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+--- Thread: Super fuel causing problems? (/showthread.php?tid=6218)
RE: Super fuel causing problems? - Rissy - 24 Oct 2021
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.
RE: Super fuel causing problems? - Chris Williams - 24 Oct 2021
Well wrote up, glad its better.
Chris
RE: Super fuel causing problems? - Guinney1971 - 25 Oct 2021
Wow. That's a very comprehensive write up Rissy, glad you are happy with the car now.
RE: Super fuel causing problems? - Rissy - 25 Oct 2021
Yes, I realise there is a lot of detail in there. Perhaps too much, but if you happen to be a person in the future wishing to do something similar, then possibly you'll remember this post and refer to it if needed. That was my thinking anyway.
RE: Super fuel causing problems? - Guinney1971 - 26 Oct 2021
absolutely mate, information like this is gold dust.
RE: Super fuel causing problems? - Rissy - 26 Oct 2021
I need to revise my figures from above. I have new findings tonight which sort of undoes the above report a bit. I can't edit my post, so I can only correct it with new findings. I want to do a further test tomorrow night before I explain further.
RE: Super fuel causing problems? - Rissy - 27 Oct 2021
Sorry for being so cryptic last night, but this is the new issue I've discovered during a new warm up curve attempt after further increasing the shimmage after work last night to try and bring my primary pressure a bit further up from Sunday. Remember I wanted keep it below 5.4 bar.
I realised I mucked it up over the weekend, when I realised last night that my previous figure was out for primary pressure due to my running the fuel pump on the battery charger, which as it turns out, is only pushing 13.5V. It's only 1V out from a typical alternator, but clearly that's enough to throw out my pressure measurements when you compare them to what you get when the engine is warmed up and running. I realised this when I took the primary pressure this time while the engine was running (not normally something you'd do), and realised that my pressure was quite a bit above what I had observed on the battery charger on Sunday! (then I measured my charger output to reach the above conclusion)
The result now, is that I had no choice but to redo my work to in fact, REDUCE BACK my fuel pressure again.
I seem to now have my fuel pressure at pretty much bob-on 5.4bar (accounting for gauge offset) with the engine warmed up and running to take that measurement. To get that, I had to reduce my shimmage down to 0.33mm! (was previously stated as 0.55mm in my post earlier, but measuring again last night after taking them back out, it was coming in at more like 0.52-0.53mm - it's very difficult to be consistent in measuring these small thicknesses with a vernier caliper!).
After returning in doors, I found a reference in a Volvo manual which states that you should get 0.1471bar increase for every 0.1mm worth of shimmage. Using that as a guide, this would mean that my fuel pressure should now be 5.48543bar (79.56 PSI) with my 0.33mm, which doesn't quite fall inline with my best observation at the gauge tonight (very difficult to be precise using these gauges. I've actually been going by the PSI figure on my gauge and converting back as the needle is narrower at the end where the PSI scale is, meaning it's easier to read more precisely.)
I observed 74.4 psi at my gauge tonight (engine running) with the 0.33mm of shimmage, which if you convert to bar, gives you 5.13barg, which then if I convert that against my look up table from my calibrated figures for my gauge, gives me 5.4bar. Then, sigh, convert that back to PSI, is 78.32 PSI, which is a bit lower than the advised 79.56 PSI (5.48543bar) I should have gotten. I guess that could be to do with the age of the spring, or me over stressing it on Sunday, or alternatively, even Volvo have rounded this 0.1471 up to 0.15 because then the maths works out almost perfect. Shrug.
The thing is, all this is extremely fickle, and very difficult to be absolutely precise with the sort of micron differences you can make and get massive swings in results. Couple that with me doing this in a less than surgically sterile environment where atmospheric dirt and finger grot can contaminate everything by opening all this hardware up and manhandling it, plus voltage differences at the pump, plus continually changing temperature changes etc etc. It's a freaking minefield!
As a comparison, I've promised myself I'll run just the pump on the battery charger again tonight, and observe my primary pressure reading again so that I can compare where I am now, with where I was on Sunday under the same conditions. This might give me an idea about how much I may have over pressurized my fuel distributor. If you use the Volvo guide above, it works out to be 5.8bar with as much as 0.55mm!
I really don't want to open it up again. I'm starting to feel that I'm putting my fuel distributor in repeated continuous risk by mucking around with it over and over. I also need to do another test drive to make sure where I have it now, is still good enough to eliminate my bunny hopping. (fingers crossed) If it's not, then I despair, cause I really wont know what else to do other than to over pressurize my system again. Only the DMC workshop manual states a maximum of 5.5bar. I can't find any equivalent statements in any of the Volvo information I have here, including a Haynes manual. Maybe someone else can find one?
The more time I've spent doing this, the more I appreciate how sensitive, and potentially dangerous for your equipment this shimming up business is. I can only hope I've not done any lasting damage to anything by coming at this carefully and conscientiously, yet still managing to be half cocked despite that!
I'll report back with my figures later one for where I am now with measuring only with the pump running at 13.5V, and hopefully after I've also taken the car another test drive to see if my bunny hopping issue is still fixed at this lower level of primary pressure.
RE: Super fuel causing problems? - Rissy - 28 Oct 2021
Well.
Some confusing, but also some great results from last night.
I want to throw away my previous results because they do not make sense against what I have now after doing things differently so this is the last time I'll discuss them in comparison to what I now have.
