xr8 s111 Have i done a coil

[aussiemart]

Hey guys i was driving home tonight and i gave it a bit of a rev as i normally do when i backed off i noticed it was running very rough anyway drove it home and it seems to be down on more than one cylinder, i was thinking a coil but it seems to be two cylinders on one coil and one cylinder on the other. no strange noises just a miss.

any help would be great

Cheers Marty

[aussiemart]

just pulled all plugs out and it is cyl 1 2 and 5 which are on different coils, so i cant imagine it would be coils? they are black and wet the rest are light brown, was thinking valve springs at first but not on 3 cylinders at once?

[aussiemart]

Okay all injectors are pulsing and it seems to have good spark at those cylinders, better bring the comp tester home tomorrow:-(

This sucks

[b2tf]

If you have done a coil it will log a fault code but it has to do the entire coil if that makes sense. If one post isnt working but the rest are it wont log an error code.

[aussiemart]

cheers Mate, i meant to say the compression tester actually:(

[AU_Wagin]

I had a similar and intermittant problem like this and it turned out to be the fuel pump. The problem only occured if it was 1/3 or less full, fill up and the problem dissappeared. I looked at plugs and replaced leads, and tried coils, and no luck, then bingo one day when it was really bad, I just happened to fill up, and the problem vanished and returned later that day after a trip, so I first thought is was a temperature thing. Mine is a wagon, and I am not sure if the wagon and sedan pump is the same. put it is a of a job to replace the pump of a wagon
Raymondo

[b2tf]

Originally Posted by AU_Wagin

I had a similar and intermittant problem like this and it turned out to be the fuel pump. The problem only occured if it was 1/3 or less full, fill up and the problem dissappeared. I looked at plugs and replaced leads, and tried coils, and no luck, then bingo one day when it was really bad, I just happened to fill up, and the problem vanished and returned later that day after a trip, so I first thought is was a temperature thing. Mine is a wagon, and I am not sure if the wagon and sedan pump is the same. put it is a of a job to replace the pump of a wagon
Raymondo

Yours is the wagon with the T3 motor in it isnt it? If so, the pump itself is the same from memory as a normal XR8 but it is mounted in the tank on a different angle or something.

aussiemart my next thing to check would be leads.

[EvilChief]

Originally Posted by b2tf

If you have done a coil it will log a fault code but it has to do the entire coil if that makes sense. If one post isnt working but the rest are it wont log an error code.

not neccessarily, all secondary windings within the coil independant to each other, which means that individual windings can burn out and cause a misfire on only one cylinder

[5.0 ED]

the coil dianosing of the AU series is very refined, if the voltage at the output of the coil is higher or lower than expected the ecu read's it back from the monitored 12volts to it, when i had stuff leads on my car, it logged a fault for coil.

[BillC]

I had the same symptons. I changed the coil/leads and plugs but it made no difference. It turned out to be a broken valve spring. Do a compression test. If nothing else it will eliminate that. I was told on the very forum that it is quite common on the XR8's.

[aussiemart]

Thanks so much guys, i love this forum:-) i have a compression tester and a fuel pressure tester and will check tomorrow morning, would be surprised if its the springs due to 3 cylinders being down not one but will check anyway, i guess it should show up in a comp test since it idles like a pig.

Cheers marty

[aussiemart]

oh, i ordered msd coils, even if it is valve springs i still wanted to do the coils at some stage soon anyway, will have them monday $110 each thought that was a pretty good price.

one other thing the last few weeks my car has been flying like it has an extra 50kw dont know why or if it has anything to do with this but even at 15 kmh if i accelerate hard it lights up the tyres :

[5.0 ED]

That could be another sign of low fuel pressure, the factory tune is pretty rich, so when the fuel pressure drops off it leans it out and the car can actually make more power from it.

My au had stuffed fuel pump and it was actually causing my car to go harder as it leaned out, once i fixed the fuel pump, it went back to normally.

Could also be though that the ecu has detected whateva fault it is and gone into limp mode giving it 30degree's timing all round. Or that cause its not firing properly on those cylinders that the self tuning has compensated, and yes it does definetly compensate full throttle, but only to the equivalent amount that the last position before full throttle was read at.

Anywhich way im only guessing and really it could be anything.

[aussiemart]

Thanks mate, i also have a fuel pressure tester, any idea what reading i should be getting? will do a comp test now and will report back with those findings

[EvilChief]

30 - 35 psi at idle and up to 50 psi under full throttle

i qouldnt get too excited over actual psi numbers as long as they fall into the above scope, however best indication is, whilst driving and u accelerate from low speed in 2nd gear (ie 15 - 20km/h) under full load (full throttle) and ur passenger sees fuel pressure increase and then suddenly drop off in higher rpm. that should not happen ;)

[aussiemart]

thanks mate

[aussiemart]

showing 4 bar at idle which i think is about 58 psi?

[aussiemart]

okay just checked the compression on the cyl with the cold extractor pipe and the wet plug and it shows 175psi which i think sounds real good

[aussiemart]

Cyl no one started of rising on the gauge then stopped at 50psi, i let the pressure out and tried again this time nothing:-( so im guessing a broken valve spring, maybe the compression can sometimes close the loose valve and thats why i got an initial reading?

better pull manifold and covers off. anyone know what springs are good and were i can get a on car spring compressor in vic?

[5.0 ED]

yeah comp sounds good, but that fuel pressure sounds rather high, should be 3bar with no vacuum on it.

pull the vacuum line off the reg when testing it, to get a proper reading of what it's set at.

[aussiemart]

mm you may have missed my last post?

[5.0 ED]

I have one but im in romsey, you can make one yourself if you have a mig and spare rocker arm.

Yeah i missed your last post

[aussiemart]

Hey mate, i have a mig and a spare rocker, you wouldnt have any pictures of it would you, if not no probs i should be able to make something, thanks for the great idea mate:-)

Cheers Marty

[5.0 ED]

What you do is cut the end of the rocker arm out so that its not pushing on the valve at all, and is pushing on the retainer, get a piece of strong straight steel and weld it to the otherside to use as a level.

you bolt it down on car, put air fitting into cylinder and fill with air, careful as engine will turn over, you tap retainer with hammer to break the collet lose, you then you use the arm to push the spring down, remove the collets and release.

It actually works very well.

[5.0 ED]

A magnet rod thingy could come in handy for removing those collets too, bare in mind when you make it that you have to get the collets out around it. And whatever you do, don't drop the valve inside the engine. Thus the air pressure.

[aussiemart]

yey cheers i have done plenty of spring changes just not on the car, i will use the comp tester hose for air line fitting and put the car in gear with piston at tdc, any idea on valve spring? do you know if the herrod ones are anygood? or the crow ones,although i was thinking the crow ones may have been the ones ford used for these engines.

Cheers Marty

[5.0 ED]

I'm using crow, herrod's stuff would most likely be crow with a more a bigger price tag, i wouldn't put car in gear if i was you, it would most probably move it.

Don't stress too much about dropping valve into engine, it still has to get past valve stem seal etc if you break the air pressure, which is a lot of force in their holding it closed, and if it does break it, you'll notice it will very quickly close the valve again.

[b2tf]

Herrod dont make valve springs, they used Crow ones in the AU. I have Edelbrock springs in mine but the crow ones will be fine.

[aussiemart]

Here is the problem child :

[BLACKAUXR8]

Im suprised mine hasn't done any yet? I never heard of this being a problem in these? Thanks for sharing the problem aussiemart. Good to hear you found the problem pretty easy