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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #41  
Old 7th June 2015, 21:27
phil.coyle phil.coyle is offline
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I don't know if this helps but, on my EFi the wiring loom from the injectors has a diode in the wire from the injectors to the ECU, this is to stop any spikes in power from upsetting the ECU and the wires from the Hall effect dizzy are all screened, and I have wrapped them in foil tape. My diode started to break up causing it to misfire, a trip to Maplins for a 20k diode (60p) and some ally sticky tape and bingo job done.
The ECU is susceptible to interference so a check on your alternator may be in order. I know of one example of a very expensive hand built British car that would conk out every time the guys mobile phone rang when he was driving in France (he lived there) when the car was returned to England no problems could be found, and as soon as It went back, problem every time the phone rang, this was 15 years ago but it shows there can be a hidden problem.
This is one reason why most engines have an anti knock sensor in the block as it picks up bad ignition (pinking etc.) which can be picked up by wires and ECUs.
Phil.
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  #42  
Old 8th June 2015, 08:38
ozi jim ozi jim is offline
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MMM.

ECU s generally have over voltage regulators, and it will throw a code.
Depending on the age as to the sophistication of the fault software,it maybe to old for missfire history.
disconnect a plug lead and see if it throws a code in.
Hint If it has no code you look for something that does not log.
EG rotor button
fuel pump
plug leads
What it will log is things like AFM, TPS, crank cam sensors bla bla bla.
It wont log if its not in the soft ware, so induce a fault by pulling a lead and that will tell you if it should or should not log a code on a secondary ign missfire.

If it where me, I would go for a drive and take an inductive timing light with you.

When it starts to miss put the pickup onto one lead at a time and look at the flashing light.,
If one is not firing it is related to that cylinder, then go on from there.
If it is all then move it to the coil lead, if this is ok then it is the rotor button.
To test a rotor, pull the cap off, pull the coil lead out of the cap and hold it about an inch or so above the rotor button, get some one to crank, if the spark is bright and jumps onto the button and goes to ground through the shaft it needs replacing.

One other thing if it has an ignition module put the timing light on the coil lead and then load it or put it into D, if the timing light goes out and the car stalls it will most likely be the ign module.

I am a mechanic, if it is running as poor as you say then you need to gather evidence see if it is all or one.

Jim

Last edited by ozi jim; 8th June 2015 at 12:10..
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  #43  
Old 8th June 2015, 21:32
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peterux peterux is offline
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Quote:
Originally Posted by MartinClan View Post
Did a round trip of 70 miles today. Ok for the first 30 and then a breif reocurence of the problem and then it went away. However on the way home it came back big time and at one point I didnt think we would make it....

I have fitted a fuel pressure gauge and that told me the fuel was fine. However I now have another clue. This time I watched the rev counter. Each time the misfire appeared the rev counter started moving erratically. (Over reading....) The rev counter is driven dire tly from the ECU as I recall. So next thing to do is change the cpu i think. I have a spare somewher purchased just in case.

The saga countinues.....

Cheers, Robin
Hi Robin,
sorry to hear you still having issues.
I think the Rev counter erratic behaviour is just a symptom of the misfire. Mine was very sensitive to noise and I suspect it's just picking up a lot of erratic pulses from the mis-fire. Sorry, I don't have any spare ECU's as I've now sold most of my e30 spares.
Whilst it could be a high temperature failure inside the ECU (dry joint or cracked PCB track) I still think it will be an input from a sensor that is driving the ECU crazy.
I guess the good news is that you have eliminated the fuel supply so can focus on the electricals.
I'd start with the cheapest things first and work your way through some simple things. You've changed the crank sensor, fuel pump and coil so those can now be assumed to be OK. I doubt it's the alternator as I think if that was faulty your red charging light would be coming on and I think you would have noticed that.
We are also looking for something that fails when it's hot and then 'cures' itself when it cools down? hhmmm.....
I think you said your plugs looked OK, but no harm in changing them all, just in case and to eliminate them.
Are your plug leads the original set from the donor car or did you replace them during the Sportster build. If they are the originals, I would invest in a new set but if they were new then leave those for now.
As Jim suggested, I think the rotor arm is worth replacing but try to get a good quality one. Personally, I wouldn't bother testing it as Jim suggested, I would just swap out the old one.
Water temperature sensors are notoriously unreliable. Usually they causing hunting or over fuelling but again worth a try as an intermittent failure might just be confusing the DME.
Throttle Position Sensor? - another fairly simple inexpensive sensors to change. Again, intermittent failure may be confusing the ECU/DME.

Finally, (for now) as your last failure was almost fatal, it may be worth another go with the code reader to see if anything has ben stored but I think the last time you tried it didn't have any codes. (Note to Jim, these early e30 BMW's had very limited code storage capability as it was pre-OBD I )

Good luck,

cheers, Peter
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  #44  
Old 9th June 2015, 08:45
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MartinClan MartinClan is offline
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Peter - thanks for your thoughts. All input is useful.

