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cturle
Joined: 04 Nov 2013
Posts: 5
Location: France
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 Posted: Mon Nov 04, 2013 9:51 pm Post subject: [924] not starting anymore |
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Hello,
i have a problem with my 924 (year 81, transistorized ignition). It doesn't start anymore since last week.
last friday, i cranked 2 times, starter ok but the car didn't start. The third time, it starts nicely and i drive home (4km)
saturday, i cranked and the car started nicely then i stopped.
monday, i cranked, starter ok but the car don't start anymore.
Test 1 :
I shunt 30-87 of fuel pump relay => fuel pump ok.
Test 2 :
fuel pump relay out to not flood the engine.
I take off one spark plug. I crank => no spark.
picture : https://drive.google.com/file/d/0B6olF0lJebH3eFV0dU9HejdXdDQ/edit?usp=sharing
Test 3 :
fuel pump relay out to not flood the engine.
I take off one spark plug but plug it directly on the coil (terminal 4). I crank => no spark.
picture : https://drive.google.com/file/d/0B6olF0lJebH3cDNOVEVBVy1uQms/edit?usp=sharing
Measures :
resistance between ignition coil terminals 1 and 15 : 2,5 ohms
resistance between ignition coil terminals 4 and 15 : 7 KOhms
tested spark plug cable resistance : 2KOhms
distributor/coil cable resistance : 2KOhms
With ignition on :
voltage between ignition coil terminals 15 and ground => 6,45 V
voltage between ignition coil terminals 15 and 1 => 5,02 V
voltage between ignition coil terminals 1 and ground => 1,43 V
Any suggestion ? |
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dpw928
Joined: 02 Nov 2002
Posts: 1860
Location: owasso, ok 74055
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| Posted: Tue Nov 05, 2013 12:20 am Post subject: |
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What is your voltage between 15 and ground at the coil when cranking?
Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black |
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larchie
Joined: 19 Jun 2003
Posts: 297
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| Posted: Tue Nov 05, 2013 1:16 am Post subject: |
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For '81 and '81 models, Hanes puts primary resistance between + T-15 and - T-1 at 0.5 to 0.76 ohms and secondary resistance between high tension T-4 and - T-1 at 2.4 to 3.5 K-ohms; so your measurements are not within specifications. (Your cables look fine as better performance wires).
Hanes says ...
| Quote: | | Replace the ignition coil with a new one if the resistance is not with the specifications |
But before you do so, since coils are normally reliable, you might check the following:
(I'm assuming when you tested your plug, it was about 0.5 cm or less from a ground and did not spark.)
(1) Check fuse A12.
(2) Disconnect high tension cable from center terminal of distributor cap and hold about 10 mm from engine block. If no spark (or spark is weak) then the coil probably should be replaced if other ignition parts are fine.
(3) This might seem obvious but make sure you don't have reverse polarity -- so check that the wire from the ignition switch goes to terminal 15 and the wire from the distributor to terminal 1.
(4) Sometimes there is a spark arc from terminal 4 to ground which can prevent the engine from starting -- check for carbon tracks into the coil tower.
Finally, here are some other things to re-check before replacing the coil:
(1) Make sure battery isn't run down.
(2) Check the wiring between the ignition switch and the coil and check for a faulty distributor. |
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cturle
Joined: 04 Nov 2013
Posts: 5
Location: France
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| Posted: Tue Nov 05, 2013 7:51 am Post subject: |
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| dpw928 wrote: | What is your voltage between 15 and ground at the coil when cranking?
Dennis |
When cranking :
voltage between ignition coil terminals 15 and ground => 7,5-8V
voltage between ignition coil terminals 1 and ground => 3-3,5V
is it ok ?
but, now i see some sparks ... dunno what has changed 
Tomorrow, i will check if the car now starts. |
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cturle
Joined: 04 Nov 2013
Posts: 5
Location: France
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| Posted: Tue Nov 05, 2013 8:21 am Post subject: |
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| larchie wrote: | For '81 and '81 models, Hanes puts primary resistance between + T-15 and - T-1 at 0.5 to 0.76 ohms and secondary resistance between high tension T-4 and - T-1 at 2.4 to 3.5 K-ohms; so your measurements are not within specifications. (Your cables look fine as better performance wires).
