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ABF'd Mk1 not starting again

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Hi All
I posted on new years day in the Modified section about my ABF'd mk1 not starting, but thought I'd try here this time due to more traffic. After some fiddling last time I 'fixed' it. Well, I think I just got lucky. It appeared to be a bad connection on relay 30 stopping power getting to the ECU. Ran lovely for a few weeks.

It was wet for a few days at the start of this week, so it stayed in the garage. Then tried to use it Thursday and no go. It just turns over with no attempt at starting. Same as before.

First place I went was to relay 30. Pulled it, tested it, re-fitted it. I have 12v on pin 9 of ECU plug when ignition is on. I believe this to mean the ECU is powered. Are there any other pins I need to check on ECU plug? I'd like to do them all in one go as it's a right pain to get to…

There is loads of batter power and the spin is solid. Not laboured at all. I keep it on a trickle charge.
Loads of fuel in tank. And it smells of fuel after cranking. I can also hear the fuel pump as I turn it off.
There is spark too. Pulled a lead and earthed it while cranking. Very sharp spark.
Its not immobiliser as I believe this only inhibits immediately after a start. I don't get that far.
All my fuses are good as well.
Earth plug above fuse box all looks clean and connectors tight. I removed and replaced the earth to relay 30 as well.

Here' the odd bit that I don't understand. With 1 spark plug lead disconnected, it made like it was going to start. Only a little kick, but enough to get my attention compared to how it is all connected up. It didn't matter which lead I tried it with either. All the same. Makes no sense why it would shows signs of catching with one lead disconnected.

I could go through every connection in the fuse board, but I'd like to try and understand what is going on and have a focussed attempt at fixing it rather that just fumbling and getting lucky.

Any help would be appreciated.
Thanks

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Forgot to add, I did a diagnostic on the engine as well. No fault codes at all. If it is reading the system, then doesn't that tell me the ECU is OK?

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As I have done a diagnostics test, I assumed all my engine sensors are good. However, would the VagCom engine scan pick up a bad Crank sensor?

I found this.

The crankshaft position sensor is an engine management component found on virtually all modern vehicles with internal combustion engines. It monitors the position and rotational speed of the crankshaft and sends the information to the engine control unit so it can make appropriate adjustments based on operating conditions. The crankshaft speed and position are some of the most important parameters used in engine management calculations, and many engines cannot run if the crankshaft position sensor is not providing an accurate signal. Usually, a problematic crankshaft position sensor will produce a few symptoms that alert the driver of a potential problem that should be serviced.

1. Issues Starting the Vehicle
The most common symptom associated with a bad or failing crankshaft position sensor is difficulty starting the vehicle. The crankshaft position sensor monitors the position and speed of the crankshaft and other parameters that play an important role when starting the engine. If the crankshaft position sensor is having a problem, the vehicle may have intermittent starting issues or may not start at all.

2. Intermittent Stalling
Another symptom commonly associated with a problematic crankshaft position sensor is intermittent stalling. If the crankshaft position sensor or its wiring have any issues, it can cause the crankshaft signal to be cut off while the engine is running, which can cause the engine to stall. This is usually a symptom of a wiring problem. However, a bad crankshaft position sensor can also produce this symptom.

3. Check Engine Light Comes On
Another issue of a potential problem with the crankshaft position sensor is an illuminated Check Engine Light. If the computer detects a problem with the crankshaft position sensor's signal, it will activate the Check Engine Light to alert the driver of the problem. A Check Engine Light can also be set off by a wide variety of other issues. Having the computer scanned for trouble codes is highly recommended.

4. Uneven Acceleration
With inaccurate input coming from the crankshaft position sensor, the engine control unit can't make the adjustments to spark timing and fuel injection as the engine speed increases. Slow or uneven acceleration can result from a lack of accuracy and makes it difficult to maintain a constant speed.

5. Engine Misfires or Idles Rough
Should you feel or hear a brief stutter in the engine, it may be a sign of misfiring cylinders from a bad crankshaft position sensor. Additionally, while idling at a red light or otherwise stopped, you may notice the engine running rough or vibrating. A failing crankshaft position sensor cannot provide the right information about piston positioning in the engine, causing a cylinder to misfire. This could also occur from faulty spark plug timing, but if the spark plug checks out, then the crankshaft sensor is likely the source.

6. Reduced Gas Mileage
Lacking accurate timing information from the crankshaft position sensor, fuel injectors won't pump gas into the engine efficiently. The engine will use more gas than it needs on short and long drives, reducing overall gas mileage. Have a mechanic inspect the sensor, as poor gas economy can occur from other issues as well.

The crankshaft position sensor is critical to proper engine functionality and performance due to the vital signal it provides for engine calculations. Issues with the crankshaft sensor can quickly lead to problems that affect the drivability of the vehicle. For this reason, if you suspect that your crankshaft position sensor has an issue, have the vehicle inspected by a professional technician right away. They will be able to diagnose your car and replace your crankshaft position sensor if necessary.

