94 Ranger No Fuel cont.

[larry4888]

This is a continuation of my earlier post, 94 Ranger No Fuel. Here is the latest.

I jumped the wire at the PCM and the fuel pump comes on so I figured that it has to be the PCM, however, the truck still won't start with the fuel pump jumped so that it is on. I am getting plenty of fuel pressure at the fuel rails with the pump jumped at the PCM. I also have power at the injectors. Why will the truck run if I dump fuel in the intake, but not when I jump the fuel pump? Could it still be the PCM doing something to the injectors so they won't dump fuel into the cylinders? I can't think of anything else that it could be and I don't want to buy a PCM if I am not sure that it is the problem. Unfortuantely, around my area, if I buy an electrical component I own it.

I am at a loss, any ideas would be greatly appreciated.

[stuzman]

Originally Posted by larry4888

This is a continuation of my earlier post, 94 Ranger No Fuel. Here is the latest.

I jumped the wire at the PCM and the fuel pump comes on so I figured that it has to be the PCM, however, the truck still won't start with the fuel pump jumped so that it is on. I am getting plenty of fuel pressure at the fuel rails with the pump jumped at the PCM. I also have power at the injectors. Why will the truck run if I dump fuel in the intake, but not when I jump the fuel pump? Could it still be the PCM doing something to the injectors so they won't dump fuel into the cylinders? I can't think of anything else that it could be and I don't want to buy a PCM if I am not sure that it is the problem. Unfortuantely, around my area, if I buy an electrical component I own it.

I am at a loss, any ideas would be greatly appreciated.

Larry you say that you have power at the injectors. How did you check this? If you just put a meter on and saw some voltage without cranking, then I suspect that's the problem. Check to see if the injectors are being pulsed by the PCM. A noid light would show you this. If it turns out the injectors are not being fired, then it's possible that the PCM has picked up a fault. I'll have to do some research, but it seems that if the crank signal is missing, the PCM won't supply any signals to the injectors. Also, since the truck starts when fuel is poured down the intake, it sounds like the ignition is working okay. Do you have a wiring diagram to see if the PCM side of the fuel pump relay goes through anything else (maybe a connector, etc.). I'll take a look at my manual tonight and see if I can come up with anything else. I'm like you, before I change that PCM, I want to feel pretty sure that it's bad.

[larry4888]

First, thanks for your response. I am at a loss. I checked the wires with a test light and it lit up on both wires. One wire is red and on three injectors the other wire is tan, on the other three injectors it is white. Should I get the pulsing light on the red or the other wire? If there is no pulsing is it the PCM? I have a wiring diagram and I didn't see any other switches or relays although it doesn't mean that I might be missing one.

[larry4888]

Also, the PCM wire that I ground to get the pump to come on goes directly from the PCM to the relay. If the PCM wasn't getting a crank signal to fire the injectors would the truck still run when I put fuel in the intake?

[stuzman]

Originally Posted by larry4888

Also, the PCM wire that I ground to get the pump to come on goes directly from the PCM to the relay. If the PCM wasn't getting a crank signal to fire the injectors would the truck still run when I put fuel in the intake?

When I had mentioned the crank signal, it was more or less thinking out loud on my part. That's when I said that if the truck would run when you pour gas into the manifold, then it must be firing the spark plugs. Thus, you have a crank signal. I'm just thinking what input is missing (if this is the case) to keep the fuel pump and injectors from firing. Oh, on the injectors, you'll have battery voltage on both sides of the injector when not being pulsed by the PCM. Battery voltage supplies one side and the PCM will ground the other, thus energizing the injector(s). I'll take a look at my diagram and see what I come up with. I'll post back tonight and hopefully have some more insight into your problem.

[stuzman]

Originally Posted by larry4888

First, thanks for your response. I am at a loss. I checked the wires with a test light and it lit up on both wires. One wire is red and on three injectors the other wire is tan, on the other three injectors it is white. Should I get the pulsing light on the red or the other wire? If there is no pulsing is it the PCM? I have a wiring diagram and I didn't see any other switches or relays although it doesn't mean that I might be missing one.

First, I assume this is a 2.3L engine. I'm sure that your injectors are not being pulsed because you say that the engine will run when you pour gas into the manifold. Although you jumped out the circuit for the fuel pump and there is pressure in the fuel rail, it doesn't matter if the injectors don't open. The red wires to the injectors are +12V fed by the PCM power relay. The tan and white wires are the return side of the injectors going back to the PCM where it grounds these wires to energize the coils. So, if you were using a scope (what I use) or meter (response may be too slow unless you use the analog bar graph which has a faster update), the ground lead of the instrument would go to ground and the signal lead of the instrument would go to the return side. Or just simply use a noid lite and you don't have to worry about which wire. You don't need to worry about this unless you just want to confirm they're not pulsing.

