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 ...
I'd take a look at your injectors.
Yh I'd say check them and the pressure regulator
Dose it bogg down like it's running weak?
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 ?
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?
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
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
I was thinking maybe co pot, worth checking
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)
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!
check your lift pump in tank !! or replace it
plus change your fuel filter
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
your lift pump may lack volume or have a blocked strainer
checking it is cheaper than a set of pistons !!!
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.
Can you rig up the fuel pressure gauge and take it for a spin, get it to "bogg down" and see what the pressure is and if it drops?
I wouldn't have thought it's fuel otherwise it would pinging it's tits off! And running mega lean, temperature gauge would rocket, possibly melty time?
RyanC , I've done that and the pressure was fine even when the car "boggs down" . when I press the gas the pressure rises a little, with the car bogging or not.
About the temperature, the car always seems to run at normal temperature, however I had a problem with one of my exhaust valves (befoe this problem started) could this be related ? (I've already replace the exhaust valves )
about disconnecting the lambda, the lambda that I have it's like... 2 years old or something. When I disconnect it the car "boggs" exactly the same. the behaviour is the same when I disconnect knock sensor or the co pot.
The only sensor that seems to change the behaviour of the car is the blue temp. when I disconnect this sensor, the car dosen't "bogg dow" but also dosen't rev up like a "good" car (and I've already replaced the blue temp, the behaviour is the same with both new and old sensor)
let me just ask a "silly" question (just to be sure :)): the co2 pot resistance is mesured between wires 1 and 3, and this process is done with the car running or not ?
Check your knock sensor out. That can cause sudden losses of power/jolting if there is an issue with it.
but, if I disconnect the knock sensor the ECU will ignore it, or am I wrong ?
Because you've been disconnecting sensors here there and everywhere have you hooked it up to a code reader to see if it is throwing up any fault codes?
Might be an idea to get them deleted and see what happens, if it still is bogging down after that then see if the code reader can shed any light on the case. I know these ECUs are a bit primative but it is worth a try.
Quote from: hangman on May 28, 2014, 11:45:10 PM
but, if I disconnect the knock sensor the ECU will ignore it, or am I wrong ?
No it doesn't ignore them. It adjusts as if reading 0 to their values. Example: for Lambda missing the car would still work but your fuel efficiency would go out of the window! Plus when u disconnect blue sensor the ecu goes into safe more. If with the blue sensor disconnected the car doesn't bog I would suggest another blue one, your new one could had been faulty to begin with.
Okay so u have pressure at the rail and you have changed the ecu so The map sensor should be okay but have you checked the vacuum line to the map sensor?
I'm guessing they are very short journeys that u are doing in it to test? Is it temperature related? Eg worse when it's hot or cold or just the same?
What dose it behave like at idle? And dose it bogg down if you rev it on the spot?
Well, think solved it (but really don't know what have I done ???)
Aparently the Co2 pot wasn't working right and the boost was very low ... I cleaned the co pot and re set it to 550. I've also replaced the v-belts,(they where old and worn out)... And the car seems perfectly fine now.
It's kind of odd, how this 2 small things can make such a difference in how the engine runs... my bet is that the engine was working super rich and causing it to "bogg"...
I'm going to use the car a little more in this next week and I will post here if anything changed