RD28 to TD42 conversion - revs too high HELP

[jesskac92]

Long story short - I've bought a Y61 patrol from a dealership, found out only after I got it home that it's had an engine conversion from an RD28 to a Y60 TD42. It's been turbo'd and mod plated.
It was doing 4000rpm @ 100kph so the rear diff was changed from 4.6 ratio t a 4.1 and now it's doing 3800rpm @ 100kph
I still think that it's way too high, it sounds terrible. I do a lot of highway driving and live out west so I need to get this sorted asap.

It's a 5 speed manual, the clutch isn't slipping and it currently has 31s

If anyone has any idea what's going on please let me know, I'm at an absolute loss as what to look at now.

[NissanGQ4.2]

Bump for @jesskac92 due 2 this thread going into moderation

[4bye4]

Bump for @jesskac92 due 2 this thread going into moderation

This is way left field but if it has had an engine swap, was the gearbox swapped as well? Maybe the gearbox ratios are wrong for the motor. Just a thought I have no experience in this.


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[Deano2506]

Bit of a long shot but is the speedo and tacho reading right?
3800 at 100 sounds massivly high

[PeeBee]

Gearboxes are different on RD28 to TD42, RD28 too small and wont fit. Transfer case ratios are the same.

[happygu]

Jess,

Not even sure that the old 4.2 in standard form liked 4000rpm .... anything past 3500rpm was a waste of time ....

Even accounting for the Diff Ratios with the engine change, it doesn't seem right and it seems like the Tacho is way out, and you may need a different adapter gear.

The 4.2 runs a different gearbox to the 2.8, so it is likely that the tacho is giving you the wrong reading.

Pretty sure mine was somewhere around 2200 - 2400rpm at 100, but it was 17 years ago that I had mine, so someone with current info will confirm.


PS I hope you changed front and rear ratios at the same time, as you can't run different ratios front and back in 4wd.

[jesskac92]

I have changed front and rear ratios, yes

I'm waiting on a tacho reader, we live in the middle of nowhere so eBay is my friend.

I'd like to think the tacho is wrong but it really doesn't sound like it, it's really singing at 100kph.

[mudski]

I have changed front and rear ratios, yes

I'm waiting on a tacho reader, we live in the middle of nowhere so eBay is my friend.

I'd like to think the tacho is wrong but it really doesn't sound like it, it's really singing at 100kph.

I reckon the tacho is out of whack. When I did the conversion from ZD to TD in my GU, I sent the loom to Killa Kustoms to get it cut and shut to suit the TD. It came back with a little box in the loom which is for the tacho signal. This box is adjustable too so they must calibrate it or something to suit.
I'm gonna guess you either dont have this box, or you do and it just not calibrated right. Theres no way you can do 100ks at 4000rpm in a TD. I had 4.3's in mine at it was at 2700rpm in 5th at 100ks. Now with 4.1's its at a nice 2450rpm. So you can't be at 4000rpm when you had 4.6's...

As PeeBee said too, the RD box is different and wont fit the TD. So we know the box is right. Can you take a pic of where the speedo sensor mounts into the box too? The GQ and GU boxes are different to each other, but i have seen GQ TD boxes used in GUs. But the speedo pickup is different.
If its a GU box, remove the sensor and tell me what colour the speedo gear is. Then take the car for a run with a GPS in hand that tells you the actual speed. We can then work out if you are actually going at the right speed too, if your speedo is out, you should be correcting this to by using a different tooth counted speedo gear.
Finding different speedo gears for a GQ box is near impossible these days.

[PeeBee]

I reckon the tacho is out of whack. When I did the conversion from ZD to TD in my GU, I sent the loom to Killa Kustoms to get it cut and shut to suit the TD. It came back with a little box in the loom which is for the tacho signal. This box is adjustable too so they must calibrate it or something to suit.
I'm gonna guess you either dont have this box, or you do and it just not calibrated right. Theres no way you can do 100ks at 4000rpm in a TD. I had 4.3's in mine at it was at 2700rpm in 5th at 100ks. Now with 4.1's its at a nice 2450rpm. So you can't be at 4000rpm when you had 4.6's...

As PeeBee said too, the RD box is different and wont fit the TD. So we know the box is right. Can you take a pic of where the speedo sensor mounts into the box too? The GQ and GU boxes are different to each other, but i have seen GQ TD boxes used in GUs. But the speedo pickup is different.
If its a GU box, remove the sensor and tell me what colour the speedo gear is. Then take the car for a run with a GPS in hand that tells you the actual speed. We can then work out if you are actually going at the right speed too, if your speedo is out, you should be correcting this to by using a different tooth counted speedo gear.
Finding different speedo gears for a GQ box is near impossible these days.

It came back with a little box in the loom which is for the tacho signal. This box is adjustable too so they must calibrate it or something to suit. Yes, my conversion has this same box, as I am running a TD42 box and RB30 Tacho. With 3.9 diff ratio, checked against the GPS I am smack on 100klm on the speedo and GPS.

[jesskac92]

I reckon the tacho is out of whack. When I did the conversion from ZD to TD in my GU, I sent the loom to Killa Kustoms to get it cut and shut to suit the TD. It came back with a little box in the loom which is for the tacho signal. This box is adjustable too so they must calibrate it or something to suit.
I'm gonna guess you either dont have this box, or you do and it just not calibrated right. Theres no way you can do 100ks at 4000rpm in a TD. I had 4.3's in mine at it was at 2700rpm in 5th at 100ks. Now with 4.1's its at a nice 2450rpm. So you can't be at 4000rpm when you had 4.6's...

As PeeBee said too, the RD box is different and wont fit the TD. So we know the box is right. Can you take a pic of where the speedo sensor mounts into the box too? The GQ and GU boxes are different to each other, but i have seen GQ TD boxes used in GUs. But the speedo pickup is different.
If its a GU box, remove the sensor and tell me what colour the speedo gear is. Then take the car for a run with a GPS in hand that tells you the actual speed. We can then work out if you are actually going at the right speed too, if your speedo is out, you should be correcting this to by using a different tooth counted speedo gear.
Finding different speedo gears for a GQ box is near impossible these days.

Will have a look at the box over the weekend and let you know

As for the speedo, I have done the GPS test and @ 100kph on the dash I was doing 104kph on GPS, so it's not out by much.

I have watched a few TD42 0-100 video's on youtube and I can see what everyone is saying about how loud these engines are. It's my first TD42 and I've never actually owned a diesel before so it's all new to me. I used to be a Nissan Import kinda girl till I went bush haha

Thanks all for your help. Will let you know what else I find in regards to the gearbox/tacho.