General Hesitation on acceleration day after filling washer bottle

[Sverige]

Thanks for the diagram flisko. Looks like my plug is "carbon fouled".

I cleaned the HT leads up and gave them liberal CRC 5-56 coating. Then popped the old plug back in with 15Nm of torque as I didn't want to over do it. Just wanted to test what difference cleaning the HT leads made.

Car started with a loud "pop" sound? Didn't sound like a backfire. Ran briefly ok on 4 cylinders then started misfiring, dropping out to three cylinders with the engine shaking as out of balance. More worrying was after 30 secs or so I smellled the burning rubber smell - what can that be? Something electrical overheating??

Not at all convinced at this point that this is down to old spark plugs but I understand I should change them anyway as so old. Anyone ideas on what the underlying fault may be, or is it still most likely plugs or ht leads?

I'm due at the supplier in under two hours and need to decide whether to buy just spark plugs or ultra expensive ht leads also (704 Swedish kronor -about £65 for the leads).

 

[Brendan W]

Could you swap a coil and see if the problem moves ?

 

[Sverige]

But I don't know which cylinder isn't firing currently, how can you tell?

 

[andydiver]

Simple first, change the plugs. You say they are very old and are certain to give your symptoms if not in good order so relax a little until new ones are in.

 

[Sverige]

Ok thanks Andy. I'll try that first. Think I'll leave the expensive HT leads with supplier until I've tried the plugs first. Like you say, maybe that'll fix things and I can relax a bit.

Have been reading scary threads on here describing same symptoms as caused by head gasket, but too soon to jump to that conclusion

 

[Sverige]

Just back from the car parts place. The original fit item was ngk dcpr8ekc. They have sold me ngk dcpr8e-n. Is that ok? Only difference I can see in the specs below is on the -n version the spark position is 3mm compared to 4.7mm on the ekc?

 

[judderbar]

My plugs are from 180,000km and on 245,000 now. They look very good. I have set the gap a few times but it has been so close it was not really necessary. Presumably computers enable the spark to be as small as possible for good ignition? Spark is fairly puny compared to old style arrangement but no problem starting or running.

Original leads.

>>ngk dcpr8e-n I think I have those. Got it written on a piece of paper here but not sure they are the ones fitted. I will check later today

 

[Sverige]

So I changed the plugs. Seemed better at first startup but then soon the engine was juddering again. Open to more suggestions please! I'm going to research Brendan's comment above about swapping coils as I misread this as cylinders earlier. Not sure where my coils are or how to swap them but will use forum search / google.

Below image shows the plugs I pulled out, arranged in the same order as the cylinders as you look at the front of the car. Would the blackening on second from left indicate this is the one which has been misfiring?

 

[Sverige]

Ok, I believe the coil pack is the unit the HT leads plug into. If so, I don't have one with two plugs which can be swapped as Brendan suggested. Mine has 1 input plug with four outputs. This is what I have.

 

[Brendan W]

I would assume that cylinder is the problem one.
Might be worth looking at the wiring to the injector and maybe swapping the injector.
A misfiring cylinder can be found by a cooler exhaust outlet.
Yeah I just remembered you have the 16V with the single coil thing.
Does the 16V have the wasted spark system?
If it does you could swap the HT lead with the cylinder that is paired with the suspect one.

 

[Sverige]

I would assume that cylinder is the problem one.
Might be worth looking at the wiring to the injector and maybe swapping the injector.
A misfiring cylinder can be found by a cooler exhaust outlet.
Yeah I just remembered you have the 16V with the single coil thing.
Does the 16V have the wasted spark system?
If it does you could swap the HT lead with the cylinder that is paired with the suspect one.

Not sure if it's a wasted spark system, but if it is does that mean I could swap 2&3? I could try that and also look into where the injector wiring is. Any reason why I'd need to disconnect the battery negative before unplugging an injector? A YouTube vid I checked out earlier stipulated this. Not sure why.

Will look at it again tomorrow. Still wondering where the burning rubber smell comes from?

 

[judderbar]

my 16v has DCPR7E-N-10 which means nothing to me but when i go to the supplier they list a hotter or colder plug. The ones I have work so I have left them alone.

Since you are running on only 3 cylinder you can just take the lead off the suspect cylinder and expect to hear it sound the same. You only have two control wires for the combined coils so that means you are using the wasted spark system like my 16V. Two cylinders spark at the same time but only one is on the compression/power stroke.

Firing order, with the numbering going from left to right as you face the engine is 1 3 4 2. 1 is on the same coil as 2 and then 3 and 4 are together on the other coil.

I am assuming it will not be easy to start changing the positions of the plug leads on the coils due to the short length of the plug leads and coil control wiring. You then have to consider that a new coil pack is 'only' about 30 euros and if it makes no difference you have a spare if you ever need it.

 

[Sverige]

Thanks Judderbar. I might be able to swap the leads at the coil end, as the connections are close to each other. Will try it tomorrow.

If each coil is feeding two cylinders isn't it the case that a coil problem would take out both cylinders? All I know is the car is running lumpy, I wouldn't know it's running on three or two cylinders, but presuming it wouldn't actually run if only two are firing.

