Truck loses power and wires are cut

[99 confused]

We recently purchased  a 98.5 laramie slt, and we have fixed the boost sensor the tps and replaced the filter, we are now looking to replace the lift pump. We rented a fuel pressure  gauge and hooked it up and we got idle pressure of 19 to 20 and reed pressure of 10 to 11, we have been told that it should run a constant  pressure  of at least 14 to 16. When we removed it we noticed some wires were cut, yellow with a white tracer going into the ecm and it is both wires. We have done a lot to this truck and we are at a loss, when we rev it up the pressure  drops and the engine starts to run flat has no power. Please help us.

[TFaoro]

The idle pressure does not have me worried a bit. The real question is how far does it drop when you're on the throttle driving.

[Hawkez]

what do you mean by reed pressure?

[dripley]

X2 on the above. 

What kind of fuel pump is on it? Sounds like you might have a good pump but someone butchered the install. 

Edited March 5, 2016 by dripley

[99 confused]

Well we think it drops about 10 psi. It real funny cause you will be driving it and it runs fine and then it just falls flat on its face and has no power but still runs, but you can hear the engine drop along with the pressure, you let it build back up and it runs great all kinds of power then repeat the process and it does it all over again. We have replaced the boost sensor, the tps, the filter and also the temp sensor, but took it back cause the old one worked just fine. We just don't know what to do next, we are spending money that we don't have and he is just frustrated and not sure what to do next. We like the truck yes it was very neglected and not in the best shape, we are dodge people and thought we would try a diesel but so far that has bit us I  the butt. Please help, we do not have 1,200 dollars to replace the vp, and it runs alot better then when we got it, everything that we have done has improved  it, this is the one thing that has us stumped. The new lift pump will be here next week and it runs at 18 psi.

And sorry that was suppose to be reved pressure, he gets it to about 2200 rpm or 2300 rpm and it just falls flat, pretty fast to, it will not take the throttle, it's just flat till it builds pressure again.

[Hawkez]

the boost sensor shouldn't have much to do with it.

What type of lift pump is in there now?  I understand that you don't want to ruin a VP44, I just replaced mine.  Even after you get the new lift pump installed you are going to want ton install a fuel pressure gauge inside the cab.  Your lift pump can completely fail and your VP44 will continue to run, however it will take a toll on the VP44.

the boost sensor shouldn't have much to do with it.

What type of lift pump is in there now?  I understand that you don't want to ruin a VP44, I just replaced mine.  Even after you get the new lift pump installed you are going to want ton install a fuel pressure gauge inside the cab.  Your lift pump can completely fail and your VP44 will continue to run, however it will take a toll on the VP44.

Also, are the fuel lines coming from the tank and into the IP stock?  You may consider an upgrade there.  Stock lines can be real restrictive and cause a drop in FP.  Is the stock filter in use?

[Me78569]

Can you take a picture of the butchered wires?

 

Any codes stored in the ecm?

[99 confused]

Yes on the fuel lines, and yes on the filter. We replaced the boost sensor, cause of codes that showed up  and the codes are gone, and we are not sure on the man. of the lift pump, it was on the truck when we got it. Also we are concerned  about the wires being cut, I can't  say it is butchered up, but we do want to know about the wires, going into the ecm.

Yes we can take a picture. We will see if we can get it done today.

The wires are yellow with a white tracer and it is both wires not just one.

[Hawkez]

Take a picture of the lift pump so we can see what it is. 

[Mopar1973Man]

Lift pump leads... Look at pins 15 & 35 on the ECM.

 

[99 confused]

Thank you, thank you. Yes that is the wires, could that be causing all the issues. It's not getting the right voltage to keep the pump working. I hope it is going to be that easy, but why would they cut them, what would cause them to do that. I know a lot of questions, but this is the closest we have got to answers. Can you run a wire direct from the ecm to the fuse box or is that just immposable, we just want it to run right and be trustworthy and not have to worry  that it's going to leave us on the side of the road.

We will try to get the pictures  posted today. We are new at this, he said he is use to mechanical  pumps and not electronic  ones. I will take the pictures,  but the pump is wrapped in a rubber sleeve, it is not standard  from what we have seen on line. 

[Mopar1973Man]

More than likely the lift pump is wired to the key (ignition switch). This is a unsafe practice. Typically done because the ECM circuit for the lift pump is fried. There is no relay or anything the OE lift pump circuit comes from these two pins in the ECM. There is a computer controlled MOSFET that switches on the pump when crank signal is detected. So if and when you do have an accident the crank signal drop to zero because of engine damage and the lift pump is switched OFF for safety. Where a direct wired lift pump will continue to feed the fire (if any) with fuel.

