24 Oct 2021, 19:24
This weekend, has been a busy, and productive weekend for my car.
Finally I got around to doing primary pressure testing and CPR warm up curve testing before and after shimming up my fuel distributor.
The end result is that after a test drive this afternoon, my car is no longer bunny hopping along the motorway at speed and seems to have an increased performance of acceleration too. There is much relief for me that this is the case.
Now for the tech-heads who're interested in the detail of getting there:
My fuel distributor originally had a 1.11mm shim in it to begin with. This gave a gauge value (barg) of 4.72barg of primary fuel pressure. When I converted this into bar actual according to my lookup table from the calibration exercise of the gauge earlier in the week, this gave a value of 5.00bar.
This is measured with the pump running only, not the engine.
At this primary fuel pressure value, which is below the minimum advised in the workshop manual, my car felt sluggish on acceleration and bunny hopped along the motorway at speed after a settling down time of about 30 secs of steady state driving.
I carried out a warm up curve, noting the CPR fuel pressure at every degree centigrade increase in temperature at the CPR where the fuel lines connect (on top of the circular steel disc area). I got relationship values of fuel pressure from 12 DegC up to 40 DegC. This is done with the CPR isolated from the engine vacuum system (plugging the vac line disconnected to prevent a vac leak for the engine) so that there is not external influence on the fuel pressure change with regards to engine temperature, with the heater power supply (grey plug) unplugged from the CPR to allow the radiant engine temperature heat the CPR naturally.
Initially I was very confused because my warm up curve doesn't resemble at all the warm up curve characteristics as shown in the graph in the DMC workshop manual, but eventually the penny dropped. Although my CPR is a DeLorean one, the rest of my air/fuelling system is Volvo. When I plotted my warm up curve against the Volvo equivalent warm up curve characteristics, it showed to be falling in between the min/max lines mostly all the way up, but with a definite low level slant half way up the warm up, which it then struggled to recover from, until it eventually surpassed the max line even, but not until almost fully warmed up (around 38 DegC).
Armed with this information, I went about opening up the fuel pressure regulator on the fuel distributor in order to remove the assembly.
Although I don't think I needed to, I replaced the larger of the two o rings on the assembly, but left the smaller of the two alone. The reason being that the larger, although probably fine, I think could have been doing with being a bit tighter, so I replaced it with a new one. After I did this, I'll admit it didn't seem much different than before, but I left it anyway rather than put the original one back. The smaller of the two still looked good, wasn't squashed and was without any tears or cracks, so that's why I left it.
Now on to the shimming.
I did two separate shim additions so that I could understand the relationship a bit better between mm of shim, and the resultant primary pressure change (and the additional CPR warm up curve changes).
I used Nick T's rule of thumb to do some maths (thanks Nick). His rule states for every 0.1mm of extra shimmage, the resultant increase of fuel pressure is around the 0.06bar magnitude. It's stated as a rule of thumb because the coefficient of change alters in the same manner as one expects physical model changes relating to the increasing strength from the continuing compression of a spring. In this case, we are compressing the spring inside the fuel distributor which acts as the pressure regulation component. The control of pressure comes as a result of the spring being forced back enough to allow fuel to dump back to tank. The stronger the spring, the higher the fuel pressure has to climb before overriding the spring tension. Since we can't make the spring stronger, what we can do is compress the amount of linier space the spring has to operate within, which gives the same results as adding a stronger spring. This is where the shims come in. By adding shims, you're reducing the space the spring has available to compress within the distributor.
My first test was to add 0.59mm worth of extra shimmage giving a total of 1.7mm. The resultant primary fuel pressure change as a result of this addition, was 5.41 bar. This was a little high for my liking (I was wanting to keep it below 5.4 bar so that I wasn't over pressurising my system) so I did another test, but with a bit less shimmage.
For my second test, I removed my 0.59mm worth of extra shimmage from the test above, and replaced it with 0.55mm instead. This meant I had a total of 1.66mm worth of shimmage. The result from this was a primary fuel pressure of 5.22bar. This was a bit lower than I wished to be, but I saw it as a definite improvement over my original 5.00bar setting. As such, I decided to roll with it with an intention to possibly further increase it later on down the line once I could cobble together the necessary shims required to get something in between these two extremes (something I've now managed to do since my test drive).
I left the car to cool down over night fully so that I could replot my new CPR warm up curve with my new 5.22bar primary pressure today.
The change in my CPR warm up curve was not a huge one, but it did definitely show an improvement to show my results much more lying inline with the max line of the Volvo warm up curve, with a similar but more gradual kick up above the maximum line, now starting at 31 DegC instead of 38 Deg C like before. I'm not worried about this kick up one bit, because this is still way lower than what would be expected for the DMC warm up curve, and my car is a hybrid of DMC and Volvo after all, so who can tell what's "right" and what's "wrong"?!
