On close analysis, that explanation makes no sense (some of the heat will be removed to ambient in the travel back to the tank, the tank is a huge heat sink, so if nothing else, it buys you a lot of time (more than no recirc) before temps at the rail rise significantly.
OK - but why was recirculating fuel system design used in the first place - it obviously costs the motherfacturers more to run a return line instaed of dumping it at the pressure regulator in the tank? There must be a reason for its use since they could save money by not doing it. Or was this a lesson-learned in the industry?
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')
Ok some other people have mentioned some TSBs so you may already have this info.
There are several TSBs for a 98 Concorde which may apply to your problem.
18-14-98 In Stock/Transit Flash Update to Minimize Vapor Lock Concerns.
- and -
18-09-98B (6/12/1998) NO RESTART/ROUGH IDLE AFTER A HOT SOAK - PCM - REVISED
This second TSB supercedes two earlier TSBs with the same title 18-09-98 (Feb 27 1998) 18-09-98A (March 13 1998) Be sure you're looking at the last version.
---------------------------------------- TSB 18-09-98B NO RESTART/ROUGH IDLE AFTER A HOT SOAK -PCM- REVISED (Jun 12 98) Applies to all vehicles built before May 12, 1998. (2.7L t'stat mod applies to vehicles built after Apr 20, 1998). Check your VIN if you're not sure when your vehicle was built.
Symptom: Hot engine no start, hot engine restart w/ rough idle, or hot engine start/die-out. May have misfire DTCs. ... May not restart until cools. Fuel vapor build up in the fuel rail may be the cause.
The summary diagnosis for 18-09-98B basically is to Check codes and repair as necessary prior to proceeding. Cold soak the vehicle for min. of 8 hours. Connect a fuel pressure gauge (Miller Tool # C4799) to svc port. Switch key to RUN while monitoring pressure but do NOT start engine. Allow fuel pressure to stabilize (48-50 psi) and switch to OFF. Monitor pressure for 15 mins. If fuel pressure drops 20 psi or more perform flash update repair procedure only. Additionally if vehicle has 2.7L perform thermostat mod. and heater hose mod. repair procedures.
The fix-it section starts with replacing the fuel pump module (if necessary per diagnostics I paraphrased above) and then flashing the PCM. [Release 21 or higher and TIL CD Release 1161 or higher]. For the 2.7L engine (which I don't think you have b/c you said Concorde LXi not LX) there are additional mods to the cooling system involving hoses. The full procedures are too detailed to post here.
----------------------------- TSB 18-14-98 Flash Update to Minimize Vapor Lock Concerns. (Mar 13 1998) This TSB applies to 3.2 L engine vehicles built prior to Feb 16 1998 MDH (0216XX) and 2.7L engine vehicles built prior to Mar 9 1998 MDH (0309XX).
There is no diagnosis section. Basically it has step by step instructions to erase and reprogram the PCM and seems to be a subset of the TSB 18-09-98B above, except it was written a little earlier so it has a lower software release number specified as the minimum to use. It lists that the MDS and DRB must have Release 21 or higher and TIL CD release 1153 or higher.
I don't know any fuel system design engineers personally. Do you? This is exactly opposite everything I've read. It would be very hard to heat up all of the gas in the tank by enough to get anywhere near enough vapor pressure to cause vapor lock. It is much easier to just heat the slow moving fuel in a non recirculation system. This is pretty simple physics. I'd like to hear your explanation as to why a non recirc system will pick up less heat in the fuel before it reaches the injector.
Maybe if the fuel tank was almost empty and the little amount of fuel returning to the pump was enough to almost make a measurable change in temperature to the fuel in the pump. Otherwise I don't see how that would be much of an issue. The advantage of a return line is that you can pump plenty of liquid gasoline through the system to keep it continuously cool enough to avoid vaporization in the lines. This is similar to a garden hose sitting in the sun that is full of hot water but if you keep running fresh water though it, it stays fairly cool even though it is still in the sun.