At this point, I would look carefully into the PCM power relay as it feeds two terminals (37, 57) on the PCM, supplies +12V to the contact for the fuel pump relay and also supplies +12V to the fuel pump relay coil. You may have checked all this...Could you verify this? If all of this checks okay, make sure that you have the +12V to the terminals 37 and 57. Also, check the ground circuits on the PCM. This will be at terminals 6, 20, 40 and 60. If all of that looks okay, then it would appear that the PCM is the culprit. Even if the ignition circuit didn't provide a signal to the PCM, the PCM should still pull in the fuel pump relay for about a second. If I remember correctly, you said that it didn't even do this when you turn the switch to the on position. Can you clarify this? If it looks like the voltages and grounds are okay to the PCM, PCM power relay and fuel pump relay, I would just go to the junk yard and get a PCM from there. If you need the factory wiring diagrams and pin-out for the PCM connector let me know. Hope this helps you out!

Terry

[larry4888]

Terry, I probably should have mentioned that it is a 4.0 V6. Last night I used a test light to check the injectors. I had power at both wires on the injector. When I cranked it over the light dimmed on both wires and I could see what appeared to be a faint pulse in the light. I am assuming that this means that they are getting a crank signal. Also, that is correct as far as the fuel pump goes. When I turn the igntion to the on position the pump does not come on at all to pressure up the system. Is the PCM relay the same as the EEC relay? The EEC relay sits next to the pump relay in the fuse box under the hood. I will check it tonight, however I do remember unplugging it with the key on and hearing the relay click on.

[stuzman]

Originally Posted by larry4888

Terry, I probably should have mentioned that it is a 4.0 V6. Last night I used a test light to check the injectors. I had power at both wires on the injector. When I cranked it over the light dimmed on both wires and I could see what appeared to be a faint pulse in the light. I am assuming that this means that they are getting a crank signal. Also, that is correct as far as the fuel pump goes. When I turn the igntion to the on position the pump does not come on at all to pressure up the system. Is the PCM relay the same as the EEC relay? The EEC relay sits next to the pump relay in the fuse box under the hood. I will check it tonight, however I do remember unplugging it with the key on and hearing the relay click on.

Yes, the EEC relay is the same as the PCM relay. This was the name given to it in the diagram which was for the 2.3L engine. I'll take a look at the 4.0L diagram and see if there is anything different between the two. Also, when the engine is not cranked, there would be +12V on both sides of the injector since the transistor(s) in the PCM is not being turned on to pull the return side low. However, there shouldn't be any pulsing on the +12V side to ground. Take your light and put it on the return side to the PCM (tan and white wires depending on the injector you check) and to ground. You should see the light pulsing while the engine is being cranked. I think it's strange that you're getting a pulsing light indicating the injectors should be opening and closing which should start the vehicle. Since you're not getting the fuel pump relay to pull in when you turn the switch to the on position, it's irrelevant about the ignition system working or not since the relay should pull in for a moment.

I had another thought...Go to the PCM, pull the connector, inspect the terminals and see if there is any obvious damage. Put the connector back on the PCM, pull it back off and repeat this several times in an attempt to clean the terminals. Then give it another try and see if the fuel pump will come on when the switch is turned on. If so, congratulations! Go and get some contact cleaner and clean the terminals. If that doesn't work, check those voltages and gnds at the PCM. If all that looks good...go get another PCM. Keep us posted with your results.

[larry4888]

Terry, unfortunately it got dark to quick tonight, but here's what I was able to accomplish tonight. I plugged and unplugged the PCM plug a few times with no luck. However, I went back to the injectors to see if I was mistaken about the pulsing. When I turn it over the light gets dim and I thought that I saw pulsing, but now that I look at again I don't think that there is a pulse. Should the pulse be obvious? Since there appeared to be no pulse I went to the crankshaft sensor with my test light. I hooked up the test light to ground and checked both wires at the crankshaft sensor, no power on either wire. Should there be power to one side? Or does it work on a ground basis to where I should have my test light hooked up to the positive side of the battery when I check the wires. I also checked the red wire at the PCM relay that feeds the ignition control module and there is power. I looked for the ignition control module to check to see if one of the two wires that go from the ignition control module to the crankshaft sensor have power but I can't find the module. The manual says that it is supposed to be on the fender well. Do you know where it might be or am I on a wild goose chase? Also, would a lack of signal from the crankshaft sensor keep the pump from coming on when I initially turn the key on or could I be looking at two problems? Thanks for all the help. I am determined to try to figure this thing out.

[larry4888]

Terry, one other question. Are the wires on at the PCM numbered? I don't seem to see any numbers on the plug or the PCM.

