Do these air/fuel ratios sound rite for 3.5EFI?

[Taz]

My 89RR3.5EFI auto has the open loop ECU with flapper air flow meter. It's bog standard, 270,000k's (new cam, lifters, rocker shaft 80,000ks ago). She really struggles to get to 4000rpm, even on the flat in second gear and is generally lithargic above 3000rpm. I estimate I would need to have the throttle wide open for 2-3mins on the flat in second gear before it would rev to 4500rpm, but it does get there eventually. I thought it might be suffering from fuel starvation - hence this test...

Air/fuel ratio sensor is an UEGO exhaust gas oxygen system that gets inserted into the tail pipe. It has been recently calibrated. This is not your standard oxygen sensor as it allows a precise measurement over a wide range of AFR.

At idle (warm engine), AFR=12.0
Going down hill with foot off accelorator, AFR = 25ish
On the flat at a steady 60km/hr, AFR=13.9
Going up slight hill at 60km/hr, AFR=14.3
Wide open throttle 2000rpm, AFR=12.0
Wide open throttle 4000rpm, AFR=12.0

So it's getting plenty of fuel, in fact probably too much. I'd have thought cruising AFR should be around 14.3 and full throttle maybe around 13 at the most?

[Lucus]

There pretty good. A tad rich maybe. I would aim for around 13.0/13.1 at WOT and 14.7 to 15.1 in cruise.

[Taz]

Tried my spare ECU (origin unknown) and got dramatically different results...

WOT, AFR=14.5
Cruising, AFR=16.5 to 17.5

This ECU has serial number 83714A (a very early one I think, as I thought the SD1 ECU's start at 83986), versus my original ECU serial number 84941A.

[simonr23]

what about performance? did that change alot also?

[Lucus]

Those mixtures are far too lean and will cost you a large amount of torque. 14.7 at WOT is asking for extremely high combustion temps and anything higher than 15.5 at cruise (imho) is going to increase fuel consumption due to loss of torque.

they are probably leaner because the AFM has been adjusted after the ecu change

Luke

[Taz]

Yes - the second ECU felt slightly more sluggish.

I reverted back to the original, applied an additional half a turn of spring pressure in the AFM and it now runs around 14.7 cruise and 12.5 WOT. I think I will try it there for a while and see if I've introduced any overheating problems, then maybe apply a little more spring tension. The performance now does seem slightly better, although I didnt do any quantatative before and after tests.

[Lucus]

Thats pretty good. if you coudl tweak it to 12.8/12.9 at WOT and 14.9/15 at cruise that would be about as good as it'l get. What UEGO are you using?

I have a techedge 2E0 and a 2zj that permanently mounted in the car.:cool:

[Blknight.aus]

14.7 is correct for cruise down to 12 is acceptable under WOT and full load and coasting the higher you can get it the better.

if your going to mess with these things excessively you really should do it on a dyno so that you can get reliable repeatability.

While you can go a little either side of ideal (by say .2/.3) without hurting too much I generally like to aim for a little richer IF I cant get it perfect. and naturally the older and poorer condition the engine is the more lenient Im willing to be with the tolerance.

you will get some engines that just wont run correctly on the right mix but pearl away in what would be an "off setting"

[mike 90 RR]

My 89RR3.5EFI auto has the open loop ECU with flapper air flow meter. It's bog standard, 270,000k's (new cam, lifters, rocker shaft 80,000ks ago). She really struggles to get to 4000rpm, even on the flat in second gear and is generally lithargic above 3000rpm. I estimate I would need to have the throttle wide open for 2-3mins on the flat in second gear before it would rev to 4500rpm, but it does get there eventually. I thought it might be suffering from fuel starvation - hence this test...



Just a thought on where to look next
If you have the fuel numbers & a full throttle then...

Consider that exhaust system!!
What sort of exhaust manifold is it? ... what type of muffler is it? ... and the exhaust pipe diameter?

If your getting air in, Have a look at how it's getting out ;)

Also.. the postive line to the coil .. check to see if it's got the right volts

[Taz]

if your going to mess with these things excessively you really should do it on a dyno so that you can get reliable repeatability."

I did look into that, unfortunately I learned there is only 1 4wd dyno in perth at maximum motorsports, and they only do subaru's. I could drop a tailshaft and use a 2wd dyno, however that might put excessing load on the viscous coupling in the TF box.

[Taz]

What sort of exhaust manifold is it? ... what type of muffler is it? ... and the exhaust pipe diameter?