After plotting that last curve, I removed my fuel pressure testing equipment from the car, and returned it to as it was before starting anything (vac lines and CPR heater supply reconnected etc). I then did a quick check of engine faultering tolerance with my fuel/air mixture ratio screw in front of the fuel distributor (this is my only mechanism for such an adjustment on my car because I have a simplified Volvo setup on my car which means no Lambda content, Frequency valve, dwell values to consider etc etc). Doing this check proved to me that I could do with adding a bit more of a richened mixture to compensate for the increase in fuel pressure (the higher the fuel pressure, the leaner your car will be, and vice versa). I turned my mixture screw right from 6 o'clock to about 7:30 (right for Rich and left for Lean). Then I took the car for a drive.
This brings me up to now.
I've managed to cobble together little bags of various shim assortments in between the value on the car now, and the maximum value I first tried yesterday.
These are: 0.56mm, 0.57mm 0.58mm.
My intention is to try these out, one by one and try the car out at each point as well as record the primary pressure. I don't think I need to bother recording the CPR warm up curve for each, but you never know, I may also do that for completeness. From the above, I'm expecting the following estimated results:
0.56mm to give 5.28bar
0.57mm to give 5.31bar
0.58mm to give 5.35bar
As an example of how the coefficient (value of pressure increase per 0.1mm of applied shimmage) changes with me having real world results for 0.55mm and 0.59mm:
0.55mm is 0.04
0.59mm is 0.07
These are derived from working backwards from the pressure increase resultant from the mm shimmage increase.
For my estimated results untested above, I'm applying the estimated rules:
0.05 for 0.56mm
0.055 for 0.57mm
0.06 for 0.58mm
Only by doing the actual tests will I get the real values, but I'm expecting them to be something close to this. Time will tell.
And that's it. For now. I'm a happy bunny even at this position (in good time for winter being is on its way! DOH!)
Oh yeah, I almost forgot! I guess I can answer the question now. No. Super fuel is not causing me problems.
Finally I got around to doing primary pressure testing and CPR warm up curve testing before and after shimming up my fuel distributor.
The end result is that after a test drive this afternoon, my car is no longer bunny hopping along the motorway at speed and seems to have an increased performance of acceleration too. There is much relief for me that this is the case.
Now for the tech-heads who're interested in the detail of getting there:
My fuel distributor originally had a 1.11mm shim in it to begin with. This gave a gauge value (barg) of 4.72barg of primary fuel pressure. When I converted this into bar actual according to my lookup table from the calibration exercise of the gauge earlier in the week, this gave a value of 5.00bar.
This is measured with the pump running only, not the engine.
At this primary fuel pressure value, which is below the minimum advised in the workshop manual, my car felt sluggish on acceleration and bunny hopped along the motorway at speed after a settling down time of about 30 secs of steady state driving.
I carried out a warm up curve, noting the CPR fuel pressure at every degree centigrade increase in temperature at the CPR where the fuel lines connect (on top of the circular steel disc area). I got relationship values of fuel pressure from 12 DegC up to 40 DegC. This is done with the CPR isolated from the engine vacuum system (plugging the vac line disconnected to prevent a vac leak for the engine) so that there is not external influence on the fuel pressure change with regards to engine temperature, with the heater power supply (grey plug) unplugged from the CPR to allow the radiant engine temperature heat the CPR naturally.
Initially I was very confused because my warm up curve doesn't resemble at all the warm up curve characteristics as shown in the graph in the DMC workshop manual, but eventually the penny dropped. Although my CPR is a DeLorean one, the rest of my air/fuelling system is Volvo. When I plotted my warm up curve against the Volvo equivalent warm up curve characteristics, it showed to be falling in between the min/max lines mostly all the way up, but with a definite low level slant half way up the warm up, which it then struggled to recover from, until it eventually surpassed the max line even, but not until almost fully warmed up (around 38 DegC).
Armed with this information, I went about opening up the fuel pressure regulator on the fuel distributor in order to remove the assembly.
Although I don't think I needed to, I replaced the larger of the two o rings on the assembly, but left the smaller of the two alone. The reason being that the larger, although probably fine, I think could have been doing with being a bit tighter, so I replaced it with a new one. After I did this, I'll admit it didn't seem much different than before, but I left it anyway rather than put the original one back. The smaller of the two still looked good, wasn't squashed and was without any tears or cracks, so that's why I left it.
Now on to the shimming.
I did two separate shim additions so that I could understand the relationship a bit better between mm of shim, and the resultant primary pressure change (and the additional CPR warm up curve changes).
