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10-02-2018, 10:13 PM #46
- Join Date
- May 2018
Hi Ed thanks for the Refresher on the Theory 😁, you certainly know your stuff.
My statement re fuel vapor locking when using a pre regulated system may have been incorrect but I know for sure with my massive Underhood heat load the car stumbles at would die in heavy traffic this went away when I went to post regulation on purpose to provide some cooling in my fuel rails until I could come up with a better solution (hood Louvers).
I know that the fuel would get hot and be sent to the tank where I hoped it would have some cooling effect but I can corroborate your your statement that the head added will dissipate very little in the lines or my aluminum tank.
My tank is about 6 gallons and it built heat very quickly...easily adding 50 degrees above ambient and I was even contemplating installing a heat exchanger in the return line.
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10-03-2018, 05:51 AM #47
- Join Date
- May 2018
Just had another thought and I think Ed eluded to it ....High underhood temps along with heat soaked fuel would cause hard starts due to less dense air requires less dense fuel so in other words if not properly compensated in the ECU tables engine will stumble or be hard to start when very hot because it’s too Rich.
10-03-2018, 10:33 AM #48
Holy smokes Ed, you get the award for most detailed & accurate response. As always, you are right on point. Your knowledge truly is impressive.
I do have a Fore check valve plumbed into my supply hose, so I know that is not the issue. The hot soak long cranking is directly related to the deadhead style plumbing, at least in my case. When the rails were plumbed via a pass through design I never had hot start concerns. It always lit off immediately, this has me thinking it is not tune related.
I have since swapped back to a y before and after the rails, all equal length hoses. FPR is after the rails. Maybe I'll switch it back over the winter (mod season). Like Jonathan, I also plan on adding vents/louvers to my hood to help with temps.
What are your thoughts on a fuel cooler in the return line? Will cooking the fuel before it returns to the tank help with the heating and loss of octane? Maybe wrap the rails in a heat barrier material?
10-03-2018, 12:06 PM #49
When you look at a Ford OEM installation Matt, it is always a dead head style because the returnless model demands the dead head style plumbing. The OEM systems provide immediate hot start behavior. As long as you use a PPRV or equivalent to maintain pressure in the system at engine shutdown there will always be fuel at the injectors at engine start. Once you have a ready supply of fuel at the injectors it is simply the cold start / hot start algorithm that determines the engine start characteristics. It is sort of like the FAST Fuel Injection folks promote in their name; Fuel, Air, Spark. If you have the first two available in the correct proportions when the third arrives you have ignition. If the ignition does not occur then the the volumes of the fuel and air are incorrect for proper ignition.
The biggest difference between the two systems is the effect that heating the fuel and returning it to the tank has on the fuel. Although the 20˚F rise in temperature was an arbitrary number that was chosen I have no doubt that it is a fair approximation of the real world event. A one time temperature increase of 20 ˚F is not the end of the world. The continuous addition of 20 ˚F to the fuel cycling back and forth between the tank and the regulator will progressively boil off the octane enhancers the refinery has added to the base stock. In time you will be running on fuel that approximated the octane rating of the base stock. This is a life threatening situation for the engine if you call on it to perform at maximum power when the fuel in the tank has deteriorated and is approximating base stock octane rating.
The easiest fix to reduce the deterioration in octane on a large capacity fuel system, is to use staged pumps. By falling back to a single pump for proletariate driving you minimize the amount of unused fuel being heated and returned to the tank. The best staging model uses a small (255 lph) pump for daily driving and stages the big pumps to come on line as engine demand dictates. The gold standard in managing this phenomena is the use of a returnless model like Ford uses where no fuel is returned to the tank.
The challenge most enthusiasts have with the returnless model is their lack of understanding in terms of PID tuning required to maintain commanded differential pressure at the rails and by implication volume to the engine. Here is a great site that helps wrap our heads around PID tuning => PIDs For Dummies. If you are really going to properly tune the PID in the ECU software for your specific vehicle then you should visit Finn Peacock's site, How to Tune Your PID Loops.
