Pinking on WOT

[Danblez]

Hi all,

I was out having some fun at the weekend with the roof down and noticed when on WOT from about 4k revs it was pinking quite heavily. It only happens on WOT on haevy load and high revs. Pulling from lower down the rev range and all is fine. I haven't noticed this before.

The only thing I have changed recently are the plugs and went for some BPR6ES which the car seems to be happier with. I also haven't changed the fuel filter but have this planned.

When I got the car one of the lambdas had been accidentally unplugged and I recently had the other one fail. I wonder if someone has set the mixture with the lambda unplugged?

I have the ecumate lite and there are no errors stored.

It is a standard 4l and I always run premium fuel. I am a little worried about this as we have a trip to Italy planned in a month which will only make matters worse I suppose so really need to get on top of it. Where should I start trying to diagnose?

Thanks
Dan

[Danblez]

Thanks both it is running standard ECU. I hope I havent done any damage. It may have been doing it since I bought it and not noticed and it has been given the beans fairly frequently.

I haven't looked at anything yet as I only noticed last weekend.

Anyways it is going in to XWorks (great garage) for some bits I wont have time to do before I go so have asked Heath to have a look. although I would like to understand the potential issues for myself. Hopefully it is as simple as timing.

I am a little apprehensive about the trip but cant bloody wait! Bring on the tunnels!

[Danblez]

My the car is still pinking, only under heavy load and high revs. I cant get it to pink at all under heavy load and low revs and is otherwise running perfectly. I have knocked the timing back to 28 degrees and it hasn't made any difference at all. When I fist got the car one of the lambdas was unplugged and it didn't pink (or wasn't noticeable at all), this is leading me to believe it may be fueling related.

I have been reading about a few possible causes but could do with some real world experience of where to start my investigations. Thanks!

It is a completely standard 400 apart from an ACT Y piece.

[Danblez]

I generally user 98 RON but occasionally 95. This doesnt seem to make any difference though.

[Danblez]

blitzracing said:

This is very likely down to an over lean mixture under load as its almost impossible to make the RV8 pink with wrong ignition timing if the mixture is correct. The effect of a lean mixture is to increase the temp in the combustion chamber, so pre detonation is much more likely once the flame front is ignited so you would be looking at a drop in fuel pressure / clogged fuel filter being the most likely cause. It wont have anything to do with Lambda sensors, as these are not used above 3400 rpm anyway.

You can check for a lean mixture with a test meter across the lambda outputs- the black (positive) and white (ground) wires if you run a long cable into the cockpit you can read with a test meter under load. Below 3400 rpm it should cycle between 0 and 1.2 volts approx, but then on WOT it should be at least 1.2 volts all the time- up to 1.4 or so, depending on the probe age. A lean mixture will show as the voltage drops away to zero as the load increases showing the AFR is running leaner than 14.7:1. This is bad news and needs to be rectified.

Great thanks for the reply, this would seem like a sensible first step. Does the lambda have to be plugged in to the loom to test?

I am also going to connect up to Roverguage, would this shed any light?

Just for info I have already changed the fuel filter to eliminate that (there is only one isnt there?) and have switched back to the 7 plugs also.

I will bear in mind your comments QBee when I have done some eliminating

Edited by Danblez on Tuesday 11th August 14:46

[Danblez]

Thanks a lot Blitz, I may take you up on your generous offer but will give it a bash first. I presume a normal multimeter will read this output? I have got an oscilloscope too but wont be able to use this on the move!

[Danblez]

I haven't managed to do the lambda thing yet but have had it hooked up to RoverGuage at the weekend.

I also checked it was running the white cat map.

A couple of odd things to note

Long term Lambda trim is sitting at +89% and +61% which I believe means the ECU is trying to increase fueling. The short term trim also hits 100% occasionally on. So this seems to tie in with the suspected running lean.

I have also done some reading of other potential causes. I believe engine load and therefore fueling is calculated from the AFM reading and engine RPM.

So I have just bought a fuel pressure tester to test system pressure and am going to test the AFM voltages also. I am also going to try and confirm the lambda readings on the move.

Am I on the right track?

Edited by Danblez on Tuesday 1st September 10:12

[Danblez]

gruffalo said:

Just a quick thought have you checked the throttle POT is doing what it should, that is also used to decide fueling and they can wear.

Good call, this is on my list of things to test although because there seems to be an issue with the car underfuelling at idle I put this lower down the list!

[Danblez]

blitzracing said:

Not far off- but i would not take too much heed to the closed loop values- as long term trim is is set at idle, and for those conditions only- so in you case of WOT and open loop the fuel requirements will be way in excess of those at idle, so a whole set of new variables comes into play. Certainly fuel pressure is worth checking- but it needs to be at WOT, which can be somewhat difficult to read a gauge strapped on somewhere at 100 plus leptons, unless you have access to a rolling road. The nice thing about the Lambda output is it perfectly possible to get a passenger to read a test meter when you floor it.

Is it not unusual to have such a high long term (and occasional short term trim)? I often bark up the wrong tree but does the fact that the ECU believes it is under fueling at idle suggest there is something going on with fuel delivery which will also be affecting WOT? Or do the other factors mean they may be seperate issues altogether?

Anyways I am just trying to get my head around how everything works so will do some further testing in the meantime.

Cheers

Edited by Danblez on Tuesday 1st September 13:30

[Danblez]

M

gruffalo said:

If the throttle pot is out at idle it will be out all the way up the range it gets magnified as the throttle opening gets bigger.

It takes 10 mins to set it up but I can't remember what voltage between which wires you need.

Cheers I have the 14cux manual which has the info I need.

[Danblez]

the 14CUX manual says fuel enrichment happens when the ECU detects the throttle is fully open which is what made it on to my "suspect" list?

For anyone following this, the site which blitz posted a while ago is very informative.

http://www.g33.co.uk/fuel_injection.htm

Links at the bottom to the 14CUX manual which has a great trouble shooting section.

Edited by Danblez on Wednesday 2nd September 13:53

[Danblez]

ahhh ok, makes sense!

[Danblez]

I managed to spend some time on this at the weekend.

Firstly I tested the fuel pressure.

Idle 1.6 bar
Light throttle 1.6 bar
Full throttle 2.2 bar - no fall in pressure all the way up the rev range. Altugh I believe to test this fully you need a long hill and 10 mins of full throttle.
Vacuum line to the FP regulator removed 2.5 bar

I also tested the lambda output and exactly as Blitz described cycling between 0-1.2 volts at idle and cruising and then 1.39volts when on WOT throttle all the way.

So the plot thickens and I dont know where to go now? I started to question whether I am going mad........

I wonder if it is intermittent. Should I test the lambda output on the opposite bank or is the likely hood on it running lean on one bank remote?

[Danblez]

QBee YHM!

I only tested one lambda Blitz, I will test the other and pull the plugs to have a look.

Thanks for your input so far!

PS in theory could blocked pre-cats cause a build up of back pressure enough to cause pinking?

Edited by Danblez on Tuesday 8th September 13:03

[Danblez]

Yep, I put BPR7ES back in after having 6s in for a while. It seemed happier on the 6s and it made no difference swapping back to the 7s