Gti6 Engine Weak Injector Pulse Troubleshooting

[randomspeedfreak 4]

Hi Gents, i need a hand - my 205 has been playing up again.

 

The other week coming off the motorway i dropped from 5th to 4th. at this point i lost all power. it sounded awful, like it had dropped a valve (I would have expected that as it is bit of a tapper)

 

As i stopped at the traffic lights the car was on 2 cylinders and was missing and backfiring horrendously. The car wouldnt run at all unless i applied full throttle for at least 15 seconds - it would slowly chug its way to about 3k, at which point it would clear up a bit and run alright, but only if you went right back to minimal throttle - any load at all and it would instantly return to missing and 2 cyl.

 

I limped the car to my garage, it had previously shown similar symptoms to these, that time it fixed itself after an hour break and me wiggling a few sensor wires! This time that didnt work. The sensor wiring all looked ok and belled through to the ecu plug ok. still thinking it could be sensor related, I swapped a few parts:

 

Throttle body (including throttle position sensor) no change

Map sensor (swapped for a new one and rewired) no change

New plugs

swapped out the coils (and swapped them around) all still gettting a spark, no change

 

upon taking the plugs out i noticed that cyl 3 and 4 were white as you like, super lean, (cylinder 1 was very oily think the stem seal has had a bad time)

 

The car consumes a little water, i have been chasing small leaks for a while but as i havent been able to find any at this point i was certain i was looking at headgasket failure.

 

Got my mate to bring over a compression tester, of course as he arrived the car started near enough on the button and performed faultlessly

 

We then performed a compression test, to my surprise 13.5 bar on all cylinders.

 

After he'd left, took it down the road for a test run and ran fine for about 5 minutes, it then tried it on again, same symptoms as before

 

I then unplugged injectors 3 then 4, no change to the running issue. unlikely that both have failed, let alone simultaneously

 

I have a spare set of injectors so i connected one in place of the injectors on 3 and 4 and ran it dry in my hand, i dont know how much these injectors are affected by running without fuel pressure behind them, but i wasnt impressed by the clicking i could feel, barely audible..a pretty tiny tick...considering they are usually the loudest thing in the bay when you open the bonnet. ohms reading across all injectors 16.3ohm.

 

The car will now just about chug onto 2 cylinders, any throttle at all kills it, unless, only sometimes if you ram full throttle on iit chuggs on for a bit

 

So whats your money on? Does the double relay have any bearing on injector fire or isit new ecu time for me?

 

Thanks for reading, any ideas appreciated,

 

Cheers, Matt

 

Edit: as soon as i can get my fuel pressure tester from the garage ill do that, but im pretty convinced its electrical

Edited August 24, 2015 by randomspeedfreak

[Richie-Van-GTi 71 2 Cars]

I think your chasing a red herring with injectors and pulse widths etc. Sounds suspiciously like low fuel pressure or crank/cam sensor failure. Only true test for the head gasket would be a sniffer test on the coolant and a leak down test on the engine itself. Very rare does a stem seal create an oily plug. They generally cause a bit of smoke on start up and increase crankcase pressure through the breathers. Oily plug sounds like scratched bore or worn ring.

[randomspeedfreak 4]

I think your chasing a red herring with injectors and pulse widths etc. Sounds suspiciously like low fuel pressure or crank/cam sensor failure. Only true test for the head gasket would be a sniffer test on the coolant and a leak down test on the engine itself. Very rare does a stem seal create an oily plug. They generally cause a bit of smoke on start up and increase crankcase pressure through the breathers. Oily plug sounds like scratched bore or worn ring.

Thanks for your help Richie, i appreciate its a bit of a read! didnt realise when i posted!

 

fuel pressure should be at 3 bar right?

 

I will test the fuel then replace crank sensor

 

Cheers,

Matt

[dobboy 231 2 Cars]

I'm almost certain i seen (on the link on the recent ViN code decoding thread) that the white and black top fuel pumps have two different pressures, 3.5bar and 4.5 bar.

 

I accessed the link from mobile, which brought the info up in French, maybe worth checking out as if you had the 3.5bar pump and if it was worn or you had any kinks in pipes etc you maybe don't have enough pressure?

 

Just a thought.

[welshpug 1,657]

fuel pressure is regulated by the fpr on the fuel rail not the pump.

[dobboy 231 2 Cars]

Understood WP, but if fuel pump can't presurise to greater than 3bar, the regulator won't have anything to regulate?

[randomspeedfreak 4]

hi again guys,

 

Ive now tested the fuel pressure and im getting a little over 3 bar, i think this is correct as it ran fine at this pressure before?

 

next step crank sensor i think?

 

cheers,

Matt