Club G40 Forum
Technical => Engine and Transmission => Topic started by: benh999 on March 09, 2010, 05:30:55 pm
-
right folks just a quickie.
My g40 has a misfire at roughly 1500rpm, below that and above it she runs perfect and pulls liek a train with no missing underload. It is a small misfire but is annoying for urban driving as it can cause the car to judder. Any ideas as this one has me perplexed???
Regards
Ben ???
-
Chip map probably needs tweeking.
-
did think that, luckily I live very near to andy so hopefully if it is that he can sort it ;)
-
Just an update, I drive about 17 miles to work and have now noticed that the miss fire always seems to be upon initially pressing the accelerator pedal, she always seems to hesitate and then immediatley clears an pulls hard as normal. this seems to be more promenant when the car has got hot especially when standing in traffic??
It also occurs when the car initially is cold???
Suggestions?
-
Check that the closed throttle switch is working properly, and adjusted to only activate on closed throttle.
Might be able to have a look for you on Friday afternoon - depends whether I end up taking my own car for an MOT or not though!
-
I think my 51mm TB may have a dicky closed throttle switch. Would a symptom be a fast idle about 1100 rpm and a tick over AFR ~11:1 ?
My standard TB ticks over at 8-900 rpm and the idle AFR is 14.7
-
nick - sounds like it might be letting too much air through
-
mine is doing this aswell ben - this is what i just cant solve. hence why i put a request up for help. i came fooking really close to burning the piece of shit yesterday
-
nick - sounds like it might be letting too much air through
Thats what I originally thought until I got my wideband fitted; 11:1 is rich ;)
Went round to a mates to borrow an OHM meter. Turns out it was a dicky closed throttle switch.
At first it looked like the switch was shagged because when fully pressed down by the TB lever (even heard it click), there was no circuit. I pressed the micro switch further with a screw driver and it worked. With a bit of super glue & pikey engineering to the TB lever, it runs spot on now :) The switch is obviously well worn (its originally a mk2 G40 TB), even adjusting the position with the two screws on the side had no effect!
Anyone know how much replacement switches are from VAG? I have a spare TB to raid if mega expensive.
-
Update.car hesitates when the throttle is initally pressed. Once throttle is open she accelerates and decelerates smoothly. Also if you hold the speed constantly she hesitates. I've checked basics like dizzy rotor arm etc. Not seeing andy till next Friday so don't want to do anything drastic however if there are some simple checks please suggest
-
Is this for sale again mate?
-
no not for sale.
Any ideas folks I had a good check over plugs leads etc. All in superb condition, W5PDO's all a colour light brown colour.
-
fuel pump?fuelpressure regulator?
-
Its not something simple like the throttle cable tension clip on the throttle body being set too tight is it? It should be set so the tension is rested on the first micro switch, not so the switch is pressed in
-
ignition timing for the hesitation or hall sender going dicky for misfire.
whenever timings too advanced g40's hesitate / try cutting out when throttle is blipped.
I'll have a look at the hall sender today, Hopefully Andy will be able to check the ignition timing for me ;)
-
Right folks quick update. Andy had a thorough look over the car today. Both Cam and ignition timing are spot on. CO pot is reading spot on. throttle body seems to be good, blue temp sender fine.
Yet to be 100% confirmed however it seems the Lambda could be one of my main problems. Drove home with it disconnected and car drove almost like normal. Need to check the wiring to the ECU as well.
WE have a list of things that need addressing before live mapping session takes place.
Change Earth straps(charger one missing, others looking not too clever)
change knock sensor (current one not looking too clever)
change vacuum pipe and clips from fuel pressure regulator.
Change HT leads
New alternator.(current one only kicking out 13.5amps at idle) with fan on only 31.1amps)
Good day in all :-)
-
Im confused, aren't you selling this?
-
Yep my car last year wouldnt turn over on the key and the battery kept discharging because the charger earth strap wasnt conncted properly and knackered. After I replaced it, car ran perfect, that little strap makes a hell of a difference.
-
Im confused, aren't you selling this?
Yup probably selling her. Finally found what I want and the g40 is just a bit too harsh for my daily needs. However I'd rather the car to be mechanically perfect when I sell her.
-
Deffo sort all the earths out first - that dodgy knock sensor connector isn't brilliant either, neither is the hose to the fuel pressure regulator. New HT leads and a dizzy cap and rotor arm wouldn't be money wasted either.
Then see what you get at the battery from the alternator, and how it runs then.
If the voltage is okay and it's still miss-firing a bit on light throttle I'd look at the lambda. Did you find out from the previous owner what wiring problem he'd had there, and how he fixed it?
I think the 'jumpyness' pulling away is partly down to a dewedged throttle body, made worse by the miss-fire you've got - so you'll never completely irradicate that unless you stick the wedges back in. Problem is, that the MAP sensor value swings around a fair bit for next to no throttle input - which makes it very difficult to map in that area. With the wedges back in the MAP value is more progressive/stable at low throttle openings.