day driving will be about 400 degrees at the most.

I imagine when i take it offroad i'll easily hit 550 degrees up sand dunes in 2nd low, but adding a front locker should fix the need to floor it.

I should mention before playing with all of this i made sure to replace my radiator, thermostat, water pump, timing belt, coolant. The 3" exhaust was also a must.

Overall I am so bloody happy with these results and my Patrol in general. I have heard too many bad things about these motors, but i'm here to tell you if your cooling system is in good nick and you really take care of these, they can be amazing cars with the right mods.

Any comments on this would be great. I have done all my reading thoroughly and believe I have done everything right and that these temps are safe. I am certainly no expert on all of this. Would be good to know what other guys have screwed the main fuel up to and how far you've wound up the boost compensator etc.

I'm thinking its pointless to take it in for a tune and pay someone hundreds to tweak a setup im already very happy with. Thoughts?
 

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nissan patrol
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I would have to say that needing to wind the pump up that far says to me that it might not be in the best condition already.

I know its really increasing the fuel down low beause the idle has come up, but is it leaning out once on boost due to the pump struggling? I would pay the $80-$100 or what ever it costs to get a dyno run locally to you with air fuel ratio just to check the pump is supplying the fuel properly.
 

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The rd28t loves to rev, changing gears at 2500rpm is that when you hooking it or just slowly accerating? I regularly mine out to 4000rpm when ive got my foot into it, changing any lower and you not back onto full boost in the next gear (cant move quickly if it isnt on boost). A na td42 can change gears a hell of a lot early and still keep pulling, but they dont like to rev as much as an rd28 (think how rb30s like to rev).

I havent done any compensator mods but everything else is the same, 68rwks and 280nms on 33x12.5r15 mts on 15x8 steelies. Yet to fit and intercooler, gu intake manifold and push it up to 16psi.

As dieseltuner said if you had to wind in your fuel pump so far it probably needs to be looked at, ive only had to put 3/4 of a turn into mine as any more was smoking off boost.


Rick
 

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Discussion Starter · #5 ·
I would have to say that needing to wind the pump up that far says to me that it might not be in the best condition already.

I know its really increasing the fuel down low beause the idle has come up, but is it leaning out once on boost due to the pump struggling? I would pay the $80-$100 or what ever it costs to get a dyno run locally to you with air fuel ratio just to check the pump is supplying the fuel properly.
The injector pump was replaced less than 30,000 kms ago...
 

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Discussion Starter · #6 ·
The rd28t loves to rev, changing gears at 2500rpm is that when you hooking it or just slowly accerating? I regularly mine out to 4000rpm when ive got my foot into it, changing any lower and you not back onto full boost in the next gear (cant move quickly if it isnt on boost). A na td42 can change gears a hell of a lot early and still keep pulling, but they dont like to rev as much as an rd28 (think how rb30s like to rev).

I havent done any compensator mods but everything else is the same, 68rwks and 280nms on 33x12.5r15 mts on 15x8 steelies. Yet to fit and intercooler, gu intake manifold and push it up to 16psi.

As dieseltuner said if you had to wind in your fuel pump so far it probably needs to be looked at, ive only had to put 3/4 of a turn into mine as any more was smoking off boost.


Rick
Just when slowly accelerating, before any of this I had to change at 3000 to get back on boost, now i can comfortably change at 2500 and get back on boost at 12-1400rpm. My boost peaks at about 2200rpm at around 12psi.
As mentioned the pump is basically brand new...

I should mention...i believe the truck is still on it's original injectors, but they seem fine, my fuel economy is around 13ltrs/100km
 

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Discussion Starter · #7 ·
I would have to say that needing to wind the pump up that far says to me that it might not be in the best condition already.

I know its really increasing the fuel down low beause the idle has come up, but is it leaning out once on boost due to the pump struggling? I would pay the $80-$100 or what ever it costs to get a dyno run locally to you with air fuel ratio just to check the pump is supplying the fuel properly.
I didnt necessarily "need" to wind the pump up that far, i just thought id start of with a full turn assuming that EGTs wouldnt be acceptable and id have to wind it back. Turns out EGTs are fine and the truck has a whole ****load of power, no black smoke...
 

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Discussion Starter · #8 ·
Yeah and only needing 12psi to match what you have adjusted your pump to something doesn't seem right
Do you think i would be better off winding it back up to 14psi?
 

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Just when slowly accelerating, before any of this I had to change at 3000 to get back on boost, now i can comfortably change at 2500 and get back on boost at 12-1400rpm. My boost peaks at about 2200rpm at around 12psi.
As mentioned the pump is basically brand new...

