IRRATIC START WHEN COLD

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pointer
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Passat model: 1741 estate 1991

IRRATIC START WHEN COLD

Post by pointer » Sat May 04, 2019 3:08 pm

My 1991 Passat B3 has an RP engine but recently I put semi synthetic oil in by mistake. Since then my oil pressure warning and light comes on after about 20 miles. I decided to install a electrical oil pressure gauge which showed approx 80 psi on start up but as the engine warmed up the pressure dropped to almost zero.

I decided to drain the oil and check the oil pump and was surprised to see the filter on its suction pipe was vitually blocked with remnants of sealant used on the sump gasket. I cleaned the filter as well as any other remnants of the sealant in a hope that that was the problem. I replaced the sump and new gasket which had been showing oil seepage, as well as the rocker box cover gasket as that had also be showing oil seepage as well.

However on attempting to start the engine from cold it took about 10 seconds before it started to fire up, all be it hesitantly. Once the tick over was reasonable, I was able to drive normally and able to travel without problem although I haven't done a 20mile trip yet! Each time I start from cold the same thing happens but if I let the engine warm up and the stop for a few minutes, on the restart it fires up OK. I've checked spark plugs which appear OK , also the distributor and rotor arm were OK.


I'm not sure if this is an ignition problem or if it's a fault on the single point petrol fuel 'injector'. Any help would be appreciated. ~x(

pointer
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Posts: 77
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Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Sun May 05, 2019 6:41 pm

This morning I tried something different! Sitting in the car, I depressed the accelerator pedal slowly and held it down. I then turned on the ignition and energised the starter motor. The engine fired straight away and was able to drive without problem with my dogs for their walk.


Unfortunately, having walked the dogs for over an hour and about to return home, I tried the same thing but this time I had the problem of not firing up the engine for about 10 or more seconds before it fired erratically and subsequently ticked over correctly . So what was different this time? ~x(

pointer
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Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Mon May 06, 2019 4:38 pm

The exact same thing happened this morning ie cold engine started OK when I had slowly depressed the accelerator pedal before engaging the starter motor but after an hour or so with the dogs and then going through the same procedure it started erratically for 10-15 seconds before firing normally. The mind boggles :-??

pointer
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Posts: 77
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Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Wed May 08, 2019 11:36 pm

Today I checked the ignition side ie coil, leads, distributor, rotor arm which all seemed OK. I then concentrated on the fuel injector. Whilst I removed the injector, I did not run the engine to warm it up as suggested in the Haynes Manual. I checked the resistances as advised in that manual and all were within the tolerances given. I then opened up the unit to clear any possible oil contamination from the leaking rocker box cover. On reassembling I started the engine OK and drove for 2-3 miles before returning home. I switched off the ignition, waited a few seconds and attempted a restart. However, this time it did not want to start, and when it did it it seemed to be firing on less than 4 cylinders ie very rough! It did pick up eventually. So I still have gremlins!!!

Any clues as to what the problem is? :-??

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Alan Gunn
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Re: IRRATIC START WHEN COLD

Post by Alan Gunn » Thu May 09, 2019 3:11 am

I would try a different set of plugs.
A set of new plugs the other week gave a good spark but one of them when fitted was not firing.
Image

pointer
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Re: IRRATIC START WHEN COLD

Post by pointer » Sun May 12, 2019 10:21 am

THANKS, I HAD DECIDED TO REPLACE THE SPARK PLUGS AND AM AWAITING DELIVERY. HOWEVER, I CHECKED ONE OF THE PLUGS AND COULD NOT SEE A SPARK. I THEN REMOVED THE LEAD FROM THE CENTRE OF THE DISTRIBUTOR AND COULD NOT GET A SPARK THERE EITHER! LOOKING AT TWO VERSIONS OF HAYNES MANUAL, ONE OLDER THAT THE OTHER THEY GAVE DIFFERENT READINGS FOR THE HT SIDE OF THE COIL, ONE APPROX 3-4 KOHMS, THE OTHER JUST SINGLE FIGURE OHMS, PROBABLY A MISPRINT(?)

ON CHECKING THE RESISTANCES, THE PRIMARY WAS OK BUT THE SECONDARY WAS OPEN CIRCUIT. THIS WAS IMMEDIATLY AFTER RUNNING THE ENGINE!!


I WAITED UNTIL THE ENGINE HAD COOLED DOWN AND I COULD SOMETIMES GET A READING OF APPROX 3.3 KOHMS BUT NOT ALWAYS. SO TODAY I WILL BE REMOVING THE COIL AND CLEANING WHAT I CAN TO SEE IF IT IMPROVES. WISH ME LUCK.

maclee
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Re: IRRATIC START WHEN COLD

Post by maclee » Sun May 12, 2019 1:00 pm

Only just seen this thread.

