Nistune Forums

I have a problem where the MAF voltage seems to be spiking. I have tried another known working MAF and it is doing the same, which leads me to think it is wiring or ECU. I have attached a log file, showing the problem, you can see it spike to 0v and up to 1.5v at idle where it should be around 1.3V. It is also happening whilst driving which can't help.

Engine specs are:-
R32 RB20DET
700cc injectors
Z32 AFM
HKS 264 in/ex cams

Does anyone have any ideas ?

try changing from 'tuner mode' to 'streaming mode' and then doing another log. it will have a lot better resolution to see the spike with

unless something is wrong with the A/D converter on the ECU I cant figure out what the problem would be. i notice that your RPM is a bit eratic also so would like to have a look at that with a stream mode log and then we can work from there

I have changed the MAF back to the original one. The idle is still majorly hunting, I suspect an airleak or bad aac/idle valve, but I can't find it. I cleaned the aac valve and it looked ok.

Attached is the stream mode log.

I logged it again in tuner mode and it still does it with this AFM.

Here is a log, you can see it at the end.

i didnt see it in those last two logs. but yeah i can see your idle timing going all over the place as it tries to stabliise your RPMs

idle problems can be an absolute bit to solve, and the cams dont help much in working out what your idle should be like

disconnecting the AFM and running in limp mode may help with determining if vacuum leak

putting up K constant and seeing if richening the mixture helps it is another option. but i see you are already around the 11-13 mark for most of it

These things can be very hard to track down cos you can't tell if the AFM voltage is changing because of what the engine is doing or if the engine is playing up because of what the AFM is doing!

The idle is quite high so the AAC valve is closed most of the time. So it's not able to help stabilise idle. Can you lower the idle speed at all? It often helps to increase the target idle speed in NIStune when cams are fitted.

This also looks similar to a problem I saw once on an SR. I'm not sure if the RB is the same but what was happening is the ECU was not seeing "TPS closed". On the SR this should happen once the TPS voltage hits around 0.5V (RB uses a switch doesn't it???). Anyway, on this particular engine the TPS was 0.5V with throttle closed but the ECU was not interpreting this as TPS closed. What the???

The idle was terrible because the ECU wasn't operating off of the idle maps - it was pulling injector and IGN timing values from the main tables. As soon as we adjusted the TPS to make the "TPS closed" signal active it was fixed. Something I never understood was that we had to adjust it to 0.32V before it would do this!

Looking at your IGN timing figures, maybe yours has similar issues? It's jumping around all over the place. Then again this could just be the ECU trying to use IGN timing to help control idle speed. Although if that was the case then (given the high idle speed) I'd expect to see low timing values. Hmmmm. Not an easy one!

You could also try filling the bottom/left corner of your IGN map with the same value. Say 15 degrees. Then even if the ECU was using timing values from the main maps you'd have stable figures. The std maps go from 5 to 32 degrees in 3 cells!

PL

Matt,

I've sprayed aerostart everywhere checking for external leaks so it doesn't appear external, so maybe disconnecting the afm might help check for internal (AAC, idle valves) leaks, but the rpm doesn't appear to relate to MAF voltage. The end of the 1531_27 log has the MAF going from 0v to 2.6v during idle, but this can't be causing the idle problems as it idles bad even when the MAF stays around 1.3v. I have richened it up changed the k const from 220 (which I think is about right it was 13-15 afr and runs well) to 200 (any more and I reckon its going to fowl plugs).

Pete,

Yes the RB uses the switch which is on the whole time. I have set the throttle body stop up a bit as I thought the AAC might have been causing the idle issues in the first place, so I had it so it wasn't using the AAC valve at all at one point, I will put it back but this wasn't the problem.

I can try setting all the maps so it maintains 15 degrees regardless, AFM,AAC (might have to put throttle body stop up a bit more) disconnected see what happens.

Thanks for the help guys.

setting all the timing figures in the main maps temporarily to 15 deg, if it still moves around, it has got to be the idle control. Next set the t/b so that the closed switch is off, disconnect all the fancy things like idle air control valve, and the idle up for the aircon / powersteer (its on an SR), check your PCV or block it off if not already, EGR if fitted, and last your bov is sealed correctly, does the idle stabilise ? then re introduce them one by one.. as fort he MAF signal check the harness out on the SR it is a screened cable and what happens is the the insulation on the signal wire cracks from age and shorts out to the shield giving you a 0v intermittently especially if your idle is rough and things and wobbling around lot.. my maf never reads zero volts even with no airflow so i think your cabling is shot or not adequately grounded and shielded.

Chris,

Thanks, I will test nothing at 15 deg later today hopefully, I have no bov and most things are blocked now, I will try to get it idling stable. You could be right about the wiring, but when logging in stream mode it never goes to 0v which doesn't make sense as it has higher resolution than tuner mode.

Matt,

Any ideas why the tuner mode log show the 0v to 2.6v variation on the MAF, yet the stream mode does not ?

not sure about that ... why you are getting the 0v show up

we poll through selected registers in tuner mode whilst it is done by the ECU and continuously sent out in streamed mode

if you aren't seeing the problem in stream mode then there most likely isnt a problem with the MAF then

You don't have your AFM close to the turbo do you? I've seen them get VERY upset if the AFM is mounted close to the compressor inlet.

Unlikely - but I thought I'd mention it....

PL

No luck with getting it to idle properly under 1500 rpm. It will idle fine above this both off the idle map (tps switch off) and idle settings (tps switch on). It still does the same with everything blocked off including aac and cold start idle valve.

Pete, it is about 200mm from the compressor wheel, and the MAF voltages are pretty stable (in stream mode), so I doubt this is it. When you have troubles does the MAF voltage relate to the rpm change ?

I can't see the cams causing all this, but I am thinking about putting standard ones back in...

200mm is closer than ideal but may be OK as long as the pipework is nice and smooth. They usually seem to run too rich - to the point where they won't idle at all. But symptoms do vary. If you get desperate you could try extending the pipework to the AFM temporarily. One of my mates did this (he actually hung the AFM out of the engine bay on a 3 foot pipe) and it totally cured his problem. His would dip down and almost stall when you stabbed the throttle. Hardly a practical solution but it proved the point.

Sounds like the AFM voltage is OK anyway. I guess you could try putting a potentiometer across the AFM wires and just set it to around 1V. I tried this once on an SR that wouldn't idle properly and it made no difference but it is another way to eliminate the AFM from the list of suspects if you're desperate.

I agree - I can't see the cams causing it. They might cause a lumpy idle but it usually doesn't cause this sort of instability.

Did you try making all the values in the timing map 15 degrees?

PL

Pete,

Yes I made it run at 15, still the same. Here is a weird log when making it run off the main map (tps switch off), I noticed the tps voltage is changing (although it is in the same position), this might be due to the battery voltage changing as the rpm rises/ falls, but it appears to be in sync with the rpm (just ahead of it, so looks like it is causing it...). I might try running without the alternator connected ....

I might try either extending the pipework or running a resister on the MAF.

OK, now there's some real weirdness going on. Neither TPS nor battery voltage should vary like that. And I suspect the actual battery voltage isn't doing that at all.

I'd suggest you take a good look at the power and GND connections on your wiring loom. Particularly the main GND lugs that (on SR's anyway) bolt onto the inlet manifold.

Also check battery to engine and engine to chassis grounding.

Have a good look at the ECU connector pins and wiring too.

I guess you could take a log while you go around and give all the wiring a good wriggle - it might show something up.

PL