Hey folks Anyone able to help, we have searched through previous threads and not really found an answer. Recently fitted the above engine into a VW Bay - starts on the button, and runs well to start with, however as it gets warm it begins to miss, probably from about half way up the rev range, is fine in the bottom half, but when you get into the top half it starts to misfire. Have pulled all the HT Leads off and they all correspond appropriately so its not one specific pot. Have fitted new plugs, leads, rotor arm, and dizzy cap. We were wondering if we had a bad earth somewhere as have heard how sensitive these are. Would that be possible? Or anyone have any other ideas? It is also running rich when its missing We did have problems with the fuel pump relay to start off with until rubjonny very kindly helped us - could that of done some damage somewhere ie ecu? What are the symptoms of a blown ecu on these vehicles? Is there an easy way to check? Many thanks in advance! Its all greatly appreciated.
I would say check for air leaks! that would maybe be the most simple solution. I had the same problem with my mk3!
The usual first thing to change is the blue temperature sensor as that is the input to the ecu for engine temperature. If you're running rich it could be giving a false input. Get a VW one as well, they are not much dearer than ecp
Thought we would give a quick update - we redone all the earths, this helped with the idler stabilisation valve as it now makes a consistent hum rather than intermittent and its running much better, however, at high revs just prior to changing up a gear, it does miss, only slightly but still not right, which leads us to think more along the lines of possible air intake - the trouble is finding it? Anyone have any ideas for this - as obviously you can't get it to do it whilst parked up Also if there is something else you think it is let us know - still running a bit rich at times too but again not so bad!
Usual method to look for air leaks is to wave an unlit gas torch around the inlet and listen for a rise in revs.
Thanks oakgreener - we have today checked for air leaks - both by the gas torch method and the old WD40 one and no signs of any air leaks. Hmph. Guess the next thing to try is the temperature sensor. Anyone think the idler stabilisation valve may have more to do with it? It is hunting occasionally when warm - especially after a run and you then pull up lights or something similar.
check the idle switch clicks and the wiring to it is ok, a quick check for wirign is hold thriottle at about 1.5k then press the WOT switch on top the revs should drop then rise again when released. if not check the wiring from it to the ecu. if it works the wiring is ok but the idle switch may still be faulty or not adjusted correctly its underneath so a bit of a pain check the pcv valve bung as well, pull the pcv out and remove it so you can check in the slot for cracking. dirt cheap from vw/gsf
the what WOT switch? guessing the pcv valve bung is where the breather enters the rocker cover? Sorry for the daft questions, I can do the mechanical side but the electrics all just go over my head. Guess thats why i stayed air cooled for so long! lol
An Excerpt. Throttle Switches The Digifant system uses a pair of throttle switches on the throttle body to report wide open throttle (WOT) and closed throttle conditions to the ECU. The WOT switch is easily seen on the rear top of the throttle body. As the throttle linkage achieves maximum travel, a cam on the linkage opens the WOT switch, signaling the ECU to richen the mixture for maximum power. The closed throttle switch is located underneath the throttle body. When the throttle closes It signals the ECU to run its idle program. Failures here are very rare but both of these switches may fail or fall out of alignment. If the WOT switch is at fault, maximum power may not be available. If the closed throttle switch fails, the car may refuse to idle or may buck and jump at low throttle openings, regardless of speed.
Thankyou Much wiser now For turning voodoo black magic into something even electrically disadvantaged people understand lol
I hear you! WOT's, WUR's, PCV's, ISV's, FPR's, ECU's etc,etc Some of the dialect here can be intimidating if you are used to points, plugs and condensers! There should be a 'jargon buster' thread for those (incuding myself) less in the know!
Indeed - well we have ordered a new temp sensor which is due in from VW tomorrow - so that will be tomorrow's try, and then if that fails the pcv valve and the wot switch thingamajigy kind of thing = however this does click.
idle switch is the main one if its hunting, plus if not working you cant set the base idle and co properly. since the wot switch is wired in parallelelell with it you can do the above test to check out the ecu wiring as ecu will see it as idle switch closed below a certain rpm
A quick update, we have changed the blue temp sensor with a genuine one and no change. I've tested the wot switch as above, there is no change when the switch is pushed, in fact, even if it is unplugged there is still no change Going to check the wiring next and see where we go from there. Not sure if it is significant but if you drive it with foot to the boards all the while it doesn't miss but when driven sensibly/steady it misses every time between 3k and 4k Revs without fail and on the dot
yeah thertes a problem with the throttle switch wiring, the ecu will think its at mid throttle at all times!
start at the 2 pin plug on the back of the throttle ody, this is usually where it goes due to exhaust heat and engine movement making the wires brittle. give the wires a tug at the plug sometimes they look fine but have snapped off inside where you cant see! to test the plug you can repeat my test above but pop a loop of wire or a paper clip between the pins on the plug, if revs drop as expected the ecu wiring and plug is all ok, the trouble is with the throttle switch loom on the throttle body itself. if not gthen its a case of trace the wires as best you can till you find the break
Thanks John - You are a star - will have a go today - guess we are getting a step closer each time we do something lol, another question for you, the brown wire on the throttle position sensor - does this go to earth or the ecu?