I should mention...i believe the truck is still on it's original injectors, but they seem fine, my fuel economy is around 13ltrs/100km

Theres something going on if you had to wind so much fuel in mate, as lewie said your boost in comparison to have much you had to wind in doesnt match up with most gq rd28t's.

I average around 16/100kms in the city and 12/100kms on the highway. Returned 12.5/100kms over a 9000km drive from Adelaide to Darwin and back. I would assume 10-14ltrs to be average for most 2.8s.

Dont see how you managed to get it boosting that low, are you sure its still got the stock garrett? Sure ive got a bit of torque down around 1500rpm but its definately not enough to warrant changing gears before 3000rpm, if its all oem gear you will probably find max torque is around 2600-2800rpm at around 12psi. Maybe i need to click my compensator over a few and see what happens but i wouldnt think boost came on so much lower.

Changing at or around your max torque rpm is not gonna see the best economy either, cruising it will but changing below it and accerating from such low rpm will be using more fuel then needed.

Take it down to your local diesel tuner and see what they reckon mate, it could be the injectors limiting your potential max fuel or something more sinister happenjng. Stock fuel pump and turbo should max out at around 16-18psi not 12 psi.

And yea with 3" exhaust, airbox upgrade and a few other minor things the 2.8 isnt so bad. Its never gonna produce the numbers a 4.2td can but it definately gets up and boogies on boost.


Rick
 
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Discussion Starter · #10 ·
Theres something going on if you had to wind so much fuel in mate, as lewie said your boost in comparison to have much you had to wind in doesnt match up with most gq rd28t's.

I average around 16/100kms in the city and 12/100kms on the highway. Returned 12.5/100kms over a 9000km drive from Adelaide to Darwin and back. I would assume 10-14ltrs to be average for most 2.8s.

Dont see how you managed to get it boosting that low, are you sure its still got the stock garrett? Sure ive got a bit of torque down around 1500rpm but its definately not enough to warrant changing gears before 3000rpm, if its all oem gear you will probably find max torque is around 2600-2800rpm at around 12psi. Maybe i need to click my compensator over a few and see what happens but i wouldnt think boost came on so much lower.

Changing at or around your max torque rpm is not gonna see the best economy either, cruising it will but changing below it and accerating from such low rpm will be using more fuel then needed.

Take it down to your local diesel tuner and see what they reckon mate, it could be the injectors limiting your potential max fuel or something more sinister happenjng. Stock fuel pump and turbo should max out at around 16-18psi not 12 psi.

And yea with 3" exhaust, airbox upgrade and a few other minor things the 2.8 isnt so bad. Its never gonna produce the numbers a 4.2td can but it definately gets up and boogies on boost.


Rick
It's a mystery to me too man, what you are saying sounds absolutely correct pre-modification but after adjusting the boost compensator and fuel screw my trucks whole world has changed. I don't see the harm in what i've done if my EGTs are accurate.

Its not maxing out at 12psi, i have a manual boost controller, it hitting 14 psi and i manually turned it down as i didnt think that much boost was needed. I could ramp it up to 15psi if i wanted to but really not keen on working the turbo that hard.

I can take a video of all this if need be
 

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Discussion Starter · #11 ·
Btw sorry if my posts are short and im not replying to all your questions. Im a bit hungover. Will drive it like this for the next week and see how she goes. Will keep you posted
 

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It's a mystery to me too man, what you are saying sounds absolutely correct pre-modification but after adjusting the boost compensator and fuel screw my trucks whole world has changed. I don't see the harm in what i've done if my EGTs are accurate.

Its not maxing out at 12psi, i have a manual boost controller, it hitting 14 psi and i manually turned it down as i didnt think that much boost was needed. I could ramp it up to 15psi if i wanted to but really not keen on working the turbo that hard.

I can take a video of all this if need be

Block the relief valve on the intake manifold and wind in some more fuel mate, add boost so your egts are about the same and see how it drives then. Maxing boost and maxing fuel are totally different, if your not exactly sure on how a turbo diesel runs i really would suggest taking it to a diesel tuner. Turning a diesel isnt exactly difficult but without knowing air/fuel ratio as well you really dont know everything, matching air to fuel correctly and having it running right is essential to longevity.

Did you install your egt gauge, didnt shorten the wires at all did you? That can play tricks on temps. Mine runs a little bit hotting then that about between 450-550c up hills in 4th travelling at 80kms, need to sort an intercooler then im hoping with more boost i can get it running a little cooler. Diesels dont mind heat either so dont be afraid to get her warm, ive found ive got more power with its hot then when im just putting around on the flats driving like my grandma.


