Coil pack XE poor running fault at idle/low revs

[Pitstoppete]

Righto guys,
I have finally broken the Cav! or it's bust itself...it's been basically a very good boy for about 45000 miles since we put it in, I rebuilt it all from all good stuff maybe 5 years ago now, it gives proper power, pulls hard and can do 40 mpg commuting.

It's still driveable though, if I get me trotter down hard!......please read on!

Cylinder 4 is asleep - or not doing a great deal at idle and off of load.

It started running strange a week ago and the stink of the exhaust and wobbly idle made me dive right in and get a new bosch O2 sensor, as it did what seems much the same as that before and a new O2 sensor sorted it. Fitted that and reset the ECU with the battery off, that changed it a bit I'm sure, but it felt better maybe for the ECU reset. Still weird idle though...

When it's cold/warm or hot it's idling really lumpy on 3 cylinders, so the second thing I did was use my IR thermometer on the manifold, and at idle with a few throttle blips we have like 200 deg C on 1/2 and 3, then 50-60 deg C on down-pipe primary no. 4. well weird.

There's no fault code light and on my commute its doing decent MPG, it just dont like idling/progression..

Go for a roar, get it hot, get out quick and check again with the IR thermometer and we have much the same temp on all manifold primaries, like 300+ deg C all the way across all 4. It goes like stink on load, revs right out and is really smooth, unless you slow right down to 1000-1500 ish and try to go slowly.
Now the obvious comment I'm sure I'll get is give it death everywhere! And I would If I could I can assure you! but that aint going to help...

So, seeing as cyl no.4 seems to be at fault I have wound into swapping out everything I have, to see If I could sort it -

Compression test was 200/220/235/215 cold, 230/220/210/225 hot. cant see anything mad there...
Plugs changed for both new then old GM ones then swapped about between the cylinders. no change. 4 is clean and a bit damp after idling. rest are normal.
HT lead swapped, no change. massive fat spark when lead is pulled off when running.
Coil pack swapped, no change. I was sure it'll be that. fail.
Cleaned ICV/AFM. ditto.
Buzzed out CTS. seems correct resistance. 1.5meg warm IIRC.
All injectors same resistance. listened to them all using a long screwdriver. all 4 have a proper click click click sound going on. swapped them round anyway and tried a spare one, no change.
Looked into all the wiring connectors at the injectors/ICV/CTS/IGN Amp/Cam sensor/Throttle pot/AFM etc etc, all good.
Swapped the ecu for another correct PT code one, no change there either.
New O2 sensor, like the old one is sooty, showing the unburnt cyl. 4 fuel I suspect.
Knowing it would do nothing I've just swapped the fuel rail/regulator assembly too, to no avail.
Also as it has had some/a quite loud tappet/s now and again that I haven't got round to changing for the new ones as yet (probably one I couldn't get apart a couple of years ago when I cleaned them) I had the lid off and checked the cam buckets/cams. Everything inside seems fine and clean as the proverbial. The tappets turn when the cam is off them, they are close to the cam lobes like the rest and dont seem to be flopping up and down which I thought could happen if a tappet had died internally..

I have another coil pack engine loom from the Calibra I broke (which needs a bit of tidying up and one repair to the broken IAT wiring that's pulled out of the plug) and I could try swapping that out too, as that seems to be the only thing I've not swapped as yet. Or I could swap the tappets for the new ones too.

It seems strange that I could commute to work tomorrow and max it out in forth again at the end of the speedo, but it wont idle on all 4 frigging cylinders.

So has anyone got any other ideas?

[vectra640]

blimey, changed a lot there and still no joy, maybe its cam timing, just a possibility

[Vinci]

What GM code head is that?

[Astra Dan]

CTS is a bit high:

15-30 degs C = 3300 ohms to 1450 ohms
80 degs C = 260-360 ohms

[Pitstoppete]

will double check both those details boys.

[Vinci]

CTS is a bit high:

15-30 degs C = 3300 ohms to 1450 ohms
80 degs C = 260-360 ohms

AFAIK the coilpack engines have the black CTS, not the blue, and they have different curves!!

