Spark plug colours

Morning guys,

Right my R's not been at its best lately. FWIW its running a chipped ECU, programmed for 1.2 bar boost which is achieved with a dawes device. It also sports an exhaust that's holier than the Pope! ( )
I'll give you a very quick run down of symptoms:

it was chucking out a heap of soot onto the back of the car.

very little power/torque before turbo kicks in.

turbo hits full boost maybe just after 3.5k rpm. The turbo was recently rebuilt with a 360° thrust bearing and updated compressor (?) wheel and is fitted with a Bogdan 3" elbow so should spool up earlier.

when at WOT the car rarely feels punchy and always feels like its being held back by something.

Things I've tried to sort it:

New engine/ECU temperature sensor.

Knock sensor replaced and temporarily located on side of head. (I know, I still have to put it back behind engine at some point!).

New ignition coil, amplifier.

New leads, dissy cap and rotor arm; all original Nissan stuff.

Re-earthed the fuel pump and relayed the power feed (showing healthy +13.5V at pump)

Reset ignition timing to bang on 20°. No messing with riding the clutch here, just turned on fans and headlights to get idle down to ~800/850rpm so very confident this is right.

Fuel pressure regulator replaced with adjustable one but set to 3 bar. I had installed a gauge on the original FPR but it was showing about 3.5bar at idle so I replaced it. It looked a bit furry inside too!?

I added a couple of additional earths to engine & chassis to rule out a dodgy contact somewhere.

Moving the (new) knock sensor to the side of the head definitely improved the sooty boot I had but the car still wasn't right. Everything I've swapped above also seems to have helped but not entirely cured the issue.
So now to the original question...about the plugs. I had a spare set lying around so thought I would change them out as the plugs had been in for about 10 months/5k miles (fuel filter was replaced then too btw).

To my unprofessional, untrained eye they look fine to me. Maybe a smidge on the lean side but nothing to say its running massively lean IMO. What do you guys think?
Also after seeing the plugs I upped the fuel pressure to 3.3bar as a trial today. The car still seems to come on boost a bit late but definitely pulled a lot cleaner up in the rev range.

You think maybe my MAF is out of whack causing slightly lean running? Looking at the plugs I wouldn't say that one or two were any different to the rest so I (personally) would rule out clogged injectors. Also (just remembered this) the car intermittently throws up a code 11 for the CAS. I don't know if this is related or not though...

cheers for now,
mike

Hiya Mike
Plugs look ok to me but maybe a little on the lean side as you have suggested.

Ok first off 'the turbo' is it a stock t28 fitted with 360 thrust? if so that should start singing at between 2-2.5k rpm so next time you drive it check the rpm and boost gauge to see when needle starts to go on + side. If it does start to move around then but car still feels like shes not boosting till later then i reckon you have a boost leak either on the intercooler ppiping or if stock 3 bolt flange my guess is that its leaking from that point.
However if she is actually not boosting and needle does not move on to + side until you have reached over 3k rpm then could be that either the wastegate is not fully closed (should be physically pulled shut by actuator arm by around 4mm. Also check the turbo itself to make sure the impellor is spinning freely, some turbo rebuilds i have little faith in through past experiences.

With regard to cas bringing up a code 11, this could also cause you issues with overfuelling and running lean points. In a nutshell that tells the ecu the cam position it is constantly being monitored, if ecu now and again recieves false information from the cas then it could fire either before or after tdc so car will feel gutless with intermittent poor fuelling so if i were you i would eliminate that issue straight away before you go ripping everything else apart.
Hope that helps

Cheers Bob
Its an uprated T28 with 360° thrust. The turbo behaved the same way before it was rebuilt so I don't think that's got anything to do with the issue (I hope!). I checked it span freely before I fitted it but haven't recently though.

It does start to boost before 3k rpm but its up around 3.5k rpm before it really pulls hard. If I'm in top gear at say 75mph and floor it it doesn't really pin you back like I think it should. That kinda behaved similar to my last one that had a turbotechnics stage one turbo but without the 3" elbow (ie just a 360° thrust bearing and nothing else). I was expecting after fitting the rebuilt turbo and 3" elbow it would be hitting full boost around 3k rpm-ish.
I've replaced all the small bore boost pipes with silicone and removed the carbon canister too to try and eliminate leaks. I'll remove the 3 bolt flange this weekend and re-seal that, just in case as you suggest.
What do you reckon would be the best way to eliminate the code 11, just replace the dissy? Could having the ignition timing out throw this code up or just a mechanical/electrical fault in the CAS itself?...have you got one kicking around more to the point?

cheers,

mike

Could be oil leaking into dizzy cam sensor or wear or harness plug/wiring causing code 11
You get/had any missing ? If clear code does it come back quickly .
Checking turbo/leaks and code 11 seems best direction at moment.
Sorting det sensor out bit more maybe good too, ecu does not show knock detection, only shows circuit fault by voltage drop to ecu (that what resistor for inside knock sensors). Knock signal is AC voltage that produced by the piezo crystal when vibration goes through it . Could be possible still getting ignition retarded if got det or sensor/sensor mounting not ideal .