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Looking in Haynes p122, §22.6, i read 1 - 1.35 Ohms for primary and 5.5 - 8 kOhms for secondary. Can you tell me the page you read ?
| larchie wrote: | | (I'm assuming when you tested your plug, it was about 0.5 cm or less from a ground and did not spark.) |
The photo is not good, but you may see i put the spark plug on the engine block.
| larchie wrote: |
(1) Check fuse A12.
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Which one is it, haynes ref ? i checked all fuses in the two box and they are ok.
| larchie wrote: |
(3) This might seem obvious but make sure you don't have reverse polarity -- so check that the wire from the ignition switch goes to terminal 15 and the wire from the distributor to terminal 1.
(4) Sometimes there is a spark arc from terminal 4 to ground which can prevent the engine from starting -- check for carbon tracks into the coil tower.
(1) Make sure battery isn't run down.
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All this is ok.
| larchie wrote: |
(2) Disconnect high tension cable from center terminal of distributor cap and hold about 10 mm from engine block. If no spark (or spark is weak) then the coil probably should be replaced if other ignition parts are fine.
(2) Check the wiring between the ignition switch and the coil and check for a faulty distributor. |
My last try results in sparks. So i will now try to start the car. |
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ThomasJoseph315
Guest
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| Posted: Tue Nov 05, 2013 8:51 am Post subject: |
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| Just a shot in the dark, but you checked the ignition relay? |
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Ozzie
Joined: 12 Mar 2005
Posts: 4448
Location: Townsville, Qld. Australia
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| Posted: Tue Nov 05, 2013 10:17 am Post subject: |
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Did you check the resistance between the dissy leads and the ignition module and coil?
Also voltage at ignition module?
Is the ignition module earthed? Later models had no earth wire and used the mounting screws to earth the module.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance |
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larchie
Joined: 19 Jun 2003
Posts: 297
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| Posted: Tue Nov 05, 2013 11:01 am Post subject: |
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I hope I'm right in assuming you have a non-turbo engine and the TCI-H ignition system with a Hall transmitter and idle stabilizer. (There are a number of precautions necessary in testing to avoid damage, especially make sure ignition is off when making or breaking connections. I think your model should have a special ignition coil and not a standard "off-the-shelf" coil.)
| Quote: | | Looking in Haynes p122, §22.6, i read 1 - 1.35 Ohms for primary and 5.5 - 8 kOhms for secondary. Can you tell me the page you read ? |
Hmm, perhaps you have an European edition of Hanes. In the Porsche 924 Owners Workshop Manual 1976-1980 by Lipton published in 1981 in England by Hanes, p. 128, Ch 5 Sec 15 primary resistance is similar to yours (1.0 to 1.3 ohms; 0.95 to 1.4 on Turbo) but the secondary resistance listed is not in K-ohms, it's 5.5 to 8.0 ohms. In this 1981 edition, there is undoubtedly a mistake in Hanes where also the secondary resistance of the ignition coil is listed by connecting the ohmmeter between terminals 1 and 15, whereas it should be of course terminals 1 and 4.
So the data I quoted in the post above above was from a more recent version of Porsche 924 and Turbo 1976 thru 1982 (now on sale in the States at that URL) by Lipton and Haynes published in the U.S. in 1984 which states the same thing with the same typo(s) on p. 128, Ch 5 Sec 15 as the 1981 edition. But there is an Supplementary Chapter 13 in this edition entitled "Revisions and information of later models" which includes changes for the 1981 and 1982 model years.
These data in Chapter 13 (1984 edition) are:
primary 0.52 to 0.76 ohms; secondary 2.4 to 3.5 K-ohms, p. 289.
| Quote: | | The photo is not good, but you may see i put the spark plug on the engine block. |
Your photos were excellent. (My apologies for making extra-sure of how you tested for spark.)
| Quote: | | [Check fuse A12] ... Which one is it, haynes ref ? |
Sorry, I wasn't clear at all here. A12 is a wire connection on the fuse/relay board. On the female side on the back of the board it's the ivory plug in position 1 (i.e., the engine compartment harness). For location see your Hanes, probably somewhere in Chapter 11 on Electrics. Since you have spark, it's not necessary to check this.
| Quote: | | So i will now try to start the car. |
If you have an intermittent problem starting post back here with more information. Hopefully it's not a hard to locate brittle or broken-when-flexed-cable. |
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cturle
Joined: 04 Nov 2013
Posts: 5
Location: France
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| Posted: Wed Nov 06, 2013 6:47 am Post subject: |
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Hi all and thanks for your posts.
I put the spark plug and fuel pump relay back and the car starts ^^ It's cool but since i don't know why, i think it's just a question of time for the problem to come back.
