wopfe

I got pretty similar problems (mine is a 4.5 from '79) and after i did a complete overhaul of my engine i changed pretty much everything to get it to run better. Last 3 things i could check where sparkplugwires/computer/fueldistributor revision. I tried new plugwires and it fixxed it. The old where like 9 years old, but somehow the ohms where wrong when measuring. Let me know if you need to try a computer (BOSCH Ignition module 92860270202), i bought one for testing. I think its the same used in your car, you could borrow it (send it via the post, from NL). Good luck!

Shark2626

Interesting. In the USA 93 is considered “super” at most gas stations, then 91 and 89 (may vary by region).

If all else fails, on your next fill up maybe try 5-6 gallons of the lower octane gasoline that’s available. Not sure what octane is recommended for your MY 928, but the higher 98 octane gasoline may be playing a role in your current issue. More octane is not always a good thing in all applications I’ve learned.

GerritD

Hello neighbor:-)
I have a spare computer. So that I can try. You'll never know.
As for the plugwires : they all have the correct ohms, although these are almost 10yrs old (but rarely used since these came from another 928 that seldom drove).
That leaves only the fuel distributor : this one is still original and has never been overhauled.

GerritD

The USA 87 & 91 is the same as the EURO 92 & 95.
So in my case EURO98 is the same as USA 93.
Porsche Europe advises for my engine EURO Ron 98. So that is the correct fuel.

wopfe

Hi Fellow European From the look of your WUR you have a guy who knows how to overhaul wurs and distributors... Otherwise i send my WUR to this guy: http://kjetronicrevisie.nl/ Very professional, ii think i am going to send mine there next year as pro-active overhaul...

GerritD

Indeed and this fellow is well known on this forum : ALLAN (https://fr-fr.facebook.com/la.clinique.de.l.injection/)
He is a really friendly and professional french guy .
WUR is very important. I tried to overhaul the WUR my self via a Salvation KIT but you need the quality parts.

wopfe

Looks good!

marine928

Check all the grounds,, clean your battery cables and if the negative strap is original I would definitely change it. The 928 regardless of year is very susceptible to electrical/voltage anomalies. Good luck, it may be the simple solution that works. If not at least you have eliminated it and know that your electrical car circuit is sound

dr bob

I've had plug wires that measured OK with the Ohm meter but had leaking insulation that didn't show up with simple testing. Similar symptom to the carbon tracking that some report in the distributor cap. You can sometimes wash and dry the inside of the cap, but that option doesn't exist for the wire insulation. Replacement is the option. Oscilloscope is a handy tool for finding high voltage leaks, if you have access to one.

giddyupp

Have you checked the timing

GerritD

Timing was OK before, so why should it be a problem ...do you think it might be an issue ? Wouldn't a bad timing cause other issues : hard start, no power..etc ?

GerritD

I received some interesting info from my fellow friend Allan who is a Kjet specialist in France :
Following tests should be done
1) I need to check the flow coming from my fuel pump : it should be 1130cc/30sec (or 1450cc/30sec with a 2nd pump in the tank)
=> here comes my idea : I recently removed the intank pump since it did not work anymore. I replaced my 1st external pump by a new original Bosch pump (0 580 254 053 )
If I still haven't got enough flow with this new pump (p.e. between 800 - 1000 cc/30sec), it would be a good idea to repair my 2nd intank pump, as it increases the flow for about 300cc
=> what would cause this bad flow ?
=> would this also be a problem at the Fuel Distributor side, since I am measuring flow at the outlet port of the Fuel Distributor ?
2) I need to make sure that the voltage at my fuel pump is at least 11,5V when running
3) If the flow of my fuel pump is OK, I should check that each of my injectors is spraying the same amount of fuel.
If not, the problem lays inside the Fuel Distributor

GerritD

First test results trying to find out whether my fuel flow could be the issue :
1. check voltage when bridging fuel pump (engine not running ) : 8,6 V
2. check voltage with engine running and revving : 12,5 V and remaining constant at any rpm

Important question : should voltage be around 11,5 V when bridging fuel pump ? Is it normal that voltage drops (only without engine running)
I believe it has no sense in measuring fuel flow if I only get 8,6 V during fuel pump bridging, correct ?

Here some pictures during the setup of the correct mixture of my CIS system :


CO = 2.2 (is within Porsche specs of 1.5 - 2.5)

Warm Control Pressure = 3.4 Bar and is within specs 3.2 - 3.6



temperature OK and rpm idle OK

oil pressure warm OK

jpitman2

I think 8.6V with only the pump running is a bad sign. Also seeing 12.5V engine running and revved is low - after a fresh start you should see something in the range 13.8V-14.1 at least, if not even higher. Are you able to check the current being pulled by the pump? Sounds like the pump is struggling and pulling more amps than it should - my single pump pulls 7A. You speak of the flow rate being a problem, but havent done the test - Why not, when its one of the easiest to do? Unless you are hot and high you shouldnt need the second pump, IMHO.
jp 83 Euro S AT 57k

GerritD

to rule out an electric issue( p.e. corrosive or bad ground connection) I will try to run the pump via new wires connected directly to my battery. If problem still persists, there must be an obstruction somewhere in the fuel line...
Shouldn’t the power regulator in the alternator limit the voltage to 12,5 just to protect any components?