I used Nick T's rule of thumb to do some maths (thanks Nick). His rule states for every 0.1mm of extra shimmage, the resultant increase of fuel pressure is around the 0.06bar magnitude. It's stated as a rule of thumb because the coefficient of change alters in the same manner as one expects physical model changes relating to the increasing strength from the continuing compression of a spring. In this case, we are compressing the spring inside the fuel distributor which acts as the pressure regulation component. The control of pressure comes as a result of the spring being forced back enough to allow fuel to dump back to tank. The stronger the spring, the higher the fuel pressure has to climb before overriding the spring tension. Since we can't make the spring stronger, what we can do is compress the amount of linier space the spring has to operate within, which gives the same results as adding a stronger spring. This is where the shims come in. By adding shims, you're reducing the space the spring has available to compress within the distributor.
My first test was to add 0.59mm worth of extra shimmage giving a total of 1.7mm. The resultant primary fuel pressure change as a result of this addition, was 5.41 bar. This was a little high for my liking (I was wanting to keep it below 5.4 bar so that I wasn't over pressurising my system) so I did another test, but with a bit less shimmage.
For my second test, I removed my 0.59mm worth of extra shimmage from the test above, and replaced it with 0.55mm instead. This meant I had a total of 1.66mm worth of shimmage. The result from this was a primary fuel pressure of 5.22bar. This was a bit lower than I wished to be, but I saw it as a definite improvement over my original 5.00bar setting. As such, I decided to roll with it with an intention to possibly further increase it later on down the line once I could cobble together the necessary shims required to get something in between these two extremes (something I've now managed to do since my test drive).
I left the car to cool down over night fully so that I could replot my new CPR warm up curve with my new 5.22bar primary pressure today.
The change in my CPR warm up curve was not a huge one, but it did definitely show an improvement to show my results much more lying inline with the max line of the Volvo warm up curve, with a similar but more gradual kick up above the maximum line, now starting at 31 DegC instead of 38 Deg C like before. I'm not worried about this kick up one bit, because this is still way lower than what would be expected for the DMC warm up curve, and my car is a hybrid of DMC and Volvo after all, so who can tell what's "right" and what's "wrong"?!
After plotting that last curve, I removed my fuel pressure testing equipment from the car, and returned it to as it was before starting anything (vac lines and CPR heater supply reconnected etc). I then did a quick check of engine faultering tolerance with my fuel/air mixture ratio screw in front of the fuel distributor (this is my only mechanism for such an adjustment on my car because I have a simplified Volvo setup on my car which means no Lambda content, Frequency valve, dwell values to consider etc etc). Doing this check proved to me that I could do with adding a bit more of a richened mixture to compensate for the increase in fuel pressure (the higher the fuel pressure, the leaner your car will be, and vice versa). I turned my mixture screw right from 6 o'clock to about 7:30 (right for Rich and left for Lean). Then I took the car for a drive.
This brings me up to now.
I've managed to cobble together little bags of various shim assortments in between the value on the car now, and the maximum value I first tried yesterday.
These are: 0.56mm, 0.57mm 0.58mm.
My intention is to try these out, one by one and try the car out at each point as well as record the primary pressure. I don't think I need to bother recording the CPR warm up curve for each, but you never know, I may also do that for completeness. From the above, I'm expecting the following estimated results:
0.56mm to give 5.28bar
0.57mm to give 5.31bar
0.58mm to give 5.35bar
As an example of how the coefficient (value of pressure increase per 0.1mm of applied shimmage) changes with me having real world results for 0.55mm and 0.59mm:
0.55mm is 0.04
0.59mm is 0.07
These are derived from working backwards from the pressure increase resultant from the mm shimmage increase.
For my estimated results untested above, I'm applying the estimated rules:
0.05 for 0.56mm
0.055 for 0.57mm
0.06 for 0.58mm
Only by doing the actual tests will I get the real values, but I'm expecting them to be something close to this. Time will tell.
And that's it. For now. I'm a happy bunny even at this position (in good time for winter being is on its way! DOH!)
Oh yeah, I almost forgot! I guess I can answer the question now. No. Super fuel is not causing me problems.
Rissy
(Forum Member 288)
(DOC Member 663)
May 1981 vin#1458 "LEX"
Grey, Flapped, Black
Chassis: #1073
Engine: #2839
Main Car(s):
2005 BMW M3 in Velvet Blue
2010 Honda Civic Type R in Sapphire Blue (1 of 115 made)
(Forum Member 288)
(DOC Member 663)
May 1981 vin#1458 "LEX"
Grey, Flapped, Black
Chassis: #1073
Engine: #2839
Main Car(s):
2005 BMW M3 in Velvet Blue
2010 Honda Civic Type R in Sapphire Blue (1 of 115 made)
