I have a 1980 318i E21 with K-Jet. I have done a fair amount of reading on the system and although they go into great detail about how each component works I am yet to find an answer about how (or if) the control pressure affects the air/fuel ratio. It could be a moot question as there may be no affect at all.
Reference picture below.
Background as to why I have the question: My car engine stalls in hot weather (100 deg F/38 deg C) if I come to a stop quickly at traffic lights. It also is a little hard to start when warm but I don't know if that is just a characteristic of the K-Jet. My engine idles OK otherwise, maybe a tad low but it idles high when cold and the RPM drops when if warms up. I have 'serviced' or checked most components of the K-Jet; auxiliary air valve was stuck when I bought it and I freed that up, cold start injector replaced, accumulator replaced, fuel pump check valve replaced, I checked the 'O' rings in the primary pressure regulator (they were good) and fuel lines/hoses are good. I have not checked the injector spray. I use 95 octane fuel. I have also removed most of the EGR but I don't think this should be relevant but included it for completeness in case someone asks.
We have had a spell of hot weather in which my car stalled a few times which prompted me to have a look at the fuel system pressures. I made my own setup using spare fuel lines, connectors and a gauge I had at home. It is fitted in between the FD and WUR. After I measured the cold control to be 9psi and the warm control to be about 35psi I decided to pull the WUR and modify it so I can adjust the control pressure. I have adjusted it to about 25psi cold and 50psi warm. The system pressure was about 65psi.
So I have adjusted the control pressures and by the butt dyno my car feels a little slower. Probably like the difference between having the belt fan fitted or not fitted. There is no knocking/detonation although prior adjusting the control pressure it would ping under load going up a hill (I have not had the chance to drive the same scenario in hot weather yet). Timing out maybe but it doesn't happen often enough for me to worry about adjusting the timing.
I understand that the control pressure varies thepressure acting on the controlplunger in the metering head. It is an effective method of providing fuel enrichment when the engine is cold. By making the pressure higher I have made the put more resistance against the air flap which in turn will not enrich the mixture as much WHEN COLD and I assume this to be the same for warm also. THIS is where I need clarification or some input from someone more knowledgeable.
Yes I can go buy HOW TO TUNE AND MODIFY BOSCH FUEL INJECTION but I am curious about this now and I am impatient. I am in Australia and postage takes a while from Amazon in the US.
Thanks in advance.
James
Reference picture below.
Background as to why I have the question: My car engine stalls in hot weather (100 deg F/38 deg C) if I come to a stop quickly at traffic lights. It also is a little hard to start when warm but I don't know if that is just a characteristic of the K-Jet. My engine idles OK otherwise, maybe a tad low but it idles high when cold and the RPM drops when if warms up. I have 'serviced' or checked most components of the K-Jet; auxiliary air valve was stuck when I bought it and I freed that up, cold start injector replaced, accumulator replaced, fuel pump check valve replaced, I checked the 'O' rings in the primary pressure regulator (they were good) and fuel lines/hoses are good. I have not checked the injector spray. I use 95 octane fuel. I have also removed most of the EGR but I don't think this should be relevant but included it for completeness in case someone asks.
We have had a spell of hot weather in which my car stalled a few times which prompted me to have a look at the fuel system pressures. I made my own setup using spare fuel lines, connectors and a gauge I had at home. It is fitted in between the FD and WUR. After I measured the cold control to be 9psi and the warm control to be about 35psi I decided to pull the WUR and modify it so I can adjust the control pressure. I have adjusted it to about 25psi cold and 50psi warm. The system pressure was about 65psi.
So I have adjusted the control pressures and by the butt dyno my car feels a little slower. Probably like the difference between having the belt fan fitted or not fitted. There is no knocking/detonation although prior adjusting the control pressure it would ping under load going up a hill (I have not had the chance to drive the same scenario in hot weather yet). Timing out maybe but it doesn't happen often enough for me to worry about adjusting the timing.
I understand that the control pressure varies thepressure acting on the controlplunger in the metering head. It is an effective method of providing fuel enrichment when the engine is cold. By making the pressure higher I have made the put more resistance against the air flap which in turn will not enrich the mixture as much WHEN COLD and I assume this to be the same for warm also. THIS is where I need clarification or some input from someone more knowledgeable.
Yes I can go buy HOW TO TUNE AND MODIFY BOSCH FUEL INJECTION but I am curious about this now and I am impatient. I am in Australia and postage takes a while from Amazon in the US.
Thanks in advance.
James
K-Jet control pressure question
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