EDIT: Checked, these are the right values for the black sensor (M2.8), blue sensor (M2.5) seems to have lower values all over... (making ECU think the engine is hotter than it really is...)

[Pitstoppete]

yes. as I say I am going to retest the CTS before work tomorrow when cold and just up the road and when at work, get a set of readings. thinking back, after it had been running a couple of mins it was 1500 ohms, which seems believable.
it did have a black sensor ages ago (as the engine was out of a Nova XE, which was out of a 93 Astra GSI) then swapped it out for a blue one when I thought I had a different minor problem to this one. The car has had a few o2 sensors, mostly due I fear to me using cheapo halfords ones to start with and taking a while to learn my lesson. I can't see how the cts can effect one cylinder and only at low revs, if you are thinking this could be at fault.
more tomorrow night after the commute.

[Vinci]

If it had a black sensor it HAS to have one again....

[Pitstoppete]

why was it fine last week with a blue one then?

[Pitstoppete]

will double check both those details boys.

this am cts was 4.4K freezing cold
then 380 ohms hot.
both typical values it seems and haven't changed since last week suddenly....

[Vinci]

why was it fine last week with a blue one then?

Lambda will correct most of it, could be a combination problem. I've seen many reports about problems with the wrong ECT sensor fitted...

[Pitstoppete]

i'm hearing that fella.
cant understand why it was alright weeks ago, then started running on 3 on a year old o2 sensor, change the sensor, same problem, with nothing else changed.
if i can find this mythical black sensor I can try one, but in theory a new blue one would be no different

[Vinci]

It is very hard to find decent info on the subject, the Germans are all moaning about with/without AC that make the difference between the sensors... In Autodata the M2.5 and M2.8 describe different temeratures and resistances, but when the values are interpolated it seems they aren't that different at all, there is some overlap at least.... It is likely both sensor can work and can perhaps be programmed properly in the ECU for the tiny differences they might have.

This is what Autodata says, maybe someone can place the values in a curve:

[paddy>gsi/turbo]

vinci will post that video tomorrow.

pitstoppete have got probs myself with my gsi hard to start from cold then misses upto 3k revs.changed loads got my cts from gsf car parts blue type.black type was fitted.
watching thread with intrest.

you tried fuel reg? going to ring vauxhall tomorrow ask about cts sensor.

[Vinci]

Cheers Paddy, love to see how you've done them up!

Here's what the germans say on a forum:

Black "without AC":


Blue "with AC":


From here:
unterschiede Temperaturf*hler blau, schwarz

Lots of them reporting after that though they are using the blue one while their cars don't have AC...

What I found very interesting is the black one apparently earths on the block and uses two NTC chips, while the blue sensor is isolated from the block and earths through the wiring. Maybe that explains some having problems and some don't have any, because when the black sensor is used instead then one chip may become bypassed and the value effectively halved....

[Pitstoppete]

successful day at the garage.

Car has been off the road for a couple of weeks pending time and a sunny day for Dan and I to get stuck into it.

Cracked on today, buzzed out the wiring from ecu plug to everything! before we cold started it and came to the conclusion as there were no fault codes when it was running on 3 before, it was "a mechanical" problem, not sensor related. This we rolled with and started to check everything we could, even taking the cams out and checking all was well under the tappets, which I wanted to change anyway, as I had a rattly one for ages and had a new set ready to go.
Went for a cold start and it's still on 3 when cold or hot and compression was again good. No# 4 is just burning.

Had another brew and fired it up again, wtf..
Gentle sucking noise from around the inlet manifold area, hard to hear with the open air flow meter giving it large, sucking away too.
Shoved digit near the gasket join.....O bugger, it's sucked in my vinyl glove!
Gosh! wheres the inlet manifold gasket gone from around no# 4 runner?




sucked in the cylinder no doubt!

Note to self and others - dont use std nuts on the inlet manifold, use locking nuts like VX intended....

Loose manifold=knackered gasket=air leak=poor running and lots of scratching of heads.

Now it's back to it's old self and is a rocket-ship once again...well, at least compared to a 1.6 auto one it is anyway.

thanks for the help and comments guys and well done Dan for the buzzin out and spannerings.