Occams Razor and fuel pump pressure after priming? | Ford Explorer Forums - Serious Explorations

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Occams Razor and fuel pump pressure after priming?

davidk

Elite Explorer
Joined
August 25, 1999
Messages
168
Reaction score
64
City, State
Sacramento, California
Year, Model & Trim Level
'93 Limited
I have a crank/no start on my "new" 93 Limited that is driving me crazy. I've looked at LOTS of posts and want to start simple first. When I turn on the key, the fuel pump runs and has 34 psi at the fuel rail. When I turn the key to start, the engine starts for about three seconds then dies (but keeps pressure on the gauge). If I crank again, no start at all. BUT, if I turn the key off, then on again, the fuel pump pressurizes, and if I turn the key to start, the engine starts again for about three seconds then dies (and won't restart). Pressing the accelerator down is no change.

Question: if after the X tries to start, if I bleed out the fuel pressure, then crank, should I get more pressure? Or is that only when the car starts?

And maybe the history of this problem might give one of you an AHA moment that has a simple solution. I bought this X because I needed to switch to an automatic due to bad knees. It has 107K on it. I drove it for a while and everything was great. I started getting a hesitation when starting and I thought it might be a clogged fuel filter, since I know it had been garaged and I have been putting seafoam in the tank. Then it quit and would not start. I had it towed it to a recommended mechanic who works on older cars. He tested and there was only a trickle of fuel coming out of the fuel filter. He changed the filter, still just a trickle, so he changed the fuel pump. It started and ran great for about three minutes, then died, and has never started since.

No CEL codes.

If one of you has a brainstorm about this, I will be eternally grateful.

Hopefully this is one of those Occam's Razor things where the simplest answer is usually the correct one. This beautiful green Limited is sitting in front of my house and I think my wife's blood pressure goes up every time she sees it. :)

David
 



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check that your key switch moves to run when it starts start and run are not the same thing
roscoe
 






You said:
When I turn on the key, the fuel pump runs and has 34 psi at the fuel rail. When I turn the key to start, the engine starts for about three seconds then dies (but keeps pressure on the gauge). If I crank again, no start at all. BUT, if I turn the key off, then on again, the fuel pump pressurizes, and if I turn the key to start, the engine starts again for about three seconds then dies (and won't restart).

Can you elaborate on 'but keeps pressure on the gauge'? How much?

As to your question: The fuel pump will run briefly when you turn the key from OFF (or ACC, I suppose) to ON. It will not pressurize every time you turn from ON to START, the key has to go back to OFF (or again, perhaps ACC).

Which is to say: Going from OFF to START basically primes or pre-pressurizes the system. The PCM detects engine start and then powers the fuel pump continuously. This is a safety to keep the pump from running with the engine off.

Well, anyway, this falls into either an electrical problem or fuel system.

Electrical: There are a pair of relays I might look at just because it's so easy: The PCM and Fuel pump relays. I could see one of these relays only working for a few seconds... they fail in strange ways. You could swap in a known good relay (if the blower works, the blower relay is a good choice to swap. All the relays are functionally identical.) If a bad relay doesn't become obvious, then, I might jump 12V directly to the pump and test. You could do this at the inertia switch under the carpet, front passenger side, Pink/Black. I'd put a 20A fuse on that jumper, just for grins. If it runs fine with the jumper, it's electrical. If it doesn't, then it's fuel. If it's electrical, that's a can of worms. I helped someone, tried to... it ended up being the PCM computer, if I recall. Let's not wish for that.

Fuel: Well, here's a quick story first. I had this Ford Contour, ran fine, and winter was coming. So, I got proactive and tried a bottle of Seafoam in the tank. Now, people swear by Seafoam, so I don't know what to tell them, but using the Seafoam killed my fuel filter. I mean, I poured it in, ran it for a while, and shut it down for the night. The next day, I got exactly what you got. Changing the fuel filter fixed it permanently. I could not blow air through the old filter. So, I wonder if you have this, but worse. Like, maybe the strainer on the fuel pump is clogged.

The brute force test for this is to set up the jumper I mentioned before, and flow-test the pump before the filter. If you get flow, then measure again after the filter, and right up the line. You can't test this by key because the pump won't stay running if the engine isn't running.

So:
1) Swap known good relays into PCM and Fuel pump locations. If that doesn't change anything...
2) Jumper hot to the pump and test. If this works... then it's another discussion going down that diagnostic path
3) If it still doesn't work with the pump on constantly, then there's a fuel blockage.

Now, you say this was garaged for a while before you got it. So, the potential is high for bad gas in the tank. The electrical is so easy to rule out, I'm suggesting you do that first. But, I have a suspicion that you may need to... (I'm sorry!) drop and flush the tank, clean the strainer sock on the fuel pump, and change the fuel filter again. Gas goes bad in just a year or two, and seafoam doesn't revive bad gas. I think it may have reacted with something, like it did in my Contour.

Good Luck. I'm not a regular here anymore, but I'll try to look in every couple of days for a while.
 






