[BigRay]

I am interested in tuning my rebuilt Jimny engine and since seeing carbon build up on the pistons I am more eager. I am mainly looking at ignition timing, spark plug heat ranges and octane ratings and the relation between them all.
The engine has nearly finished its running in period and still guzzles the fuel and stalls quite easily. The plugs suggest that the engine is running perfect but the way it drives and the way the combustion chambers look suggest otherwise. It has a new 02 sensor, vacuum lines, PCV and reco injectors. It also has a 1&3/4" straight through exhaust system with a hi-flow cat. Before the first run, the compression on all cylinders was around 150psi but I have been told it will increase as the rings bed in. I haven't measured it again yet. The cylinders have been bored slightly I think and the block has been shaved and the head and also once in the past.
Ignition timing. The sticker on my timing cover is a #4, which indicates a -2 resistor is installed. Does this mean the timing is -2 BTDC or is it an adjustment to bring the timing from one setting to another. I have also read that changing the advance can change plug operating temperatures. Which brings me to octane ratings and spark plug heat ranges. I've always thought that octane requirement was determined by the compression ratio but after doing some reading it seems there are also alot of other factors. I've heard of running hotter plugs and using premium fuel, but are the plugs only a hot spot and heatsink or do they mirror the cylinder temperatures, meaning a hotter plug = hotter cylinder = higher octane fuel burns better and quicker? I know that the plugs don't create heat, they only carry it away to the cooling system, so like I said before, hotter plugs carry away heat slower meaning you have a hotter environment for higher octane fuel to burn efficiently. I hope I haven't lost you!

Thanks,
Ray

[GraphicX]

i'm going to be fiddling with my timing after swapping engines soon, here's a bit about it in my thread here that talks about how that resistor influences timing:

viewtopic.php?f=4&t=47361&start=120

from memory, the info about all of that is in about page 497 of the service manual, let me know if you need a link to download it (rhinoman has very generously uploaded & shared it).

hope this helps.

[BigRay]

Thanks mate I'll have a look, and yes I already have the manual. This tuning business is a dark art haha

Ray

[GraphicX]

all going well i'll be fiddling with mine soon so if you figure out something or need help nutting something out let me know. from best i can tell it's pretty easy, just the matter of starting with your base resistor value (which you know) & comparing that to what you want your timing to be & changing it from there.

[BigRay]

Sounds good mate

Ah yes I see, I think at idle it's meant to be 5 degrees BTDC so my -2 resistor must've been and adjustment to bring it from 3 BTDC to 5 BTDC?

[GraphicX]

not 100% sure, but say you wanted +5° & you were getting +3° & had a 2 on your timing cover, you would need to swap it to a 5 resistor (if i haven't stuffed up the math)

all it alters is the ignition timing, so every time you rebuild the engine, change a timing belt or replace the engine it needs to be altered to suit (cam & crank timing will be sent by the timing belt). from best i can tell it will also compensate for any variation in refitting the little cam sensor lug on the end of the cam (if it's refitted & out a couple of degrees) which is where i'm going to need it most as there's no marks on that nor any info on refitting it in the service manual (my guess is at the factor they simply used this resistor to fine tune it).

does anyone know what the 'ideal' timing is for the g13bb ?? i'm guessing it'd be slightly advanced but no idea how much (& don't have the manual here to check).

[BigRay]

Ahh now I understand, I was thinking along those lines. Well in that case my engine has had heaps of changes! The engine will benefit from a bit more advance if running higher octane. I'm interested in optimising the engine for 98 as well. The G13bb engines also have pretty decent compression, 9.5:1 I'm pretty sure.

[GraphicX]

i was at autopro a moment ago, the guys are going to see if they can source these resistors (so we can get around soldering etc), not sure how much luck they'll have though. there's a thread on bigjimny about it, if you google 'jimny ignition resistor' you should see it.

[BigRay]

Getting a timing light today and will start looking for the resistor. Does it connect into the ecu? Been trying to work it out in the manual

[GraphicX]

i believe it plugs in next to the ECU, i haven't personally had a look under there yet though.

[Rhinoman]

You can use an ordinary resistor if you fit a couple of appropriately sized spade terminals to it. You could also use a variable resistor if you want to make it easier to adjust. From what I recall the resistor value is only 'read' at key on so you can't adjust it on the fly.
If you have a -2 resistor then your base timing is 2 degrees advanced without correction so if you wanted to advance to 5 degrees over stock then you would need a +3 resistor.

[Rhinoman]

Check out this thread here:

http://www.suzuki-forums.com/suzuki-jim ... alues.html

Edit: I see you already posted it in the thread linked above.

Don't forget to fix timing using the monitor coupler or a scan tool before you check the timing.

[GraphicX]

thanks rhinoman, soon as i get my engine running i'll be tackling this =)

[BigRay]

Thanks Rhinoman
I've been looking at your USB Diagnostic plug and software and really like it. I have noticed on one of the screenshots of the software that it shows ignition timing. Does this mean I don't need a timing light to check my ignition timing?

Ray

[BigRay]

On the inside of my bonnet it says it should be 5deg BTDC at idle with the engine warmed up and timing fixed. Are you saying my timing with my resistor is 2deg BTDC? Sorry, still trying to get my head around all this.

Ray

[Rhinoman]

BigRay wrote:

Thanks Rhinoman
I've been looking at your USB Diagnostic plug and software and really like it. I have noticed on one of the screenshots of the software that it shows ignition timing. Does this mean I don't need a timing light to check my ignition timing?
Ray

The tool tells you what the ECU thinks the timing is, the ECU 'assumes' that the base timing is set correctly, it has no reference other than the cam sensor.

[Rhinoman]

BigRay wrote:

On the inside of my bonnet it says it should be 5deg BTDC at idle with the engine warmed up and timing fixed. Are you saying my timing with my resistor is 2deg BTDC? Sorry, still trying to get my head around all this.
Ray

It should be 5 degs BTDC with the resistor fitted.

[BigRay]

Ok, thanks Rhinoman!

Ray

[GraphicX]

located the resistor on my car today, it actually has a 5 on it just like the timing cover did.

[GraphicX]

@ rhinoman; does the wattage of the resistance matter ? ie. would a 1 watt resistor be sufficient ?

[Rhinoman]

I'll have to calculate it. I'm looking at an 81A11 tomorrow so I'll check that.

[Rhinoman]

The power dissipation will be very small, in the region of 1mW so 1Watt would be more than enough. Looking through my data it appears that you can monitor the ignition correction through the diagnostic link, I don't think I've implemented the maths for that in RhinoView but I'll check that as well, in any case the raw value will appear in the dataviewer.

[GraphicX]

thanks for that rhinoman, soon as i get my manifold to exhaust leak sealed i'll be adjusting the timing.