AUIII XR8 massive misfire/hesitation

madmelon · 08-09-2010, 12:09 AM

Anything below 2k rpm, anything other than 0% throttle it just wont go properly. Shakes like nothing else but at no throttle it's as smooth as ever. At one point it did backfire but every test since then it hasn't.

Idles smoothly, revs out properly, balancer isn't visibly shaking, checked coil packs with old ones (new ones are 3 months old), new leads two weeks ago and double checked that they were seated properly today (put heat socks on it at the same time). Car is standard except for exhaust, has 3/4 tank of petrol.

Any ideas? Going to try to get it to Ford tomorrow but don't like my chances and would like to have ruled certain things out.

AUIIPURSUIT · 08-09-2010, 12:27 AM

could be TPS, o2 sensor, MAF is dirty, leaking injectors, blocked fuel filter... go get a diag done at ford first and foremost, try and elimate a few off the list.

im booked in for monday diag with the same problems... seems very common. coilpacks and balancer seem to be the *main* culprits from my research, but it really is a bit hit n miss.

XH5LWEPN · 08-09-2010, 12:30 AM

Cam position sensor gets my vote.

urbancowboy · 08-09-2010, 12:47 AM

My Au2 XR8 had the diagnosis put on it a week ago and came up with cam sensor, even though it really does go fine, it has a very slight desire to bunny hop a bit at low revs (but im thinking thats my minimal throttle driving style when im trying to keep the noise down!)
The faults were erased and car is fine, will be getting it done again in a week or so to see if the codes came back.

madmelon · 08-09-2010, 09:21 AM

Quote:

Originally Posted by urbancowboy

My Au2 XR8 had the diagnosis put on it a week ago and came up with cam sensor, even though it really does go fine, it has a very slight desire to bunny hop a bit at low revs (but im thinking thats my minimal throttle driving style when im trying to keep the noise down!)
The faults were erased and car is fine, will be getting it done again in a week or so to see if the codes came back.

Actually, it has bunny hopped a bit more lately than it has in the past. I also have the minimum TP, minimum rpm driving style.

I seem to recall reading somewhere on here about horrendously expensive cam sensors from Ford and relatively cheap aftermarket ones. Is this the case? Does anyone have a part number?

Booked in at Dominelli tomorrow...

madmelon · 08-09-2010, 09:38 AM

Quote:

Originally Posted by madmelon

I seem to recall reading somewhere on here about horrendously expensive cam sensors from Ford and relatively cheap aftermarket ones. Is this the case? Does anyone have a part number?

All good, found the threads about the cam sensor and sensor drive. Probably best to get both replaced at the same time... not paying $800 for a Ford one though!

madmelon · 09-09-2010, 08:26 PM

Quote:

Originally Posted by urbancowboy

My Au2 XR8 had the diagnosis put on it a week ago and came up with cam sensor, even though it really does go fine, it has a very slight desire to bunny hop a bit at low revs (but im thinking thats my minimal throttle driving style when im trying to keep the noise down!)
The faults were erased and car is fine, will be getting it done again in a week or so to see if the codes came back.

Well mine went into Ford today. Apparently it threw a whole lot of codes, mostly due to my fiddling around. No cam sensor code and the senior mechanic went on to tell me it's clutch slip and that there isn't a misfire. I told them not to bother any more as the only way that gearbox is coming off is if a different one is going back on. Oh well.

Mr_Monty · 09-09-2010, 10:58 PM

Id put my 2 cents in as a cracked spark plug insulator. the only time mine has backfired was when i had a cracked plug insulator. drove me nuts for 3 months until pulled out the plugs, there where a couple ever so slightly cracked from the extractor install. pretty easy to check.

My apologies if im pointing you in the wrong direction.

I did the Leads on mine twice because of this, after leads it showed a marked improvement but only as the silicone was tight around it, a few weeks later they loosened up and spark was leaking again.

Best of luck.

madmelon · 09-09-2010, 11:18 PM

Any info helps.