Is the ignition coil on your car the box-shaped version (called an ignition transformer),


transformer.jpg


or is it the standard cylindrical type?




coil.jpg
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pointer
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Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Sun May 12, 2019 9:18 pm

Hi, it's the box type Not the cylindrical type. However, I removed the device and cleaned everything I could and replaced it. I have now realised why I sometimes got a reading on the multimeter and sometimes appeared open circuit. It was because I had inadvertently reversed the connections on the multimeter probes, so all appears well with the ignition coil itself, probably due to a diode in circuit(?) :-o

What I did find was that the LT and HT resistances were correct, and although there was a +ve supply at the coil, there was not a -ve which appears to come from either the TCI-H Control Unit or the Relay for the Lambda Probe Heater, Haynes wiring diagrams do not make it absolutely clear, I suspect the former but clarification would help!

On my car, there is only a single wire connected to the Lambda probe, ie there is NOT a Lambda Probe Heater or that I am aware of ! This appears to substantiate my reasoning that the problem lies with the TCI-H Control Unit. However, where is that located and are replacements available? :-?

maclee
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Re:ERRATIC START WHEN COLD

Post by maclee » Sun May 12, 2019 10:48 pm

Around that time VW were using both styles of coil and it seems that the RP engine more often had the cylindrical version, so I guess yours is probably a later example to have the transformer rather than a conventional coil. I will refer to yours as a transformer from now on, for clarity.

I have not had any dealings with the single point injector engine, BUT in the past there have been two B3s in my family, both 91 models, both with the multipoint 2E engine and transformer style coils. There has also been a MK1 SEAT Toledo of about the same age, and while I am not certain what engine code it had, I am certain that it too had the transformer style coil.

All three cars at some point in there lives suffered failure of the transformer. If I remember correctly, in the first instance (B3) the car refused to start intermittently, and I think this happened when the engine had been running, was stopped, and then would not restart until it had been left a while, (presumably giving it time to cool down). After a while it then refused to start at all.. In the second instance (B3) the engine refused to start at all... no spark. The third car, the SEAT, started to exhibit signs of intermittent no starting, (again no spark), so the transformer was changed immediately, and the problem was cured.

I did cut one of them open, (cannot recall which), and found that there was a carbonised path within, suggesting internal tracking from the HT terminal to ground, (effectively shorting the spark voltage to ground within the transformer).

There will not be a rectifier (diode) on the HT side of the transformer, there is no reason to have such a thing. What I think you found with your resistance measurements is probably an intermittent open circuit on the HT winding, perhaps going open circuit when warm. Remember that this transformer sits at the back of the engine bay, right over the exhaust. It is my guess that the transformer is OK when cold, and when the engine is running heat is carried away from the engine bay by the passage of air. When you stop the car, the heat from the exhaust rises and bakes the transformer which then goes open circuit, produces no spark or a weak spark and prevents the engine starting correctly. Once it cools again all is well.

I arrived at this theory from previous experience of the petrol burning heater of my Dad's 73 412LE, which had an ignition coil mounted on the top of its housing. The heater worked fine when first switched on, and as it switched off and back on to regulate the car's temperature, it would work fine because its blower was constantly running, BUT if you turned the blower off, heat from within the device would not be carried away and would heat the housing on which the coil was mounted. The next time it tried to fire up nothing happened because there was no spark, (until it cooled down again), because the coil went open circuit when heated. This was fixed with a new coil (and its relocation away from the heat source). I think this is possibly what you are experiencing with your ignition transformer.

A new transformer is about £20 on ebay, (pattern part of course), so is probably worth a shot.

If you want to change it, have a look at the existing one and see if it has a part number on its label. There are a number of different transformers so that number will assist in finding the right one. If there is no part number or any other identifying marks, please count the number of pins in the LT connector, it is probably 3, but may be more.

I cannot guarantee that a new transformer will fix your problem, but from experience (and the low cost of a new one), that is where I would start.

Good luck!

pointer
B1
Posts: 77
Joined: Mon May 16, 2011 6:48 pm
Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Mon May 13, 2019 10:28 pm

Thanks, very encouraging to say the least.

Having now worked on it over the weekend, I find that starting from cold but not driving away, the engine ticks over reasonable well for about a minute, then it speeds up and races without the throttle being pressed and the throttle arm on the single point injector not moving either. That happens for another minute or so when the speed drops to a nice gentle tick over better that when I first started the engine, but it still will not start again if I switch off and then on again and try to crank the engine.


Query, do I appear to have two problems, a) possible ignition transformer as explained by Maclee as posted above, and b) a fuel injector problem?


If I am unable to find a suitable transformer, do you think I could swap it with a canister type coil, although that would also means changing the method of electrical connections to it?

pointer
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Posts: 77
Joined: Mon May 16, 2011 6:48 pm
Passat model: 1741 estate 1991

Re: ERRATIC START WHEN COLD

Post by pointer » Tue May 14, 2019 7:05 pm

Today the car would not start at all!!!!

