Kjet CIS Fuel delivery issue
05-26-2023, 09:27 PM
#16
Rennlist Member
If pump voltage is low (very common in 45 year old 928) you can use jumper wires direct from the battery terminals on the pump ... it will sing like you've never heard. then check your volume test. To troubleshoot low voltage to the pump clean and check every connection in the pump circuit, including the ground point. There will still be "some " voltage loss though the various connections. I have found that a relay located in the rear of the car to power the pump eliminates these low voltage problems.
05-26-2023, 10:02 PM
#17
Rennlist Member
Thread Starter
Youre talking about two different things: Volume test and pressure test. Pressures are passing tests, but you can have correct pressures on various volumes. test the voltage AT the fuel pump. the voltage test must be using the positive wire AT the fuel pump, and the ground wire AT the fuel pump (not a chassis ground) this enables you to see what voltage is actually running the pump. Voltage loss though the various connections to the pump (including the ground to the pump) will result in lower volumes and a failed volume test.
If pump voltage is low (very common in 45 year old 928) you can use jumper wires direct from the battery terminals on the pump ... it will sing like you've never heard. then check your volume test. To troubleshoot low voltage to the pump clean and check every connection in the pump circuit, including the ground point. There will still be "some " voltage loss though the various connections. I have found that a relay located in the rear of the car to power the pump eliminates these low voltage problems.
If pump voltage is low (very common in 45 year old 928) you can use jumper wires direct from the battery terminals on the pump ... it will sing like you've never heard. then check your volume test. To troubleshoot low voltage to the pump clean and check every connection in the pump circuit, including the ground point. There will still be "some " voltage loss though the various connections. I have found that a relay located in the rear of the car to power the pump eliminates these low voltage problems.
good idea, although in the past I already tried to power the pump directly via battery....but at the time there were some other issues.
I will check and get back.
Stupid question : I have replaced my intank pump by a strainer. Because of this the 2 power wires of this pump were not used anymore.
I then connected a solenoid valve to these wires so that when car doesn't run, the solenoid closes the air breather tube of my tank. This to prevent fuel odors coming out of the breather line
Once my fuel pump gets power, the wires to the solenoid are also powered and solenoid opens for breathening my tank
Can this solenoid influence the functioning of my pump ?
05-27-2023, 01:14 PM
#18
Gerrit,
Perhaps we should revisit your initial problem statement. Hard cold start. So break that down into pieces. My 79 car will cold crank 3-5 seconds before firing, (particularly after sitting a few days) with another 2-3 seconds of uneasy idle. I suspect the uneasy idle to be the fuel pressures stabilizing. After the 8-10 seconds of crank/start drama, engine runs smoothly. A video would really help, to see what you see. A leaking pump check valve. will let the system take several second to re-pressurize.
Fuel flow, recognize if you are meeting CCP and WCP, at idle, you have pressure enough for start. Low fuel flow is a load limit to high RPM/load. So while a data point, not a player in your cold start. Drooman's comment well describes pump power and flow relationship.
My 79 is coming out of a long, 6-7 year slumber. so many issues; replaced injectors 1 and 5, and there may be one more weak one. These cars are like working with babies, they cry; and you go through your checklist; sniff for poop, wet diaper, hungry, teething, diaper rash,,.. And like babies, when you solve the latest problem, our cars are all good for a while, if you have talc powder, LOL.
The previous owner on my 79, decided to replace the entire electrical and dash cluster (installed full Autometer gauges, speedo, and tach.. So quite a bit of drama rewiring to stock, almost finished. had i looked closely, should have passed on the car. I did replace the CEU, and original dash panel.
Perhaps we should revisit your initial problem statement. Hard cold start. So break that down into pieces. My 79 car will cold crank 3-5 seconds before firing, (particularly after sitting a few days) with another 2-3 seconds of uneasy idle. I suspect the uneasy idle to be the fuel pressures stabilizing. After the 8-10 seconds of crank/start drama, engine runs smoothly. A video would really help, to see what you see. A leaking pump check valve. will let the system take several second to re-pressurize.
Fuel flow, recognize if you are meeting CCP and WCP, at idle, you have pressure enough for start. Low fuel flow is a load limit to high RPM/load. So while a data point, not a player in your cold start. Drooman's comment well describes pump power and flow relationship.
My 79 is coming out of a long, 6-7 year slumber. so many issues; replaced injectors 1 and 5, and there may be one more weak one. These cars are like working with babies, they cry; and you go through your checklist; sniff for poop, wet diaper, hungry, teething, diaper rash,,.. And like babies, when you solve the latest problem, our cars are all good for a while, if you have talc powder, LOL.
The previous owner on my 79, decided to replace the entire electrical and dash cluster (installed full Autometer gauges, speedo, and tach.. So quite a bit of drama rewiring to stock, almost finished. had i looked closely, should have passed on the car. I did replace the CEU, and original dash panel.
Last edited by Alan 91 C2; 05-27-2023 at 01:16 PM.
