Ignition has me stumped

Northern924 · Mar 13, 2008

Not had anoy problems with the car sicne it went back on the road last Nov. but I've just spent the past 3 days trying to start it!!
Just over a week ago, started having problems, would be driving along and for a few seconds would lose all power, then all be fine again, anyway Monday it just wouldn't start.

So bought a new rotor and cap, still nothing, checked the HT leads, bought a new coil today, and still nothing.

Went through all resistance and voltage checks, all came back OK, connected a HT lead and plug direct to the coil, and I've got a good strong spark, but when I connect the coil to the cap and the HT lead with the plug on back into place, no spark [

]

Checked the resistance of the coil to cap lead and HT, coil to cap reads 1.4k, HT reads 6.7k.

Its an '82 and I notice they don't have a condenser at this age, so does anyone have any ideas what could be causing it??

mr brightside · Mar 13, 2008

if your dizzy hasn't got a condenser that means it signals the coil through a hall sender unit, i'd eliminate that next.

Northern924 · Mar 13, 2008

Not had to work on the ing. system of a '24 before, other classics I've had have been basic condenser/points setups.
I've checked for voltage at pin 4 on the ICU and its the same as the battery out, also check resistance between pins 1&2 and that comes back at 1044 which is right in the middle of the tolerance range.

Just wondering, does the dizzy pickup sensor have any bearing on getting a spark?

924nutter · Mar 14, 2008

Yes it does but the 924 of that vintage does not have a hall sender a'la golf. It has a coil under the four legged spider. The ends of the spider pass through the air gap where the magnet is situated generating the signal due to lines of force crossing a conductor. The fact that you have a spark direct from the coil means you should at least be able to reproduce that when the leads are in place; as you can't it must mean that the HT is not able to pass from the coil to the lead. Check all the components in the chain;(coil-to-distributor lead, carbon contact in the cap, and rotor arm) one of them might be faulty but perhaps the tab in the rotor arm is not in its slot You also need to check that the spider hasn't slipped on the shaft and that when no.1 cylinder is at T.D.C., the spipder is in the airgap and that the rotor arm is pointing directly at the segment for no1 cylinder. I was once called in by a local mechanic to diagnose a rough running 924 which I had test driven before some friend of mine bought it and it drove beautifully. On the crypton analyser the spark was ocurring 15 or so degrees after tdc and the reason was that some one in the mechanics employ had forcefully rotated the spider on the shaft and the spark was just able to jump across the huge gap to the segment which by then was some 8 degrees past the segment. If all these things prove to be in order then I would suspect the ignition module. It has a habit of failing in such a way that it still sparks but at completely the wrong time and it could be that the module is firing so late that the spark cannot jump to the segment and along the lead.

Northern924 · Mar 15, 2008

924 technical advisor, what a very apt title!!
That is the most in depth help I've had yet, so I must thank you.

So far I have replaced the coil, cap, and arm with new.

I have even changed the distributor, and still nothing so can only think it is the module now. Didn't know about the spider alignment, so will check that later, but I'd be surprised if 2 dizzy's are out of line (although stranger things have happened!!)

The spark is getting through to the carbon bush, and both the dizzys have been AC test and are both throwing out a charge when spun by hand, checked for continuity of the green wire from the ICU to the dizzy, and done all the haynes resistance test.

So as of now the only thing I havn't changed is the Control Unit, know where there is one in Newcaswtle (I think!!) so will go and get it Monday and hopefully that'll solve the riddle, at least I'll have a full new ignition system by then [&:]

924nutter · Mar 15, 2008

Northern, you have to find out why the spark wont "ackle" with the cap on. Have you checked the coil-'strib lead? The ignition module is a last resort, the very last as a good 2nd hand one will set you back upwards of £85 nowadays, and a new one cost me £314 in 2001. Also, before we go to madly technical, check that the engine earth strap isn't now flapping about in the breeze due to the exchanging of components.

Fred Hindle · Mar 15, 2008

Could it be the fuel pump relay. I seem to recall my bil having intermittent problems that were caused by a faulty relay. Just a thought. Are the plugs wet when you take them out?

Cheers,

mr brightside · Mar 15, 2008

greetings 924nutter your kung fu is strong i see! it seems as a rookie 924 driver and Mk1 Golf GTI veteran tinkerer i have made the mistake of assuming they share the same subsystems. as an electrical engineer i understand your description of the coil electronics perfectly, an EMF is generated by a conductor cutting the lines of magnetic flux, exactly the same way an induction motor works! perhaps if you get a minute you could read my post on 924s 944 gearbox similarities. cheers.

Northern924 · Mar 16, 2008

Went out again this morning and checked all the earth straps, all seems good, the lead from the coil to the distr' is good, I've had the cap off and checked the carbon bush for voltage on turn over and its strong, just can't get a spark to the plugs, and all HT leads are good.
Fred did think of the FPR, but I've shorted between pins 87 & 30 and the pupm runs fine, also loosened the fuel in pipe at the fuel dist' and its feeding through OK.

