In the last few weeks both my wife and I have noticed occasional stutter/misfire under gentle acceleration. The first time this happened to me I was driving along a 40mph bit of road and had the headlights on, wipers on and radio on. I quickly turned off the radio, heater blower and wipers and the car returned to normal behaviour. Its since done the same thing even without much electrical load on the system, and seemed to be getting worse. Additionally, the automatic gearbox was getting even dozier than usual, often not kicking down, or flicking between 3rd and 4th (4 speed box) several times at a set speed.
I scanned for fault codes and there was nothing present. The engine management/check engine light didn't come on at all.
I have replaced the battery because the old one was wrong, underspec and old. The spark plugs were new 18 months ago, and its covered about 3000 miles in that time. On removing #1 plug, the end was pale grey/brown colour and gapped correctly to 1.1mm. There was no oil or other contaminants down any of the plug wells. The ATF was changed 3 times with ~100 mile intervals between (to get about 90% fresh ATF) in 2019, its done about 4000 miles since that, faultlessly. Since then it has not lost any ATF, the level is fine.
Its had an oil & filter change by me to the correct level within the last 2 weeks. Same oil I always use.
I took it for a long run last night, about 60 miles around my local backroads to give it lots of work through all gears. Its a mix of 30mph villages up to 60mph a-roads with stops and starts throughout. To begin with it behaved fine, but then the stuttering became evident after I tried to accelerate up to 60mph after a 3-4 mile stretch of 40mph. It stuttered and the gearbox wouldn't kick down until I gave the accelerator pedal a good push, it then kicked down and revved fine. It did this a few times until about 2/3rds of the way around the drive, when it started behaving fine.
By this point, I was down to about 1/8th of a tank so stopped and put 3 gallons of super unleaded into the tank to take the gauge to a bit under half a tank.
The car then drove perfectly the remaining 20 miles back home.
To begin with, I wondered whether the car doesn't like E10 fuel, it was brimmed with the stuff when fuel-geddon kicked off a few weeks ago and does few miles. My drive last night used up the last dregs of the full tank I slopped in when it was kicking off. Its run OK since putting fresh, premium into the tank (though not very far as yet). Was it a bad batch of fuel, or full of all the crap from the bottom of the petrol station filling tanks?
The car had been running OK on super unleaded, having put 3 gallons of super in the tank a few days later I threw caution to the wind and used it to drive 160 miles to buy a longboard for my daughter. This involved 120 miles of motorways and dual carriageways and about 40 miles of Wiltshire's finest B roads.
The car behaved impeccably, idle was smoother, no stuttering or misfires, it accelerated normally, even from 60mph overtaking trucks on the A34.
I've instructed the wife that if she ever fills it up, only use premium unleaded. Yes its £1.60 a litre round here, but thats cheaper than a new engine or a new car.
A few days later I lifted the Daewoo up and replaced the fuel filter. This went mostly smoothly, except for breaking the clip that secures the rearmost pipe to the filter itself as I tried to remove it. The new filter did not have clips included.
The clip is horseshoe shaped, and from some googling is GM part number 96434270 - looking like this:
It snapped along the curved bit, so I now have 2 'legs' detached from one another. To keep it all intact, I poked the 2 separate legs back into the hole in the end of the plastic pipe connector but would ideally like to secure it properly with a new clip. I rang Vauxhall and quoted the part number and they said they could get it for me and that someone would ring me back. They haven't, yet....
A few days later this got worse. Like, LOTS worse.
It began to buck and misfire like mad under load, especially uphill. revving it does not help, it stutters and misfires really badly. It threw the EML on and after reading the fault codes it came back with P0300 - Multiple misfire (geee, thanks... Insightful...) which on googling generally seems to be both severe and vague. A wonderful combination. Today was the first time its been so bad as to trigger the EML - it's been getting steadily worse over the last 3 months though.
Since this began to manifest I have changed the fuel filter to a brand new one, checked - but not replaced - the spark plugs. Its been run only on super unleaded which initially helped but is now worse than ever. It was serviced with new oil, filter and air filter within the last 500 miles. Oil level is fine, ATF level is fine. It got a new battery too as the old one was a bit weak. charging voltage is fine at 14.7v or so.
No sign of oil in water/water in oil. Gets up to temp and stays there.
The car only has very basic diagnostic capabilities, and I'm not getting any specific cylinder at fault. The misfiring is not consistent enough for me to pull plugs off while running to isolate it.
Some further Googling uncovered this: https://toyota-club.net/files/faq/lacetti_eng.htm
"But the most important, the most significant and most expensive problem of these engines - valves. It begins as the misfires at cold engine and appearance the nightmare of all the owners - P0300 error. In rare happy cases, the cause is in the ignition system, but for most it means a standard disease - the valve covered with soot deposits are no longer normally closed. It can be as a deposits on a working facet of valve head, and deposits on the valve stem, preventing it to move in the guide. The consequences of this failure are clear - misfiring, power loss, overheat of catalyst because of unburned fuel.
The defect occurs massively and irregularly, in a variety of operating conditions, at low and high mileage, several times... Rubbish about "poor fuel quality" - is just a cheap trick to escape from the warranty obligations - hundreds models of other brands use the same gasoline and do not even know the term "hanging valves", but for GM brands this problem is notorious since early 2000. However, Daewoo in 2005-2007 released several updated versions of the intake and exhaust valves, valve guides, authorize warranty repair, but the final solution to the problem did not happen. So owner must be ready at any time spend at least $250 for work and $250-300 for spare parts to cylinder head overhaul."