On Sunday, as mentioned first in my earlier thread, I thought I had administered 0.55mm worth of shimmage. Taking that out again on Monday night, it measured more like 0.52-0.53mm. Don't know why. Just did. From that, I got 4.96barg of pressure at my gauge with just the pump running off the battery charger and a warm up curve with the engine running which hovered mostly along the MAX Volvo warm up curve line, but with a kick up at the beginning and a bigger kick up at the end (40 DegsC).
Now though, with 0.33mm worth of shimmage, and the same experimental method as Sunday, that I've just discussed, I got 4.97barg of pressure at my gauge with just the pump running off the battery charger. The associated warm up curve sits slightly lower than Sunday's and has less of a kick at each end. This is the bit I can't get my head around. Why would the warm up curve be LOWER with a HIGHER primary pressure?! That shouldn't be the case, so now I'm going to stop comparing my results now with Sunday's because something doesn't ring true with that at all and it messes with my head TOO much. I put it down to too many variables and conversions and factors to consider.
I'm not messing with my fuel pressure any more. That's it. I'm as close to 5.4bar actual primary pressure as I'll probably ever manage to get without an even finer tuning set of shims. By my reckoning, I'm definitely somewhere between 5.4bar and 5.42bar (possibly 5.48!?) depending on which methods of reasoning you apply and having hoards of calibration offsets and unit conversions to carry out, each with their own rounding errors! I'm definitely lower than what I was on Tuesday night when I realised with the engine running, the primary pressure was too high.
BUT....
Good news! I may have managed to hit upon a sweet spot or something. Once I finished putting the car back to a complete condition ready for a test drive (all measuring equipment removed and vac lines put back etc) I started it up and gave the accelerator a few blips at the throttle. The noise that car makes now, is amazing. I've never heard it sound like that. It now has a really nice pulsating rumble through the overall roar which I've never heard before.
The missus and I took the car for a spin and not only does it sound nice; it feels smoother and it accelerates like I've not felt for a long time, if ever before! Even the missus said she's never felt the car feel so smooth or pull so well in acceleration as it did last night. We were both impressed.
Oh, and still no bunny hopping any more, which is a big relief.
To those who I also mentioned that I was suffering some sort of resonance frequency vibrations during acceleration. Well that has more or less also gone. I say more or less, because the car does feel/sound more throaty with the new exhaust on it, so the little difference I have now compared to before could just be put down to that. The point is, it's no longer HORRIBLE to drive it! It's very livable with.
That's me now for the winter. I'm not messing with the car any more. My next stage is reassess my vacuum plumbing on the car, but that will be a job for next summer to experiment with and see if I can make things better or worse by addressing some changes there.
RE: Super fuel causing problems? - Chris Williams - 28 Oct 2021
Quote:Good news! I may have managed to hit upon a sweet spot or something. Once I finished putting the car back to a complete condition ready for a test drive (all measuring equipment removed and vac lines put back etc) I started it up and gave the accelerator a few blips at the throttle. The noise that car makes now, is amazing. I've never heard it sound like that. It now has a really nice pulsating rumble through the overall roar which I've never heard before.Good news mate.
The missus and I took the car for a spin and not only does it sound nice; it feels smoother and it accelerates like I've not felt for a long time, if ever before! Even the missus said she's never felt the car feel so smooth or pull so well in acceleration as it did last night. We were both impressed.
Oh, and still no bunny hopping any more, which is a big relief.
To those who I also mentioned that I was suffering some sort of resonance frequency vibrations during acceleration. Well that has more or less also gone. I say more or less, because the car does feel/sound more throaty with the new exhaust on it, so the little difference I have now compared to before could just be put down to that. The point is, it's no longer HORRIBLE to drive it! It's very livable with.
That's me now for the winter. I'm not messing with the car any more. My next stage is reassess my vacuum plumbing on the car, but that will be a job for next summer to experiment with and see if I can make things better or worse by addressing some changes there.
RE: Super fuel causing problems? - Guinney1971 - 02 Nov 2021
wow, well after all that its good news that the car is behaving and driving nicely, you sounded
so down and frustrated with it all last time we saw you the other week, so to have possibly 'cracked
it' is really good to hear.
RE: Super fuel causing problems? - Rissy - 03 Nov 2021
(02 Nov 2021, 21:42)Guinney1971 Wrote: wow, well after all that its good news that the car is behaving and driving nicely, you sounded
so down and frustrated with it all last time we saw you the other week, so to have possibly 'cracked
it' is really good to hear.
Yes indeed. It WAS getting me down. Ok, the bunny hopping was a new thing this year, I reckon as a result of putting my free-flow exhaust on there during its down time from 2018, but i've also had a starting issue for about 6yrs. Considering I've owned the car for just over 12yrs. Around half of that time, I've been having problems with the engine area of the car. For the first time in 6yrs, I'm starting to feel happy about the car now that these issues have been FINALLY resolved.
It was getting me down so much this summer, as I was explaining to others just a few weeks ago, that I was literally hating driving the car now, despite all of the efforts and money I've literally poured into the thing since it moved to Rugby to live with me in 2018. That's no way to feel about your pride and joy and hobby car. It should be an enjoyable thing, not something you dread taking out of the garage every time!
Anyway, now hopefully, i'll feel differently. Just unfortunate that will now have to wait until NEXT summer now! DOH!
RE: Super fuel causing problems? - Guinney1971 - 04 Nov 2021
I would suggest regular start ups between now and next show season, keep the engine fluids
and fuel system running, maybe even take it round the block once a week. That'll stop any crud
settling and causing future problems.