Still have coldstart problems on my G60!!! Aaarrgghh!

[Tempest 0]

OK folks, short request for help again, see what you can make of this:

 

My C G60 starts fine when left for say 4 weeks, now that I've started using my C on a daily basis again (as I've got my Dad to cart around ;-)), it stutters for a few seconds on a coldstart, hotstarts are fine. After the stuttery start all is fine.

 

Changed:

Blue Temp sender several times (new ones, tested old ones, determind Temperature-Resistance plots, OK)

 

CO-Pot set to 490 Ohms, tried 515 Ohms, 550 Ohms, all to no avail, pot definitaly working

 

tested temperature sensor in CO-Pot: Reacts (changes resistance) when blowing onto it

 

checked ECU wiring loom several times, all connections OK

 

used 2 different ECUs (B and CR) with 3 different chips (95-octane, 98-octane oem chips and Zoran V-Power/100-octane with 98 and 95-octane maps)

 

lambdaprobe changed (used unit admittedly) 1.5 years ago, seems to run fine, Vince at Stealth Racing confirmed it working anyway with his wide-band probe

 

new fuel pump fitted November

 

tried different fuel pump relays

 

new fuel hoses in engine bay

 

tried 3 different FPR (including a new one)

 

tried 2 ISVs (cleaned et al)

 

new injectors fitted December

 

cleaned all ground connectors and greased to keep humidity from contacts

 

1. Keep on noticing black deposits on all 4 spark plugs, 3rd cylinder smelled of a bit of oil this morning.

2. Keep on noticing oil deposits on bottom part of boost pipe to Intercooler (as I use a metal sieve on the junction of the 2 boost pipes going to the Intercooler, I do, of course not have an airtight seal at that point, resulting in a 4-bhp power loss, but also a simple location to reveal oil !!!).

 

Points 1 and 2 above I have noticed for some time, and have never been able to get to the bottom. ISV was clean this morning (carb sprayed and no oily gunk came out).

 

Any ideas guys and gals?

 

Thanks for any help!

 

Tempest

[Tempest 0]

A few more additions, that I suddenyl thought of ;-)

 

Vacuum hose to the ECU has been replaced with a shiny new silicone one from G-Werks :-)

 

Compression on all 4 pots at 11 bar.

 

Exhaust gas test (using an MOT test station exhaust gas sniffer) on coolant reservoir (2 days ago) showed no signs of HCs

 

That would indicate that my head gasket is still intact.

 

Tempest

[Tempest 0]

Set the CO-pot to 490 Ohms, 2 daily starts seem to have gone fine so far, without a stutter ...

 

If anyone, however, has another idea as to what could be the cause of my coldstart problems, then I'm still ears :-) There could still be this Eureka-effect, where I have simply overseen something, where I then will give off my best Homer Simpson impression :lol:

 

Tempest

[bcstudent 0]

I have absolutely no idea what you should be checking next; it just seemed like you were a bit lonely in here :)

[VEEDUBBED 0]

Have you checked the fuel pressure when first starting the engine?,i rigged up a mech.fuel pressure gauge inside my corrado because every corrado i've owned all had the same defect that you described i.e, low pump pressure on initial start up,1st turn of key the gauge's needle barely moved,2nd turn and the pressure went up to~1.5Bar but on the third it went up to the required 3 bar and stayed there.

I then modiyfied the O/E pump housing and installed a bigger/higher press. bosch golf 2 pump and all problems regarding fuel press. vanished...

[Tempest 0]

Have you checked the fuel pressure when first starting the engine?,

 

Only did the 2 or 3 fuel pressure tests (using a nifty genuine Crypton fuel pressure gauge) described in the Bentley manual, and after having compared the results to Steve Mac's former G60 back in December decided that my injectores were leaking, which were then replaced.

 

The pressure tests described in the Bentley measure the pressure at the fuel rail entry end (taking in the path from pump, filter, to the fuel rail entry point, FPR disconnected) and at the pressure switch end of the fuel rail (taking in the complete path from pump, FPR, to the fuel rail including the injectors). The latter test revealed a premature drop in pressure compared to Steve's former G60.

 

The initial pressure after having turned the ignition key was fine each time I measured it.

 

Tempest

[Tempest 0]

OK, thought I dig up this old thread again, as I seem to now have finally got to the bottom of my problem, and it may be of interest to others :-)

 

In indeed what I would call a small Eureka moment, my last remaining brain cell suggested to look at the fuel supply again, especially the fuel pump afterrun gubbins.

 

This stuff works as follows (for those who care to know or don't know this yet :lol:):

 

A pressure switch at the end of the fuel rail senses when the fuel pressure is above 1.6 bar, signals this to a fuel pump afterrun relais. This relais is powered by the radiator fan afterrun thermoswitch located near the FPR, so when the thermoswitch closes (at temperatures above 90°C) the rad fan kicks in, and the fuel pump afterrun relais is powered. When it senses that the fuel pressure is above 1.6 bar (from the fuel pressure switch) it activates the fuel pump, provided that the ignition switch is in the off position (i.e. engine off, engine hot, engine was just run).

 

This whole procedure is to avoid formation of fuel vapour in the fuel rail.

 

If fuel vapour does form due to the engine cooling down, on a next start (typically within 24 to 48 hours) the engine is actually being fed air through the injectors instead of fuel, and hence the stuttering that I was suffering from, until enough fuel is delivered in the rail by the pump again.

 

I replaced the fuel pump afterrun relais, only to notice that its ground contact on the fuse box side was pushed up in the fuse box! No wonder then that the fuel pump afterrun relais never could switch on, let alone activate the fuel pump. That's why within 24 to 48 hours I would always have vapour in my fuel rails which needed to clear first (stuttering of engine) before fresh fuel could be delivered (engine running sweetly).

 

OK, I also decided that it was good idea to replace the rad-fan afterrun thermoswitch, clean all the brackets to get a good ground contact there, and hey presto, yesterday after a run in my C, I on turning off the engine could finally not only hear the rad fan kick in, but also heard the fuel pump running.

 

As said, might be helpful for others, as this only took me 3 years to sort :lol:

 

Tempest

[mattkh 0]

Hi Tempest

 

Well done.

Thank you for sharing your experience.

 

Where is the fuel after run relay ? What are the numbers on it.

 

Cheers

[Guest]

yep as above handy to remember that one, also whereabouts is the rad-fan afterrun thermoswitch thanks..

[Tempest 0]

Fuel pump afterrun relay IIRC has a 91 stamped onto it.

 

Rad-fan afterrun switch is located right next to the FPR.

 

Tempest