Technical Squirrely acceleration around 1800-2000 rpm

[gadb]

Hello,

I have a 2008 1.4 16v 500 and have recently had some issues with squirrely acceleration (engine is definitely missing). The engine starts fine and doesn't sound like it's misfiring when idling. However when out on the open road, if I pull out and put my foot down to accelerate, the acceleration is jerky and soon after an amber flashing "check engine" light comes on. Once things settle down (after about 5 seconds) the warning light goes out.

I've replaced all the plugs with Bosch Super-4s. After which things seemed to improve for a short while, but then reverted. I've tried Liqui Moly Injection Cleaner in half a tank of fuel and again things seemed to settle down, but then reverted again as soon as I filled up again at the supermarket (I confess, I always buy the cheapest fuel I can find, which is nearly always the supermarkets').

I've plugged in MultiECUScan and the only two error codes listed are:
P0300-98 - Ignition failures (generic), Component or system over temperature, Present
P0303-98 - Cylinder 3 ignition failures, Component or system over temperature, Present

The car is obviously fairly old, although otherwise in good nick and low mileage for the age (60k). I have done a cam belt / water pump change recently, but this issue predates the change so I don't think it's that.

The oil and coolant levels are ok and the air filter was changed recently (it had a major service about 12 months ago).

I wondered if it might be either the coil sitting above the spark plug or the injector. Thought I might swap coil 1&3 and injector 2&3 and see if the problem moves to a different cylinder. I've no idea how to take the injectors out though and can't find any "idiot's guides" on the internet sadly.

Any ideas / help would be gratefully received.
Many thanks,
Graham.

 

[DaveMcT]

Remove the exhaust manifold cover.
Soaks the rusty metal in water
Start engine and watch the water boil off as the manifold heats up. This that stay wet for longer probably have faulty coils or the trigger wires have failed.
Let it cool down and swap a suspected boil with a good one. If there’s no change it’s not a coil. If the problem moves you’ve found a failing coil.

 

[John202020]

Whilst not the same as we have no errors, our 1.2 almost 100k 09 car has a distinctive "rough" spot at 1750 to 1900 or about 30 in 4th and it's impossible to hold the car revs stable whilst stationary above 1000rpm over 1000 a minute increase causes the engine to slowly climb to 3800 or so a fraction off and its back to a stable 1000, drives normal

 

[gadb]

Thanks for the suggestions. I'm really suspicious of the injectors and would like to get them off and take a good look at them (i.e. check the spray pattern). It looks like a complicated job getting them out though. Does anyone know of a good howto / tutorial that would help me with this?

 

[gadb]

Remove the exhaust manifold cover.
Soaks the rusty metal in water
Start engine and watch the water boil off as the manifold heats up. This that stay wet for longer probably have faulty coils or the trigger wires have failed.
Let it cool down and swap a suspected boil with a good one. If there’s no change it’s not a coil. If the problem moves you’ve found a failing coil.

Thanks. Does the existence of the P300-98 code along with the P303-98 indicate that more than just the 3rd cylinder might have an issue?

 

[Ralf S.]

If the car thinks there is an ignition issue, then it's most likely to be a duff coil.
Try swapping the coils - it's the easiest and cheapest investigation option.

A dodgy injector would just work badly, and the ECU won't know whether it's giving you a saucy spray or a dribble, so you wouldn't get any error codes.


Ralf S.

 

[chris3234]

Petrol injectors rarely have issues if look at the coils first

 

[puntodeltathema]

Yes sounds like one or more of the coils to me. Had this on a Panda 100HP recently (same engine) and a couple of strategically placed new coils sorted it. Bit odd that more than one should fail at the same time perhaps but the plugs had never been changed so I wonder if excessive spark gaps had placed strain on them...

 

[gadb]

You're right, it's the number 3 coil. Was sure it had to be the injectors because I use supermarket fuel, filled it up from a jerry can once, can never smell petrol from the exhaust and the way the power gets twitchy when overtaking at 50-60, together with the "over temperature" seemed to suggest one/more of the cylinders wasn't getting enough fuel.
However, swapped coils 1 & 3 (leaving those hard to get at injectors well alone), wiped the error with MultiECUScan, went out onto the A20, floored it in 6th from 50mph up to 70mph and check engine light starts flashing again. Get it back home and lo, the error has moved to cylinder one.
I, too, hadn't changed the spark plugs since buying it and don't know how old they were. But I've recently just gone over 60k, so they may have been overdue. If aged plugs can cause coil problems, then this might have been a factor for me as well.

THANKS FOR ALL YOUR HELP!

Fingers crossed the issue resolves once I stick a new coil in.

Interestingly, I tested the resistance across the 1 & 3 pins on the bad coil and found them to be 1.0 ohms (I think that's the expected value).

 

[DaveMcT]

The catalyst cleans up excess hydrocarbons. A faulty coil increases the O2 in exhaust, the ECU sees that as running weak so richens the fuel mixture. That soots up the combustion chambers making any misfire even worse and ruins your miles per gallon.

The water on cold exhaust manifold test will tell you which cylinders are warming quickest. An IR thermometer is better.

 

[John202020]

You're right, it's the number 3 coil. Was sure it had to be the injectors because I use supermarket fuel, filled it up from a jerry can once, can never smell petrol from the exhaust and the way the power gets twitchy when overtaking at 50-60, together with the "over temperature" seemed to suggest one/more of the cylinders wasn't getting enough fuel.
However, swapped coils 1 & 3 (leaving those hard to get at injectors well alone), wiped the error with MultiECUScan, went out onto the A20, floored it in 6th from 50mph up to 70mph and check engine light starts flashing again. Get it back home and lo, the error has moved to cylinder one.
I, too, hadn't changed the spark plugs since buying it and don't know how old they were. But I've recently just gone over 60k, so they may have been overdue. If aged plugs can cause coil problems, then this might have been a factor for me as well.

THANKS FOR ALL YOUR HELP!

Fingers crossed the issue resolves once I stick a new coil in.

Interestingly, I tested the resistance across the 1 & 3 pins on the bad coil and found them to be 1.0 ohms (I think that's the expected value).

Use Iridium plugs not standard

 

[gadb]

The catalyst cleans up excess hydrocarbons. A faulty coil increases the O2 in exhaust, the ECU sees that as running weak so richens the fuel mixture. That soots up the combustion chambers making any misfire even worse and ruins your miles per gallon.

The water on cold exhaust manifold test will tell you which cylinders are warming quickest. An IR thermometer is better.

Cheers. I'd noticed my that mpg had dropped from about 45 to 38 (I use E10). When I read your post I had a look at removing the heat shield, but the bolts are so rusted I thought if I so much as went near them with a wrench they'd disintegrate and I'd never reattach the heat shield. I find rust is a bit of an issue with a few fittings here and there, but I'm loath to use grease on the bolts due to the affect on torque settings and gunking up the thread.

 

[gadb]

Use Iridium plugs not standard

Alas, it will have to be next time. The idea of messing up the spark plug threads fills me with dread.