Ye Olde HPi Misfire

[DaiRees]

Me again

Ages ago, James said that the slight misfire I'm experiencing might be a sticky cam follower, and that an oil change might cure it. Well I serviced the car on the weekend, she had a flush and is now full of brand new Total Quartz semi synthetic, but the misfire is still there....

I'll try to describe it for you. It only seems to do it under light throttle, and particularly when you just feed the powerback on after coasting. I've also noticed it when I use the cruise buttons to accelerate, say at the end of a roadworks. Been constantly bimbling along at 50 for a few miles, press plus to co up to 70 and she misses the odd beat or too. I only seem to notice it around the 2500 rev mark, say from 2200 to 2700. If you're "pressing on" it doesn't do it. Some days it doesn't do it at all, but it is definately getting more frequent and more pronounced.

I've also taken note of the suggestion that it might be the coil pack, but I'd rather see if there are any other ideas before I start spending money I haven't got. Any Ideas?

[puggy]

Am sure you have tried this Dai but have you looked under the bonnet when its
dark to see if you can see any flashes where something maybe shorting out and i
guess you have tried different plugs

[jameslxdt]

with the fault code reader you used to diagnose the egr unit, can you use it to read off live data?

[DaiRees]

I very much doubt it James. That reader is Neil's so I'll ask him what it does. Is this misfire likely to have stored any fault codes?

[DaiRees]

Sorry Puggy, missed your post.

Errrm, no I haven't tried looking in the dark, will give that a go. Yes it used to do it on the previous set of plugs too.

[steve_earwig]

Found a few ignition faults looking at it in the dark...

Tried a plug chop? Clean plugs, go for a drive, see if you can reproduce the symptoms, when it happens kill the engine and coast to a stop. Then whip your plugs and see if one's a different colour (you know the drill). It might tell you which cylinder to concentrate on.

[jameslxdt]

I very much doubt it James. That reader is Neil's so I'll ask him what it does. Is this misfire likely to have stored any fault codes?

well EOBD is rather annoying you see, as it will probably log a fault code, but something like 'random misfire', duh we already know that
so if you could read the live data it would make sense to go for a drive with it plugged in so you can see whats going on when it misfires

[DaiRees]

Right, sorry for the delay folks. Wasn't able to get hold of the elusive Mr Davies and his code reader for a while.

His reader won't do live codes, and there are no codes logged

However we noticed yesterday that there's an odd sound coming from the engine bay. With the ignition on but the engine not started there's a high pitched whine, as best as I can tell it's coming from this thing here....



What is that? I don't think it used to be noisy.

[Black Pearl]

The jobby you got circled there is the stepper motor for the throttle, it controls the butterfly valve that regulates the air/fuel mixture, on our cars mate, you will notice that the throttle cable itself is up by the main brake cylinder doing a fat lot of nothing but turning a variable resistor like you get in a scalextric set to control the speed of ya car. same thing here but instead of a plastic metro, it controls the opening and closing of that stepper motor you got circled there. The noise your hearing i hear as well, i can only think it being the motor " zeroing " itself before the car starts. When im just about to start mine it sounds very similar to the petrol pump on the back end of the car. Its not uncommon for the motor to make a noise, maybe with your misfiring it might be the throttle system not controlling the air/fuel mix properly. If so give the variable resistor on the end of the throttle cable a spray of switch cleaner, or WD40 and work it a few times. The motor there aint a great deal ya can do with that other than take the air filter pipe off and see if the butterfly valve is clean, then try with the engine running, and the air filter pipe off, rev it from the cable under the bonnet whilst looking at the butterfly valve, see if its moving freely and not sticking anywhere. Hope this helps mate

[DaiRees]

Does yours buzz for a few seconds after you switch the ignition on though mate, or does it keep squeeling? I'm pretty sure it didn't used to make this noise.

[jameslxdt]

The jobby you got circled there is the stepper motor for the throttle, it controls the butterfly valve that regulates the air/fuel mixture,

partially correct, the unit circled is the ETM or Electronic Throttle Module, instead of a conventional throttle cable controlling how much the throttle disc opens, then engine ECU decides how much it should open, depending on load, rpm, coolant temp, throttle pedal postition, to name a few, the reason its buzzing when you turn the ignition on is because its testing the potentiometers inside it and making sure it turns without resistance,
when these are at fault you dont get a misfire of any kind, just a huge loss in power
ideally you need to get some live data from when the misfire occurs as that will help a great deal
the only problem the HPi suffers with is the HP pump, and a misfire of this type is typical of the pump pressure being too low

[DaiRees]

How painful is that likely to be then James?

How do I go about getting the live data read? Is that stealer only?

[jameslxdt]

well my fault code reader can read live date, i also have a laptop and cable with software which can read live data with, so you could go to a stealer but if you ask them to just read the live data i think they will laugh at you, you would end up having to get them to diagnose the misfire, but if you buy your own fault code reader or the cables and software to use with a laptop you could do it all yourself

[Welly]

HP Pump trouble?




*lets out a small fart*

[DaiRees]

Oh yeah, you've had a HP pump replaced haven't you Welly. How much was it?

Something like this James? http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :IT&ih=020 I'm guessing that the PC interface type will give more detail than the handheld ones?