Misfire at idle - 1.4 16v BBZ

[LB123]

I think that's an 8v 1.4 engine. Somewhat different layout. TMB gives correct location and later bbz 16v engines with plastic manifold have it in pretty much the same place. Awkward to reach. Changed mine 4ish months ago when chasing similar fault.

I don't know what my fault was anymore than I know what yours is. I do know these engines seem very sensitive to even small intake leaks and throw an EPC light while still running virtualy normal and they also blow coils for a passtime.

[TMB]

4 hours ago, Xsr said:

 

 

Its underneath this thing. Take off the hoses and remove a couple bolts. And you'll find it plugged into the intake manifold with 2 bolts. Can't miss it.

Just use some electrical contact cleaner to clean it

 

That's all well and good but the engine in question is not an 8 valve. I've already posted the correct information 🙄

Edited 14 May, 2019 by TMB

[isambard]

So what is my best bet? Change the sensor or look for the air leak?

I haven't actually got a MAP fault code, just the misfire code

[sepulchrave]

Looking for a leak costs no money and won't take long, at the age these cars are now I'd be surprised if there were any left with the original vacuum pipework intact. 

[isambard]

Ok i will look for vacuum leaks first but I am not completely sure what I am looking for; am i checking all hoses from the throttle body to the intake manifold for holes/splits etc?

 

I just watched a youtube video of a guy spraying the various hoses with carb cleaner to find the leak (ie when you spray the leaky bit the engine will run differently momentarily). Is this the right approach?

 

Cheers

[LB123]

Visual inspection first. Torch and mirror needed so you can eyeball all round the hoses. Common for the plastic servo hose to split at its ends where it is stretched. Example below. Nice easy one to see. The other end was split underneath, hence the torch and mirror.

[isambard]

Thanks LB, will do my best to have a look this weekend

[isambard]

Hi all

 

Update time (not looked for any vacuum leaks yet!)

 

To recap above, I keep getting a misfire fault code on cylinder 3. Since the last fault code i have swapped the ignition coils in cylinder 2 and 3 over to see if the problem moved to cylinder 3.

 

This morning i was driving along and the check engine light started flashing and the car lost some power. I pulled up and the car was idling slightly rough.

 

I scanned the fault codes BEFORE turning off the car, and surprise surprise the fault was still on cylinder 3. I then cleared the fault without even switching off the engine, and it immediately began to idle smoothly. I took it for a drive and it was fine.

 

So what could be causing this behaviour? I suspect that i might ALSO have a vacuum leak which causes issues in hot weather, but surely what i describe above is a separate issue to that?

 

Thanks as always

[LB123]

You have eliminated the coil as the cause of your misfire. That leaves the wiring to the coil, the plug, the injector, the wiring to the injector and compression in cyl 3 still to look at. Should be a fairly quick deal to swap plug and injector to different cylinders and check again. I would have thought loss of compression was least likely to cause an intermittent fault (sticky valve, burnt valve, head gasket, bore wear or rings) so would concentrate on injector and plug for the moment.

 

Someone correct me if I'm wrong but I believe clearing a fault code also clears the ECU's learned adjustments for that item (or even all learned settings) so that may explain the immediate improved idle despite nothing having been done to clear the problem that registered the fault code.

Edited 18 May, 2019 by LB123

[Breezy_Pete]

I lost track of whether or not injector number 3 ever moved to another cylinder, if not that should be tried.

Compression test shouldn't cost much, especially if DIY.

[isambard]

Thanks guys, sorry i am slow at replying some times!

I will swap the injector as soon as i get a few minutes, and i will do a compression test at the weekend (will need to borrow the gadget from my parents' house.

The spark plug has already been changed as part of this issue, so i probably won't swap those around

I'll report back

[fabdavrav]

The wiring connection in the picture way back is correct...that's how multiple joints & branches are correctly done at factory......

 

 

However with the wiring directly on the cylinder head over time is suffers heat brittling….like the well known problem with the old 1.8T VAG engine coil pack wiring.....VW produced a repair kit for that old engine & I have done a mates car!.....

 

I recon yours has the same problem invisible internal break......so resistance test the wires

[isambard]

Thanks for the suggestion Fab. I will investigate it if i don't find anything from swapping the injectors around (this morning I have swapped injectors 3 and 4 so hopefully the misfire will shift)

 

I also had a good look for split hoses this morning. I disconnected the two red-circled ones and they looked perfect. I also disconnected the green one but i'm not really sure what that is; it doesn't look like a vacuum hose?

 

I'll report back as soon as the car does something interesting!

[Breezy_Pete]

Green hose is output from PCV system being fed back in. 

[isambard]

Hi all,

Update:

As mentioned i swapped the injectors on cylinders 3 and 4 on Saturday. On Sunday the misfire and check engine light came back, still on cylinder 3.

So i have now swapped/replaced the ignition coil, spark plug and injector for cyl 3 yet the misfire remains.

What should be my next course of action? Investigate the wiring as Fabdavrav suggests, or a compression test (which i didn't get done at the weekend), or something else?

Thanks as always!

[nige8021]

Compression test, this engine in the Polo is well know for burnt valves

[Breezy_Pete]

Compression test. 

[sepulchrave]

1 hour ago, nige8021 said:

Compression test, this engine in the Polo is well know for burnt valves

 

Not really, that's the 1.2 6V, not the 1.4 16V.

[nige8021]

27 minutes ago, sepulchrave said:

 

Not really, that's the 1.2 6V, not the 1.4 16V.

 

Nope the BBZ I've seen it on several Polo's have a look on clubpolo, the 1.2 6v that usually jumps a tooth on the slack timing chain

[isambard]

Hi all, finally got a compression test performed this evening:

 

Cylinder 1: 182psi

2: 181psi

3: 148psi

4: 186psi

 

So this looks like the cause of my problem!

 

Do i assume from this that the engine requires major repair/there are no explanations that are simple fixes/

 

Thanks

[sepulchrave]

You should drop a little oil through the spark plug hole and rerun the test to check if it's the valves or the piston rings.

[isambard]

Hi all

To close the thread, albeit unsatisfactorily, I have sold the car (without hiding anything!) and purchased a Honda Civic

Thanks all for your help; i hope to be back at Briskoda at some point in the future!