1, 2, & 6 - yep! Got to be worth a try for relatively little money!

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Got a new crank sensor and fitted it tonight. After a bit of cranking she started, but was very lumpy and low idling. I put it down to all the fuel in the chambers from all the start attempts.

Once it was ticking over at about 900 ish rpm, it was still lumpy. Thought it was missing so I pulled each spark lead in turn to see which cylinder it was. However, none of them made much difference. It was only when I pulled 2 at the same time did the revs drop off. Didn't stall mind.

So, the fact that it runs tells me all my engine sensors work, and there are still no fault codes.

Therefore, I'm thinking one of the following:-

1 - Dizzy cap and rotor. I took them off for a look and they could be better, so i'll get new ones.

2 - Plugs. I haven't pulled one yet as I can't find my socket.

3 - Coil. Does this break down causing a weak spark? Or is it a case of it either works or it doesn't?

4 - Fuel. What would happen if my fuel pump is on the way out? I can't imagine it causing an issue at tick over. Maybe at full throttle. I can also hear it buzzing away quite vigorously while its running.

Oh, I also disconnected the lambda probe and started it. Didn't seem to make any difference. Connected it back up while running and it cut out immediately. Was that bad? Started up again into same condition after wards though.

So its better, but still room for improvement.
Any pointers???
Thanks

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I would suggest that you verify that your fuel pump is at the correct pressure, and volume before saying it is good or bad… Pressure tests are actually a good indication that all is well.

How is the Timing?  Have you checked that it is in time.

Coils do go bad, but there is usually a weak spark or dead, not an iffy spark.  If the spark has the ability to lightyoureyeballsanddropyourprivatesinthedirt then you are probably good.

The sensors like o2 if bad will cause you weird things as unplugging it usually makes the ECU's go to default and enrichen.  Plugging them in causes them to go back to the way it was… so that is one way to say it is or isn't the issue.

Vacuum leaks..Kill them or else you get lumpy running as well.

I can tell you that if you hear a fuel pump running or whining, that is a bad thing, but the fuel flow and rate will tell you more…

If the Pump is making noise, then you have a restriction prior to it.  On my 2h digi, that is usually the in-tank pump or connector hose that is the issue.

On older Diesels it was garbage in the in-tank screen.

my 2 pence worth of thought.

What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

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Thanks Briano

Some good pointers.

Fuel is definitely my first thing to check. I have read if I put the fuel pipe to the engine in a pot I should get about 300cc for 10s of pumping. Is this correct for 1800 Gti pump? My accumulator has been bypassed and the lines front to back were replaced a few years ago with rubber ones. Hope to get on this tonight.

I will also check the timing out, but when I drove it into the garage last week it was running fine. Is there an easy way to do this without unbolting half the engine to see the belt and pulleys?

There is a spark, but do I have to put my tongue on it? LOL Seriously, how do you tell if it's a 'good' spark?

I've cleaned up the dizzy cap and rotor for now as I can't see that having such an immediate effect. I'll also pop the plugs and have a look, but same comment applies.

Many thanks

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Checked fuel - no problems there. Didn't check pressure, but there was loads pumping through after the engine bay filter, so all good.

Pulled the plugs and they were black from all the start attempts and rich running after finally getting it started. Once cleaned up a little they look in really good condition. Spark looks strong, but no way to measure it specifically.

Thoughts:-
Could the crank sensor cause an issue if it is not fully home? I have tightened up the bolt that holds it in, but is there a way for it to get slightly twisted on insertion and cause issues? Or would the engine just continue to not run if it wasn't fully home? Just curious as everything is done by feel.

Timing. If the drive belt had slipped would it still run? Is there an easy way to check the timing without stripping down the belt side of the engine to get at the belt? I'm not sure it would run as well as it does, but that's why i'm asking.

My final option is lambda probe. I need to get it off the car and test it.

Proper frustrating this…. was tempted to just take it for a little run on Friday, but I thought better of it just in case the timing has slipped…

Thanks
Huw

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Had all the covers off and timing is fine. Long section of belt only moves about half inch either side of center, so plenty tight enough and no change of slipping. All looks in great condition.

Had Lambda probe of car and tested it with blow torch. Responds as it should and returns very rapidly when heat removed, so seem fine.

Proper head scratching!
I'm back to ignition. GSF had a 60% off yesterday, so i bought Coil, ignition leads, rotor arm, spark plugs. Hopefully it'll all be delivered Friday.
Bought a Beru dizzy cap of the bay as GSF were out of stock.

The car starts up fine, but just runs lumpy. Very slow to respond to throttle opening, and hunts a lot a idle. I did find a small hole in the inlet pipe between filter and throttle body, but that will not contribute.

Just about to order some vacuum hose. Any one know if I need 3.2mm, 3.5mm or 4mm ID?
Thanks

The search continues….