If your getting air in, Have a look at how it's getting out ;)

Also.. the postive line to the coil .. check to see if it's got the right volts


Thanks Mike,
She has the original dual downpipe manifolds and each bank is 4 into 2 into 1
, before both banks combine just before the muffler. Apart from necking at the bends (i.e. not mandril bent) they look pretty good, although the diameter of the primaries is pretty small at about 34mm. Then there is a large muffler and resonator (details unknown).

You would think that this exhaust design, which I understand supported the engines 160bhp at 4,750rpm when new, shouldn’t be having problems flowing that amount of air. Unless perhaps the muffler has collapsed or something on the inside, but it looks like it's in good shape on the outside.

My engine is very drivable, having adequate torque from 1000 to 2500rpm. Even towing - as long I keep it in this zone it performs very well and I dont feel that I need more cc's. It's just the odd occasion that when I need to floor it, there aint as much there as I would have expected. Although maybe I'm expecting too much? Does anyone have a bog standard 3.5EFI auto that will reach 5000rpm in second gear on the flat?

Perhaps going to 38mm or 41mm primaries together with some porting of the heads will do the trick. I'd prefer to keep the standard cam as I dont want to sacrifice any low end torque.

[Blknight.aus]

I did look into that, unfortunately I learned there is only 1 4wd dyno in perth at maximum motorsports, and they only do subaru's. I could drop a tailshaft and use a 2wd dyno, however that might put excessing load on the viscous coupling in the TF box.

if you know someone who has one borrow an accelorometer and use that on a sheltered hill a good one will give you G's to the hundredths which is good enough for general tuning the kit one from jaycar is accurate enough if you set it up with a good laptop or digital reader.

[Lucus]

Is your cam timed correctly?

I wouldnt be too worried about running it on the dyno with the front driveshaft removed. The viscous coupling will be fine with the power levels your producing.

(iirc the rear wheel are mechanincally driven through the coupling and the front is fluid driven)

Luke

[mike 90 RR]

Thanks Mike,
She has the original dual downpipe manifolds and each bank is 4 into 2 into 1
, before both banks combine just before the muffler. Apart from necking at the bends (i.e. not mandril bent) they look pretty good, although the diameter of the primaries is pretty small at about 34mm. Then there is a large muffler and resonator (details unknown).

You would think that this exhaust design, which I understand supported the engines 160bhp at 4,750rpm when new, shouldn’t be having problems flowing that amount of air. Unless perhaps the muffler has collapsed or something on the inside, but it looks like it's in good shape on the outside.

My engine is very drivable, having adequate torque from 1000 to 2500rpm. Even towing - as long I keep it in this zone it performs very well and I dont feel that I need more cc's. It's just the odd occasion that when I need to floor it, there aint as much there as I would have expected. Although maybe I'm expecting too much? Does anyone have a bog standard 3.5EFI auto that will reach 5000rpm in second gear on the flat?

Perhaps going to 38mm or 41mm primaries together with some porting of the heads will do the trick. I'd prefer to keep the standard cam as I dont want to sacrifice any low end torque.

You have the same manifold as mine
I don't see any advantage in "Extractors" as they would only be good if the exhaust port openings that are "milled" larger than the stock manifolds

I believe that the manifold with dual downpipe set up is OK, however my line of thought is on the rest of the piping system.

If you don't have it already...
Try a 2.5 inch system with a aftermarket "flow thru" muffler :)

If anyone else has had success with a "Good system".. Could you let me know? :)


Also.. check that voltage to the coil .. as it part of the same symptoms that i had suffered, that you are describing (hard to get past 4000rpm) ;)

[streaky]

If you are running Tech Edge then you'd be advised to get the tewblog software and plug into a few more user logging perameters.
I have just purchased the latest Tewblog software from Justin Luton and now I can watch & record my Throttle position sensor voltage, the Airflow meter voltage, Engine RPM and the Air/Fuel ratios.
Plot the whole lot onto an Excell file and give them to someone who knows how to translate them.
I didn't have a clue how to do it at first, but once you know what voltages to look for, what AFR mixtures are acceptable etc...you actually get to enjoy messing with it.

Stay away from the lean numbers...anything above 14.7-15.0 is considered lean.
Yes...a rolling road dyno would be nice...but using your Tech Edge as a data-logger will provide you just as much information on your laptop. (apart from HP & torque numbers)
I use the LX1 LCD display as a means to monitor my right foot and get the most out of a tank of fuel.


Techedge also has a website forum full of really helpfull people.

[Lucus]

Good post Streaky, this is exaclty what i do. Its amazing what you can pick up from afr volts,t/pos and rpm.

I can also log through the wolf software engine load (% of atmospheric) This makes for an awesome tuning tool.