I don't want to be too rude as I know the people at Ford trawl these forums (and I've gotten in trouble with that once before) but frankly, I can't understand how it could possibly be the clutch or a flywheel balance problem. It bucks around below 2000rpm, regardless of which gear it is in, even at very low throttle positions (but NOT 0%). Above that, where torque is higher, no problems at all. I even took it out before and deliberately put my foot down and started pressing the clutch pedal- went a long way before it got even close to slipping. Yes, it shudders when the clutch engages- it always has. I gave it the beans in 1st and backed off as quickly as possible at about 5k rpm, if it was clutch slip, the engine braking power (which is substantial) should have instigated it at some point too...

It's also dead smooth on the overrun, regardless of rpm. That would suggest that it's NOT a balance issue, either flywheel or cranskhaft dampener.

I took the liberty of disconnecting various sensors and starting/driving, results as follows...

Cam Position sensor- made no difference at all. Still misbehaves badly.

Throttle position sensor- was rather unhappy from the get go, didn't drive it.

Temperature Sensor- No difference, but I wouldn't expect to feel or hear one.

MAF sensor- idle started fluctuating but drove EXACTLY THE SAME as it had before, light and high throttle positions, all revs. It's now sitting in front of me, after cleaning with contact cleaner. Will wait to see if any effect.

I'll try the crankshaft sensor when I can get to it/engine cold in the morning or Saturday.

Also put the timing light on it- seemed ok at slightly higher revs but did jump about a bit at idle. Probably not much of a diagnosis.

I'll take oxygen sensors off next see how that goes...

Honestly I'm really really p***** off at being told it's clutch and/or flywheel and that there is "no way it was an electrical misfire". I know what a damn misfire sounds and feels like, I know what my cars exhaust should sound like (and it's bloody loud too so it shouldn't be that damn hard to hear when it doesn't sound right, even with the windows up...)

It also missed going up and out their driveway without shuddering or hopping at all really- just felt two brief instances of power loss and heard it in the exhaust thanks to the reflection off the fence.

I'm not a total dumb ***, why to 'experts' always treat customers like they are regardless...

Mr_Monty · 09-09-2010, 11:49 PM

You mentioned the word Bucked, thats exactly what mine did, does it do it worse under and load in lower revs? to me it felt like random thuds like the whole engine skipped a beat. the the backfire sounds like a fluff, more then a bang.

the customer's always Right dammit, and its your car! your damn property and your say.

sorry for the second post. Have you had any extractor work done? this is what damaged my plugs.

madmelon · 10-09-2010, 12:34 AM

Quote:

Originally Posted by Mr_Monty

You mentioned the word Bucked, thats exactly what mine did, does it do it worse under and load in lower revs? to me it felt like random thuds like the whole engine skipped a beat. the the backfire sounds like a fluff, more then a bang.

the customer's always Right dammit, and its your car! your damn property and your say.

sorry for the second post. Have you had any extractor work done? this is what damaged my plugs.

Under any load at revs below 2000, except 0% throttle. I've just had all the plugs out and checked them, typical that I'd break #5 on the way out... What a mongrel header design that is. All other plugs free from cracks.

What I did notice, however, was that my plugs (from WeaponX, as with coils) have screw on end caps. ALL WERE LOOSE. Now they're all tightened beyond vibration loosening and it's all back together with the one odd plug in #5.

Interesting to see that there was (only slight) visible erosion on the iridium plugs. I'm a massive sceptic but that would seem to support the claims of WeaponX that their coils output much higher voltage... All gaps still within spec, so don't claim that one as the culprit.

About to go drive...wish me luck...all the pain in my hands had better be worth it...damn plug leads.

madmelon · 10-09-2010, 12:37 AM

Oh and any backfire with my exhaust would sound like a 50 cal. only 1 muffler each side...

madmelon · 10-09-2010, 01:12 AM

Epic fail. If anything, it's worse than it was. Could really hear it misfiring badly this time, definately down to 7 cyls at that point. Also filled up with fuel and went for a drive, didn't help it at all.

How difficult is it to replace the crankshaft sensor?