Ummm, that sounds an awful lot like the issue I was seeing, and a potential GAMEOVER scenario.
A few days later I called in to a friend and was able to borrow a compression tester to check the above scenario. Luckily, I don't think its the worst possible outcome. Measured from cold, all 4 cylinders read 220psi/15bar compression without needing to add any oil or anything - this suggests to me that the valves and rings are still good and the misfire issue is elsewhere.
Since I had them all out anyway, I replaced the plugs with the brand new ones I had here. I made sure they were gapped to 1.0 - 1.1mm as per the manual and with it all back together I took it for a drive. It seemed OK with the new plugs, the idle was smoother and it wasn't misfiring, though I wasn't able to go very far, or crucially test it driving up a steep incline.
The plugs I removed - which are all of 2500 miles/18 months old looked OK, there was a small amount of oil round the base of the worst one, but what I did notice was the electrodes were all covered with white deposits, rather than the usual orangey-brown. The tips aren't melted, though the insulation has browned a bit? The engine doesn't run hot (conversely, and due to another manufacturing novelty of GM Korea at the time, these don't run at 90c, at best it sits between 1/4 and 1/2 on the temp guage. The thermostat has been changed, its just the way these all are).
The timing should be fine, its had the cambelt replaced by a real garage within the last 3 years and they timed it up, its certainly no different to how its always been. I get no error codes for fuel mixture being too lean, but was running out of ideas.
The plugs (both ones removed, and new ones) are Bosch R6s which is what various motor factors recommend. There was no visible damage to the leads, and no error codes from the coil packs (except when I disconnected the 2x king leads when I was compression testing, which threw a code for each of the 2 coil packs - so I know they are monitored by the ECU and will throw error codes if they were faulty (which they weren't doing).
Frustratingly, this didn't help either. Next was to replace the coil packs as the misfire manifests most at low revs, and can be provoked by lifting off the throttle entirely at ~40mph, letting the car coast in D down to about 25mph, then trying to accelerate back up to speed. This is pretty much a surefire way to make it stutter to varying degrees.
Booting it when it starts to misfire usually clears it - unless going up a steep hill in which case it just seems to bog down and drop to firing on 2 cylinders (I think). It being a auto makes it difficult to drive around the issues, or at least harder than it would be if it were a manual when it could be left in a gear lower than normal and probably be about 80% better.
I checked the leads by going out at night and starting the car, letting it idle and lifting the bonnet to see if any arcing to ground was obvious from any of the leads. It seemed that all the electrons were staying inside the leads, there were no flashes evident, ticking another option off the rapidly dwindling list of potential root causes.
Next up was to get really messy. I removed the rear seat of the Daewoo and lifted the sikaflex'd on access hatch to get at the in-tank fuel pump.
Prior to this, I needed to play musical-cars to get two working cars onto the drive so they could be used, and the Daewoo into the garage where its dry and has lights so I could work on it. It had sat for 4 days, but was a complete pig to start, churning over fine, but not firing. Eventually it burst into life after very careful balancing of the accelerator pedal and settled into a normal idle.
Moving on, with the lid off the access hatch, I knocked the retaining ring round, unplugged the wiring harness, unplugged the two fuel lines and lifted the combined pump and fuel gauge assembly out. It dribbled fuel all over the shop, initially it was normal petrol colour, then it vomited some hideous dark brown muck all over the floorpan under the rear seats. Frustratingly, I couldn't see exactly where this foul grot had emanated from, but it was definitely from inside the pump housing.
Having removed the housing completely, I tipped it upside down into a mop bucket to see what colour the VERY EXPENSIVE premium petrol that came out was. Oddly, it was normal greeny-clear, with no bits or discoloured grot at all.
I then set about taking it apart to get at the filter element at the bottom. I was covered in petrol by this point so wasn't able to take any pictures - think of a teabag that pushes tight onto the pickup spout and you're about there. This was browny, and after removing the filter from the pickup pipe, I washed it in the clean petrol in the mop bucket and a load of gritty browny-black crud came out. I kept washing it in the petrol bath and it seemed cleaner now. Is this normal? The fuel I can see in the actual tank is crystal clear.
I left it all apart overnight as I had run out of time, but the following day I was able to reassemble the pump and refit it into the tank. My thinking was that maybe the in-tank pump filter was mega gunged up and wasn't delivering enough fuel to the engine, causing the misfire potentially. Incidentally, the pump thats in there had writing on the side, suggesting its a replacement from a scrapper anyway. The Sikaflex sort of backs this up...
With no real improvement after this work, and no useful fault codes to pinpoint what might be wrong I'm going to cut my losses now. Its a shame, as the engine has only done 50k miles (in 16 years) but its borderline undrivable right now. I only paid £700 for it 3 years ago and its been OK for most of that time, but this issue has me stumped. Its not consistent enough to pinpoint anything other than what I have already repaired/replaced and its not worth enough to keep throwing parts at in the hope it fixes the issue. So I've arranged for it to be scrapped and will be pocketing the £260 the metals yard is offering.
Running costs aside - which I'd have with any car - it's only cost me £540 plus about £50 in parts over 3 years which I'm not too upset about. Some people pay that every month to lease a car! I'll have to see what options I have for replacing the Daewoo with something with 5 doors and a decent sized boot for under £1000. Watch this space!