The ignition timing being out wouldnt throw that code up but an irregular reading possibly could i.e a slack timing chain etc where reading fro9m ex cam would constantly be changing but you would hear that rattling especially at fast idle.
I would suspect the cas is faulty and intermittent signals recieved by ecu but check all wiring connections first and make sure the harness to ecu is firmly bolted on as ive seen some that have bellied in the middle causing bad connections to outer pins, all are 5 minute checks really.

If you do need one we have recon units in stock and some used ones which are cheaper but untested.
Delete the code 11 first though and check all connections etc as suggested above and if the code 11 comes back again after a drive then i would replace the dissy.

If I delete the code it can be off for days at a time before returning. There's nothing obvious to tell me the code's come back or not though as it seems to drive exactly the same with or without the code. It doesn't miss at all but doesn't feel entirely smooth when booting it, I suppose it would be borderline missing/hesitation but not quite. Maybe its the CAS not reading 100% as you say Bob.

I'll have a poke about at the wiring and see whats up, hopefully its something simple.

Keep the ideas coming guys

Take dizzy out and have a look at it and connectors, code 11 is indeed linked to sensor assembly or wiring. clean all connectors with elec contact spray etc and clear code and see how goes.
det sensor could be playing role in driving power issue if is signaling knock signal to ecu whether it picking up real knock or false knock .
Seems moving det sensor made some noticeable difference is interesting but possibly coincidence, needs looking at bit more though .

How tight is your knock sensor to tight or slack will give faulse readings slack is probably worse but over tight is not best

Leaks or exhaust will not help at all mate

As Mr B said above Mike
I would check ohms reading on knock sensor if its easy to get at, reading should be aound or above .556 if its a good one if lower then replace it but put it back where it should live lol

Other possibility is a faulty ecu (especially if it has an aftermarket chip in it as they are not the most reliable things in the world.
Pity your right up in Scottyland otherwise i would have said pop it down and reckon i would have it all sorted in a couple hours.

That's a good point Johnny, I'll double check the torque on the sensor. I still have an unadulterated ecu so I can try swapping that over as a trial too. The car starts to make positive boost just after 2.5k rpm, I'm not sure if that's good or bad.
I'll hopefully get a chance to have a look at her tomorrow weather permitting and report back.
You don't do house calls by any chance do you Bob?

Ok I got a little time to have a poke about today. I slackened off then torque the knock sensor properly. Had a look at the the 3 bolt flange that Bob suggested; it indeed looked like it had been leaking so sorted that out. I checked out the multi plug at the dissy and it was clean and made good contacts. I then started the car up and didn't really see much difference. This time though I pinched the blow by hose at the back left corner of the cam cover and the revs didn't change at all. I then thought I'd unplug the maf while it was running to see if that made a difference. The engine had been running for a couple of minutes and so the 'choke' was off and the engine was running a bit lumpy. As soon as I unplugged the maf the idle picked up slightly and smoothed out!!? I plugged it back in and the car died. So methinks my maf is borked? That would certainly explain why seemingly normal fuel pressure was making the car run slightly lean and higher than normal makes it run better.
So the next question is, can i do any sort of resistance checks on the maf to see if its outwith spec or not?

May not be the maf Mike it may be rhe chip in the ecu why not try the stock ecu and see what happens then

Air Flow Meter Diagnoses

Ok i tried the original ecu and the maf behaves exactly the same; rough until you unplug the maf and almost stalls out when reconnected.

Thanks for the link Mr B. The annoying thing is ive already checked the voltages and earths some time ago and they were all within nissans broad acceptance range.
I managed to check another couple of things while the ecu was out and cant find anything out of the ordinary either.
The cars definitely pulling better now but i think thats more to do with that turbo flange leak now fixed.
I still suspect the maf is out of spec but cant narrow it down sufficiently for a definitive diagnosis! And theres nobody else local to me that i can swap bits with, bah!
Ive heard theres a trim pot inside the maf thats protected by a cap you need to drill out, anybody tried fiddling with it to adjust mixture?

