All,
My mk3 SPi 1.8 Golf is giving me a headache at the mo:
Was fine tues, got in it fri to go to work and it started instantly, but ran on 3. I thuoght, that's prob due to the bad weather (damp, although it's not usually a prob)and it'll be fime when warm. WRONG, it didn't get any better when warm. If you cruise at low load it steadies itself. But if you move the throttle or give it some gas it runs on 2- 3, really rough. It always stars first time, the fault is just the same on LPG or petrol. Any ideas?
So far i've changed:
Coil
Plugs
Leads
Rotor arm
Dizzy cap
Distributor
ECU
Whole Throttle body, with TPS, etc sensors
Checked:
Cambelt is tight, timing's OK.
Water pump, PS, Alternator ,airco, all free.
Engine itself isn't tight.
Dizzy it tight (not loose)
Voltage OK
compression, all about 170 psi
ECU plug, soldering, etc
Spark plugs all look the same
Exhaust is free
There are no vacuum leaks.
In VAG.COM measuring blocks, all the variables are all in green text, the ECU thinks they're all OK. There are no fault codes logged.
The LPG ECU also gives no faults.
So, what's up? I'm lost.
Any ideas welcome...
Edited by Dynamic Dave on 22/01/2008 at 13:38
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Mark
Is it really on 3 cylinders at idle, or just generally rough? Have you tried removing HT leads to check if they're all running?
Could this be a failed cat blocking the exhaust? What are the injector durations at idle?
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I removed the plugs leads one at a time, and connected them to a spare plug, there wasn't much difference with any cylinder. It ran a little worse on 3.
It's just running rough, like it's running on 3, more like running on 2 if you open the throttle hard. But all the plugs are the same colour.
It seems to be blowing nicely out end of the exhaust. That's not to say there isn't extra restriction in there, i will try and see if the cat rattles. Injection duration comming up.....
Mark
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Injector duration (SPi there's only 1) is:
3.5 to 4 mS at cold startup
falling to 2 -3 mS after a few mins
Then 1.7 mS when warm, after say 5 mins
Mark
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Mark
My info suggests that it should run at around 3.2ms at idle; so that would account for the lean running. [What's the oxy sensor voltage doing at idle?]
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VAG.COM says 1.050 or so, my indicator in the car says it's flicking (normally) between 0 and 0.8v.
Bear in mind, it has the problem running on LPG too. This has a seperate ECU that works of it's own MAP sensor. The fault is the same with both fuel systems. I've dissconnected the LPG ECU to see if that makes a difference, same, i've also dissconnected my Lamda readout, same.
The ignition is always controlled be the original ECU though. IIRC that is determined by Throttle Position Sensor, TPS, (reads fine, although there are at least 2 potentiometers and only 1 readout) and distributor hall sender for r.p.m. rev counter works/as does vag.com r.p.m. I've also tried dissconecting the coolant temperture sensor, Lambda probe, also, no change.
I would say, from driving it, that it runs lean open loop on the ECU map, but sorts itself out a bit when the Lambda feedback loop starts operation.
The fault is the same for a fuel system that only looks at the throttle position as it is for a fuel system that looks at manifold pressure.
I'm lost! thanks for you input Screwloose.
Kind Regards Mark
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Mark
Not a lot is making sense to me either; you've virtually replaced the whole ignition system and, while the acceleration fault sounds possibly spark-related, a spark so weak that it would barely idle shouldn't be able to drag itself along.
So I was going for a weak mixture; but if the oxy sensor is sweeping 0-.8v then the mixture at idle is fine.
What about ignition timing; presumably you had to reset it when you changed the dizzy? Cam timing and worn cam lobes are the only other things that I can think of.
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...So I was going for a weak mixture; but if the oxy sensor is sweeping 0-.8v then the mixture at idle is fine.
It is at constant load or idle, where it runs better. But if i move the throttle it reverts to the ECU map only it runs really rough, suggesting that the map is not good for my engine anymore. But Lamba closed-loop feedback will correct for the error.
What about ignition timing; presumably you had to reset it when you changed the dizzy? Cam timing and worn cam lobes are the only other things that I can think of.
