1986 302 fuel injected electrical problems
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1986 302 fuel injected electrical problems
I'm having an interesting problem with my 86 F150. The engine turns over OK but will not start so I suspected fuel problem. Dropped the tank (needed to be claned and painted anyway) and tested the pump. The pump works fine when given power. Then measured power at the connector. I get power there but only for two seconds and then it shuts off. I checked the fuel pump relay and found the same thing. The two wires that drive the relay both meter twelve volts after the two seconds have passed and the key left on. Both these wires go to the EEC so I pulled the connector on it. Found a small amount of corrosion but nothing serious. Cleaned the terminals and blew them out. Reconnected but still getting same problem. What could cause the EEC to turn the fuel pump off after a couple of seconds? Any help is appreciated.
John C
John C
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From: Suffolk, VA USA
That's normal. Essentially, the system builds fuel pressure, then the pumps shut down until there's demand for the fuel.
There are several things you can do to help diagnose the problem. Get an OBD1 code reader and see if the computer is storing any codes. Codes can greatly help narrow down the problem. Check for spark while cranking. If there's no spark, check for simple things like loose/broken wires. In particular these are two ground wires that go to the EEC that need attention...one runs directly to the negative battery terminal, the other to one of the wiper motor mounting bolts. Make sure they are clean and tight.
Let us know what you find.
There are several things you can do to help diagnose the problem. Get an OBD1 code reader and see if the computer is storing any codes. Codes can greatly help narrow down the problem. Check for spark while cranking. If there's no spark, check for simple things like loose/broken wires. In particular these are two ground wires that go to the EEC that need attention...one runs directly to the negative battery terminal, the other to one of the wiper motor mounting bolts. Make sure they are clean and tight.
Let us know what you find.
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I had a similar problem with my truck about a month ago. It turned out to be the pump in the tank, and the ignition module was going out. Mine would turn over but never start. Have you checked out the secondary pump on the fuel rail? That may also be the problem. I replaced mine, I thought that was the problem but it wasnt for me. Another reason mine wasnt starting is because it flooded from me turning it over to start it, so you might want to see if yours is flooded also.
Hope this helps
Blake
Hope this helps
Blake
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I checked for pressure on the fuel rail. No pressure. Disconnected the fuel pump in the tank and tried. Relay still only stays on for two seconds even though it dosen't make pressure. Checked the grounds and they seem ok. Starting to think it might be the ignition but it does the same thing every time. Someone told me to check the EEC relay. Does anyone know where it is located?
Thanks
Thanks
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The EEC relay is under the dash just to the right of the computer. The fuel pump relay is controlled by the EEC, so the EEC is getting power. Have you checked the high pressure fuel pump yet? That's located on the inside of the left frame rail just behind the front wheel. Do you have a single or dual tanks? Also, have you checked for spark or codes yet?
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I checked for spark and it looks good. I don't have a code reader but I did try the old flash method. I seem to get three flashes and then one flash. Sometimes I get the single flash first but usually the three flashes show up first-- so either 31 or 13. I read these codes but don't understand why either would cause it to not start.
On the no fuel situation I got under the truck and measured voltage at the tank pump. Got no voltage even for the two seconds the relay is on. Then jumped the relay and put power on the wire going to both pumps. Still do not have power to the pumps. I found an old wiring diagram from a Chiltons book and it shows an "inertia switch'" on the wiring to the pumps. Does anyone know if this switch exists and where it is located? It seems to me I've got to get fuel to the rails but the pumps don't get power even for the two seconds before the ECC turns the fuel pump relay off. Any thoughts?
On the no fuel situation I got under the truck and measured voltage at the tank pump. Got no voltage even for the two seconds the relay is on. Then jumped the relay and put power on the wire going to both pumps. Still do not have power to the pumps. I found an old wiring diagram from a Chiltons book and it shows an "inertia switch'" on the wiring to the pumps. Does anyone know if this switch exists and where it is located? It seems to me I've got to get fuel to the rails but the pumps don't get power even for the two seconds before the ECC turns the fuel pump relay off. Any thoughts?
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The inertia switch is located under the dash, passenger side, on the firewall just to the right of the heater outlet.
Getting back to my earlier questions because they can help narrow down the problem. Do you have single or dual tanks? And are you getting power to the high presuure pump on the left side frame rail? It's not clear when you mention not getting power to "both pumps" whether you are writing about the high pressure and in-tank pump, or two in-tank pumps. It makes a difference to the diagnosis. Also, when you write about the fuel pump relay being on for two seconds, are you hearing a whirring sound for two seconds, or are you just hearing the relay click? Have you checked the fuel filter?
Getting back to my earlier questions because they can help narrow down the problem. Do you have single or dual tanks? And are you getting power to the high presuure pump on the left side frame rail? It's not clear when you mention not getting power to "both pumps" whether you are writing about the high pressure and in-tank pump, or two in-tank pumps. It makes a difference to the diagnosis. Also, when you write about the fuel pump relay being on for two seconds, are you hearing a whirring sound for two seconds, or are you just hearing the relay click? Have you checked the fuel filter?
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Mine does this, so I have to unplug the TPS and it starts right up.
Just give it a shot and let me know if it makes any difference. I have a bad TPS *I think*.
Just give it a shot and let me know if it makes any difference. I have a bad TPS *I think*.
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Sorry for the vague info. Its a single tank fuelly, so it has one pump in the tank and one on the rail. Neither one was turning. I checked the inertia switch and it was OK. It turned out to be the single wire connector below the power brake booster. Looks as if the rain drained off the window, under the hood and puddled on the inner fender right where the connector sat. The connector didn't look to bad on the outside but when I took it apart it was totally rotted. Repaired the connector and all is well again. I put a code reader on my shopping list for next time.
Thanks for all your help. You guys came through again.
John
Thanks for all your help. You guys came through again.
John
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Your problem could be the tps, especially if you have a tps code. If the computer thinks the throttle is wide open when you are cranking the engine, it will turn the injectors off. This is a "clear flooded engine" mode.