HELP! Fuel problem

[Turdle]

Bad connections can develop in the power distribution box. This is what I suspect
Do you have the 12v signal from the PCM?

 

[BggedRanger]

I'm going to go check and make sure I'm getting power from the pcm, when I get off work. I will lewt you know what I find out.

 

[dogfriend]

I can run a hot wire to the #5 socket on the relay and the pump will start pumping fuel. What does this mean? Is the fuel pump and inertia switch suppose to get 12v of power?

If you run a wire from the battery to the #5 terminal on the Fuel Pump Relay, you are wiring around the Fuel Pump Relay. So, your Inertia Switch is working correctly, your Fuel Pump is also working. The problem is "upstream" of the Inertia Switch.

Check the #3 terminal on the PCM power relay, you should have 12v from that terminal to ground. If that is ok, then it sounds like the Fuel Pump Relay is bad or there is a wiring problem between the two relays.

 

[budwich]

I assume that by "the relay"... you mean the "fuel pump relay"... ? From the circuit above, it means that the fp relay isn't getting voltage in on 3 or isn't getting a grd on 2 from your pcm and voltage on 1 from the pcm relay to operate the fp relay. It does mean that your inertia switch is fine and is not the problem.

 

[BggedRanger]

I think I have a wiring issue at the power distibution box, or the computer has went out. If i'm getting POwer from the pcm realy, does this mean that the computer is bad? Since i'm not getting power to the inertia switch?

 

[budwich]

don't jump to any conclusions.... you have the diagram that is posted. There are simple checks to make sure things are "in-place" for normal operation. The problem with the "problem with the computer" is that the computer turns the circuit up for only about 3 seconds during initial start and if it doesn't start, the computer turns things off (ie. takes aways the grd). What you need to do is check that you have voltage coming in on pin 3 of the fp relay. You need to check that you have voltage coming in on pin 5 and pin 1 of your pcm relay (on pin 1 in run, on pin 5 at all times) and grd on pin 2 of the pcm relay. These are the "pre-conditions" to make things happen.... if they ain't there, it ain't going to happen. Hope that helps. Oh... I assume the diagram in this post is for your vehicle as the diagram do differ for models and engines.

 

[dogfriend]

I think I have a wiring issue at the power distibution box, or the computer has went out. If i'm getting POwer from the pcm realy, does this mean that the computer is bad? Since i'm not getting power to the inertia switch?

Although, it could theoretically be the PCM (computer), it isn't likely. They are usually very reliable. It is more likely to be a problem with wiring or the relays themselves. Budwich has some good advise - check for voltage on the appropriate pins of the PCM Power relay and FP relay.

 

[budwich]

Actually without doing those aforementioned checks, try grounding pin 2 on the fuel pump relay with the key in run... if the pump starts up, then you have all the conditions setup for "normal operation".... then you can focus on just figuring out why the ground isn't there which is another step in the trouble shooting. If it doesn't start up (ie. the pump), then you need to do those checks as a first step.

 

[BggedRanger]

Thanks everyone for the help. I will go home to night and try these things and let you know what happens. Thanks

 

[BggedRanger]

well i went home and tried these things last night. It seems that I'm not getting a ground to the pcm relay, or the fuel pump relay. I can ground pin 2 on the fuel pump relay. The pump will then start pumping. Where does the pcm relay get its ground from? The computer?

 

[budwich]

okay... that's great.... well at least, that's a start in eliminating things. So now your focus is probably somewhere else as opposed to the fuel area. The grd for the fuel pump area comes from the pcm. The pcm controls when to put it on based on a number of conditions. Before going any further, can you please repeat or tell us what problem you are actually trying to solve.... ie. no start, poor running, start and die.... what? your first post says no power to the inertia switch.

In terms of the pcm, have you checked for any codes related to check engine lights?

 

[dogfriend]

Where does the pcm relay get its ground from? The computer?

