Fueling issue - failed emissions

[28hodge 22]

Having a fueling issue. 1.6gti basically stock engine and injection system.
 

Went to MOT it yest and failed on emissions. Badly, co is fine but hydrocarbons are 4000-6000ppm and all over the place. 3 plugs look fine plug nearest the cam is sooty. compression is all good and 150psi ish across all 4. Valve clearances all in spec. I had the plugs out doing the compression test and when I looked down the bores afterwards there was a pool of fuel on cylinder next to the cam (cyl4). I thought a stuck leaky injector, and it’s a bugger to start once hot and takes maybe 5-10secs of cranking to get it to start, so that would make sense, but it always does/will start.

 

So I have changed cyl4 injector for a spare  and initially it ran much better with zero hesitation from idle and not sounding like it had a slight miss. 

 

However after 10mins it seems to have done the same and if I remove the plugs and crank it over I again get a pool of fuel on the top of the piston of cyl4. And it’s not liking starting same as before once hot.

 

So I’ve now swapped the fuel rail and pressure reg for spares I have along with swapping out cyl4 injector again for another spare. It again seems much better and starts from warm a lot easier!

Can a faulty pressure reg cause over pressure and damage/cause a injector to weep? Seems odd I’m having a problem with cyl4 injector regardless as to what injector I have in there.

Original injectors were sent to be cleaned etc 1500 miles ago ish. About 2 years ago.

 

Starting to stress as we have grizedale stages next weekend and MOT ran out today!

 

Anyone any ideas I have a spare ecu afm and a new coolant temp sensor I could try next. I’ll take it back to the garage tomorrow and see if changing the injector rail and prv has helped at all.

[SRDT 146]

Injectors are batch fired so it shouldn't be the ECU itself.

Take a look at the wiring harness, maybe just disconnecting the injector is what fixed it and after 10mins heat and/or vibrations brought back the fault.

[welshpug 1,622]

9 hours ago, 28hodge said:

 

Can a faulty pressure reg cause over pressure and damage/cause a injector to weep? Seems odd I’m having a problem with cyl4 injector regardless as to what injector I have in there.

 

 

Yes, especially if the reg is leaking down the vacuum reference hose, which is plumbed into the manifold next to the number 4 inlet runner....

 

Fresh plugs and get it adjusted on the emission machine, see how it goes.

[28hodge 22]

Well I took it up to the MOT station at lunch, it was running properly when cold and the station is only a mile away, so got there had it tested cold and HC were 150. MOT passed.CO was 1% i think.

 

I don't think I have fixed it and id never have thought about the reg leaking down into the inlet, that's a great shout!

 

Someone on FB did say they had the same issues and it was an ECU fault when it got up to temp, the HC went sky high, he said he changed the ECU and it resolved the issue.

 

I am going to pull the injectors out and connect them all up into bottles, then crank it and see if they are leaking/spraying evenly etc, if they are then maybe it is/was the PRV leaking back into the inlet.

[petert 550]

I thought the ECU was multipoint. If batch, two injectors fire simultaneously. If multipoint, all four fire simultaneously. I'm sure it's the later, meaning that all four plugs would be the same. However, I assume there are four injectors drivers in the ECU. One of which maybe faulty. If you don't have a scope, I'd suggest swapping the injectors leads on #3 and #4. That will tell you more.

[28hodge 22]

Think I’ve sorted this, it was always cyl4 next to the end of the rail that was getting flooded, regardless to which injector was in there or wiring put to that injector.

I changed the entire rail and pressure relief valve and re MOT’d it yesterday, HC was down to 150 from the previous 4-5000 it was. It also starts a lot better when hot.

I think the prv has been leaking back down the vacuum into the inlet and then into cylinder 4.
 

As per welshpugs post above, that’s assuming that the prv can fail in that manner?

[SRDT 146]

10 hours ago, petert said:

I thought the ECU was multipoint. If batch, two injectors fire simultaneously. If multipoint, all four fire simultaneously. I'm sure it's the later, meaning that all four plugs would be the same. However, I assume there are four injectors drivers in the ECU.

Sorry a bit was lost in translation, I mean full group. The LE2-Jetronic only has one driver on pin 12.

As for Multipoint in France it mostly means that you have one injector for each cylinder as opposed to Monopoint (Single-Point/TBI).

[Zetec7 4]

Check that where all the 4 injector earth wires are crimped together you haven't a loose 1.