ok ive looked in haynes manual and a mk2 16v ecu loom seems to goto ecu temp senser tci dizzy and earth and coil and vacum from servo What i want to know is how does the ignition exactly retard the timming as on all over models i belive its done on the vacum on the dizzy but mk2 16v doesnt have this?
on my mk1 im running twin carbs with mk2 16v dizzy and mk2 16v tci. The timmings well off though when i took it to rolling road they said the ignition timing isnt changing i.e advance or retarding throughout the rev range basiclay its stays the same.was told this is because it has no ecu and i need to fit one so the ecu will control the timming and retard it at high rpm ????? Edited by: Gti mad man
Yep, the ecu has a vacumn pipe connected to it which detects the load on the engine (from the vacumn in the induction) It alters the amount of advance dependant on the load.
thanks gary but what i want to know is what actualy does the advancing if its thew dizzy is it told this from a signal from the ecu or does something else do it?
Changing the position of the Dizzy sets the base timing. The ECU then advances the timing with reference to that. It uses engine vacuum as an engine load indicator and the hall sender as a position/speed input. From these it works out how much advance you need and outputs a simple squarewave signal to the ignition amplifier which then goes to the coil and dizzy. Joe
athanks lee so i was right ultimatly its the hall senser that does the actual advance retarding then . so in throry all i should need is a mk2 16v ecu and loom thjat contains 1)ecu 2)tci 3)coil 4)vacum from servo 5)earth Then wire all that up (simple loom of its own) then set the timming on idle back to normal and it should be ok ????????
It`s the ecu itself that sets the timing, it sends the pulse to the coil relative to vacuum, hall sender pluse etc as Joe said. The dizzy is just used as a contact to fire the spark (an set base timing) the actual moment the spark is fired is all down to the ecu. Another tread on here said the vacuum wasn`t used on carbed engines desined for racing and the timing base was set to give the best power at high rpm`s although they must lose low down responce as a result?
Well, umm, it's all a matter of terminology. Turning the dizzy sets the static timing. The advancing/retarding of the ignition due to engine load and speed is ALL done by the ECU. The hall sender just picks up where the effective position of the crank is, this is then an input to the ECU so it knows when to fire the plugs with reference to that. Either way, it's academic. You NEED the entire Mk2 setup, so all the bits you mention. See the left hand diagram of this Hope this helps, Joe Edited by: Joe_G
its not so much the power im worried abotu strangely enough kieth its the fact that as the timings not advance or retarding at high rpm it caqn and has a few times pinked causing possible bad consequences! So if i wire up that ecu with a vacum feed(so the ecu has something to go on) im hoping that as the engines goign through the rev range the ecu will adjust the timing acordingly therefore id be getting a change of timing ?
Yeah, so here again we have the problem of what to do when you have carbs. How are you running your brake servo? I presume it's a vaccum connection from Cylinder 4 of the inlet manifold?? If so there's a bit of a problem in that the ECU is mapped for the expected vaccum in a Mk2 16v inlet manifold which will be 4x more than in your carb version I guess. This means the vacuum advance will be out. Thinking about it, what you really need to do is measure the vacuum from a normal 16v and then your carb setup and you could almost certainly do an electronic mod in the ECU to take account of the different vacuum level. Could probably do it with a couple of resistors to quadrouple the voltage output from the vaccum sensor so that your vaccum advance would be correct. Have to get one of these ECU's so I can strip it down and see how it could be modified..... If anyone's got a junk one they wanna send me, I'd be more that welcome ..... Joe
yup from cylinder 4 to brake servo is were the vacum is , gotcha so the ecu is pre mapped for a set vacum from a mk2 16v it doesnt just take any vacum figure then work it out from there then? Hum this is being a pain i dont want to have the expense of getting a engine management system seems bit over the top thing is the cars running fine at the moment idles great nice power but the timmings at 32 degrees throughout the rev range
Well get all the Mk2 16v stuff running and it'll still be much better than now as you'll be getting the advance due to engine speed at least! I can't believe it really runs at all with a static timing throughout engine speed and load!!! Joe
The ecu should advance the timing up to a point, the higher the vacuum the bigger the advance. If it`s set to give top end power then it may pink lower down? Timing on the valver is 7 dbtdc at idle and then the ecu advances it from there. I get the point about the hall sender Joe, just used as a crank trigger for the ecu.
Yeah, the ECU also advance the timing for engine speed, as well as load. On an older type car, the advance due to engine speed was set by centrifugal weights in the dizzy and the vacuum advance was set by vacuum diaphragm on the dizzy. There's none of this on the 16v dizzy so you'll have no advance at all. If you use the mk2 ECU, you'll get advance due to engine speed but not vacuum (assuming it's disconnected). Joe
There was a lot of rubbish talked in that thread. Assuming that the car is going to be running at a specific load and rev range all the time is, in my opinion, stupid. It's bodges like that which make people complain about how poor their fuel economy and running is on carbs. How about talking to an expert in NA VW race engines? I suspect Grant Motorsport or even TSR would be able to tell you a proper way of doing it? I'd also be interested to hear what Jason (urgti) and Louis (mk1.) have to say - I know Jasin uses MSD programmable ignition and Louis probably knows how to use the Peugeot (Magnetti Marelli?) ECU on the ignition only (may need a throttle position sensor and crank position sensor though?). I would also suggest that there may be a way of doing it the old fashioned way, using a combination of vacuum and centrifugal advance on the dizzy to provide a good enough "map" (although not as good as electronic control). Edit: don't forget that for the vacuum feed you'll need to tap into each runner on the inlet manifold and combine the tubing or you'll only have vacuum advance a quarter of the time. Edited by: gregs
hey thanks guys to be honest hadnt thought about the vacum part only workign quarter of the time ,silly question but wont it work out the advance based on signal from ther hall sender i.e speed anyway or is this not enough?