[stuzman]

Originally Posted by larry4888

Terry, unfortunately it got dark to quick tonight, but here's what I was able to accomplish tonight. I plugged and unplugged the PCM plug a few times with no luck. However, I went back to the injectors to see if I was mistaken about the pulsing. When I turn it over the light gets dim and I thought that I saw pulsing, but now that I look at again I don't think that there is a pulse. Should the pulse be obvious? Since there appeared to be no pulse I went to the crankshaft sensor with my test light. I hooked up the test light to ground and checked both wires at the crankshaft sensor, no power on either wire. Should there be power to one side? Or does it work on a ground basis to where I should have my test light hooked up to the positive side of the battery when I check the wires. I also checked the red wire at the PCM relay that feeds the ignition control module and there is power. I looked for the ignition control module to check to see if one of the two wires that go from the ignition control module to the crankshaft sensor have power but I can't find the module. The manual says that it is supposed to be on the fender well. Do you know where it might be or am I on a wild goose chase? Also, would a lack of signal from the crankshaft sensor keep the pump from coming on when I initially turn the key on or could I be looking at two problems? Thanks for all the help. I am determined to try to figure this thing out.

I believe Larry that your ignition system is working okay. The reason I say this is because you say the truck would run when you put the carburetor cleaner down into the intake. This would imply that the crank signal is there and that the ignition module, etc is all working. Otherwise, you wouldn't get a spark at the plugs. If you want to verify it, go ahead and check for a spark at one of the plugs while the engine is being cranked. If you get a nice crisp blue spark, forget the ignition system as its working. Just for some info for you, the crank sensor known as a VSR (variable reluctance sensor, just means that the magnetic field can be varied) is a two wire device with a third wire acting as a shield. This would be a permanent magnetic sensor where an AC signal is generated when a 36 toothed wheel is rotated past the sensor. Therefore, this sensor will generate an AC voltage without a voltage source. Some crank sensors uses three to four wires which use a hall-effect sensor and these sensors would need a voltage source. Anyway, I think your ignition is going to be fine, but just to satisfy you and me, go ahead and check for a spark. I've enclosed some links for your referral on the ignition system so you can learn more about it. I believe your ignition module should be located somewhere on the intake manifold. At least that's where it's at on my 2.3L.

http://www.wrenchead.ca/HTML%20Prese...der/sld069.htm

https://www1.autozone.com/servlet/Ui...3d8019f629.jsp

http://www.megasquirt.info/ms2/EDIS.htm

http://www.tomco-inc.com/Tech_Tips/ttt18.pdf

I'm having a feeling that the PCM is probably giving you the problem. It sounds like you're using a trouble light for all of your troubleshooting. You may want to invest into a digital meter since you're working around the computer inputs, outputs, etc. You never know if you're a fewer volts lower which could be enough to give you a "correct" reading and yet you would never know it by its brightness. Besides, trouble lights are not recommended for working with electronics as the resistance from the light is much too low. Digital meters will have an impedance of around 10Megohms which won't load the circuit down when working with the computer. Anytime, I work on electrical/electronics systems, I always use a digital meter. I want to know without a doubt what the voltage/current is in a circuit. Otherwise, you could be making assumptions about its operation. Anyway, If you know that you have +12V at the terminals on the PCM (the terminals mentioned earlier for the 2.3L are the same for the 4.0L) and your ground connections look good at the PCM, I would say that your PCM is giving you the problem. Just verify that you have the correct voltages and ground connections. Holler back if you need any other help!

Terry

[stuzman]

Originally Posted by larry4888

Terry, one other question. Are the wires on at the PCM numbered? I don't seem to see any numbers on the plug or the PCM.

Most connectors are numbered but yours may not be. I'm not sure. Just send me an email and I'll send you the wiring diagrams and pin-out for the PCM connector.

Terry

[larry4888]

Terry, as you suggested I checked the grounds at 6 20 40 60 and for 12 volts at 37 57. All of them appeared to be good (I just matched up the wire colors with the terminals in my book). Sounds like it is going to be the PCM. I will head out to the junkyard to see if I can find one. I will keep you posted. Thanks again for the help.

Larry

[stuzman]

Originally Posted by larry4888

Terry, as you suggested I checked the grounds at 6 20 40 60 and for 12 volts at 37 57. All of them appeared to be good (I just matched up the wire colors with the terminals in my book). Sounds like it is going to be the PCM. I will head out to the junkyard to see if I can find one. I will keep you posted. Thanks again for the help.

Larry

Good luck with it Larry and let us know how it goes!

Terry

[larry4888]

Terry, turns out that it was the PCM. I went to a junkyard today and installed the used one and it worked! Thanks for all of your help. It's nice to know that there are people out there like yourself that are willing to give someone a hand.

Larry