I then removed the coil and have taken measurements of all resistances, some of which may be of concern ie high resistance to the frame which -ve, may be tracking (?). See attachment.
igntion coil resistances.xls
I'm not sure if this means the module is US, can any one advise please? ~x(
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maclee
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Re: IRRATIC START WHEN COLD

Post by maclee » Wed May 15, 2019 1:47 am

Basic coil diagram from Hella website:

coildiag.png

The resistance measurements on your diagram all look right EXCEPT for that 3.9k from terminals 15 & 1 to ground.

First things first. Are you sure that is a leakage value in the transformer? For example, if you were holding the meter probes in place, by their metal tips to make the measurement, that 3.9k value could just be the resistance of your body. If you were not in contact with the terminals or the probes during the measurement, then the leakage is within the transformer and should not exist.

Assuming it is a genuine leakage value....

Ordinarily, a 3.9k leak from a 12v supply would only account for a current of 3mA, which is nothing, especially in car terms. However, since the HT terminal is connected internally to terminal 15 (and then 1) though the windings, it is also connected to ground by the 3.9k leak, - plus the resistance of the secondary, which is 3.3k in your diagram, making a total of 7.2k between terminal 4 and ground, which to a high voltage (especially a pulse), is virtually a short circuit.

I assume that the leak to ground is being measured with a standard multimeter. Were you to use a 500v or a 1kv insulation tester you would probably find that leakage value was lower.

In any case you are measuring things cold, (as if the engine were cold) and without anything having been subject to load testing under supply conditions.

You may well have a fuel problem as well, but from what you have said here it certainly looks as if you transformer is in need of replacement before you can make any further trustworthy diagnostics.
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pointer
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Posts: 77
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Passat model: 1741 estate 1991

Re: ERRATIC START WHEN COLD

Post by pointer » Wed May 15, 2019 6:50 pm

THANKS, JUST SEEN YOUR REPLY BUT I DID ORDER A REPLACEMENT COIL/TRANSFORMER LAST NIGHT WHICH SHOULD ARRIVE BEFORE THE WEEKEND.

AT LEAST FROM WHAT YOU SAY THE COIL/TRANSFORMER DOES APPEAR TO BE AT FAULT, SO HERE'S HOPING THE SAGA WILL BE AT AN END (UNLESS THE LIGHT AT THE END OF THE TUNNEL IS AN ONCOMING TRAIN!) I WILL LET YOU KNOW IN DUE COURSE.


THANKS AGAIN

pointer
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Passat model: 1741 estate 1991

Re: ERRATIC START WHEN COLD

Post by pointer » Thu May 16, 2019 5:02 pm

Hi, new replacement coil arrived today but it looks like that light at the end of the tunnel is an oncoming train!

Having replaced the 'coil' it would not start. I checked several connections but no difference. I haven't opened up the replacement but disconnected it and took a reading between the HT terminal 4 and its outer body which gave a resistance of 17.17kohms compared with the old 'coil' which gave a reading of 7.1kohms today. I wonder if the new one is also faulty(?) I might add that my probes are insulated virtually up to the point of contact and not touched by me.


Realising that the high voltage is obtained when the supply to the primary is charged and then collapses, probably created by the Hall Generator, I disconnected the connection to the coil and put my multimeter probes into its cable connector between the brown wire and the green wire to check voltages when the engine was rotated. Although the multimeter kept fluctuating (as I believe it should) I could not get a spark when I replaced every thing and cranked the engine. So do you think that the new one is also faulty due to the high resistance between terminal 4 and ground?

I also took a voltage reading of approx 12.3 volts from the 'coil's' connector between the green wire and the black wire (Ignition 12volt+ve) and was surprised that it indicates to me that the green wire is effectively to 'ground' through the Control Unit, is that Unit faulty?


Chapter 4 to follow!

pointer
B1
Posts: 77
Joined: Mon May 16, 2011 6:48 pm
Passat model: 1741 estate 1991

Re: IRRATIC START WHEN COLD

Post by pointer » Sat May 25, 2019 11:02 pm

Sorry for not keeping in touch recently but I’m slowly going bonkers!

I decided to replace most things for the ignition circuitry ie, ignition/coil, leads, spark plugs but still would not start. The only thing I had not changed was the rotor arm.

I ordered one from Eurocarparts but when it arrived it would not fit as the mounting shaft apertures were different, mine being smaller at 10.2mm diameter even though their web site stated it was correct for an RP engine.

On their web site, there were other rotor arms having the same diameter aperture as mine although it stated they were for an ABS engine. However, I exchanged the over sized one for a smaller diameter aperture but when I fitted it there was no change as the engine would not start.

I could not get a spark at a spark plug so I disconnected the HT lead from the distributor and to my amazement there was a spark from that. The rotor arms looked the same physically as my old one so what could be the problem now? ~x(

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