Mystery problem - Help needed -

[hangman]

Hi !

First of all , let me tell you that i've read almost everything on this foruns and other ones about g40's missfires or erratic behaviour or everything else I remembered about it, but I have not been able to sort this... that's why I need some help (please)

The problem seems quite simple, you are driving at constant speed you feel the car "loosing" some power, the normal reaction is to push the throttle a little and nothing happens...flat out... and nothing happens... the car keeps dying until idle, and then picks up; if at any time you fully release the throttle and step it on again the car will respond. This is a "cycle" and the car keeps doing this: good for 4/5 secons then looses power.... my first gess was that the spark plugs weren't sparking when the car fails...

I replaced:

spark plugs (from the ngk to bosh)
ignition leads
Distribuitor
rotor
Distribuitor cap
Blue temp sender (form vw)
relays (booth)
coil pack
fuel filter
ECU
Checked fuel pump
checked earths on car and the hidden ones on wiring loom
opened the engine, replace the exhaust valves, checked everything, close it all up with new headgasket and timming belt
compression test
checked thottle body switches

any ideas ?
this seems an unsoluble problem, and I starting to loose faith ...

[SuperMario]

I'd take a look at your injectors.

[RyanC]

Yh I'd say check them and the pressure regulator

[RyanC]

Dose it bogg down like it's running weak?

[hangman]

it bogs like .... someone turned off and removed the key, and then put it back on ....

a few days ago I connected a pressure dial to the outlet on the injectors ramp (I don't know the correct name in english) and took it for a drive . the pressure on the dial was constant and when I accelerated the pressure went up a litle, with the car bogging or not...  so I discarded problens with the pump or regulator ...

and is it possible for all 4 injectors to be dodgy? (because if it's the injectors it seems like all 4 are failing at the same time) what will cause them to do that ?

[RyanC]

Hmm if u have good pressure then I can't see it being injectors, you would get more of a misfire, what pressure were you getting?

[z3i]

I remember having something similar to this but no where near as bad as what you described
My throttle body was playing up in various ways, I got a standard one and re set the Co pot which improved things massively!
It might be completely different to your problem bit it does sound very similar, so have a quite check of the resistance across the terminals on the Co pot and make sure your throttle butterfly is sealing properly when off throttle as mine wasn't
Taylor

[z3i]

Yeah I remember now! I'd be driving along and the car would be at a constant, if I pressed the throttle a little more nothing would happen, a little more... Nothing I'd have to stamp right down and it would aggressively bark into life

Again you say about having to release the throttle and back on again for the engine to respond, I had exactly that too. It was a while ago, but I'm sure I fixed it with the above. Done so much work around that time can't remember what else I would have done to solve it

[RyanC]

I was thinking maybe co pot, worth checking

[hangman]

thanks guys,

the exact value of the fuel pressure I can't remember but I remember "it seemed good"...

about the co pot: I set it to 550ohms and didn't make any change, if disconnect it the car still bogs (connected or not the car still bog) ...

what am I supose to "feel" when I disconnect the co Pot ? (trying to figure out if the co is actually doing anything)

[GR40]

It definitely does! I remember having the metallic ring that fits at the end of the plastic tube (to prevent the plastic from caving in when you torque the silicone hose over it) slip in and block the co pot and it would behave similar to what u describe! It was bothering me cause it would be totally random depending on whether the ring would block or not the co pot as it was moving around from the boost. Took me about a week to get to source of the problem. I only realized what was going on when I stack a finger through the co pot hole and touched the metal ring! Removed it, and everything went back to normal. Worth taking out the tube and checking!

[brownysblower]

check your lift pump in tank !!  or replace it
 plus change your fuel filter

[hangman]

thanks GR40  i'm gonna check the co pot then... I know that the co pot electric connector does not seems to be in very good health , but I was far to assume that could actually be the source of the problem , because when I run the car with the co pot disconnected its behaviour is exactly the same ( still bogs)

about the lift pump, if I get pressure at the injector ramp how could be the lift pump not working ? I think that if it is anything wrong with the pumps (lift or "master") I would not get any pressure at front, am I right ?
and the fuel filter has already been replaced 

[brownysblower]

your lift pump may lack volume or have a blocked strainer
checking it is cheaper than a set of pistons !!!

[kwijibo_coupe]

I had a similar issue to this in my old GT. Maybe the G40 runs off it's own sensors differently but in the GT when this happened it turned out to be the Lambda had completely shit itself.
Once it was unplugged the car ran fine.

Worth a check anyway, just unplug the lamda sensor and see it the issue improves.

Haven't had an issue like this in my G40 but for a while I did experience small coughs and mis-fires which gradually got worse until the car completely died. This turned out to be the coil failing. Once replaced the car has run fine since. Again it's worth checking if you can get hold of a spare one.