The plug leads are like new. I don't remember if I replaced them or not but they are certainly not 30 years old! I changed the main lead to the coil when I moved it (it needed to be longer). The rotor arm is also new as I recall - but you are right - this is a cheap and simple thing to replace - so it will be next on my list.

I checked the temperature sensor some time back - it was fine. Even if it had an itermittant fault I cant imagine it would produce the extreme symptoms I am getting. Worth changing the AFM though. I have a spare somewhere I think...

The missfire itself is odd. It starts off as a small reduction in power - I guess it is just missing on one. This comes and goes for a few miles getting progrssively worse. I guess missing on more and more cylinders - its difficult to tell from behind th wheel. Evantually it gets so bad that there is not enough energy to move the car! And it sounds like a tractor. Strangely though there is never any backfire.

The reason I am suspicious of the alternator is that I changed it just before the problem started. Of course it may just be a coincidence. I was wondering whether it could be generating some spikes that are interfering with the ECU.

I have sourced an ECU - it should be arriving in the next few days. But before I swap it you are right - it would be useful to try reading the diagnostic codes again.

Cheers, Robin

Edit. I hadn't thoght about changing the throttle postion sensor. Is it just a switch or is it a pot - does anyone know?
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  #45  
Old 9th June 2015, 09:37
phil.coyle phil.coyle is offline
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You are right in thinking it is a potentiometer. You can reset them very simply, because the values of tickover and flatout are already programmed in the ECU you can re-learn the ECU to read the TPS by ,
1. Turn on ignition.
2. Press throttle pedal fully down and up quite quickly about 10 times should do it.
3. Turn ignition off and wait a few minutes, or finish your tea!
4. Start engine.

The number of times you press the pedal varies with different cars, some more some less, but I find 10 is about enough. At resting position with the ign on the TPS should read 0.4-0.5 volts or thereabouts, if it reads 0 volts it is dead.
Phil
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  #46  
Old 9th June 2015, 10:57
ozi jim ozi jim is offline
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You are not thinking it through.
You scanned and none of the sensors came up as an issue, you have to trust that and move on.
An ECU will throw an internal error code or a bunch of codes that make it a liar.
If you think its an alternator then when it starts to missfire remove the fan belt if its causing any RF then that will prove a point, if it aint turning it should not be an issue.
I assume the alt is charging and battery is full.

I would be very surprised if its an ECU.
Only time I have seen BMW ECU fail is water.

Is this engine fitted with an ignition module.?????

It sounds like an ignition module because that will cause the rev counter to flick,the counter circuit is linked to the ign coil primary circuit, and so is the module and the primary side of the ign coil.
And also will stall when put under load because the circuit is failing.
Ign modules are matched to the coil, I gather you put a different coil on it (from the auto store) non BMW this can cause the module and or coil to fail if there is a miss match.

Before you do anything you should change the coil and module.
You said the coil is new but if not suited to that module they only last a week or two.

Why did you change the coil originally ??????? was there a problem.


jim

Last edited by ozi jim; 9th June 2015 at 11:15..
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  #47  
Old 9th June 2015, 11:27
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MartinClan MartinClan is offline
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Quote:
Originally Posted by ozi jim View Post
You are not thinking it through.
You scanned and none of the sensors came up as an issue, you have to trust that and move on.
An ECU will throw an internal error code or a bunch of codes that make it a liar.
If you think its an alternator then when it starts to missfire remove the fan belt if its causing any RF then that will prove a point, if it aint turning it should not be an issue.
I assume the alt is charging and battery is full.

I would be very surprised if its an ECU.
Only time I have seen BMW ECU fail is water.

It sounds like an ignition module because that will cause the rev counter to flick,the counter circuit is linked to the ign coil primary circuit, and so is the module and the primary side of the ign coil.
And also will stall when put under load because the circuit is failing.
Ign modules are matched to the coil, I gather you put a different coil on it (from the auto store) non BMW this can cause the module and or coil to fail if there is a miss match.

Before you do anything you should change the coil and module.
You said the coil is new but if not suited to that module they only last a week or two.

Why did you change the coil originally ??????? was there a problem.


jim
Thanks Jim.

Removing the fan belt can't easily be done as it also drives the water pump. However I had thought about putting an isolator switch in the alternator output so I could easily disconnect it as a test.

There isn't an ignition module! Motronic 1.3 drives the single coil directly - sparks are then routed with a conventional distributor. I changed the coil as it was a simple thing to do and it's orginal location meant it was getting cooked by the exhaust manifold. The replacement coil is for electronic ignition so it should be fine (and now on the bulkhead so cool as well...). But of course it hasn't made the slightest difference.