JC · 10-09-2010, 01:52 AM

7 cyls? Sounds like one of your plugs or leads is buggered or the leads are not on properly.

Cranjshaft sensor not too bad (search on synchronizer and you should yield a food how to - I followed it and it's fixed my random no start isue).

madmelon · 10-09-2010, 10:24 AM

Quote:

Originally Posted by JC

7 cyls? Sounds like one of your plugs or leads is buggered or the leads are not on properly.

Cranjshaft sensor not too bad (search on synchronizer and you should yield a food how to - I followed it and it's fixed my random no start isue).

The leads are on properly. Checked that several times. I suspect the 7 cyls was only during that period due to a loose injector connector, had it off and looks like I didn't put it back on properly. Misfire is still present though.

How could it be cam sensor if it makes no difference when I unplug it? It should simply revert to batch fire mode and if it was the culprit that would have solved it.

BillC · 10-09-2010, 11:24 AM

I'll throw some other possibility into this thread. I have an XR8 and had almost the same symptoms. Turned out to be the alternator was intermittant. It charged just enough to keep the battery charged but the voltage at times were so low that the sensors did not work. This caused total hovoc with the car. On a final note my car has done 150,000 K and I am on my 3rd alternator.

sd1800 · 10-09-2010, 11:42 AM

Have you driven around without the o2 sensors connected yet?

When I had a issue with my cam sync/sensor, when I disconnected the o2 sensors it was fine as it went into closed loop(??) and ran richer.

See this thread:
http://www.fordforums.com.au/showthr...hlight=Surging

madmelon · 10-09-2010, 03:04 PM

Quote:

Originally Posted by sd1800

Have you driven around without the o2 sensors connected yet?

When I had a issue with my cam sync/sensor, when I disconnected the o2 sensors it was fine as it went into closed loop(??) and ran richer.

See this thread:
http://www.fordforums.com.au/showthr...hlight=Surging

Not yet I haven't. They look to be a bit of a pain to access and I haven't had time- at uni working on racing car today.

As for the alternator,
The car starts great and the instruments show the correct voltage. Perhaps I'll check that in diagnostics mode though as it reacts much faster than the analogue gauges.

Dropped in to Repco today, apparently Bosch, FuelMiser (Champion), ACA and whoever else don't do a crankshaft sensor for the AU V8. Anyone know who does, other than Ford, and a part number?

JC · 10-09-2010, 03:55 PM

Quote:

Originally Posted by madmelon

Not yet I haven't. They look to be a bit of a pain to access and I haven't had time- at uni working on racing car today.

As for the alternator,
The car starts great and the instruments show the correct voltage. Perhaps I'll check that in diagnostics mode though as it reacts much faster than the analogue gauges.

Dropped in to Repco today, apparently Bosch, FuelMiser (Champion), ACA and whoever else don't do a crankshaft sensor for the AU V8. Anyone know who does, other than Ford, and a part number?

Yep, search for synchroniser (maybe with a z) and all will be revealed.

CFOUR · 10-09-2010, 05:31 PM

http://www.fordforums.com.au/showthr...t=synchronizer

madmelon · 10-09-2010, 11:33 PM

Not camshaft sensor, CRANK sensor. I can get cam sensor easy.

Just cleaned it- was a but dirty but otherwise looked physically ok from the outside.

Just looking at the oxygen sensors now, does anyone know how to remove the plugs? They're in a tight spot and I can't see much more with the lighting I have (under-bonnet light)

madmelon · 11-09-2010, 12:34 AM

Ok, finally some progress. Disconnected the oxygen sensors and it wouldn't idle properly, even from cold start. If the revs were close to idle when I took the foot off the clutch, it wouldn't be too bad- it'd pick it up within 2 complete fluctuations. If it was higher rpm, it would hunt between about 300rpm and almost 2000.

Now that might suggest oxygen sensors aren't at fault but when driving it (from cold to completely warmed up), the miss was much less severe, even absent at some points.

Now with the oxygen sensors unplugged, shouldn't it rely entirely on TP and MAF for its input values? If that's the case, is it possible that there is something wrong with the MAF? surely it should be able to control mixtures enough to not hunt over such a huge range...