[dripley]

Are the cut wires just cut and hanging or are they connected to anything?

[99 confused]

We will try to get the pictures  posted today. We are new at this, he said he is use to mechanical  pumps and not electronic  ones. I will take the pictures,  but the pump is wrapped in a rubber sleeve, it is not standard  from what we have seen on line. Two of them are cut and just there and I just spoke to him and he said that one of them is wired to the fuse box. We just don't know where to draw the line we don't have the money  to keep putting into it, we are just stuck. Some people have said that the Vp is bad others have said the lift pump and now maybe the ecm, we just don't know what to do. Should we hook the wires back together and start over or what. We don't know what others have done to it that we can't  see. Please help I really don't want to get rid of it but if a simple fix is not found it looks like we are going to have to get rid of it and look for a v8 that will pull our 5th wheel. I'm sorry I just keep ranting.

[dripley]

Picture will definitely help. Sounds like the PO hacked something in to by pass another issue. 

the lift pump is connected up in some strange fashion.

Edited March 5, 2016 by dripley

[99 confused]

My husband just drove the truck, it ran great, he floored it for aways, when he went to go again it would hardly move. After a little ways it got power again, he wonders if there is a sock filter in the tank and if it can cause the problem.

Edited March 5, 2016 by 99 confused

[Mopar1973Man]

1 hour ago, 99 confused said:

he wonders if there is a sock filter in the tank and if it can cause the problem.

Again fuel pressure would show this issue. If the suction side or pickup assembly plugged up the pressure would sharply fall off like a rock to ZERO. Need a good test gauge with a long enough hose to see pressure while driving.

 

2 hours ago, 99 confused said:

pump is wrapped in a rubber sleeve

Sound like an Airtex lift pump.

2 hours ago, 99 confused said:

I just spoke to him and he said that one of them is wired to the fuse box.

Which confirms what happen the lift pump circuit in the ECM failed so they hot wired the lift pump instead of repairing the ECM. This is a band-aid solution to the problem it will work but eventually you'll have to consider getting the ECM repaired.

Well... The bad part is we need to get back to some sort of normality. So what we need to do is insure fuel pressure is staying above 10 PSI no matter what. As for the performance issue lets do a bit more testing. Now if some can do a AC noise test on the alternator would be great. Basically take a DVM that can measure small voltage on the AC scale. Now probe the alternator BATT and the case. It should measure 0.01 to 0.03 AC volts roughly. 0.05 is getting marginal. 0.1 and more is failed alternator. I want to be sure the power being supplied to the computers is clean and not driving them nuts.

Next I would clean all grounds you can most important ground is on the passenger side battery. The master ground for the ECM, PCM and VP44 are on the passenger side battery. Be sure the batteries are in good condition and terminals are clean and not corroded or lead-oxidized (black).

Edited March 5, 2016 by Mopar1973Man

[dripley]

The oe basket has some screens on it. Some like mine were fitted in tank pumps that had a screen on the pump. They both could clog and cause fuel starvation. Hard to say what you have. It is hard to know whats going on without knowing what has been changed on your truck.

I agree with Mike on the lift pump power. By passing the ECM for power is a sign that part of it has failed. It is a work around many folks have used.

[99 confused]

2 hours ago, 99 confused said:

 OK to answer the questions yes that is the same exact pump. And also we seem to think that the alternator is going bad, cause it looks like it will charge sometimes, he has even hit it to try to get the brushes to work. We will check all the grounds and also the battery. Where would we take the ecm for it to be fixed. Will that fix the fuel issue or will it still be messed up. The new pump will be here Tues not sure if I already said that or not. And we will have to set up a fuel gauge line for driving. We are hoping to get this mystery  solved with all your help.

 

Thank you for all your help so far

[Mopar1973Man]

Wow.

6 minutes ago, 99 confused said:

And also we seem to think that the alternator is going bad, cause it looks like it will charge sometimes, he has even hit it to try to get the brushes to work.

Good bet the alternator didn't help the failure of the ECM. When an alternator age and brushes get short like that it starts to create AC noise. Computers don't like any AC power at all because it puts stress on everything that is a transistor, MOSFET, or diodes. As you'll see in the video below it causes all kind of weird issues. Just make sure to have any alternator tested before you leave the store new or reman'ed.

 

8 minutes ago, 99 confused said:

Where would we take the ecm for it to be fixed.

You could try Module Masters in Moscow, ID and see if they can fix the ECM. They a bit fussy about what they will fix Dodge wise.

http://modulemaster.com/rebuilds/

Double check for any P0336 (crank sensor) or P0341 (cam sensor) error codes. That might cause issues with the alternator as well.