The "funny" thing is I used to be an electronics engineer fault finding on control systems far more complex than this. I was good! Which only makes my lack of success with this even more frustrating!

Cheers, Robin
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  #48  
Old 9th June 2015, 12:51
ozi jim ozi jim is offline
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The other thing I have struck with these is the cam sensor cable was falling apart and shorting.

Whe I said disconnect the belt its only to see if the miss goes away, not till it cooks.

The problem I can see is lack of equipment to confirm, ign scope ect.

Jim

Last edited by ozi jim; 9th June 2015 at 13:03..
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  #49  
Old 11th June 2015, 22:20
8 Valve Ed 8 Valve Ed is offline
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Robin, having made my first journey with the Berli, and suffered with a heat related refusal to start, I thought of your issue.

Might it be related to ethanol? I am guessing your engine isn't the latest, perhaps an early fuel injection unit, I don't 'know' the BMW engine types so please excuse my ignorance but I wonder if your problem might be related to vapour locking? On the face of it that seems to match the symptoms you describe, it won't lave a fault code and self corrects once the engine has cooled.

At least worth a thought?
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  #50  
Old 19th June 2015, 21:12
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I had thought about a vapour lock. But I recently put a pressure gauge in the hp fuel line which indicates all is well on that side.

Last weekend I replaced the ECU. Interesting result. The missfire is worse! All I can think off is that the missfire is being caused by interference and the new ECU is more suseptable. Hmm....

I have reinstated the BMW check engine light. It's flashing madly indicating a problem. You are supposed to be able to read the fault codes using it and something called the stomp test - but I havent been able to make thst work.

I am going to try running without the alternator tomorrow. It seems I just need to remove the charging indicator lamp which provides the excitation current and the alternator ceases to err alternate....

Robin
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  #51  
Old 19th June 2015, 22:16
8 Valve Ed 8 Valve Ed is offline
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Quote:
Originally Posted by MartinClan View Post
I had thought about a vapour lock. But I recently put a pressure gauge in the hp fuel line which indicates all is well on that side.

Robin
I don't properly understand the 'Vapour Lock' phenomenon but unless the vapour lock is in the pump, I would expect the test pressure to be OK, but for some reason the injection mechanism (or carburettor) seems unable to function properly to feed vaporised fuel into the induction side of the engine.

I need to read up/research this because it seems pretty fundamental. I am in correspondence with somebody who seems to have some experience of temperature control in IC engines.

I know my carbs are being supplied with cool (liquid) petrol but the engine refuses to fire, when a few seconds before, it was running well. I know this isn't exactly your problem but it's similar, it seems to me that as soon as the engine stops and induction ceases, the carb venturi heats up, or to put it another way, ceases to be cooled by the passage of air in depression, which cools the air and the carb venturi. The latent heat in the carb body then immediately warms the venturi and the vaporises the fuel in the jet, apparently preventing the venturi from sucking liquid fuel from the jets.

Allowing the engine mass to cool below a critical temperature, allows the engine to start, because the liquid fuel is no longer vapour, the main jets which are not designed to pass vapour therefore the mixture isn't rich enough to start the engine.

That's the rough bones of my theory but it needs some meat, in the form of accurate temperature monitoring at the critical points. Some research as to what temperature ethanol bearing fuel vaporises, also what effect atmospheric depression has on all this, the boiling point of liquids varies with atmospheric pressure, therefore the depression in the venturi may affect the boiling point therefore the formation of vapour which seems to stop the show. Wish I was a chemist! LOL

Hope some of that makes sense.
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  #52  
Old 21st June 2015, 15:25
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A fueling problem was my first suspect. So I changed the fuel "route" so that the high pressure return goes straight back to the tank without the possibilty of it recirculating through the hp pump and getting overheated. It may still be worth trying a tank of the more expensive stuff though. I'll try tyat next time I fuel up.

I just came back from a run without the alternator working. Still has the missfire - so that eliminates that.

One other thing that is odd though is that the characteristic of the missfire has changed since I changed the ECU. Something else to think on....

Cheers, Robin
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  #53  
Old 23rd June 2015, 08:45
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I have done some thinking and poking arround on the E30 zone web site. It seems the only transducers that really affect the engine management are the Crank Position Sensor and the AFM. The other various sensors are only use to tweak the fuel mapping depending on temperature etc. It shouldn't be possible for them to cause a missfire. I have changed the CPS. And I don't see how the AFM could cause the pattern of missfire that I have. So on to new ideas...

Next step is a new set of leads - although that seems to be grasping at straws as the existing leads look fine. But I didn't replace them when I built the car so they could be the originals which makes them 25 years old!. They are Beru which is one of the OEM brands. I have decided to DIY them as a new OEM set is It's cheaper to buy the proper crimping tool and the various bits required.