I wouldn't jump twelve volts to the fuel pump relay that was the "fix" on many bronco II I think it put too much voltage back into the computer check the computer ground br the battery plug with two 10 guage wires to the negative post on battery
roscoe
 






Yeah, I should clarify, for the purposes of testing, you would disconnect the inertia switch and then go +12 to pink/black. That will take the computer out of the picture. Well, here's a schematic.
 






How much pressure is at the gauge when it dies?

How much have you driven the explorer since you got it?

When the mechanic changed the fuel pump, did he use a quality pump and change the strainer?

I agree with roadrunner. I would start with the relays. I was driving once and hit a bump and had something very similar happen. Ended up being a bad relay. Swapped it out and been fine since.
 






Thanks everyone for your help!

I drove the "new" Explorer for around three months after I got it and loved it. No problems.

When I turn the key ON, the fuel gauge reads 34, and it stays there, even after it tries to start. I don't know what replacement brand fuel pump, mechanic did say he replaced the sock. He spent MANY hours trying to figure out the problem and finally gave up (didn't charge me beyond $500 to change fuel pump). I should have had the tank drained and cleaned while it was out - hindsight... I finally just had the X towed back to my house.

Interestingly, when I turn the key ON, the CEL lights like it should. When I turn the key to START, it cranks but the CEL stays on. I was reading that means no data going to the computer? With my "old faithful" red Explorer, when I crank, the CEL goes off and it starts. Maybe a crank position sensor?

This weekend I will check all the suggestions.
 






I had something similar happen before. Did a trans swap and somehow fried the ECU, would not start, CEL stayed lit, wouldn't give me any codes or perform any self tests. Wound up replacing the ECU and it finally ran.

Have you tried a KOEO test to see if you can pull any codes?
 






KOEO Test: I hooked up my code reader and did a KOEO test, got the 111 everything is normal code.
Spark: I also hooked up a spark tester and I am getting good spark while cranking.
Fuel: I get 34 psi when the system pressurizes. It holds that pressure (until I release it). If I release the pressure (without turning the key off) and crank the engine, I get 0 psi.
Relays: I cleaned all the connectors, checked for "good" relays for ones that ran the blower, so good relays in system.
Inertia Switch: I'm guessing if the inertia switch was bad, then the fuel pump wouldn't run to pressurize the system (and the red button is not up).
Crank Position Sensor: I disconnected the crank position sensor wires (they had a lot of oil on them), sprayed tv tuner cleaner everywhere, dried off and reassembled. But alas, no start.
I'm really wondering if the Crank Position Sensor could be the problem.
 






I forgot to mention what really stumped the mechanic is he said there were no injector pulses.
 






Some good news, I think. When I connect the fuel pump test connector to ground on the EEC IV Tester, the fuel pump runs and runs, every time, with 34 psi.

Can I leave the pump running that way and see if the X will start, or should I do it by bypassing the inertia switch?

I checked a number of grounds, all good. I connected the crank sensor wires to my voltmeter, turned on the ignition and no voltage. I connected voltmeter (on AC volts) to leads to the sensor itself, cranked the engine, got 0.4 V AC. They are hard to connect to, I may redo those two tests tomorrow.

Thanks again for all the help from everyone. I never dreamed I'd have to learn so much about the EEC IV and fuel system, good thing I REALLY like 1st Gen Explorers!!
 






Do you have little pins for backprobing? Sometimes that is the only way
 












I had something similar happen before. Did a trans swap and somehow fried the ECU, would not start, CEL stayed lit, wouldn't give me any codes or perform any self tests. Wound up replacing the ECU and it finally ran.

Have you tried a KOEO test to see if you can pull any codes?
If the ECU is fried, will it still give a 111 after doing a KOEO test?
 






It wouldn't give me any codes at all. It wouldn't even do the real quick flashes at the beginning of the test.

The only real way to know for relative certainty is to use an ECU from a similar jy Explorer and try it out.
 






It wouldn't give me any codes at all. It wouldn't even do the real quick flashes at the beginning of the test.

The only real way to know for relative certainty is to use an ECU from a similar jy Explorer and try it out.
Can I swap the good ECU from my 93 5 speed (the X I'm having a problem with is an automatic)?
 






I bet it will throw trans codes
roscoe
 






I bet it will throw trans codes
roscoe
My goal would be to see my X automatic would start with another ECU (my 5 speed's). Then I would figure the automatic's ECU was bad and I'd replace it. I wouldn't drive it! :) Can I swap them without damaging the good one?
Thanks!
David
 






I would guess that you can go to a book store and see if they can get you a book "'how to understand service and modify ford fuel injection & electronic engine control by Charles o. Probst, sae" this book helps immensely on obd1 fords shows most pinouts on computer for engine control
roscoe
 



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I would guess that you can go to a book store and see if they can get you a book "'how to understand service and modify ford fuel injection & electronic engine control by Charles o. Probst, sae" this book helps immensely on obd1 fords shows most pinouts on computer for engine control
roscoe
Thanks, Roscoe. I have wiring and pinout diagrams, the Haynes book, etc. I just don't know if cross swapping different drivetrains would damage the ECU/PCM.
David
 






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