Knock on wood!

Weather is reliably mid-90's every day (most of the night, too) and I've yet to see any sign of the vapor lock gremlin, 38 psig.

Eddie

 

[font size="1" color="#FF0000"]LAST EDITED ON 07-Jul-01 AT 01:36 AM (EST)[/font][p]By the way what color is the tailpipe?! Still a nice shiny gray or sooty coal/black. Just curious?


1994 Ford F150
300-6
Highly Modified and more to come!

 

I just gotta ask...why are you worried about vapor lock? My 90 4.9L has a heat shield that fits between the upper and lower intakes that resembles an air bake cookie sheet. Also, if you really are worried about heat soak, why would you not try to reduce/ eliminate it with something like ThermoTec cloth tape. I have used it for years on the exhaust pipes coupled with a heat shielding blanket around the exhaust manifold (also made by ThermoTec). It dramatically reduced the underhood temps and gave me one extra MPG to boot. I also have it wrapped around my fuel rail. I figure cooler fuel is denser fuel which means more fuel in the cylinder!
I mentioned the air bake cookie sheet like heat shield. It was Ford's fix to heat soak on the 87-89 models. These models had electric fans that blew air over the fuel rail and the #5 & #4 cylinder fuel injectors. If I remember correctly, it was called an "after run fan" and would cycle on for about ten minutes after the engine had been shut off. If you do experience heat soak, maybe you could retrofit one of the older setups to your truck.
Youngster

BTW, the smog inspectors didn't care that I was using the heat tape over the manifold, pipes or fuel rail.

 

Nice idea there youngster!


1994 Ford F150
300-6
Highly Modified and more to come!

 

Youngster,
Check the archives, we've been over this several times before. The reason for the concern about heat is simple. One reason that Ford went with 12# injectors and raised the pressure to 55 PSI was to overcome hot restart problems. Going to 19# units @ 38 PSI gives a lot more fuel at WOT, but it reduces residual pressure in the rail and introduces the possibility of vapor lock. Heat wrap may not help much and may actually hurt since the heat can be passed from cylinder head and exhaust manifold thru the intake manifold directly to the injectors rather than being absorbed from the underhood air. (Remember this is the ONLY non-crossflow EFI engine Ford produces in the US.) The fuel rail is in constant flow when the pump is running, so it is unlikely to be the source of a problem. Boil the fuel in the injector or the down leg feeding it and who knows? Eddie was one of the first to make the swap to 19s and living in Houston, he's probably the most likely to experience heat problems. The progress report is very useful information to the rest of us.

 

SR,
I had read most all previous posts regarding this subject before I put in my two cents. Crossflow or non crossflow, heat is the problem. Vapor lock (or heat soak) is caused by radiant heat. If you reduce or eliminate most of it, you reduce or eliminate your chances of heat soak on the fuel rail. I live in So Cal. I regularly drive throught the desert at mid day. In summer I am driving my truck weekly in temps up to 120F. I had a heat soak problem on my 90 that the dealer couldn't fix when I first got the truck new. ThermoTec heat wraps have lowered my underhood temps substantially and eliminated the problem. How much lower? According to my notes the wrap (which is on my exhaust manifold, pipes and fuel rail) on a 119F day cut underhood temps by 118F. From 352F to 244F. How did I measuse the temps? Three digital Thermistors with wiring routed to the cab. One two suspended from the hood--one over the exhaust and one over the intake runners. The third was taped to the fuel rail. The Truck was parked for 15 minutes over asphalt and running at 1000rpm.
I was very skeptical about the claims from the mfg. The most surprising number I got was from the fuel rail itself. After the heat wrap was applied, the rail never got above 90F -- regardless of ambient temps or when I measured it after the engine was off.

As for injectors. Take a good look at them. You might notice that only the tops are plastic. The bottoms tend to be ceramic. Mine are -- both the stockers and the 19# motorcraft ones I just got. Ceramic is an excellent insulator. I wouldn't worry about fuel boiling inside it.

No hard feelings. I was just throwing out a different idea to solve a problem. If you want to measure the temps under your own hood, the guages I used came from a commercial refridgeration supply house. Cost is about $150 for a unit with four probes.

 

What was the average heat-soaked fuel rail&injector temp while running after having run for a time? In other words, how hot does that fuel get, before the heat-wrap installation?