At this rate I'll have a complete new engine management system.....

Robin
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  #54  
Old 23rd June 2015, 09:09
8 Valve Ed 8 Valve Ed is offline
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There is a very easy check for the integrity of the plug leads, lift the bonnet after dark and blip the accelerator, if you have a minor firework display they are leaking.

But it's a good idea to replace them anyway.
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  #55  
Old 25th June 2015, 13:25
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GreatOldOne GreatOldOne is offline
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The TPS is a switch, and nothing else. All it does so send WOT signal to the ECU

The AFM meter is a potentiometer, and the tracks can become worn. You can move the wiper arm onto Virgin carbon track:

http://youtu.be/-11J8XawQtc

The other thing is to get another, known good ECU. I had the Devils own job with the original motronic 1.1 system I had, and when I finally swapped all the engine loom and management for 1.3, I opened up the old ECUs to find and absolute horror show:

http://www.greatoldone.co.uk/blog/20...here-fast.html
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  #56  
Old 25th June 2015, 13:49
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Quote:
Originally Posted by GreatOldOne View Post
The AFM meter is a potentiometer, and the tracks can become worn. You can move the wiper arm onto Virgin carbon track:

http://youtu.be/-11J8XawQtc
Wow - I didn't realise it was that primative. As my engine has done 170k I will certailny have a look at that.

Quote:
Originally Posted by GreatOldOne View Post
The other thing is to get another, known good ECU.
Yep - done that. It's getting to the point where I almost have enough bits to build a complete new engine management system....

Cheers, Robin
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  #57  
Old 25th June 2015, 22:48
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Quote:
Originally Posted by MartinClan View Post
I have done some thinking and poking arround on the E30 zone web site. It seems the only transducers that really affect the engine management are the Crank Position Sensor and the AFM. The other various sensors are only use to tweak the fuel mapping depending on temperature etc. It shouldn't be possible for them to cause a missfire. I have changed the CPS. And I don't see how the AFM could cause the pattern of missfire that I have. So on to new ideas...

Next step is a new set of leads - although that seems to be grasping at straws as the existing leads look fine. But I didn't replace them when I built the car so they could be the originals which makes them 25 years old!. They are Beru which is one of the OEM brands. I have decided to DIY them as a new OEM set is It's cheaper to buy the proper crimping tool and the various bits required.

At this rate I'll have a complete new engine management system.....

Robin
Robin

Have you considered fitting new plugs/sockets to the loom wires that connect to all the sensors? I had a broken connector to my TPS which caused me problems similar to yours, and I only found it by luck - I caught a wire with my sleeve while poking around at something else and it disturbed the engine revs.
There was a fractured wire/pin contact inside the connector which gave an intermittent fault that was impossible to diagnose.

My 5 is still on it being an electrical fault..........!

Mike
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  #58  
Old 27th June 2015, 11:06
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Default Some progress

Yesterday, for some reason, I decided I would strip down all the fuel system just in case there was some odd problem or obstruction. I lined up an old icecream box under the swirl pot in attitipation of 1 litre of petrol pouring out and removed the bottom fuel union. Only a teacup of fuel came out. The rest of the contents was air. Err - that's odd...

It turns out that the low pressure pump, an expensive Facet Red Top, is completly dead. Open cicuit in fact implying some catastrophic failure of the internal electronics.

So - the Walbro HP pump had been sucking fuel directly from the tank through the empty swirl pot and the dead LP pump. Very impressive - but I am guessing responsible for at least part of my problem. It begs the question of course whether the LP pump, swirl pot, HP pump set up is really necessary. Anyway rather than redesign the fuel system I have ordered a new LP pump (more ). Should arrive next Tuesday - I can't wait.

I have to say though I am not convinced that this is 100% the problem - but it must have been at least a contributary factor.

What this space....

Robin
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  #59  
Old 27th June 2015, 13:25
phil.coyle phil.coyle is offline
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Well at least you have something to go on, and I almost got it right when I suggested a fuel problem.
The down side is, and I really don't want to spoil your weekend, but the extra strain put on the HP is the reason for the cutting out and restarting a few minutes later. This is something I have experienced myself and even though my HP was only a few months old it would cut out through overheating. In my mind the pump was brand new it could not possibly be that but the extra strain on it meant that it would run, get hot and then stop, but you could leave the engine running all day. So even after changing the LP you may still experience the cutting out problem it depends on how overworked the HP has become. At least you can easily access your pump, mine is in the tank and a right pain in the backside every time I was fault tracing. Don't get despondent at last you know you are on the right track,and my apologies for the bad news.
Phil.
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  #60  
Old 27th June 2015, 22:31
jeremy jeremy is offline
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Default HP pump

Hi robin, I have a spare HP pump should u need one, regards Jeremy
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