DDK - Die Deutschen Klassiker

Hi, my 914 has a 911 2.4T with PMO's installed. Ignition is by Electromotive HPX Direct Ignition System. It missfires, and cuts out, and its been to two Porsche specialists who can't sort it out. I'm not certain that the plug leads are connected in the right order. Any help would be appreciated.
Cheers,
Tony

and what do the instructions say?

Nick Moss wrote:and what do the instructions say?

I'm afraid that I don't have any. I imported the car from the USA earlier this year, Black Forest Racing built the engine a couple of years ago but have been less than helpful with passing on any info .

Looks like a wasted spark system, so these fire as pairs , 1&4, 2&5, 3&6. This is what you have. Without knowing how the ECU wires these out, I can't know how the pairs wire out, but you do have the pairs in a logical combination. You could try swapping these pairs around. Remember that the 3 pairs fire in this order 1&4, 3&6, 2&5.
By missfire, do you mean , consistently wrong, or just the occasionally miss ? Occasional miss may be caused by wrong spark plugs. Do you have "resistor" spark plugs? My system, missfired until I used the resistor version of your usual spark plugs. I'm using Ford EDIS so not exactly the same though.

impmad2000 wrote:Looks like a wasted spark system, so these fire as pairs , 1&4, 2&5, 3&6. This is what you have. Without knowing how the ECU wires these out, I can't know how the pairs wire out, but you do have the pairs in a logical combination. You could try swapping these pairs around. Remember that the 3 pairs fire in this order 1&4, 3&6, 2&5.
By missfire, do you mean , consistently wrong, or just the occasionally miss ? Occasional miss may be caused by wrong spark plugs. Do you have "resistor" spark plugs? My system, missfired until I used the resistor version of your usual spark plugs. I'm using Ford EDIS so not exactly the same though.

Thanks for your reply. The motor doesn't run cleanly unless over 3000 rpm. If you hold the revs at 1500 in neutral the revs suddenly increase to over 3000+. The original plugs fitted when I got the car were Bosch Platinum RO 302. My garage fitted Bosch WR 4 CC. I thought the problem might be the PMO's but they have been stripped and cleaned. I'm sure its an electrical problem, but can't find anyone in Berkshire to help.
Cheers,
Tony.

Got a strobe? Connect it to all leads in turn to see if they are all firing.

What's the timing at idle? Could need more advance.

What's the trigger, standard dizzy or toothed wheel?

I believe the manual is here

https://electromotive.com/wp-content/up ... /hpXv2.pdf

(If not then look on here https://electromotive.com/support/technical-manuals/ to find the right one)

sladey wrote:I believe the manual is here

https://electromotive.com/wp-content/up ... /hpXv2.pdf

(If not then look on here https://electromotive.com/support/technical-manuals/ to find the right one)

Thanks Sladey, as my Dad used to say, "If all else fails read the instruction book". I bought the car from the US, it was advertised as an historic racer with a road legal, fast road set-up. Originally on a 2ltr and raced successfully by Chuck Piazza , the next owner installed the 2.4T with S heads and hot cams. I am beginning to think that for my purposes in need to find a "softer" engine !
I will work my way through the manual, and if all else fails, try to find a local expert.

Cheers,

Tony.

What does the engine sound like when turning over/starting,does it spin freely or does it sound tight anywhere?
how lairy a cam does it have?
Does it back Fire?

Presumably all the basics were done, compression test, carbs checked leads and plugs?

First thought is a faulty coil pack as its wasted spark you would expect to get a misfire on 2 cylinders if it was.

You can try swapping leads on the coil packs as in 1/4#3/6#2/5, that should make no difference to the running so but should help to eliminate a possible lead issue.
You can also try moving the coil packs around, have you checked that all cylinders are getting a spark?Is it crank fired ignition with an ecu and coil packs?

Hi davidoft,
the motor cranks over freely, and fires straight away. I don't have a build sheet for the motor but suspect that the cam is pretty hot as the car competed in the Rolex Historic Series regularly and was a top runner. Comp and carbs checked and new plugs fitted. It does backfire, sometimes with flames ! I know the problem is with 4, 5 or 6 cylinder because each set of headers has its own silencer, thus easily pinpointed. I will try switching the leads around tomorrow, and yes it is crank fired ignition. My last 4 Porsches were 968's so air cooled motors are completely new to me, and I am on a steep learning curve !

tp_reading wrote:

impmad2000 wrote:Looks like a wasted spark system, so these fire as pairs , 1&4, 2&5, 3&6. This is what you have. Without knowing how the ECU wires these out, I can't know how the pairs wire out, but you do have the pairs in a logical combination. You could try swapping these pairs around. Remember that the 3 pairs fire in this order 1&4, 3&6, 2&5.
By missfire, do you mean , consistently wrong, or just the occasionally miss ? Occasional miss may be caused by wrong spark plugs. Do you have "resistor" spark plugs? My system, missfired until I used the resistor version of your usual spark plugs. I'm using Ford EDIS so not exactly the same though.

Thanks for your reply. The motor doesn't run cleanly unless over 3000 rpm. If you hold the revs at 1500 in neutral the revs suddenly increase to over 3000+. The original plugs fitted when I got the car were Bosch Platinum RO 302. My garage fitted Bosch WR 4 CC. I thought the problem might be the PMO's but they have been stripped and cleaned. I'm sure its an electrical problem, but can't find anyone in Berkshire to help.
Cheers,
Tony.

Possibly one for Tim to sanity-check before you set-to, as he has way more experience with this sort of thing than me, however two things sprung to mind based on your comments above..

1) Could this be a crank signal issue that's being covered up at higher rpm's? Might be worth checking the sensor clearance is correct, and if you have an oscilloscope (or something else which can provide a crank signal trace) checking you have a decent crank trigger signal at low RPM - it might be you need to tweak the settings a bit to get a decent trace at idle..

2) Assuming you have a throttle position sensor, could this be faulty or damaged causing issues with ignition timings when you back-off? That should be easier to check (if its a consistent fault) by reading a nice clean 0-5v sweep with a multi-meter

Jonny Hart wrote:Got a strobe? Connect it to all leads in turn to see if they are all firing.

What's the timing at idle? Could need more advance.

What's the trigger, standard dizzy or toothed wheel?

Its by toothed wheel.

Misfire sorted thanks to Magnacor. Really helpful customer service. Problem was simply with the HT leads.

Yay! Congrats!

Good to nail the problem