Got the oxy sensors re-connected now and battery is currently disconnected. Just to check and see if a reset makes any difference.

Is it possible that both oxy and MAF are together causing a problem?

urbancowboy · 11-09-2010, 02:28 AM

Quote:

Originally Posted by BillC

I'll throw some other possibility into this thread. I have an XR8 and had almost the same symptoms. Turned out to be the alternator was intermittant. It charged just enough to keep the battery charged but the voltage at times were so low that the sensors did not work. This caused total hovoc with the car. On a final note my car has done 150,000 K and I am on my 3rd alternator.

Although i don't think this is the cause of these problems,
I do agree with this post, The XR8 alternators are under driven from standard IIRC, and i know that when i start my car at night, and then turn the lights on, and then try to let the clutch out with 0% throttle i can actually see the headlights dim down! And at night when i turn on my blinker i can see the lower part of the dash (DTE etc.) dimming in time with the blinker. The stereo doesn't seem to effect it only the lights.

Best of luck with your problems!

madmelon · 11-09-2010, 10:57 AM

Quote:

Originally Posted by urbancowboy

Although i don't think this is the cause of these problems,
I do agree with this post, The XR8 alternators are under driven from standard IIRC, and i know that when i start my car at night, and then turn the lights on, and then try to let the clutch out with 0% throttle i can actually see the headlights dim down! And at night when i turn on my blinker i can see the lower part of the dash (DTE etc.) dimming in time with the blinker. The stereo doesn't seem to effect it only the lights.

Best of luck with your problems!

Yeh I have this too- can see things dim at idle with blinkers, power windows, etc.

I'm going to change fuel filter, it's due anyway. Also will change oxygen sensors seeing as they did seem to change how the car drove last night. May change the MAF too, depending on how much of a difference the oxy sensors make.

Ugh... at least it's not clutch or flywheel.

XR8AU2121 · 12-09-2010, 09:47 AM

Also check the the fuel pressure and the FUEL PUMP RELAY. My rough running disappeared when the fuel pump relay was replaced. Wasn't switching the fuel pump on and off correctly.

madmelon · 12-09-2010, 07:19 PM

Changed the fuel filter today. It was pretty clogged- difficult to force air through, unlike a new one. It seemed to help a bit- misfire now no longer evident above 1500rpm or so. Oxygen sensors seemed to have that effect too so it's looking more and more like a fuel problem. Perhaps pump is the next job.

Only problem is I've got 65L of Ultimate on board and be damned if I'm going to throw that away- but not driving the car doesn't use it... ugh

T3man · 12-09-2010, 08:11 PM

Why would you have to throw the fuel away?

madmelon · 13-09-2010, 02:27 AM

Who knows what sort of crap is at the bottom of the tank... it may be the cause of all these problems.

I think the service/repair book said tank shouldn't be more than half full to do the job... but still would prefer to clean the tank if possible.

RG · 13-09-2010, 10:33 AM

Quote:

Originally Posted by madmelon

Who knows what sort of crap is at the bottom of the tank... it may be the cause of all these problems.

I think the service/repair book said tank shouldn't be more than half full to do the job... but still would prefer to clean the tank if possible.

The fuel pick up doesn't collect from the very bottom so you'll be fine.

Have you checked the coil packs yet? These are consumables and only last about 80k before giving issues. If your car has done >100k then the oxygen sensors will need replacing anyway, I'd recommend NTK branded ones. About $60 a side.

If you haven't already pull the plugs and inspect them for cracks, or better yet replace them with BPR-5EFS-13 NGK standard ones @ $4ea. Leads also need to be checked if over 100k, A1 Hi-Performance in Perth can make a set of MSD for the AU for around $200 delivered.

FTe342 · 13-09-2010, 04:24 PM

A simple no cost test for the leads (and other electricals) is to run the engine in the dark and look for sparks shorting to earth. No sparks doesn't completely eliminate the leads but its a process of elimination and a good place to start