The lower part of the injector is ceramic? I thought they were metal. Are you speaking of the pintle-style, or the flat-tip 4-hole variety?

You are correct about Ford's using an "after-run" blower, and FoMoCo was obviously concerned about vapor lock from heat soak.

We've changed the manufacturer's specifications, and any time you do that you do that you re-weight a compromise that mfg.'s made, and possibly (usually?) inviting trouble.

I've had those 19# units in there for awhile now, and we were all wondering about starting difficulties in hot weather. I don't have that afterrun blower, just the heat shield (which I'm going to get Jet-Hot coated, along with the header I just bought), so I was kinda waiting with my fingers crossed!

Eddie

 

So that's where that fan noise was coming from, Hell when I bought my 88 F150 with the inline six, I thought my blower motor was shorted out..but there was no air moving through the vents....I thought I was going nuts

 

[QUOTE]What was the average heat-soaked fuel rail&injector temp while running after having run for a time? In other words, how hot does that fuel get, before the heat-wrap installation?
[QUOTE]

Eddie
I am not sure what your question is here. My truck is days away from being done (new motor install). If you would like I will redo my temp test with and without the thermal tape. I need to break in the motor and order new tape so it could be about a month befor the tape test. Tell me where you want the probes and I will run up to the high desert for the day.

As for the injector question, I took two different ones to the shop and cut them apart. The pintle style I have is all ceramic and the five hole injector I aquired is actually a pintle style (ceramic) with a metal sheath over it that has a cone in the bottom and five holes to direct the fuel when the pintle opens.

In response to changing the spec. FoMoCo is in business to make a profit first then a product. As a shareholder I expect this. If they can save $1.00 on every truck they make--well, it adds up. If ford could have used the same fuel system on all its motors it would. Obviously it was cheaper to increase fuel pressure. The after run fans are very expensive to replace.

If you want to try something kinda off the wall, what about a hood scoop. Make it functional -- use the incoming air and direct it to the fuel rail and injectors. You would have to fabricate some sort of duct to be attached to the underside of the hood. I would think it would work well and look cool--especially when you popped the hood.

I spoke with my freind at Ford SVO about vapor lock. He told me that it is only an issue with FI in the lower western states (CA, AZ, NV, NM). I didn't have problems until I was in temps consistently over 115F.
Youngster

 

There ya go, approaching a problem scientifically, rather than my rather more off-the-wall, er, empiric, approach.


Your idea of Themo-tec wrapping parts is interesting, to say the least. I think I'll do that to the EGR feed tube; that particularly useless POS has to be contributing to higher underhood ambients.

My question, basically, is: how hot does the fuel get in the fuel rail? Ford put that "afterfun" blower there for a reason (and withdrew it for a reason), same for the 12#/hr. spec injectors which hurt performance on the 4.9L.

I'll fight anybody that sez Ford's hanging EFI off the 300 wasn't one of the better things they've ever done! Duel: swords or pistols, before or after dawn or dusk, winner buys (I drink alone or with someone).

But-yeah, Ford made some compromises, and I've said it right along, since the 'net put deviants like ourselves in contact (real bad for Big Brother) that our job is to figure out what those compromises were and remedy them; with the 300-6/4.9L motor, FoMoCo skewed the recipe toward low-rpm torque, ultimate reliabiltiy. All we have to do is "unskew".

Eddie

 

I apologize...I forgot to explain about poor Strange Ranger; have mercy on him, he ain't but 12 inches tall (on all fours; no offense to little people, it's only a measurement and he really isn't human or anything else), drools a lot, and has a calculator grafted to his...well, you know.

Cool engineer, though; has the only working calculator tattoo that I know of!

A Semi-Lucid Eddie

 

Eddie
I don't know about your EGR tube but mine came from the factory with ThermoTec material already on it. As for the Fuel rail temp -- with the wrap on it never got hotter than ambient air temp. I will hook up the probes when the truck is back up and running and get some before and after numbers.. I have a friend with an 89 and she has the afterrun fan but no heat shield between the intake and exhaust manifolds -- go figure?!?
Youngster

 

 

having problems w/hot starting and am curious about the 19 injectors what is required to change?

 

Probably ought to solve the hot starting problem first. The 19# injectors probably won't cure that.