Porsche Bosch K-jetronic - 924 System Pressure + More
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- Äas pĆidĂĄn 22. 08. 2024
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Porsche 924 2.0 NA 125bhp Metering Head
Early non adjustable type so it just flows what it flows and thats a lot at 200cc/min at 5 bar system pressure
Slight difference in the system pressure relief valve as shown but the same principle applies.
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/ @greygooserestorations - Auta a dopravnĂ prostĆedky
Hopefully you're reading this and can suggest some ideas as I'm tearing my hair on on a 924 Jet. Summary of symptoms:
Car runs either way to rich but starts and runs okay when cold if control mixture set rich, or if I set the mixture so its has correct CO when warm, its coughs, splutters and barely runs when cold.
So it must be the WUR then?
This is what I've done so far to try and find the issue.
Full system pressure check - all within Bosch spec when cold and warm, confirming WUR working.
Rebuilt and cleaned WUR just to make sure. No difference. Swapped out WUR, no change.
All new injectors.
All new injector seals / screw in bosses.
Flow check on all injectors - even and correct.
Cold start injector, tested, functional and working - issue of poor cold running exists long after cold start injector fires either way.
All new coil, distributor, plugs and leads.
Swapped out ignition module, no change
Stripped and rebuild metering head valve - new kit, fully ultrasonic clean etc, etc
Cleaned out and checked all the injector lines.
New fuel pump in tank and engine bay + filter
Fresh clean fuel
Inspected, cleaned and checked flow plate mechanism in metering head and test swapped ith a known working one, no change.
Replaced inlet manifold gasket and resealed.
New air filter.
Smoke check for vacuum leaks, small one found and corrected.
Timing checked and rechecked.
New timing belt fitted and timing checked.
Compression and leak down all within spec and even.
When warm, car runs great but coughs, splutters and barely runs when cold.
Make the mixture way to rich and car starts no issue, but then is poor when warm as too rich.
Pressures and WUR checked, rechecked and different WUR swapped in to test, no different,
All correct Porsche components fitted, nothing after market or high performance.
Only other issue is that the auxiliary air valve didnât appear to work very well,m i.e did not increase cold idle speed so had to modify this to give a 1,500 rpm fast idle which sovced that problem. Cold start mixture was same before or after so dont believe related.
Lost as to what to do next?
Whats the CO % when the car is cold and what does it read upto when the car is warm?
The auxiliary valve needs to be working as it should be as that will cause issues
@@GreyGooseRestorations Thanks for the quick response. If the warm idle is set at 0.6 CO, when cold it goes to about 1.5 then gradually reduces. As it warms up the problem goes away. If I set the mixture so it runs when from cold, it's at about 12!! but then is horribly rich when warm and not useable, fouling the plugs. The Aux air when not working just had the cold iddl at 600rpm and struggling. After winding it a little more open, it then went to 1,500 rpm from cold and was working fine. With ot without the aux air valve, the engine would just splutter, cough,m mis and pop as I tried to rev it up, gradually improving until it was warm then it would run great. With the aux air valve in place and working, the misfire, hesitation and popping etc remained without changem just that the starting posiiton was 1,500 rpm, not 600. Hope that all makes sense. Given swapping out the WUR made no difference and all the pressures were as per the manual, I resorted to changing the inlet manifold gasket as I thought the only thing it could be was a vacuum leak that healed and closed a gap as the engine warmed up? But again, no difference. It really has had me scratching my head,.
@Otto-AutoPilot when you rebuilt the WUR did you remove/replace the little inlet filter screen thats at the base of the fuel inlet
@@GreyGooseRestorations Yes, ultrasonically cleaned them too.
@Otto-AutoPilot unfortunately that won't clean them, there's 5 layers, one being a plastic type, id take the feed pipe off the WUR and poke the old filter out and put the bolt back in and run up the car and see if it makes any difference
I'm finally starting to understand cis thanks largely to your videos. You mentioned you had a 300hp turbo cis VW. It would be great if you could do a video about running cis with boost. There is zero information on it. Thanks!
I dont have a turbo CIS (would love too) ill see what i can do ref cis-turbo
You didn't touch that the warm & cold control pressures as well as the A/F adjustment are also factors that impact fuel flow. Also there are O-Rings inside the metering head that can cause flow imbalance to each cylinder.
I've previously covered those points in other videos đ
So if you increase system pressure, does it increase control pressure and scale the air meter up? Meaning do they stay in correct relation and the air valve will now require more air to move to, say, half fuel flow and it will be sending more fuel at half way?
Yes, increasing system pressure will raise control pressure, so that will need adjusting to suit the car.
More fuel will increase performance on the engine with inturn will increase the capacity to draw in more air which will then lift the air plate more...which will give more fuel
Its all a balancing act and best results are live testing with AFR guage to see what the car is actually doing
@@GreyGooseRestorations right. Basically I'm asking if the air meter is capable of more total power in relation to how far the flap is moved when pressure is increased.
Yes
Would you be able to service the K-jet metering head off my XR3i? Looks like you have a good setup there to test and work on them.
Hi, yes I've done a few ford ones over the years. Send me a message via my Facebook page Grey Goose Restorations đ
@@GreyGooseRestorations Thanks. Iâll get my brother to message you, Iâm not on Facebook
Hello there, would the Porsche unit also work on a MK2, PL KE-Jet, or just on a KR K-Jet? What would you reckon you could get out of a PL Engine ?
KE-Jetronic is a different kettle of fish and wouldn't work with this unless you convert to K-jetronic but you then have the issue of emissions to battle with. The KR and PL engines are physically the same
@@GreyGooseRestorations many thanks for your reply, much appreciated. I do have an original 16V fire and ice, machting numbers, therefore i feel that i want to keep it, meaning i would like to keep it a KE-jet. Surely it could be changed to KR specs and even doing the necessary wiring but i would like to keep the appearance original. Would would you suggest besides of cams, exhaust, head valves? Can the the Blackbox updated or anything else to get a bit out of it?
Sorry, i was typing with one I closed..hahah but i hope you make sense out of it
Just having the car set up with ignition timing and fueling adjusted would completely change how the car performs đ
The black box (ecu) is what it is, you can replace the crystal to raise the rev limit thats about it unfortunately
Whatâs the merc injectors youâre speaking of, Iâve got a 924
This is the part number 0 437 502 054
Brass finish ones without the top hat heat shield on the end ?
Yup