Mechanics

CAR WONT START, FAN COMES ON WHEN KEY ON

1996 Ford Mustang

Electrical problem
1996 Ford Mustang V8 Two Wheel Drive Manual 87000 miles

I recently came across a problem with a OBD 2 code P1401 and while testing the signal pin on the DPFE sensor connector from the engine harnes probabluy created a short somewhere in the car when I attempted to start again the car to do more vacum testing, it wouldnt start I can smell the fuel so I know its trying to start and that the fuel pump is working it will crank but wont start, what happens now is that the cooling fan automaticly starts with the key in the ignition ON, when Im guessing I created a short while they key was in the ON position the cooling electric fan came on automaticly so I know I did something by mistake touched another wire or something on the connector now how do I fix this problem so I can start the car now I checked fuses in the engine compartment and inside the car and they all have a pass while checking ohms did I possibly damaged my PCM, Also I replaced the dpfe sensor the egr valve the vacum lines and cleaned all the passeges in the intake manifold and changed the selonoid and the Evr sensor but when I turn my car on the second time to do the drive cycle my engine light ccomes on always at the same time with the P1401 CODE please if someone can help I would greatly appreciate it, I love this car and would not want to loose it, even if I have to replace my PCM im willing to do it as long as I can get some information about it and where to get it so PLEASE HELP ME.
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Psychostang
June 5, 2008.




Did you clear the codes before turning the key back on? If so and it continues to give the code with a new sensor and you have tested the wires, the PCM could be at fault especially from what you describe with the fan and no start condition. Might need to take it to a shop with a scan tool capable of watching the sensors to see what is and isnt working. It will probably have to be in a shop to reflash the PCM anyway since it is OBD-2

Tiny
Jack42
Jun 6, 2008.
The car started and I drove it before I tested the connector on the dpfe sensor I had the key on and the light was off at that time while I was testing, but when I pulled the pin off of the connector I must have created a short somewhere and now the car wont start it cranks up but wont start and when I turn my key to ON position the cooling fan turns on where should I go for the problem now is it a blown fuse, or could it be a bad relay and how can I check a relay if its bad, Im basicly gettiung 12V to the cooling fan on this car right now so I know there has to be something between so that it distributes voltage equally everywhere else, now can a ford dealer refresh my pcm or if I get a used pcm from another 1996 ford mustang cobra like mine can I just plug it in?

Tiny
Psychostang
Jun 6, 2008.
Needs to be flashed off the old PCM. The problem is that the PCM is telling the fan to come on. Does it have spark? Also check for injector pulse. Check all fuses in the underhood and interior fuse blocks with a test light

Tiny
Jack42
Jun 6, 2008.
I just noticed that when I disconnected the fan connector and I turn the key to the ON position the fuel pump doesnt upload, you know the noise that it always makes when you turn your key to ON position it makes the noise of starting or preloading before you actually crank up the engine with your key, but when I looked at the fuse under the hood which is a 20A it looks good and I was checking it with a ohm meter on 200ohms setting and it has passege as in it goes to zero when I touched the two metal prongs on the fuse itself, is there another fuse for a fuel pump under the hood of the car that is seperate from other fuse boxes and maybe its somewhere on the firewall or under car, also I have other cars at home here and when I looked at them under I see a mesh style ground wire going to the exhaust from chassie and engine block as well as transmition to chassie, my mustang doesnt have those underneeth is that a big deal, and can it cause different voltages to be send throughout the car if the engine block is not grounded with that wire to the chassie. By the way I really appreciate your help and troubleshooting suggestions, all I want for now is for this car to start like it did before I tested the sensor yesterday I was driving it and the only problem I was having was the check engine light and I obviously made a wrong choice by testing it again, hahaa.

Tiny
Psychostang
Jun 6, 2008.
Find the fuel pump relay. Should have two that are hot, one to the fuel pump, and one that should ground when key is turned on, that is the trigger from the PCM to turn on the pump. Need to test the fuses with your meter on 12 v or with a test light

Tiny
Jack42
Jun 6, 2008.
Ok I did one more thing just to see what would happen I disconnected the big harnes wire under the hood of the car by the windshield the harnes had like 30 different wires going from al the sensors like tps and all the others and the harness had a bolt on it so when I disconnected that harness im guessing its the one that connects the PCM and put my key to the ON position my fuel pump started but was going constant now when I plug that harness back in as soon as I turn my key onto the ON position I can hear a lil shock under the hood so does that mean my Pcm is bad or is it a short somewhere, see when I created that short by testing one of my connectors im guessing could that shock the wire so now everytime I turn my key to ON it creates a shock so the PCM just shuts everything off, I was checking the dpfe connector to thebig harness connection for resistance and I got 3.69ohms in that wire or between those connections but when I touched another wire pin on that big harness connector I also got a negative ohm measurement so is that a short? And how can I find out how much resistance im suppose to get in that wire to make sure its good? That is the wire I was testing yesterday and thats the one that I created short with more likely when I heared a lil shock sound and all the sudden my cooling electric fan came on and thats when I couldnt restart my car, hope to hear some more suggestions I getting closer just not there yet and I definetly dont want to cut any wires yet if I dont have to
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Tiny
Psychostang
Jun 6, 2008.
You are doing more harm than good by unplugging and plugging in PCM harnesses with the battery hooked up. Go to this link and go to "engine performance and follow the trouble tree for "no start" Did you test at the fuel pump relay like I suggested?injector pulse? spark?

http://www.2carpros.com/articles/mitchell1eautorepair-car-repair-manuals

Tiny
Jack42
Jun 7, 2008.
Ok yes I was doing all these tests but you know I got the car started and believe it or not I finally took my PCM out and it had a diablo sport performance chip on top of it but it was dock taped. Hahahha, I know its not suppose to be this way and there was also a ground wire on body itself next to the PCM so I took it off and cleaned it and when I pluged my PCM back into the harness and reconnected everything the car started but now its running rough when I floor it so im guessing a bad maf and ive noticed my injectors are 42lb and the maf is bigger aftermarket too so its not working properly and I was always careful by unplugging the battery when I was disconnecting the harness

Tiny
Psychostang
Jun 7, 2008.
I have 42# fuel injectors(green cap) and possibly a bigger size MAF Sensor without a supercharger, would that make more nox in the emission system and would bring the P1401 code on the car, some people told me that I just want to make sure because as soon as I took my DIABLO PREFORMANCE CHIP out of the PCM the car runs rough when I give it a full gas, is it because the diablo chip was telling computer that there were different injectors on car and different maf sensor and now that I took it off its working off of the default stock numbers and all, the code is still p1401 which is a high output voltage from the dpfe sensor can I just put a resistor in the signal wire and lower the voltage would that be one way I can fix that problm?

Tiny
Psychostang
Jun 7, 2008.
If the injectors are the ones that are supposed to be in the s/c engine you are fine. Have you done anything to the exhaust system? The Have you tried replacing the DPFE sensor? Have replaced a ton of them, they fail quite often, not like it woulld be a rare thing, a resistor wont fix it

Tiny
Jack42
Jun 9, 2008.

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