Vapor lock has been a hot starting issue for some piston aircraft engines with fuel injected engines. When return lines are used it becomes less of an issue as running the electric fuel pumps for a short while is an item on the pre-start checklist.
I'm not sure what the PCM update (mentioned in the TSB I posted in a separate message) does, but it probably turns on the fuel pump a little longer before cranking or some similar trick. On my 99 (built after they fixed the problem in the TSB) I can hear the fuel pump come on for a second or two when I turn the key to ON before START. On the other hand I have a California Emissions-Certified vehicle that needs a leak detection pump which may work differently then vehicles sold in the other 45 or so states that did not use this type of pump.
Personally as in ; I visit their home at least once a week for dinner? The answer would be no. Why would it be necessary to know one personally? Does one need to have a personal relationship with an engineer in order to avail themselves on how a (any) system works? I hope not, otherwise there is probably only a handful a people out there who are capable of servicing any given component or assembly on an automobile. Do I know any engineers? Yes. Do I know any Chrysler/GM/Ford engineers? Yes, I've met them on a regular basis during various training sessions/conferences/committee meetings, etc. Are there Chrysler engineers here, lurking? Yes Are they/do they laugh at the pomposity that is posted here? You betcha!
before you commit to that Matt, you might want to familiarize yourself with the criteria set for monitoring EVAP pressures on any vehicle built to 1996 or later OBD2 standards, because fuel heating is a very major component used in the EVAP strategy.
Please explain how the fuel in the tank is heated by engine heat in a non recirculating system.
It would be much more interesting to hear why you think a recirculating system -wouldn't- raise the temperature of the fuel in the tank in spite of the fact that a portion of the fuel has traveled to the engine compartment, sat in the fuel rail for a period of time soaking up heat, and was returned to the tank repeatedly. Especially since it -is- a known occurrence and is something that has to be dealt with in the OBD2 EVAP strategy.
The fuel ahead of the pump is at 35-40 psi, at that pressure, it isn't at all susceptible to vapor lock. Doesn't mean it can't happen, but as it's been since the advent of EFI, usually the only time vapor lock becomes an issue is when the gasoline supply is blended for winter and a geographic area receives an unusual for the season warm/hot spell which makes it a specific function of the gasoline's vapor pressure.
Not at all like a garden hose, the fuel lines do not sit in the sun like your garden hose does, soaking up heat. Also, once purged of the hot water from the sun soak, your garden hoses supply of water comes from underground where the ambient ground temperature keeps it cool(er). Bad analogy
A purge function which is separate from the causing event. Run the aircraft for enough hours to sufficiently heat the fuel and the problem will return I suspect.
Or; they increase the pulse width of the injectors to purge vapors. Running the fuel pump longer would do nothing since there's no recirculation involved, so what if anything would it do?
Same as any other EFI car.
Nope. AFAIK, LDPs are used federally also, I see enough of them for service here in Wi.
Oh yeah, that fuel sure is going to cool down in the whole three seconds that it resides in the return line.
You're implying that heat sinks do not warm up.
Where did 'temps at the fuel rail" become an issue? Why would they be/ The fuel rail is under pressure where as the inlet to the pump is not.
Proximity of the fuel pressure regulator and the attendant manifold vacuum source, for one. Complexity and the lack of (to that point,) OBD2 regulations.
I think it's pretty obvious that the industry as a whole has been evolutionary, a large part of which has been because of lessons learned.
It isn't, but then vapor lock doesn't occur in the tank in occurs in the engine compartment typically where the fuel line runs past a hot component such as the exhaust manifold.
I don't think that it won't heat the fuel in the tank. However, since that is largely irrelevant to vapor lock, what does it matter? What matters is when the fuel in the fuel line vaporizes before reaching the carbuertor or fuel injector. And the temperature of the fuel in the fuel lines in the engine compartment will be much higher in a non-recirculating system that has a low flow rate and thus higher dwell time near the hot components of the engine.
I would (belatedly) interject here that apparently all you've got to go on is what you've read, and it's certain that you may not have read all that is necessary, and it's also certain that you lack practical experience.
