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TobyWD40
Dodge Dakota
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10/22/2007
18:14:08
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 Subject: Oil Pressure Sending
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Hey Everyone, I'm still working on my 92 Dakota 3.9 MPI. On one of my other posts Daddio told me to put a pressure gauge on the sending unit and if it was building pressure it might be sending a message to ASD to kick in and tell computer not to give fire to the coil. Did you mean not building pressure. The Haynes man. shows a special tool to remove the sending unit what is it,(the tool)? I'm guessing but does the sending unit somehow convert physical pressure inside the engine to an electrical signal? I'm thinking like a rheostat with a plunger type thing. If that is the case I should be able to get a reading as I crank the engine of some sort on at least one of the wires - right/wrong? Has anyone had that part go bad? It is not located as if they planned to ever change it - I may be able to get to it but not if there is any other way to check it and Haynes has nothing except they say to remove it to change the Crank. Pos. Sen. and say it takes a special tool. Thanks everyone, TobyWD40
P.S. Let the record read Daddio was correct there is a wire splice between the PDC and the fire wall of red/wht wires HA! The Cajun Rocks!
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dakota49
Dodge Dakota
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10/22/2007
19:21:37
| RE: Oil Pressure Sending
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Toby, the oil sending unit does just what you are thinking, it uses oil pressure and changes it to an electrical signal, like you thought.
You can use a big cresent wrench to remove the sending unit, then use a regular oil pressure gauge to see if its building any oil pressure, it won't be much, but should be a couple of pounds. The best way to see if you are getting any oil press. is remove the spark plugs to allow the engine to spin faster, and making more pressure. Just be sure you have enough oil in the engine. The only thing is, the oil pressure sending unit only stops power going to the fuel pump, not the coil. You might try running a wire from the battery Pos. post to the coil pos post and see if that will give you any spark, if so, then I would think some where between the coil and computer is the problem. Or maybe the computer its self.
Good Luck
Dakota49
1988 3.9 4X4 5speed
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Dan M
Dodge Dakota
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10/22/2007
19:29:56
| RE: Oil Pressure Sending
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I replaced the oil sending unit in my old 95. It sits back next to the distributor. I replaced it using a special socket, i got one from advance but it was not deep enough. I bought one from NAPA that worked perfectly.
I posted about it sometime ago, i tried searching but could not find it. NAPA should know what you're talking about.
- Dan M
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daddio
Dodge Dakota
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10/22/2007
20:08:02
| RE: Oil Pressure Sending
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i would do as dakota49 suggested. jump the coil to the battery and see if it fires then. check your wiring diagram should show which is + to the coil. in fact you may as well hook the ground and + directly to the coil from the battery just in case it's a bad ground.
glad you found that splice. i guess it wasn't the cure. sorry about that.
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Dan M
Dodge Dakota
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10/22/2007
21:05:06
| RE: Oil Pressure Sending
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check the grounds at the PCM. I think it's pins 11 and 12 but I may be wrong. It's 2 black wires side by side (may be black and tan). One of the wires was loose and thus I had a loose ground that took me several days and much time with my Multimeter to find. I would intermittently get power to the coil. sometimes it would start and run before cutting out, other times it would not start at all.
I disconnected the PCM and tested from the PCM side. One of the wires was a little lose and if I would tap the PCM while the truck was running it would cause the truck to miss and/or die. Also, I would lose tone if I wiggled the cable from the back end of the connector.
I wound up just testing with my MM listening for tone while I 5 minute epoxied the wire in to the connector. If this is the case, you'll probably need help to hold to repair.
It was still holding up when I traded the 95 in on my 02.
- Dan M
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dakota49
Dodge Dakota
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10/24/2007
08:37:18
| RE: Oil Pressure Sending
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Hey daddio, its not a good idea to make a solid ground on the coil. I'll explain, using a point sysetm, that may be easier to understand.
You turn on the ingition switch, power goes from the battery to the switch, to the coil. (among other places) the ground wire from the coil goes to the dist. when the points are closed, that charges the coil, when the points open, the coil discharges, sending a jolt of electricty to the dist. cap through the rotor to a spark plug wire to the spark plug. So if you ground the coil ground wire to a solid ground the coil would most likely over heat and fail. That does however bring up another question, if the coil ground wire has gone to ground through a short that could explain why the coil isn't putting out any fire.
Toby when you get your test meter check to see if you do have a constant ground through the coil ground wire. If you do, have someone crank the engine to see if it breaks, in which case that would show that part of the system is working. Then, if it shows that the ground is open, and it doesn't go to ground, then some where in that part of the system is bad.
