928 s4 sparkplug firing random

[Ydna_928s4]

Hey, my name is Andy.

To start things of i apologize for my bad English since it isnt my native language.
I came here since i'm pretty much stuck and i couldn't find anyone whit the same problem.

I'll kick off about the history: bought about 5 months ago a 88' 928s4 whit 275k miles on it and had a decent history of maintenance till about end 2012-begin 2013.
Used it for about 2 month whitout any problems (beside not enough oil in the auto gearbox). After that i decided to replace the following: timing belt + all the rolls, waterpump, the 2 timing chains between cam shafts, pretty much all rubbers from valve cover on upwards, 2 knock sensors, TDC sensor, HAL sensor, ignition cables, spark plugs and all the belts like airco altrenator etc..

i needed about 3 months for this. after the work was done i fired it up and besides some ticking noises(wich i blame to the 3 months whitout oil) it run by it self let it run to temprature and back off. The next day the ticking noises were gone, but the reather heavy vibration was still present (wich again i linked to to bieng dry for 3 months opend up etc). Again let it go up to temprature to see if it didint run hot and tok it for a drive. Beside the vibration it seemed normel.
later that day (Wasnt fully cold again) fired her back up to go driving about.
At this point i thought it was the gearbox creating the vibrations so i tryd the kick down wich didnt shift back till it was actuly flored and the car hardley
accelerated. at about 2800 rpm it felt like the engine disconnect in an instant and went to about 4000 rpm in a blitz(felt like trying to accelerate whit a nearly gone clutch).I released the gas, and it just fell back at 2000 rpm and acted like nothing hapend. Drove home and didnt toch it till i had time to get back to the garage wich was 2 days after the above event.

That day it didnt start atall, didnt even try to start just went round whitout a sign of compression so i did step by step to look what it was: Feul compression and flow, cheked the relays cleaned all ground leads. Then i did what i should do to start with put all 8 spark plugs ontop of the engine and watch it fire.
This is what hapens: first cycle of firing i get a normel cycle of all 8 the second cycle is either the 4 outer cylinders or the 4 iner cylinder as "illustrated" below x=fire 0= no fire

xx 00
00 xx
00 xx
xx 00

Thinking about the EZK or output amplifier(?)(The two small bosh units close to the front bumper, no idea what its called sorry) but not certain, anyone know how i can test it for certain or any other ideas? i dont have units that i can borrow and they are rather price to buy at random! sorry for the lengthy post and a thank in advance!

[stepson]

The vibration is probably from not running on all cylinders. Do you have an inductive timing light? This will tell you if you are getting spark on the individual plug wires. Test them and write down which has spark and which do not. Swap the connectors on the ignition amplifiers (the Bosch units close to the front bumper) Test again and write it down. If the spark moved with the change of connector, chances are one of the amps is bad.

Report back.

What country are you in?

[Mrmerlin]

I would also look at the coil wires,
remove them and make sure the ends are not corroded ,
and that the wire isnt hitting any part of its run. if it is it can short out
Run the engine in the dark look for jumping sparks

Also make sure the transmission is filled to the proper level.

[Ydna_928s4]

Originally Posted by stepson

The vibration is probably from not running on all cylinders. Do you have an inductive timing light? This will tell you if you are getting spark on the individual plug wires. Test them and write down which has spark and which do not. Swap the connectors on the ignition amplifiers (the Bosch units close to the front bumper) Test again and write it down. If the spark moved with the change of connector, chances are one of the amps is bad.

Report back.

What country are you in?

Dont have an inductive timing light, did it the old school way by just putting them atop of the engine. the first round of the engine going round is a correct firing order at all 8, on the second run however is either 4 outer or 4 inner for example:

I start crank the engine -> get a normel firing order on all 8
engine starts a new firing cycle and only fires the 4 inner sparks continuously.
I stop cranking, now i do the same again crank engine get a normel firing order on all 8 but now instead of 4 inner sparks, the 4 outer sparks fire continuously.

I tryd swap the ignition amplifiers wich didnt change anything.
I'm from belgium btw :-) And thank for the quick reply!

[Ydna_928s4]

Originally Posted by Mrmerlin

I would also look at the coil wires,
remove them and make sure the ends are not corroded ,
and that the wire isnt hitting any part of its run. if it is it can short out
Run the engine in the dark look for jumping sparks

Also make sure the transmission is filled to the proper level.

Did chek all of the ignition cables from coil to spark plug. They seemed pretty ok since the coils is the only part of the ignition i didn't put in new. also no burn or smoldering marks; but ganne try cranking it in the dark, you never know!

Gearbox is filled proper way by running the engine fill it bit by bit get every gear etc.
Thanks for the advise!

[harborman]

I wonder if you are getting some kind of voltage drop when the engine starts. How is your battery voltage? have you checked all the ground connections? Connections to the ignition box in passenger footwell. It appears to be doing something strange between the two distributors. As you mentioned it switches 4 at a time, does not seem random. Just some ideas. Hopefully, some of the more expert guys here can point you in the right direction.

[Ydna_928s4]

Originally Posted by harborman

I wonder if you are getting some kind of voltage drop when the engine starts. How is your battery voltage? have you checked all the ground connections? Connections to the ignition box in passenger footwell. It appears to be doing something strange between the two distributors. As you mentioned it switches 4 at a time, does not seem random. Just some ideas. Hopefully, some of the more expert guys here can point you in the right direction.

Hey,

Tryd with a full charged, warm battery engine dosnt crank as fast as i think it should not 100% sure tho. I did clean most of the ground connections.
Thanks for the advise!
And yes im running out of ideas indeed

[harborman]

You might also post this on Rennlist 928 forum as well.

[Danglerb]

Get a cheap inductive timing light or borrow one, right now seems like you are wasting time and following a funny light into the deep dark forest.

Ignition computer is generally very reliable, it only tells the ignition amp when to fire, where is a function of each distributor.

Cranking on many cars bypasses the ballast resistor for a hotter spark.

[harborman]

Originally Posted by Danglerb

Get a cheap inductive timing light or borrow one, right now seems like you are wasting time and following a funny light into the deep dark forest.

Ignition computer is generally very reliable, it only tells the ignition amp when to fire, where is a function of each distributor.

Cranking on many cars bypasses the ballast resistor for a hotter spark.

Good point. I remember those resistors years ago. Car would start but quit when key was in run position. Not sure if the 928 has that. It would apply full voltage on the coil, but only for starting.

[Danglerb]

Early cars have ballast resistors, not sure on later dual ignition cars.

[harborman]

I was looking at the ignition wiring for my 86. Ignition coils fired through Trigger units 1 & 2. Shielded cable from each Trigger Unit to the EZF. Center conductor from Unit 1, pin 5 to pin 1 on EZF, Unit 2 , pin 5 to EZF pin 13. Both shielded cables appear to be going through a connector of some kind. I don't see any resistor on the coils. Grounds on Trigger Units look to be on pin 2 going to ground point MP III.

I would also check the function of the "RPM Reference Mark Transmitter" going to the EZF.

Hope this is of some help.