Club G40 Forum

Technical => Engine and Transmission => Topic started by: Lost_Cause on February 09, 2012, 10:00:29 pm

Title: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on February 09, 2012, 10:00:29 pm
Hey lads, always lurking around here soaking up the info, always searching hard before asking (as I've done now).
I know yer all sick of this question but after reading through every similiar post, i'm at my wits end.

3 weeks ago, I did the timing belt, water pump & got my head rebuilt (skim, valve stem oil seals, re-ground valves), put in a G40 Schrick cam (lift/duration unknown because I bought it about 6 years ago & can't remember), put it all back together with new inlet/exhaust gaskets, new thermostat housing, new blue & black temp sensors, & new CO pot. Fired it up, ran fine but advanced. Had to wait 3 days to time it fully due to not having a timing light.

When evetually timing it, did everything accordingly, (unplugged blue temp sensor, all the throttle blipping, set ignition timing, set idle speed, ensured CO pot was connected to correct connector, same for knock sensor, plugged blue temp sensor back in, revs dropped to approx 950-ish).

Car ran grand for around 3 days then developed a mis-fire. It doesn't happen at idle, just under load.
It's constantly intermittent (if ye get me?) but most apparent when accelerating at 1/2 to 3/4 throttle in 3rd or 4th below 3k revs.
She coughs,splutters, hesitates, sometimes producing no power & and actually dropping in revs regardless of throttle position.
Been doing this for approx. 2.5 weeks now.
Not so apparent on full throttle accelration & less so up around 5k.
Also, on cold start up, she's really lumpy for around 30secs. Again, it sounds like I'm down a cylinder. But after 30secs, it goes away until It's driving under load.

I've checked:
all earths, removed & sanded
boost leaks
vacuum leaks
hall sender being loose (relatively new distributor <5k miles)
points are clean
HT leads are magnecor competition leads (<5k miles)
Plugs look ok (Bosch platinum (<5k miles)
CO pot set to 600 ohms
ECU vacuum pipe untouched at 500mm

new alternator regulator & producing loads of volts
coil was replaced with a Seat Arosa item a good while ago.
fuel pump (< 15k miles)
fuel filter (< 5k miles)
Charger isn't torqued but belts are tight with around a 5-8mm deflection
sprayed a show of WD40 into the ISV in case it was sticking.

I've considered dirty injectors & have a set of standard G60 items on the shelf but are un-cleaned and slow to use them.
Threw in some Redex injector & fuel system cleaner yesterday because I did run the tank a little low 2 weeks ago but I'm sure the mis-fire was there before that.

I noticed the black rubber sheathing over the knock sensor has degraded & come off in all the work that was done. Is it possible it's receiving some kind of magnetic interference? Would magnetic interference even affect it?

Have considered the coil is breaking down again but not convinced because the thing that is getting to me is that it ran grand before all the major work, ran ok before the final timing (was advanced timed to 1500k for a few days, due to not having a timing light), & now it runs like a pig.

Everything appears to be plugged in & plugged in correctly. No apparent wire breaks (except at the blue temp plug- wires got bared from all the plugging & unplugging, but continuity to ECU pins is good & revs still rise when unplugged. Have wrapped a little insulation tape around them for time being).

The scuttle tray cover was left out after the final timing for a few days due to forgetting to replace it & not being able to retreive it from the garage where I did the work. In that time, the car got rained on alot. Is there anything in there that could have gotten damp that cause the issues. ECU damage maybe??

The rest of the spec is: R1 charger, standard airbox for road use, ashley manifold, de-cat, jetex exhaust.
There is a slight leak between manifold downpipe & centre section but again, hasn't cause problems before.

Any help/advice would be greatly appreciated because after finally getting it back on the road 5 months ago, keeping the revs down whlie trying to afford the work that's been done, I'm still afraid of driving it on & causing damage & yet more expense.

Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: PeteG40 on February 09, 2012, 10:15:57 pm
i personally would see if you can borrow a coil/leads from someone, i'm not convinced about magnecor leads and i know coils can just go at any time really.
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on February 09, 2012, 10:35:01 pm
Thanks pete,
Had the original coil go on me years ago when......'entertaining' a girl. It was about 3am, November night in a mountain forestry. Had to push the car 3-4 miles to the entrance because it was also an army artillery range that was going live in the morning. Not a night I want to remember really.

No-one I know locally has anything old enough to borrow them off, but I'll figure it out.
Would a continuity check on the leads reveal anything?
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: GR40 on February 10, 2012, 12:11:59 am
What you describe sounds like a cut out! I had similar problems in the past and turned out to be the three different thinks in 3 different occasions:
Exhaust leak. The car would have a small rattle at idle and hesitate under load turned out to be a small crack on the manifold that would leak in oxygen, thus giving the lambda false data and enriching the cylinders as soon as it was getting on temperature. Very tricky to spot.