Rick
 

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This is my dyno from last year before our trip, i took the fuel back slightly by about 1/8-1/4 turn due to it smoking a little while on boost. It drives well enough for now but wouldnt mind a bit more, with 370000kms on her now it will be interesting to see if i can squeeze 16psi with enough fuel without pump and injector rebuild (brought a 310k kms and unsure of when it was last done).


Rick
 

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Now knowing your injector pump had just been rebuilt I'd say it wasn't setup to factory output hence having to turn up your main fuel screw so much
 

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Discussion Starter · #15 ·
Now knowing your injector pump had just been rebuilt I'd say it wasn't setup to factory output hence having to turn up your main fuel screw so much
So would it seem everything is probably ok then? I mean if my exhaust temps and fuel economy is ok then really what is there to worry about?
 

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Discussion Starter · #16 ·
Block the relief valve on the intake manifold and wind in some more fuel mate, add boost so your egts are about the same and see how it drives then. Maxing boost and maxing fuel are totally different, if your not exactly sure on how a turbo diesel runs i really would suggest taking it to a diesel tuner. Turning a diesel isnt exactly difficult but without knowing air/fuel ratio as well you really dont know everything, matching air to fuel correctly and having it running right is essential to longevity.

Did you install your egt gauge, didnt shorten the wires at all did you? That can play tricks on temps. Mine runs a little bit hotting then that about between 450-550c up hills in 4th travelling at 80kms, need to sort an intercooler then im hoping with more boost i can get it running a little cooler. Diesels dont mind heat either so dont be afraid to get her warm, ive found ive got more power with its hot then when im just putting around on the flats driving like my grandma.

Rick
Sorry if this sounds dumb but what purpose would blocking the relief valve serve, and where abouts is it? Also not sure why i would need to wind in some more fuel if ive already wound in so much? What is wrong with what I have currently done? It drives like a rocket with relatively low temps.

I installed the EGT gauge, and no the wires are the original length. Made sure to buy a decent gauge too (Auto Meter Cobalt) If you want more boost why dont you install a manual boost controller? Then you can wind in some more fuel to match. I

I definitely get more power when shes warm too, and dont get me wrong flogging it up to 3000 revs is no worries for me, and very fun too. i just dont see the need to unless overtaking or something like that, or off road of course.

I reckon the intercooler would too much of a headache to install with these. If i was going to do it, id steal one off a 2.8 GU maybe with the GU manifold but even then the guys who have actually done it don't sound amazed at the difference in performance/temps from what i've read.
 

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Cant wind in any more boost due to the relief valve, it vents intake manifold pressure and if i wind anymore boost in it spikes up to 15psi and losses all boost (its located on the front of the intake manifd facing the radiator). Gu manifold doesnt have one and it also suits an intercooler better so it might be what i do.

More power doesnt specificly mean more fuel used, if i can get it running the right air/fuel ratio with more boost and fuel why not. Sure it will use more fuel if i have my foot down but for general putting around it should be about the same.

As lewie has said it sounds like your pump isnt setup right, for the amount of fuel you put in and the amount of turns on your idle screw it isnt the same as factory. Not sure if your timing would be correct either, im no expert with the ins and outs.

Where do you live mate? Maybe someone can suggest some where too take it to get it looked over to make sure its running right.



Rick
 

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Discussion Starter · #18 ·
More power doesnt specificly mean more fuel used, if i can get it running the right air/fuel ratio with more boost and fuel why not. Sure it will use more fuel if i have my foot down but for general putting around it should be about the same.
This is exactly the way I have it now, if i put my foot down it will eat fuel hard, but i only need to gently press the pedal and the turbo comes in with no lag at all at about 12-1400 revs and peaks at 12psi @ 2000 revs, then i change at about 2500, could change at 3000 but would just be exercising unnecessary power for everyday driving. What boost pressure are you currently running? I managed to get it to 14psi without it spiking but as i said i felt it was too lean, and sure enough, winding the little turbotech back -still no smoke.

Just called the guy that did the injector pump, going to take it back for new injectors and get the pump checked at the same time.
 

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Discussion Starter · #19 ·
Just thought id mention im getting much better fuel economy since ive played with fuel/boost and im by no means driving like a grandma. Im on track to get about 600kms from my 75L tank, whereas before id get about 550. Be interesting to see if it improves even more after new injectors this friday!
 

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Just thought id mention im getting much better fuel economy since ive played with fuel/boost and im by no means driving like a grandma. Im on track to get about 600kms from my 75L tank, whereas before id get about 550. Be interesting to see if it improves even more after new injectors this friday!

Tank should be a 95ltr, fuel light turns on pretty early and ive managed to get 100-150ks with light on.

Fixing my boost leak next weekend so hoping my fuel economy improves a bit, will also turn the compensator a few clicks and see what happens. Will let ya know if my boost kicks in any sooner.


Rick
 
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