05-27-2023, 05:36 PM
#19
Rennlist Member
Thread Starter
Gerrit,
Perhaps we should revisit your initial problem statement. Hard cold start. So break that down into pieces. My 79 car will cold crank 3-5 seconds before firing, (particularly after sitting a few days) with another 2-3 seconds of uneasy idle. I suspect the uneasy idle to be the fuel pressures stabilizing. After the 8-10 seconds of crank/start drama, engine runs smoothly. A video would really help, to see what you see. A leaking pump check valve. will let the system take several second to re-pressurize.
Fuel flow, recognize if you are meeting CCP and WCP, at idle, you have pressure enough for start. Low fuel flow is a load limit to high RPM/load. So while a data point, not a player in your cold start. Drooman's comment well describes pump power and flow relationship.
My 79 is coming out of a long, 6-7 year slumber. so many issues; replaced injectors 1 and 5, and there may be one more weak one. These cars are like working with babies, they cry; and you go through your checklist; sniff for poop, wet diaper, hungry, teething, diaper rash,,.. And like babies, when you solve the latest problem, our cars are all good for a while, if you have talc powder, LOL.
The previous owner on my 79, decided to replace the entire electrical and dash cluster (installed full Autometer gauges, speedo, and tach.. So quite a bit of drama rewiring to stock, almost finished. had i looked closely, should have passed on the car. I did replace the CEU, and original dash panel.
Perhaps we should revisit your initial problem statement. Hard cold start. So break that down into pieces. My 79 car will cold crank 3-5 seconds before firing, (particularly after sitting a few days) with another 2-3 seconds of uneasy idle. I suspect the uneasy idle to be the fuel pressures stabilizing. After the 8-10 seconds of crank/start drama, engine runs smoothly. A video would really help, to see what you see. A leaking pump check valve. will let the system take several second to re-pressurize.
Fuel flow, recognize if you are meeting CCP and WCP, at idle, you have pressure enough for start. Low fuel flow is a load limit to high RPM/load. So while a data point, not a player in your cold start. Drooman's comment well describes pump power and flow relationship.
My 79 is coming out of a long, 6-7 year slumber. so many issues; replaced injectors 1 and 5, and there may be one more weak one. These cars are like working with babies, they cry; and you go through your checklist; sniff for poop, wet diaper, hungry, teething, diaper rash,,.. And like babies, when you solve the latest problem, our cars are all good for a while, if you have talc powder, LOL.
The previous owner on my 79, decided to replace the entire electrical and dash cluster (installed full Autometer gauges, speedo, and tach.. So quite a bit of drama rewiring to stock, almost finished. had i looked closely, should have passed on the car. I did replace the CEU, and original dash panel.
I measured the voltage across my fuel pump
1. Voltage during 2 seconds prime when putting ignition on without starting , pump voltage = 10,74 V
https://youtube.com/shorts/uCumPPrQyws?feature=shares
2. Battery voltage during 5 seconds cranking , battery voltage drops till 10V for a second
https://youtube.com/shorts/ZQ-yIdxxByY?feature=share
When I measured the voltage on my pump with engine running,
voltage is 12,5 V while voltage with alternator is 14V
06-08-2023, 09:42 PM
#20
Rennlist Member
My hot start problem was caused by fuel rest pressure that was not maintained. I had a bad check valve in the passenger rear wheelwell (I found that after thousands of dollars spent at mechanics). I know that the fuel distributor and WUR can both have check valves that cause this.
I never had a cold start problem.
But if I had a fuel delivery problem and the fuel pump was good, I'd pull and rebuild the fuel distributor.
I never had a cold start problem.
But if I had a fuel delivery problem and the fuel pump was good, I'd pull and rebuild the fuel distributor.
06-09-2023, 03:09 AM
#21
Rennlist Member
Thread Starter
My hot start problem was caused by fuel rest pressure that was not maintained. I had a bad check valve in the passenger rear wheelwell (I found that after thousands of dollars spent at mechanics). I know that the fuel distributor and WUR can both have check valves that cause this.
I never had a cold start problem.
But if I had a fuel delivery problem and the fuel pump was good, I'd pull and rebuild the fuel distributor.
I never had a cold start problem.
But if I had a fuel delivery problem and the fuel pump was good, I'd pull and rebuild the fuel distributor.
As for the check valves, I have replaced check valve in fuel pump and system pressure relieve valve in distributor.
Both are working fine because rest pressure is according WSM after 10,20 & 30 min
This is how my sparkplugs look like, is this a normal color since I find the bottom of my sparkplugs quite black ? :
My timing is set correctly and CO is 1,7%
Last edited by GerritD; 06-09-2023 at 03:10 AM.
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GerritD (06-09-2023)
06-09-2023, 11:12 AM
#23
Rennlist Member
The most common fix for a hard cold start on CIS systems is the thermotine sensor is bad. It's in the water bridge. You can verify resistance and see if it's in range. Dollars to donuts that is your problem.
06-09-2023, 11:51 AM
#24
Rennlist Member
Thread Starter
problem is not thermotime sensor because the hard start is cold and warm. Btw, resistance is 35, 0 and 35 measured with cold engine over the G W and earth. And when measuring directly on connector towards csv I get continuity .So within range.