So on that logic it points back towards a bad ht lead? If so, and if I can swap them and use Brendan's trick of touching the exhaust header to see which isn't firing, then I might be able to narrow this down a bit further tomorrow.

I also have Ross-tech VCDS software and interface cable, which is really a vw audi diagnostic tool, but some google results suggest it might function as a basic obdII reader on a Fiat. So maybe I can try that to see if there's any error code which will give me a clue.

 

[judderbar]

Thanks Judderbar. I might be able to swap the leads at the coil end, as the connections are close to each other. Will try it tomorrow.

If each coil is feeding two cylinders isn't it the case that a coil problem would take out both cylinders? All I know is the car is running lumpy, I wouldn't know it's running on three or two cylinders, but presuming it wouldn't actually run if only two are firing.

So on that logic it points back towards a bad ht lead? If so, and if I can swap them and use Brendan's trick of touching the exhaust header to see which isn't firing, then I might be able to narrow this down a bit further tomorrow.

I also have Ross-tech VCDS software and interface cable, which is really a vw audi diagnostic tool, but some google results suggest it might function as a basic obdII reader on a Fiat. So maybe I can try that to see if there's any error code which will give me a clue.

Sounds like you are progressing. The ross tech cable and software might work to connect to the engine ECU. However, there is a specific free software for fiats called multiecuscan that will connect to the engine ECU with your cable.

http://forum.multiecuscan.net/viewtopic.php?f=5&t=255&start=10

So you can get your misfiring codes with that cable but to read all the other ECU's the cable needs modifying as per that link.

Just disconnecting one plug cable at a time is going to give you information about your engine before you have to start messing with the coil connections.

I suppose it is possible that a weak cylinder might fail more often with a weak spark than a better cylinder with a weak spark? So potentially a new coil pack can help.

 

[Sverige]

Well I didn't manage to get the multiecuscan software to work with my cable. The cable talks direct via USB to vcds software rather than via a com port. Ross tech do provide a virtual USB driver to simulate a com port but even that was not working, so I still haven't been able to scan for codes.

I ran the car with ht leads 2&3 swapped at the coil pack and with them in normal orientation and in both cases it runs the same. Starts normally then starts missing on one cylinder when the engine is warm. Still cannot tell which cylinder isn't firing - is it safe to pull an ht lead off one of the cylinders while the car is running? That would tell me as I could pull the lead while it's running on three and if it runs the same then I know the lead I pulled was the misfiring cylinder.

Brendan's trick of touching the exhaust header isn't working as the engine is already warm by the time it starts misfiring, so all four exhaust ports still feel hot.

 

[g8rpi]

Well I didn't manage to get the multiecuscan software to work with my cable. The cable talks direct via USB to vcds software rather than via a com port. Ross tech do provide a virtual USB driver to simulate a com port but even that was not working, so I still haven't been able to scan for codes.

I ran the car with ht leads 2&3 swapped at the coil pack and with them in normal orientation and in both cases it runs the same. Starts normally then starts missing on one cylinder when the engine is warm. Still cannot tell which cylinder isn't firing - is it safe to pull an ht lead off one of the cylinders while the car is running? That would tell me as I could pull the lead while it's running on three and if it runs the same then I know the lead I pulled was the misfiring cylinder.

Brendan's trick of touching the exhaust header isn't working as the engine is already warm by the time it starts misfiring, so all four exhaust ports still feel hot.

The Rosstech lead should work with MES but you need to look at what virtual comport the driver puts it on. You can do this using windows device manager.
Yes, you can pull a single lead off but in a wasted spark system it will cause both cylinders to stop unless you let the disconnected lead spark to ground. Ideally connect it to a spare plug with the body of the plug connected to ground.


Robert G8RPI.

 

[Sverige]

Thanks, it was com7 which was assigned to the virtual driver and I selected the same in MES. I'll look at the com port settings to see if speed, etc is adjustable.

So it sounds like I could pull one ht lead and connect one of the old spark plugs to it and leave it laying on the exhaust shield then run the car to observe the spark to see if it dies when the car is warmed up. I could try this with each cylinder and if the car stalls when warmed up it would be a clue that one of the three "live" cylinders has started missing (as I suppose the car will idle lumpy on three but not run at all on two cylinders?)

Only if the ht lead I've pulled belongs to the cylinder which has the misfire problem would I expect the car to remain running on three cylinders even when warmed up. Does that sound like a reasonable plan?

 

[Brendan W]

Only if the ht lead I've pulled belongs to the cylinder which has the misfire problem would I expect the car to remain running on three cylinders even when warmed up. Does that sound like a reasonable plan?

If a cylinder is completely dead, pulling the lead will not change the running. However if the motor is jumping the spark is intermittant and pulling the bad one will stop the jumping.

 

[Sverige]

Well today I changed the HT leads and so far it seems the problem is fixed, so it looks like the "burning rubber" smell was a side effect of one of the leads having a high contact resistance. I'm glad it was something simple after all.

Maybe I could've got away with not changing the spark plugs, but you can't begrudge a car a new set of plugs every 17 years or so, eh?!

Huge thanks to all of you who helped with advice in this thread. The tip from Judderbar about the click-R pliers was especially useful as those clips went back on very easily with the right tool, and I would probably have broken them struggling to bodge them back together.