'86 2.9 vapor locking
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'86 2.9 vapor locking
i have a fresh 2.9 (250mi) f.i. all stock, we live in yuma,az. it is 110* f.deg daily, it runs decent during the cooler periods of the day, but during peak heat it quits running. eng. temp gauge reads fine(mid gauge). is there some way to troubleshoot/seperate the fuel pump/regulator/filter/computer?
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From: UT
At 40+ psig design pressure, it's real hard for a EFI engine to "vapor lock"
Whenever you suspect fuel delivery issues, the best place to start is to put a fuel pressure gauge on the fuel rail. Ken00 has a decent write up on how to test fuel pressure in his tech info post at the top of the BII forum. There's also a decent little troubleshooting chart jfor fuel pressure in Chiltons for the '90's Explorer/Ranger (I'm not sure this chart was put in the '80's BII/Ranger Chiltons).
A 2.9 that stalls only when it's hot, though, is a classic symptom of a bad TFI module. A common failure mode for the TFI module is to fail when it gets hot. My '87 would stall once in a while, and only in the middle of summer. Pull trouble codes from the computer and look for ignition related codes (14 and/or 18 is what mine would give me). Next time it stalls, check for a good blue spark. If the spark is yellow or non-existant, you might have a failing TFI module. If you get other trouble codes, or fuel pressure is off, then diagnose those issues as well.
Whenever you suspect fuel delivery issues, the best place to start is to put a fuel pressure gauge on the fuel rail. Ken00 has a decent write up on how to test fuel pressure in his tech info post at the top of the BII forum. There's also a decent little troubleshooting chart jfor fuel pressure in Chiltons for the '90's Explorer/Ranger (I'm not sure this chart was put in the '80's BII/Ranger Chiltons).
A 2.9 that stalls only when it's hot, though, is a classic symptom of a bad TFI module. A common failure mode for the TFI module is to fail when it gets hot. My '87 would stall once in a while, and only in the middle of summer. Pull trouble codes from the computer and look for ignition related codes (14 and/or 18 is what mine would give me). Next time it stalls, check for a good blue spark. If the spark is yellow or non-existant, you might have a failing TFI module. If you get other trouble codes, or fuel pressure is off, then diagnose those issues as well.
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update! 
i've replaced the TFI module($65), even though i had good spark with a dead motor, there was no way to know if it was sporadic or on time. i also replaced the fuel pump and fuel filter($100), with new out of the box parts, it has had no effect. i have put a PSI gauge on the fuel rail, and have discovered that the engine stumbles while fuel pressure is at 40PSI. when the engine stops running, i've discovered that the fuel pressure has dropped to 20PSI . the fuel gage is under the hood, it was difficult to know which occurs 1st while driving, engine die or PSI loss. in the shop with the hood down, the car idling with a/c on, the fuel pressure bobbles and drops to 20PSI 1st and then the engine dies (which is what prompted me to replace the pump and filter). also i NEVER see a "check engine" light, not even at the initial "on" condition prior to starting, and the fuel rail does not achieve full pressure until the engine is actually running. shouldn't the fuel pump initially pressurize the system to 40PSI prior to starting? D@MN i miss points and carbs!
i've replaced the TFI module($65), even though i had good spark with a dead motor, there was no way to know if it was sporadic or on time. i also replaced the fuel pump and fuel filter($100), with new out of the box parts, it has had no effect. i have put a PSI gauge on the fuel rail, and have discovered that the engine stumbles while fuel pressure is at 40PSI. when the engine stops running, i've discovered that the fuel pressure has dropped to 20PSI . the fuel gage is under the hood, it was difficult to know which occurs 1st while driving, engine die or PSI loss. in the shop with the hood down, the car idling with a/c on, the fuel pressure bobbles and drops to 20PSI 1st and then the engine dies (which is what prompted me to replace the pump and filter). also i NEVER see a "check engine" light, not even at the initial "on" condition prior to starting, and the fuel rail does not achieve full pressure until the engine is actually running. shouldn't the fuel pump initially pressurize the system to 40PSI prior to starting? D@MN i miss points and carbs!
Last edited by azjay; Jul 12, 2007 at 07:13 PM.
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From: UT
Your '86 doesn't have a check engine light, those were introduced in '88, I believe.
The fuel pump should run for 2-3 sec when the key is first turned on to bring the pressure up. However, the computer doesn't monitor pressure, so it doesn't actually know if the pressure came up enough or not.