I would not suggest that personally,probably more so on a stock ecu. If you have swapped Ecu and tested/wighled wires incase there is a break then all you have left is try swapping maf. You cleaned it ?

Yeah its been well cleaned too

Ok so I had another wee poke about today. I took the dizzy semi-apart so I could assess the shutter disc (?) with all the little slits in it. Turns out it was spotlessly clean and firmly attached to the shaft; certainly no sign of contamination or oil leaks. I'm fairly certain the dizzy is ok now as the code 11 hasn't come back yet.

I had another look at the maf too while I was there. I get full battery voltage to one orange wire and 0.5V to the other orange wire, tested with ignition on but not running.

While idling I get about 1.48V on orange signal wire. When I rev the engine (not sure what I revved it to!) the signal voltage only went up to 3V. The voltage on the white earth wire while running is less than 1mV as I've re-grounded it direct to the battery.

Again as soon as the 'choke' switched off the engine idles about 600 rpm and generally isn't happy. Unplug the maf and the revs rise to about 800/900 rpm and it smooths out. Plug it back in and if it doesn't stall its back to running like shit again.

The more I think about it the more I think the maf is FUBAR
Oh and I lowered the fuel pressure today to a smidge over 3.1 bar and it definitely didn't feel as smooth or powerful as it has done recently.

Anyone got a good maf for sale just now?

cheers,

mike

Is beginning to sound like your maf Mike. Just check the pins in connector on maf to make sure they are clean and not bent up in any way. The 0.5v is correct with engine not running but ignition on.

I have a car to setup this afternoon on dyno so i will monitor the maf signal to see what voltages are but the 1.48v seems correct at idle.

If all seems ok and it does seem like a dodgy maf i will send you one up to try (just cover postage cost) if it solves the issue then you can buy it off me if no different then send it back to me so in theory its only costing you postage unless it solves your problem and you purchase it (dont want your old one back though)

The pins have been cleaned with contact cleaner and seem to be straight. I even slightly bent the female connections inwards a tiny bit so they would bite onto the maf pins tighter, but didn't really do anything.

If you wouldn't mind sending that anyway Bob that would be appreciated. Just name your price mate & i'll send you the cash

It might be good to measure the resistance between the pins on the maf for comparison between your and my maf. I could certainly do that just out of curiosity to see if there's an obvious difference...could be useful

Well, I managed to get Bob's replacement MAF installed last night. To my horror though when I did the old unplugging/plug back in trick after the 'choke' switched off it still didn't seem to make much improvement compared to the old MAF. Regardless I thought I would take the car out for a spin to see if it was any better....indeed it was! The car is definitely pulling better from down low, in fact I can use 5th gear below 3.5k rpm again! However when coming to a stop it was idling poorly, even when fully warmed up. I then remembered that I hadn't reset the fuel pressure from before. A quick twiddle and that was sorted then I thought to myself, what about if I just turn the idle up a little?
That seemed to cure the rough idle issue. I don't know why the idle had dropped after installing the new MAF but there you go. I'm still keeping a close eye on it but fingers crossed that's is sorted now.
While I had both MAF's to hand I thought I would have a poke around with the multimeter to see IF there was any difference between them (see picture).
I guess that my old MAF having slightly higher resistance than a working one was the issue. Looking at the values noted on the picture, my old MAF was about 30% out of calibration compared to the replacement one. That could be a handy additional check for folk along with the standard voltage tests to diagnose a fault. The higher the resistance in the MAF the less voltage going back to the ECU...or summit like that.
Note that there must be diodes inside the MAF as I didn't get any readings while probing the pins one way but then got resistance when switching the probes over.
A big thanks to Bob though who sent me the replacement MAF, much appreciated indeed mate (again)!  

Pleased shes all sorted Mike, it had to be a dodgy Maf as you tried everything else.

That info is very useful as i can now test all those i have in stock without fitting them to a vehicle to try so could you save that in the relevant section please Leighton / Stu

Out of curiosity i wonder what the ohms reading is on a new maf, unfortunately i havent got one but i knew that one was good as tried it out on a car first to make sure i hadnt sent you another dodgy one lol

*agree*
It would be nice to be able to check a brand new one for sure. I wonder how many R's have had their base fuel pressure upped to mask a slightly out of whack MAF?!

I know that on my last R, even after getting the injectors cleaned out & fitting a 044 it was still a little lean when on the rollers. With hindsight it was probably the MAF...oh well shit happens I spose :p

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