So, apparently it is not "very hard to heat up all the gas in the tank by enough to get anywhere near enough vapor pressure to cause vapor lock." If you knew anything about OBD2 EVAP criteria, you'd be familiar with the pressure built and the conditions where they are maximum.
That equals a head start as far as the fuel system is concerned.
Hog wash. Vapor lock is more likely to occur on the suction side of the pump and is virtually non existent on the pressure side of the pump up too the point where there is a component problem such as a failing fuel pump. You could easily win this by describing in detail the precise movements of the fuel in the tank to the pump, from the pump to the filter/regulator and its return to the fuel tank in an LH chassis and include the where and why that causes the (cited in TSB by Greg Houston) vapor lock condition. IOWs, cite the specific failure mode that contributes to the vapor lock. (hint, it's got nothing to do with anything you or Bill have posted so far). I'll tell you this much; Chryslers description using the words "vapor lock" is a bit disingenuous.
I'm under the hoods of a lot of LH cars, exactly where is this?
Fuel temperature is "irrelevant" to vapor lock? Does raising the pressure of a liquid tend to increase or decrease its boiling point? Pick a point in the fuel system where the fuel goes from a negative pressure to a positive pressure and then cite why the side under positive pressure is (according to you) more likely to boil of form into a vapor.
Again, vapor lock on the pressure side of the fuel is quite rare and would probably take some pretty extreme temperatures to facilitate. And, in the case of the LH cars, it doesn't occur there to begin with, it starts at the inlet to the fuel pump. (you can go ahead and do the math since I already know what the root cause of the LH vapor lock is)
This totally ignores the fact that the fuel can pick up heat on the return path from things like the pavement and/or the exhaust system. But then, you -did- say that fuel temperature was "irrelevant."
There is no indication of that all, either in your posting or the Chrysler service bulletin regarding the vehicle in question.
Exactly which OBD2 criteria are you referring to?
There are service bulletins issued by Chrysler for vapor lock conditions on the pressure side in the pump (more specifically inside the engine compartment) for some M.Y. 1998 LH vehicles.
The hot component cited for sure is the engine cooling lines, at least for the
2.7L engine.
I don't think he indicated anything like the question you propose.
The vapor lock problem occurs while the engine is off. If pressure is not maintained while the engine is off (but the engine is still warm) the vapor lock problem can occur. The first step for diagnosis in Chrysler's service bulletins is to check if fuel pressure is maintained for 15 minutes after the fuel pump is turned on, then off.
Careful there, your statement is resembling begging the question. First Chrysler published a TSB for vapor lock conditions on the pressure side of the fuel pump. Second, what math are you referring to? If you honestly know some math which supports your position don't be afraid to post it. You may already "know" what the root cause of the LH vapor lock is, but Chrysler published a service bulletin that disagrees with your diagnosis. Given the choice, I'll lean toward Chrysler's analysis and repair.
To be fair, you've made an irrelevant conclusion policy here. His "irrelevant" comment was only referring to the temperature of gasoline in the Fuel Tank, not any fuel temperature anywhere. As stated in Chrysler's own bulletin, the vapor lock problem occurs near the hot engine, not in the tank. However according to the TSB the fuel pump module is a source of the problem due to its inability to maintain fuel pressure after being switched OFF.
It's only at 35-40 psi after the engine is shut off (while the engine remains warm) IF the fuel module is working properly.
Actually the fuel line is adjacent to warm engine components, where they can soak up heat. The TSB states as much as well. It is also why the TSB refers to modifying engine cooling lines. The combination of the fuel lines absorbing engine heat and a malfuntioning fuel pump that doesn't keep pressure high enough after it is shut off causes the vapor lock condition.
Not at all. Running the fuel pump is a warm engine start checklist item. (i.e. after the aircraft has been run for hours.)
With the LDP you can also hear the LDP sequence (only when starting an engine that is cold [it doesn't do it when it is really really cold in the winter). In later years CA cars used another technology in lieu of the LDP--I think around MY 2001 or 2002.
According to the Chrysler '99 LH service manual the LDP was only on CA emissions cars, at least for that MY.
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