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It seems I am chatting to myself, but just in case….

Started it up tonight and had a fiddle around with the vacuum hoses. I pulled the vacuum hose off the ECU and the revs picked up and got a bit more stable. Still lumpy, just not so much.

Does that tell me anything useful?

Also, there seems to be air coming out of the filter just above the alternator. The one attached to the fuel pressure regulator. Any ways to test it?
Thanks

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Vacuum on the ECU?  don't sound right to me.

Vacuum leaks are the bane of these critters, they don't like vacuum leaks at all.


What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

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There is a vacuum pipe running from the inlet manifold to the ECU, right next to the main connector.
New hose is on order so will replace the lot.
Thanks

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Starting to get a little frustrated now. I don't mind spending money where necessary, but I HATE waste.

So far I have replaced:-
ECU coolant temp sensor
Crank sensor
Rotor arm
Dizzy cap
Spark plugs
Ignition leads
Coil
Vacuum pipes for FPR and ECU

What else have I done…
Fuel pumps through well after engine filter
Fuel pressure after engine bay filter is 35-38 psi
Tested my lambda probe
Pulled out the FPR and tested it with a bike pump
Unplugged ISV and it doesn't start.

It starts well and stays running.
Tick over drops to about 600 ish rpm on occasion.
Hesitant when revved, but does rev well once going.

Took it for a run. Not good. At very low reves and throttle input, its a pussycat. Push the throttle and its like someone is flicking the boost switch on and off really fast. Really uncomfortable.

Run VAGCOM when I got back - no fault codes.

I'm really at a loss as to what to try next.
I have heard there is a short vac pipe inside the ECU that can fail, but would it really create the sudden on/off power I'm getting.
Gutted its not running  :(

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Also just changed the fuel filter and opened ECU to check the vacuum hose inside hasn't perished. 
No change. 
Only things left to change now would be FPR and fuel pump. 🙁

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Just stumbled upon this thread about some guys having a similar problem.
https://www.clubgti.com/forums/index.php?threads/abf-16v-idle-issue-getting-desperate.276934/

They had an ECU issue, but in the thread Rubjonny mentioned bridging pin 30 and 87 for relay 30 to rule it out.

Well guess what. She ran like a dream, full power and no hint of hesitation.
Who'd have thought a relay could cause such a problem??? I thought they were either on or off.  :lol:Where do I get a decent one then? VW? Cos this KRACKER one is going in the bin!!!

Wish I'd tried that first rather than spending so much on parts I didn't need.  :dry:Oh well, every cloud and all that…

Last edit: by huw169

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Go to VW for the 30 relay, cheap and best quality :)

are you sure your relay is being triggered? maybe its lost the ignition trigger on pin 86 or the earth to pin 31/85

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

VAG Documents & Downloads

You'll need to sign into google/gmail for the link to work! (its free!)

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Thanks Rubjonny. I got a Meyle one in the end from ebay. £8. Orderd Monday and it arrived Tuesday.

I popped the old one open and it was very rusty on the inside. There was a rust tide line where it has been sitting in water  :$
Must find that damn leak!

I thought the car wouldn't start if the relay was not being triggered? It started fine with the rusty one, and ticked over ok. Under load it was just cutting in and out with the power and totally un-drivable, never stalled though.

Works a treat with the new one fitted.  :thumbs:

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as you have found out yourself, it will start and run without the ecu relay but it wont be happy about it :P

theres an extra ignition live to the ecu from the fusebox, the plus side of all this is you know that wire is ok :lol:

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

VAG Documents & Downloads

You'll need to sign into google/gmail for the link to work! (its free!)

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huw169 said

 There was a rust tide line where it has been sitting in water  :$
Must find that damn leak!

Windscreen seal, antenna missing the drip stop loop,
Plugged rain drains, missing grommet on the firewall and in the rain tray, missing the rain divertor are the usual suspects.


What do Divorces, Great Coffee, and Car Electrics all have in common?

They all start with GOOD Grounds.

Where are my DIY Links?

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Thanks guys.
Must admit, I don't recall trying to start it with the relay out, as I was under the impression it wouldn't start at all. Will try that next time i've got the fuse box down.
How do I ID the ignition live wire you refer to RJ?

Yes, I think window seal is my issue. It has leaked for years, but recently I removed the window spats that also tuck under the seal. I'm going to use some grease to fill it (worked a treat on my van) as I don't want to use any sticky gunk.

Very wet on the south coast at the mo, so she's tucked up in the garage….
Thanks again.

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I mean the extra ignition live is what the ecu used to fire up, so if it ran with no ecu relay you know this is ok. this feed also powers the isv so if thats buzzing again you know its all good. If I had made the loom it would be fed from D2 or D7 which are fuses 17 and 18

Hello my name is John and I'm a dub addict.



My wiring diagrams and other documents have moved here:

VAG Documents & Downloads

You'll need to sign into google/gmail for the link to work! (its free!)
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