I will change my spark plugs, my rotor cap and check all spark plug cable resistances.
other points :
- my haynes is a 1989 edition. The chapter 13 is included. The mistake is there. I now see the measure you were talking about. It is in the TCI-H description. But, in fact i'm pretty sure i have an early-type control unit (transistorized ignition, chapter 5, §22)
- i see the ivory plug. What is the A12 wire conection about ?
- Ozzie, i didn't check the module connections since i don't know which connections to measure.
- Thomas, ignition relay ? do you mean the fuel pump relay ?
I will try to drive tomorrow and see what will happened. |
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larchie
Joined: 19 Jun 2003
Posts: 297
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| Posted: Wed Nov 06, 2013 1:49 pm Post subject: |
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| Quote: | | ...in fact i'm pretty sure i have an early-type control unit i see the ivory plug. What is the A12 wire conection about. |
The introduction to Chapter 13 (the only part of the manual written by John Hanes himself) says this chapter was added to apply to differences of the 1981 and 1982 from the previous model years or the 924. So if your ignition system has parts looking like Fig. 5.11a and fig. 5.11b rather than Fig. 13.5 in Chapter 13 your coil is probably fine, and the differences in ignition setup occurred at a higher VIN than your car. If when you tested the spark with the spark plug initially the plug was touching the engine block rather than a few mm away, then you might not have seen any spark since the plug was grounded. What you would be normally looking for is a blueish "blat!" between the plug and the block.
The reason for the initial suggestion of checking the black/blue wire from the position 5 connection on the female side of the A plug on the fuse board is that it goes to terminal 15 of the coil and would be a minor step in checking the continuity of the ignition system. (See Ch. 13 Fig 13.4 track 11 of the current flow diagram for the '81 - '82 924 in your Hanes.)
If the problem comes back or you have further similar starting problems, then it seems your next best bet would be to test the fuel delivery to the cylinders. When all is said and done, as far as I can tell, your 924 has had these symptoms: (1) engine didn't start when cranking, and (2) engine stopped after starting. Fuel pump works and you have spark.
If there is some restriction in fuel delivery (e.g., stuff like rust in the fuel tank, clogged fuel filter, leaky or ruptured accumulator) then this might cause the car not to start on occasion and to stop running after start on other occasions.
Later Edit:
| Quote: | | Ozzie, i didn't check the module connections since i don't know which connections to measure. |
Testing at the ignition control unit is covered in Ch 5 Sect 22 Step 8 of Hanes. If you still suspect an ignition problem after driving tomorrow, it would be useful to go through the troubleshooting steps in procedure outlined in Sect. 22.
For proper air delivery, check that the air sensor lever and the throttle by-pass valve move freely. |
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cturle
Joined: 04 Nov 2013
Posts: 5
Location: France
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| Posted: Thu Nov 07, 2013 6:03 am Post subject: |
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more news :
The car started this morning and this evening  Perhaps cleaning rotor cap did the trick. I will see.
| larchie wrote: | | Quote: | | ...in fact i'm pretty sure i have an early-type control unit. |
The introduction to Chapter 13 (the only part of the manual written by John Hanes himself) says this chapter was added to apply to differences of the 1981 and 1982 from the previous model years or the 924. So if your ignition system has parts looking like Fig. 5.11a and fig. 5.11b rather than Fig. 13.5 in Chapter 13 your coil is probably fine, and the differences in ignition setup occurred at a higher VIN than your car. |
In fact the control unit looks exactly like picture 16.2 (p130)
| Quote: | | The reason for the initial suggestion of checking the black/blue wire from the position 5 connection on the female side of the A plug on the fuse board is that it goes to terminal 15 of the coil and would be a minor step in checking the continuity of the ignition system. (See Ch. 13 Fig 13.4 track 11 of the current flow diagram for the '81 - '82 924 in your Hanes.) |
After checking more closely, my ignition system is described with the diagram p258 chapter 11 (model 1980 standard).
| Quote: | | your 924 has had these symptoms: (1) engine didn't start when cranking, and (2) engine stopped after starting. Fuel pump works and you have spark. |
not exactly, (2) => I stopped the car after starting, it doesn't stop running by itself.
| Quote: | | For proper air delivery, check that the air sensor lever and the throttle by-pass valve move freely. |
Sometimes, i have some oil on the air plate sensor, i will check it and clean it as needed.
Thanks for your help. |
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