If the fuel pressure drops off, is it because one of the the fuel pumps is cutting out? I don't know if you've noticed, but you have two pumps: a low pressure "lift" pump in the tank that delivers gas to the high pressure "boost" pump on the frame rail. If either of those pumps is cutting out, then you can see a drop in pressure and the kind of stumbling/stalling problem you are seeing. Do you have a voltmeter and a wiring diagram so you can set yourself up to monitor power supply to the pumps?
Another thing to look at would be the fuel pressure regulator, but I'd probably start by verifying that the pumps are working correctly.
The fuel pump should run for 2-3 sec when the key is first turned on to bring the pressure up. However, the computer doesn't monitor pressure, so it doesn't actually know if the pressure came up enough or not.
If the fuel pressure drops off, is it because one of the the fuel pumps is cutting out? I don't know if you've noticed, but you have two pumps: a low pressure "lift" pump in the tank that delivers gas to the high pressure "boost" pump on the frame rail. If either of those pumps is cutting out, then you can see a drop in pressure and the kind of stumbling/stalling problem you are seeing. Do you have a voltmeter and a wiring diagram so you can set yourself up to monitor power supply to the pumps?
Another thing to look at would be the fuel pressure regulator, but I'd probably start by verifying that the pumps are working correctly.
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re; fuel delivery, i spent almost all day sunday working with it. i have confirmed, w/ strategic multimeter placement, that the fuel pump relay is working, it remains energized until the the engine stops running. from underneath, bypassing the computer, both fuel pumps operate (the front one is new, i can hear it, and when operating makes 50psi at the fuel rail) i have confirmed in a heated, non-running condition, that the rear pump flows excellent into the fuel filter housing (it flows like a drinking fountain). i also discovered that the return fuel, from the regulator is dropped into the housing (in a poor fuel flow condition that would be hot air/gas). during this same heated, non-running condition, i do NOT get fuel at the input to front pump/ output from the filter housing.? i see that there is a return line out of the filter housing to the tank, i can hear fuel and air bubbles being returned to the tank. does the filter housing contain a built-in PSI regulator that has failed? we have an '85 E350 motorhome that used a similar continuous flow fuel system with a filter/regulator on the 460 4bbl engine, it failed in a similar manner.
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Been out for a few days. I don't quite understand your last post, but I'll try to comment.
Sounds a little high. Spec is 35-45 psi, though the pump should be capable of generating much higher pressures. If you are getting 50 psi at the fuel rail, I would check that out (more to come).
What "housing"? The filter housing between the pumps? Just trying to understand what you are saying.
The basic flow of fuel should be: in tank pump -> filter cannister -> hi pressure pump -> hi pressure filter -> fuel rail -> fuel pressure regulator (a mechanical back pressure regulator) -> return line to the tank (which I believe does flow through the low pressure filter cannister).
From what you see, I would check the fuel pressure again. If it is 50 psi, figure out why the fuel pressure is too high. If fuel isn't getting to the high pressure pump, figure out why.
makes 50psi at the fuel rail
i also discovered that the return fuel, from the regulator is dropped into the housing
The basic flow of fuel should be: in tank pump -> filter cannister -> hi pressure pump -> hi pressure filter -> fuel rail -> fuel pressure regulator (a mechanical back pressure regulator) -> return line to the tank (which I believe does flow through the low pressure filter cannister).
From what you see, I would check the fuel pressure again. If it is 50 psi, figure out why the fuel pressure is too high. If fuel isn't getting to the high pressure pump, figure out why.
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Fixed!!
i replaced the rear fuel filter housing, ford calls it a resevoir now, it contains the low pressure fuel regulator, appearantly when it fails, much of the fuel is returned to the tank, allowing the high pressure system to starve for fuel, allowing a vapor lock/fuel starved condition. we have not had any vapor lock in a week, since i replaced the resevoir. the local ford dealer keeps one on the shelf, and sells 1-2 a month, they used the resevoir/low psi regulator on many models f150, e150, etc into the mid 90s. of the 4 BIIs at the local salvage yard, 3 have had this part removed, seemingly, a high failure item in this part of the country. i did update our '86 fuel system, to the '87 style with a new in-line filter added on the hi-psi side ('86 didn't have hi side filter only lo side) the mounting bracket and hoses came from one of the bone yard cars, and no filter in the rear housing. i'm not overly concerned with 50psi on the fuel rail, the guage could easily be off 5psi.
thank you very much for your assistance, i hope to return the favor sometime.
thank you very much for your assistance, i hope to return the favor sometime.
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