I haven't checked it on the crank mark. I have however moved the dizzy fore and aft a bit, no change. VAG.COM say 6 deg BTDC at idle. Which is normal, bearing in mind that is w.r.t. the dizzy, not real TDC. But that's the normal omount of correction that the ECU puts in. I put the dizzy electrical plug back in the same place as the old dizzy to keep the timming the same. Nothing loose in the dizzy BTW. Cam lobes look fine, for 260 K miles, see here:
www.clubgti.com/forum/showthread.php?t=153747
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If i move the throttle it reverts to the ECU map only it runs really rough suggesting that the map is not good for my engine anymore. But Lamba closed-loop feedback will correct for the error.
What!!? Where on earth did you read that?
I haven't checked it on the crank mark. I have however moved the dizzy fore and aft a bit no change. VAG.COM say 6 deg BTDC at idle. Which is normal bearing in mind that is w.r.t. the dizzy not real TDC. But that's the normal omount of correction that the ECU puts in. I put the dizzy electrical plug back in the same place as the old dizzy to keep the timming the same.
The timing is critical and the mark is directly related to TDC. Check it with a strobe after selecting basic setting in the ECU.
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What!!? Where on earth did you read that?
That's how it works. It has a 15 x 15 map, TPS vs RPM. The map is shifted with coolant and air temperature. Under steady loads the ECU shifts from the open-loop map to closed-loop Lambda feedback. This takes about 3 - 5 seconds in my car. If you move the throttle it goes straight back to the open-loop map for the duration of the movement + about 3 - 5 secs for it to re-stabilise in closed-loop mode.
The timing is critical and the mark is directly related to TDC. Check it with a strobe after selecting basic setting in the ECU.
Haynes says you can't do that, because the ignition timing at idle is dynamic, not fixed. The ECU's always adjusting it (with the throttle) to maintain the tickover rpm at the desired value. If i had a strobe, what would you suggest i set it to? 6 deg BTDC @ tickover when warm, or so?
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Mark
You've read a mish-mash of various [correct] facts; but got them in the wrong context. There's nothing wrong with the mapping in your ECU; there is simply a fault with the car.
You must set the timing; it's unthinkable to fit a dizzy without re-doing it. Do it as said - select timing basic settings with Vag-Com [see Ross-Tech's Wiki] and then use a strobe. Until that's right, you're nowhere.
If Haynes really say that you can't set the timing on these dynamically [how else would you?] then I'll have a word with the author of that book [a very good friend of mine] and get it re-written.....
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Mark You've read a mish-mash of various [correct] facts; but got them in the wrong context. There's nothing wrong with the mapping in your ECU; there is simply a fault with the car.
That's what i've been trying to say! There's a fault with my car which means the open-loop ECU FUEL map(S) (in both ECU's) don't work anymore. Both ECU's can correct for the fault when they switch to closed-loop Lambda feedback operation.
I sprayed butane round all the vac hoses and the brake servo, none got sucked in and made the engine run faster.
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If Haynes really say that you can't set the timing on these dynamically [how else would you?] then I'll have a word with the author of that book [a very good friend of mine] and get it re-written.....
Good! While you're about it tell him/her to include some info on the ECU, like add it to the wiring diagram, etc. It's not that handy that you have to make your own ECU wiring diagram before you can check the wiring and sensors! Maybe they thought the SPi injection unit looks like a carb, so there isn't an ECU. Judging by the quality and informativness of the rest of the book (compared to a mk2 haynes) it wouldn't supprise me...
Funny how they've changed the manuals from workshop manuals, to repair and maintenance manuals, with an appropriate dumming down of the content, but kept the price the same LOL.
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We've discussed this matter at length. The main reason for deleting so much of the original "Workshop" manuals [although they've now changed the name back] was the risk of litigation - particularly in this H&S-obsessed culture.
The other concerns were getting DIY-ers out of their depth; as you've found; it's not easy to grasp even the simple ones like this SPi - imagine a common-rail diesel multiplexed ECU....
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Few years later but did this issue ever get sorted I'm having exactly the same
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usually brake servo pipe! servo or rubber elbow coming of manifold end up with a big crack in it, Has that been eliminated.
Doc
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