Daddio, I'm not trying to be a smart@ss, just trying to explain why going to a straight ground won't work for testing purposses.
To confuss things a little more, if you had the coil on a bench, you could run a wire to the pos post of the coil, and a ground wire to the batt. and a plug wire to a spark plug, as well as a ground wire from the plug to the ground on the batt. then touch the ground wire from the coil to the batt. just for second and if the plug ground wire is in contact with the batt. grd. it should cause the plug to fire. A solid ground from the plug to the batt. a solid pos wire to the coil, and a loose wire from the coil ground to the batt. (so you can make and break the ground) should cause the plug to fire.
Toby if you still have problems you can e-mail me at bertgrauatyahoo.com. Just remeber to use the @ instead of at.
Good Luck,
Dakota49
1988 3.9 4X4 5speed
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daddio
Dodge Dakota
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10/24/2007
10:00:12
| RE: Oil Pressure Sending
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dakota49, thanks for setting me straight on that. no offense taken. i do not mind being corrected at all.
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TobyWD40
Dodge Dakota
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10/25/2007
10:00:51
|  RE: Oil Pressure Sending
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I think I understand Dakota 49, if the truck was running, the ground on the coil would be off and on as the coil fired, should be the same just cranking engine and if not something is wrong in that circuit. Looking on the wiring diagram in haynes at 1st diagram typical diagram for multi-port fuel injection it shows the coil negative going straight to comp. pin 19 and the positive goes to pin 57 and also to each of the 6 injectors and to and to the plug behind battery where it goes to asd relay and other stuff. If I'm thinking right the positive is always hot with engine running and the negative flashes. So on the injectors the common wire for the coil positive and injectors positive is steady and the other wire which is a different color for each injector and each wire runs to it's own individual pin on the comp. flashes as the injectors fire. If the coil was bad would the injectors still get the signal to fire? If one injector was bad would it keep the others and the coil from firing? It seems like it would because of the wire they all have in common. This might be a big breakthrough in my brain or a brainfart as Daddio my Cajun pal puts it HA! What about it it Dakota 49, Dan, Daddio ? Thanks I almost feel useful HA! Toby
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daddio
Dodge Dakota
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10/25/2007
10:15:16
| RE: Oil Pressure Sending
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if the coil is bad the injectors should still fire. and if one injector is bad the rest would still fire. haven't looked at a schematic but don't the injectors get their signal to fire from the distributor?
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shadetree
Dodge Dakota
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10/25/2007
11:54:54
| RE: Oil Pressure Sending
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Thats what Ive heard. They say that when you rotate the dist. you actually are adjusting the fuel timing not spark. The manual I have is from 94-01 but it shows the yellow wire from the dist going to the pcm at a18 and then it shows that the gray wire from the coil goes to the pcm at a7 which they call the coil driver and and the other wire dark green and orange goes to the output side of the asd. So if its not firing i would see if you have power at the pin on the pcm and start working my way back to the coil. could just be a broken wire or pin.
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dakota49
Dodge Dakota
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10/25/2007
13:12:04
| RE: Oil Pressure Sending
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Toby, you are right, the positive should be hot all the time the engine is running, and the ground is the one that turns on/off.
Have you received your meter yet? That should be a big help. Daddio, is right, even if one injector is bad the rest should fire, unless the wiring harness doesn't have any power. It seems to me that is what your problem is Toby. Again, when you get your meter you will be able to tract down where you are not getting any power and where you are.
Good Luck
Dakota49
1988 3.9 4X4 5speed
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TobyWD40
Dodge Dakota
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10/29/2007
17:50:19
| RE: Oil Pressure Sending
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Breakthrough! I finally found something and you all pretty much nailed it. It's pretty much the same that Dan has a loose wire in the pcm. Daddio guess which one-ya got it the red and wht. one before the splice actually in the pcm. It still hasn't started though. I'm fixing to check from coil on and the ground on coil to see if it's alternating while engine cranks. The positive wire is feeding power to the coil, injectors and fuel pump. The wire I'm talking about is the red and white wire that jumps from the asd relay to the fuel pump relay, that explains why no fuel or fire I think. Having home comp. problems will try to update soon Thanks again guy's, TobyWD40 If I had a $100 per hour for my time I'd have $4600 not counting the reading on here just truck time.
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dakota49
Dodge Dakota
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10/29/2007
20:54:40
| RE: Oil Pressure Sending
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Toby, have you got your test meter yet?
Congrates on finding the problem so far, or at least some of it.
Keep us posted.
Dakota49
1988 3.9 4X4 5speed
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