Looking at the schematic, the PCM power relay is grounded all of the time. When the key is turned to start or run, the current flows from Pin 1 (Ckt 845) thru the coil to Pin 2 and to ground thru Ckt 570. When current flows thru the coil, the relay turns on connecting Ckt 37 to Ckt 361 .

The FP relay gets current from Ckt 361 but is grounded by the PCM thru Ckt 926.

I would put an ohmmeter from Pin 2 on the FP relay to Ground with the Key off. Then have someone turn the key on and watch to see the resistance from Pin 2 to Ground goes to zero when the key is turned on.

 

[budwich]

Hold it..... don't get the pcm relay and the pcm module mixed up. They are two different things. As I originally indicated, by grounding the FP relay (I assume you found the right one), you are testing that the PCM RELAY is activated (as mentioned, it has a grd on it all the time BUT it only gets power when the key is in run/start) and that you are getting power thru the PCM RELAY to the FP RELAY which is then "actuated" from the grd you put on to pass voltage to your FP. That is it. Clear I hope. Now as for why the PCM MODULE is not putting a grd on the FP relay.... that is the question. As I indicated, if your truck is not starting within a short time (ie. 2-3 seconds), the PCM removes the ground. You have to have someone crank your truck and then look at pin 2 on the FP relay and see if you ever see that ground (ie. come and go).... again assuming the problem that you are trying to solve is a "no start" one.... still waiting for you to clearly state your original problem.

Finally, the PCM MODULE's (computer) operation is based on a few conditions, one is not having power in a couple of forms... in run and hot all the time (hint these are both fused seperately).... if these aren't there, the pcm module (not the relay) will not function correctly. This is just the first check. BUT if there are problems with the PCM at this level, it is likely that you would see codes and a check engine light on.... actually, if you turn your key on.... do you see the check engine coming on.... if not, this is actually a sign that your PCM MODULE is not functional... most likely from lack of power.

 

[BggedRanger]

My original problem is that the truck will not start it just turns over and over. I'm getting spark to the plugs. I'm not getting any power to the fuel pump or inertia switch. I haven't checked for any codes, because the bettery has been disconnected. Will the computer still throw a code even though its not running? I do havew a check engine light that comes on when I turn the key on.

 

[budwich]

That's helps... disconnecting the battery will "disturb" some codes but usually keep most. The computer usually has to be reset with a scanner to clear everything. You might want to check for any codes with a scanner. There might not be any. As I stated, during "start", the "check engine" light is used to indicate the state of the PCM system (among other things) and needs to be on. If you didn't notice any codes (ie. check engine light) when the truck was previously running, then that's one more observation but you should connect your battery and do a scan. I will take a look a PCM operation to see about the grd and conditioning for the PCM module to cause the grd and keep you posted.

 

[budwich]

I guess one more question, what engine do you have?

Also, do you have an anti-theft system???? Is it working?

PS. I was "confused" about the PCM module requiring both hot at all times and hot in run/start. It only needs one "type of powering".

 

[BggedRanger]

v6 3.0 Flex fuel

 

[budwich]

My "hold it" a while back was to Bggedranger not dogfriend.... dogfriend's checks are exactly right. There are a few conditions that happen to get that grd coming from the PCM module towards the FP relay. One is the PCM has to sense / detect a CPS (camshaft position sensor) to create a PIP signal which is used internally for timing and to indicate to the PCM that the motor is indeed turning. That's probably happen since you say you have spark. Probably your best bet is perhaps the ground on pin 25 of the PCM (although there are others on the unit... from the diagram.... it is likely that this is the one that gets "sent"). Check to see if its there. Finally, if you say that you can get your fuel pump going by causing the grd at the FP relay, then my question is, does your truck start? (ie. did you try the jumpering and see if it then starts with the key in place).

 

[BggedRanger]

So i need to check and see if im getting a groung coming out of the computer, and if I am than that means I have a short between the computer and the relay. No I didn't try to start it.

 

[budwich]

You got it.... assuming there is a ground there to begin with. The PCM module gets grounds from a number of places... some are used within the unit and some are "switched" thru to control things.