Just can't understand why the spark can't get from the centre of the rotor arm to the tip [

] rotor arm is new and tested

peanut · Mar 16, 2008

ORIGINAL: Northern924

Just can't understand why the spark can't get from the centre of the rotor arm to the tip [] rotor arm is new and tested

well there's the answer I would say [

]

if you definitly have Hi tension at the end of the coil lead and definitly have a good rotary arm then it has to be the distributor cap.
Somewhere between the coil lead entry to the distributor cap and the spark plugs there is either an open circuit or a short circuit .Or it is firing at the wrong time and therefore the spark is not reaching the dizzie electrodes.

If you do need some cheap bits heres a good source. Hall sender £55 Ign control unit £25.00 etc http://www.autoguide.net/apf/porsche-ignition/924-catalog.html

Have you seen this troubleshooting guide ?
http://www.924.id.lv/Heynes%20Manual%20924/05_Ignition.htm#_05_001
it gives a good overview of the transistorized ignition system as well

geoff Ives · Mar 16, 2008

I had similar problems with my 924 Lux some years ago. I went through all the usual including a replacement spark box. It turned out to be the factory fitted imobiliser that had previously been bypassed causing the trouble and believe it or not we got a 15 year old from a nearby council estate to fix it.[:-]

Other troubles have been caused by the relay and disributer caps. I actually change the cap on my Turbo every 2 years as they are cheap and it prevents a lot of heartache.

Good Luck and if you have a few quid left over, why not join the Club?

Northern924 · Mar 16, 2008

Should have mentioned peanut the cap is also new, having replaced everything now, I can only think its the TIU, just out of interest there isn't a relay connected with the ignition other than the fuel pump one is there??

Geoff, was going to ask that next

is there much club activity in the northern counties (Scottish Borders, Northumberland, Cumbria), just that most clubs seem to concentrate their events from the Manchester/Leeds down.

Oh and its never had an alarm fitted had the dash out during the rebuild last year, and there was no extra wiring (thankfully)

geoff Ives · Mar 16, 2008

ORIGINAL: Northern924

Should have mentioned peanut the cap is also new, having replaced everything now, I can only think its the TIU, just out of interest there isn't a relay connected with the ignition other than the fuel pump one is there??

Geoff, was going to ask that next is there much club activity in the northern counties (Scottish Borders, Northumberland, Cumbria), just that most clubs seem to concentrate their events from the Manchester/Leeds down.

Oh and its never had an alarm fitted had the dash out during the rebuild last year, and there was no extra wiring (thankfully)

Look in the Region 5 Forum pages and on the website www.porscheclubgb.com
Contact the Regional Organiser and have a chat with him.

924nutter · Mar 16, 2008

?????

924nutter · Mar 16, 2008

Have you been sold the correct rotor arm? Do you still have the old one? Have you checked that the plug are actually firing, or are you asuming they aren't because the engine wont run? When you swapped 'stribs (sorry but this is the old world war two and, in my view, the correct abbreviation of distributor & whilst not wishing to cause offence, dizzie is too max pwer for me[:-]) did you check the position of the cam lobes? You can line up all the marks but be 180 out if you overlook checking to see if the lobes on no.one are in the 10 o'clock/ two o'clock position.

peanut · Mar 16, 2008

ORIGINAL: Northern924

Should have mentioned peanut the cap is also new, having replaced everything now,

thats why i would suspect that first ! its untested .. don't ever assume because a part is new that it must be operational. As TVRO says check that dimensionally the rotar is identical in all respects ,reach and fitted height etc then check the spark is occurring when the rotar is opposite the distbtr terminals.More than about 2.5 mm gap anywhere you are unlikely to get a spark jump .
Have you tried the original equipment again ?

924nutter · Mar 17, 2008

ORIGINAL: mr brightside

greetings 924nutter your kung fu is strong i see! it seems as a rookie 924 driver and Mk1 Golf GTI veteran tinkerer i have made the mistake of assuming they share the same subsystems. as an electrical engineer i understand your description of the coil electronics perfectly, an EMF is generated by a conductor cutting the lines of magnetic flux, exactly the same way an induction motor works! perhaps if you get a minute you could read my post on 924s 944 gearbox similarities. cheers.

Wiring very similar. Fuel pump relay Mk1 GTI round pins, Porsche 924 flat spades. No hall effect sensor. Warrrrhoowah.

geoff Ives · Mar 17, 2008

ORIGINAL: 924nutter

?????

If you read the question you would understand the answer.

924nutter · Mar 17, 2008

I understood the question but I am not sure if you understood the answer[

].

geoff Ives · Mar 17, 2008

ORIGINAL: 924nutter

I understood the question but I am not sure if you understood the answer[].

This was the question I was answering...Do pay attention[

]

Geoff, was going to ask that next is there much club activity in the northern counties (Scottish Borders, Northumberland, Cumbria), just that most clubs seem to concentrate their events from the Manchester/Leeds down.