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Muz924 · Posted: Sat Aug 25, 2012 7:38 pm Post subject: Likes to start on 3 cylinders !!

Hi Guys,

This one has been bugging me for a while, I go to start the car (cold) and it cranks over strongly but wont fire.

As part of the resto I have replaced the following with new:
Spark Plugs & Leads, Dissy Cap & Rotor + Ignition Coil. (breakerless dissy).

I thought I had it solved buy running a new wire from the starter motor terminal to the +Coil terminal. Started fine for a while but now the problem is back again.

The only way I can get it started is by removing spark plug #1 and she fires up straight away.

I think its some kind of weak spark issue, maybe the ignition control box.

Any help/suggestions would be appreciated

Cheers
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

musicalannette · Joined: 21 Feb 2012 Posts: 413 Location: UK

i would do a compression check just to rule out any problems with cyl 1. If there similar readings (say 5% of each other) you can rule that out.
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I KNEW white wall tyres were invented by Americans .....just not at Boeing.... to be fitted on the 737.....

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Agree with the compression check. An over tight/iimproper intake valve clearance on the #1 cylinder could cause blowback into the intake and affect the starting/running of the other cylinders.

Dennis
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81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

rat · Posted: Sun Aug 26, 2012 7:02 am Post subject:

Had the same problem with mine. Not limited to plug #1 either. Once started on three, and with the plug then replaced, started instantly every time.

New plugs, rotor, wires, and fixed up a few low voltage circuits with earths/supply not to my satisfaction. No change.

It seemed to reduce in occurrence when the battery was replaced (so faster cranking).

The car was then taken off the road so I've not had much chance to further fault find.

It didn't really cause me much of a problem since I just always carried a plug spanner to enable the 3 cylinder start method.

Muz924 · Posted: Sun Aug 26, 2012 12:11 pm Post subject:

Thanks for the replies, I did a compression check before I started the resto, however that was about 3 years ago

I will give that a go so I can rule bad compression out.

I start the motor every 2 weeks and run it up to temperature, only driven the car once on road and performed very well

The battery is around 2 years old and I charge it regularly.
The Starter Motor has been reconditioned and cranks strongly.
I have replaced just about everything!!!

Next time it plays up I will try another spark plug (only do #1 because it easy to get to).

I am still leaning towards electrical because when she is playing up I don't hear the fuel pump. (it also has a new fuel pump relay).

The mystery continues.....
Cheers
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

+2 to a comp test.
Look to see if any plugs are wet as they come out.

Change or at least swap plugs and leads around to try isolate the problem. Do you get a good blue spark all round?

Sure you get 12V (nominal) at the coil+ when cranking?

Hope its not the same cause as in this thread:
http://www.924board.org/viewtopic.php?t=36211
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Muz924 · Posted: Tue Aug 28, 2012 8:56 pm Post subject:

I am hoping NOT a HG!!

Tried it after work tonight and it started first crank

I am getting 10.6V at coil when cranking, which is a bit low.
I pulled out the plugs and they looked black and dry, oil looks clean no foam or bubbles and coolant is also nice and clean.

The spark wasn't blue...more orange, not sure what that means.

I will try and get hold of a compression tester on the weekend and hopefully rule that out.
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

Ozzie · Posted: Wed Aug 29, 2012 10:38 am Post subject:

Is the CSV working ok?
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Muz924 · Posted: Thu Aug 30, 2012 8:08 pm Post subject:

Good point Ozzie, I shall check the CSV on weekend as well.

The AAV is brand new, I have clamped that off (soft rubber pipe) with round pliers when cold and idle dropped so it would seem to be open when cold and closed when warmed up.

Got the compression tester today, so will I run some tests on Sat.

I am thinking maybe a not so good injector, car hasn't been driven properly for a long time...it might just need a good long drive

Cheers
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

Muz924 · Posted: Sat Sep 01, 2012 7:19 pm Post subject:

OK, I did a compression test today got these readings:

#1 = 155
#2 = 160
#3 = 161
#4 = 151

I am pretty happy with those figures, thats with warm engine, all plugs out.
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

dpw928 · Joined: 02 Nov 2002 Posts: 1860 Location: owasso, ok 74055

Since the problem occurs when cold, you may want to repeat the compression check with a cold engine so see if there is more drop off on the #1 cylinder.

A partially plugged injector could cause the cold miss but it wouldn't explain why removing the wire would allow it to start. Since it had sat for a while, it wouldn't hurt to run some Techron or Gumout injector cleaner through it.

Dennis
_________________
81 931 5 sp
78 928 5 sp Silver
78 928 AT Euro Black

rat · Posted: Sun Sep 02, 2012 8:03 pm Post subject:

Assuming it is the same problem as mine, it's not the act of removing the wire that allows it to start, but the removing of the spark plug.

Therefore my conclusion was it was to do with either fuelling or pressures(compression).

Compression tests on mine came in within 5psi when cold (didn't test hot since it runs fine once started once).

That left me with either injectors, or the fuel metering.

Ideas for discussion:
1) The open spark plug hole reduces the air inducted through the metering plate?

2) The one deactivated cylinder makes the metering plate bounce and compensates for over/underfueling of the csv?

3) The reduced pressure on the open cylinders injector allows fuel to freely flow, either leaning out the other three, or shifting a partial blockage in the fuel system. Maybe the fuel control plunger is getting stuck?

Muz924 · Posted: Mon Sep 03, 2012 4:32 pm Post subject:

Thanks for all the suggestions.....

I will run a cold compression test tonight.

Next time she plays up I will manually run the CSV to see if it helps, I manually activated the CSV when motor was running and the idle dropped so it would seem to be working when told to. Maybe the thermo switch is only running the CSV intermittently on cold starts??

Can't help thinking its a weak spark problem and by removing the plug it "unloads" the system and allows a decent enough spark to get things going on 3 cylinders.

I shall keep digging and testing.

Cheers
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

Muz924 · Posted: Mon Sep 03, 2012 8:48 pm Post subject:

Did a cold engine compression test with these results, I have incuded hot results as well:

.........Cold.....Hot
#1 = 149......155
#2 = 153......160
#3 = 152......161
#4 = 135......151

#4 looks a little lower when cold relative to the others.

She is starting up OK at moment!!!
I am getting 12V at the CSV for a very short time (maybe half a second) when cranking (ambient temp approx 16deg C).

I will have to wait for it "play up" again and see what works without the spark plug trick.

To be continued......
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)

Muz924 · Posted: Sat Oct 13, 2012 6:09 pm Post subject:

Hi Guys,

It played up again today, refusing to fire.
Hadn't been started for around 3 weeks.

I pulled off spark lead #1 (spark plug still in) and it started straight away!

Any ideas?
_________________
1978 924 RoW 5-Speed (Current Project)
1980 924 RoW 5-Speed (Donor Car)
1985 Alfa Romeo Alfetta GTV 2.0 (Previous Project Car)