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1994 4.0 wont restart at running temp.

jmilston

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1994
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Hi. I'm a new owner of an old Ranger. and the biggest problem i'm having with it is trying to figure out why it starts fine in the morning, then once its up to running temp, it wont restart after it sits 10-20 minutes. i get a crank with no start. it'll run on starting fluid until it runs out, so my best guess is that its fuel related. can someone send me in the right direction?
these are the codes ive pulled:

koeo
327 DPFE low voltage

koer (having to goose the throttle to keep it from stalling)
121 high TPS voltage signal at closed throttle
136 HO2s 2 lean
172 HO2s 1 lean
337 DPFE above max voltage
411 "cannot control low RPM"
412 "cannot control high RPM"

should i just replace the DPFE? is that something that would make it not restart?
 
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hank857

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These had/have a history with fuel pump relays. It is located in the black box on the driver side fender. A replacement will run about $6. Get one and when you have a problem insert it and see what happens. I keep my old one in the spare position in the box. I was talking to a guy and he told me it was due to corroded contacts where blades on the relay fit. Maybe, I changed mine several time and now have no issues (knock on wood).

Let us know if it works for ya.
 

jmilston

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well i'll be damned. it seems to have done the trick. thanks! i figured it had to be something stupid and simple that someone had dealt with before.
 

jmilston

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Spoke too soon I suppose. Replacing the relay definitely made a difference, but it happened again. I was on a county road, cruisin 55-60 for about 45 minutes. Then I shut it off for about half an hour. Then it wouldnt fire again. I was able to roll it down a hill in 1st and eventually it seemed like it was able to start getting gas again about half way down the hill. Once it was going it got me home just fine. Then I let it sit 10 minutes and crank, no start. Could this be a vapor lock situation? Pressure regulator? Whats going with this goofy thing?
 

slamdstorm

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Test the dpfe sensor. The information to do so is here or on a link this site has to ebsco for a manual if you dont have access to one. Autozone.com has a troubleshooting and vehicle repair guide too. You can replace it if you like but if it ends up being wiring or a vacuum line then you will still have the same problem only less funds.

Dont quote me on what comes next because I'm not familiar nor have I done the neccessary homework of your vehicle to be sure but I think that sensor determines the position of the diaphragm in the egr valve. This lets exhaust back into chamber for combustion and when it's off the pcm will make it lean. I'm thinking that o2 sensors cause it to be rich but I'm sure someone more educated on it then I, will correct me when I'm wrong and if not you were forewarned.

I would check to make sure you're egr valve isn't carboned up to the point of not functioning or poorly. My 96 cougar is and I have it sitting on the bench waiting on me now. This could possibly trick pcm into thinking it's your sensor and also it's a cheap gasket. Think of troubleshooting as what besides the obvious trouble code for a component could cause these symptoms. Poor grounds that are shared or wiring that is in the same harness that goes through a point where it could be damaged.
 

hank857

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94 should not have an egr valve, unless a kalif model. My 94 (90 Build) does not and none is listed. The explorers did I believe.

When this happens again, PULL the FP relay and see how hot it is and then reinsert the old one/spare one if ya have one. Like you I had this issue till finally I guess got the contacts clean by changing relays. Try to clean contacts in wire harness with cleaner and reinsert/extract the relay several times. See if you can borrow/buy a fuel pressure gauge ($30-45) and check fuel pressure to make sure the fp is in good operating condition.
 

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