The guys at Sullivan Performance took the first steps in that direction for Ford EEC-V ECU's more than a decade ago. I have attached their excerpted contribution to the Fuel System Hesitation thread that describes how they fixed the problem for their customers over a decade prior to this post. Towards the end of the write up I have included Jerry Wrobleski's commentary. Jerry was the Ford calibrations engineer that founded SCT Performance. The pdf makes for excellent reading. It is the first step in managing the PID controller to do your fuel delivery bidding. This is a great beginning but you need to visit and absorb the PIDs for Dummies stuff and the Finn Peacock work to really get the job done correctly. Finn Peacock's tools and explanations are simply excellent.
With respect to cooling the fuel as it returns back to the tank there are several challenges with this solution. The easiest analog is the flat beer comparison. If you heat a beer without opening it or leave it unrefrigerated for sufficient time the effervescence leaves the beer. No matter how long you wait or how cold you make the beer the carbonation will never reassociate with the beer. Once it goes flat, it is flat and it ain't coming back. It is the identical situation with the octane enhancers the refinerys add to the base stock to attain their target octane ratings. Once the gas goes flat, the octane enhancers are gone and they are not coming back.
Providing a heat barrier on the return line does not help either. The damage has already been done and the fuel is already hot from its dwell time in the engine compartment. Additionally the PTFE lining or the elastomer lining in the return hose manufacturers use is an extraordinarily good insulator. Remember the thermal conductivity for these two materials is 0.2 and 0.3 Btu/(hr oF ft) which is excellent insulator country heat transfer wise.
Once the beer goes flat you can't put the fizz back in and similarly once the gasoline goes flat you can't put the octane enhancers back in.
Last edited by eschaider; 10-04-2018 at 11:26 AM. Reason: Forgot add pdf file
10-03-2018, 12:39 PM #50
Apologies Jonathan I should have replied to your two posts first but I was reading the thread backwards. The small size of your tank means the in tank fuel will be heated more quickly. However you car is more of a race car IIRC than a street car so the effect will be less than on a street car — except when you are driving on the street. Your observation about the temperature of the under hood air or IAT1 temps is correct. In a speed density style system the effect of the rise in IAT1 temps will be more apparent than in a MAF based system because of the different approaches to measuring air mass in the case of the MAF and inferring air mass in the case of the speed density systems,
If you are running a speed density based EFI system it is possible the hot start environment could produce a temporarily richer than wanted condition at start. That richer than wanted environment will produce a more challenging start up experience.
The original code in the OEM (and aftermarket) ECUs provides for both hot and cold start logic used to produce different fueling models for the engine when hot or cold starting. Some times in a modified engine it is to our advantage to data log what the engine is seeing and then revisit those code sections to see what the ECU is being commanded to do in order to get the engine up and running. This is typically a tuner issue not an owner issue — unless the owner is the tuner (or wants to become the tuner).
In the final analysis an engine with a differential fuel pressure across the injectors of 39 psi / 43 psi / 50 psi or whatever the tuner has commanded, does not matter to the engine. The injectors do not know how the differential pressure was created they only know what it is. My suspicion is that the flow through system will build pressure at the rail more slowly than the dead head model. The lower pressure at start up in hot weather produces a leaner start condition that ignites more readily and starts more easily because of the higher IAT1 temps that produce a correspondingly lower air mass. That phenomena is speaking directly to the cold start / hot start fueling logic in the ECU, how it is programmed and which fueling model you use.
Remember all of Fords OEM systems are dead head and they do not exhibit the start up problems we are discussing.
p.s. Almost forgot, didn't mean to. The stumble on acceleration is almost certainly a transient fueling (accelerator pump in carburetor terms) issue. The fueling logic in your MSPro has several very nicely implemented transient fueling algorithms to help correct the problem. Data logging the phenomena will provide the necessary information to determine how to adjust the transient fueling algorithms to correct the problem.
Last edited by eschaider; 10-03-2018 at 07:26 PM. Reason: Spelling & Grammar
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