Knock sensor shorting. If you have spotted a split on it, try some insulation tape and see if it gets shortened.

Water on the electrics. That one was a mess cause I never really found where the shortage really was. I drove really slowly across a pond that was formed on the road after an enormous rainfall and it seems that either my car seating very low got something wet or the fan was on and sprayed the entire engine. The funny part is I drove away just fine and the problems started the day after. I dried everything I could think of and a couple of days later it was fine.

Last but not least since your spark plugs are new you should check the coil. Even if it works fine at idle if the spirals have collapsed in it, they will short and drop the amps thus creating the problem on higher rpms or under boost. Try climbing the revs without going on boost, if it drives with occasional to no cut outs its probably the coil.

Sorry for my English, I am really tired at the moment and can barely think correctly, especially in a foreign language.
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: AlexG40 on February 10, 2012, 12:22:44 am
Have you rechecked your timing?
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on February 10, 2012, 01:16:33 pm
@Alex- Will check the timing as soon as I can get the timing light again.

@GR40- yeah, it is a cut-out problem.
Really don't think the small exhaust leak I have is causing the problem, it's on the de-cat section after the 4-2-1 manifold.
Had it before all the work & never caused an issue.

On the knock sensor issue, it's only the black rubber sheathing that has come away, the silvery lining is still in place & still intact. But will wrap it up shortly to rule it out.

The damp electrics are worrying me in case the ECU has become damaged & needs replacing.

With reference to the coil, it was always my understanding that the higher the revs, the harder the coil would have to work, thus at high revs, a problematic coil should show itself. But in my case, it's happening the worst low down the revs with gentle acceleration.

Took it for a spin this morning & concentrated on where it misses most. As I just said, it struggles & spits anywhere from take off to about 3k rpm. This is with gentle accelerating, nothing aggressive.
Something that happened agin earlier & last night (but last night I thought it was my imagination), that when searching for the worst point of the miss, at about 3k rpm in 4th, I just backed off a little when spluttering, then fed throttle back in again, no power, nothing, so I dipped the clutch & released it and she backfired 2-3 times.

I think this definitely points to a spark issue & not a fuel issue, so whilst not ideal, at least it means that I won't burn a hole in a piston. Famous last words.........

While I'm searching for a coil & leads, would it worth taking out the ECU & sticking it in the hot press to dry any dampness?
Would it be pointless?
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on February 15, 2012, 11:24:06 pm
Just an update,

Managed to dig out a set of old HT leads, only 1 of which was of any use, but from swapping out each individually, turns out no.1 cyl lead was the problem. Was one of my original thoughts, but because Pete said check it, I thought if he took the time to respond, only fair I check it. (Gutted now I have a horrible standard lead in place of a lovely red silicone one).

Everything else is still ok, timing was still spot on.
Split a piece of rubber hose & encased the knock sensor, just in case too.

She's still kinda sluggish so I advanced it a hair to allow for the cam, approx. 970rpm now, but no good.

Haven't found anyone with a 86c/6n to check the coil awhile so looking at changing the plugs, just in case.

With reference to a recent post here, Bosch Platinum W5 DP0 vs NGK Iridium BPR 7EIX (Ferrari Spec ones)
Cheapest I can find the Bosch are 55 for 4, posted whereas the NGK can be got for 30 for 4.

Does it really matter which??

Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: PeteG40 on February 16, 2012, 11:02:27 am
you ne ngk bp7evx if going for ngk- plenty folk use them - about £18 delivered for 4 on ebay
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Bucker on February 16, 2012, 07:02:27 pm
Sorry, but what is the mis-firing??  ???
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on March 29, 2012, 03:24:42 pm
Just a update for anyone that's interested, after changing out plugs,leads,etc. etc., I just decided to put back in the original cam. And low and behold, everything seems grand now again.

Reason for taking it back out was that I convinced myself that it either needed a vernier pulley to set-up 100% or it was the wrong cam I was given all those years ago.

Now, I bought it new at the time, off a dealer that supplies Schrick products, and I know there is a couple of different types of cams for G40s, with different lift/duration, depending on what you're after, but how can I figure out which 1 it is that I have?
If indeed it is even meant for my car.
Tried checking the cam for part numbers, but very little marked on it. 028 is the only real number on it. Tried googling and various sites, but no joy.

Any info appreciated,

Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Yoof on March 31, 2012, 09:47:26 am
Post a pic of it, will be able to tell if it's a Schrick or stock- does it have two positions for the woodruff key that the cam pulley uses?
Title: Re: Coughing, spluttering, mis-firing, etc.
Post by: Lost_Cause on April 02, 2012, 03:25:59 pm
It's definitely a Shrick, Shrick marked on the cam, even still have the box, (but nothing marked on it).
Yes, it has the 2 woodruff keys on it.