What would cause this?

[DonM]

Im still having problems...I put a new fuel pump on a few weeks ago and im still having problems. Which isnt nearly as bad as before. Problem now arises once a week only for one day, mostly for a few starts! Both Fuel Pumps would run longer then the normal 2-3 sec. NOt all the time though. Maybe once a week during one or two starts. Today after work, I went out to start her up and I turned the key to the on posistion and it ran(Fuel Pump) for like 20 sec and then It started up and ran a little ****ty. Shut it down and turned the key in the on position and the Fuel Pump came on for 3 sec and then stopped. The engine then started right up and ran fine.

The Fuel Pump relay is new as is the Fuel Pump. What would cause the Fuel Pump to run longer?

As some of you know, this has been going on for many months now! No one can find the problem.

 

[SteveVB]

May be a FPR letting fuel pressure bleed down after shut down- so that it takes longer for the pressure to come up after prolonged shut down.

Ive read some reports on here that after replacing the fuel pump the seat on the FPR is somehow affected and results in the valve not seating properly.

I would do a leak down test on the fuel system see how the pressure looks after various periods from shut down. See what shows up.

Good Luck.

 

[DonM]

Thanks Steve, Ive done all the obvious.

Problem with checking the Pressure is... I never know when the problem is going to happen. So that would mean checking the pressure ever night, and I just dont have the time to do so.

It's also like clock work, seems to happen ever 6-7 days.

 

[rocco123]

Injectors leaking down?

 

[DonM]

Wouldnt leaky injectors cause other problems? Wouldnt the engine run crappy?

 

[rocco123]

When pressure checking does it leak down? It shouldn't. Leaky injector(s) could cause a rough idle & you may not notice it above idle.

 

[DonM]

Pressure check was done a few times. But, the pressure check was done when the problem wasnt around!

I never know when the problem will arise, so that would mean hooking up a guage every night. I dont have the time for that.

 

[DonM]

I just thought of something.

I just changed my spark plugs last weekend, after inspecting the old ones. They looked fairly normal. From what I could tell, the old plugs where normal looking!

If I had leaky injectors, wouldnt the plugs show it?

 

[DonM]

Well it's no longer just a cold start. Drove around for an hour last week, came home for about ten min and then left for the store. Came out and wouldnt start right away. Now it's just guess work. ECM relay and FPR are the only two things left?

I went for almost two weeks without one problem, then it started all over again.

As much as I love this truck, im thinking about trading it in? Im tired of having this starting problem and not being able to find it.

 

[MrShorty]

This is one I thought of tonight while responding to another thread with a no start. Are the fuel injectors "firing" when it won't start? A loose connection or broken wire between the PCM and injectors would prevent them from opening and letting fuel into the cylinders. I use a stethoscope to listen to them, and it's pretty obvious when they are working.
Not sure if it will help, but I thought it might.

 

[DonM]

As far as I know, the injectors are working fine? Ive never checked them, but I'll look into listening thing. How hard is that? I dont have to take apart the engine to get to the injectors do i?

All along Id thought the FP and FPR were the problem. Something that would make the FP run longer then normal. Im not so sure the injectors would do that?

 

[Opera House]

Fuel pump running longer

The only two things that would cause the pump to run longer would be a defective ECM or a bad electrical connection to it in power or ground since the relay has been replaced. I had an intermitant power connection and it caused the ECM to reset and open the IAC wide open at stop lights. Still, I think the pump running longer is a red herring. You could monitor the fuel pump current by running wires frome fuse connection to meter in the cab. Current should be about 5A, never less than 4A. This would give a general indication of pressure. Less invasive than a pressure gauge. Without any other drivability problems this will be difficult to diagnose.

 

[DonM]

Operahouse thanks for the reply

Another thought was the FPR was sticky, maybe causeing the fuel pump to run longer because it had blead off. The only reason i still think this is because it seems fuel related.

I will look into what you said above. What do you think about the FPR theory?

If the FPR had a sticky valve. Lets say it sticks open sometimes, causing the fuel to bleed back to the fuel pump? This might cause the FP to repressureize longer? Im no mech, so Im most likely wrong.

Thanks

 

[DonM]

PCM relay is the same as ECM?

Im looking at my chilton manual right now. I dont see a ECM relay, but I do see a PCM relay.

I have a spare FP Relay sitting here and was wondering if I could use the FP relay for the PCM. Not sure if there the same. Doesnt say in the manual...

Btw, are you talking about the ECM fuse or relay?

 

[410Fortune]

Why do you say BOTH fuel pumps?

a 95 Ex only has one, correct?

I would FIRST check the wiring terminals at the FUEL PUMP relay, just because you replace the realy doesnt mean you fixed the problem, check the wires down in the box, maybe even take the box out and look inside.


The COMPUTER (EEC, PCM< whatever) tells the fuel pump when to come on based on signals from the key, inertia switch, etc.... so YOU CAN TEST THE wire that goes from the EEC to the FUEL pump relay to see if the signal is being sent wrong.

The fuel pump and fuel pump relay do not KNOW HOW much pressuere is in the fuel lines, meaning it does not keep the pump on until pressure is built up, it turns the pump on just for a couple seconds before start.....

 

[DonM]

410, both pumps meaning..."old and New". I had a new fuel pump replaced last month.

I would like to replace the PCM reply, can I use a spare FP relay?

 

[DonM]

410 I really apreaciate the help. This has been a very anoying problem and would love to solve it.

Inorder for me to test the signal from the PCM and the PCM relay, what type of meter do I use? Im guessing a Multi meters have the feature to do this?

Thanks again.

 

[DonM]

Hey, so can someone tell me what meter I use to test these wires?

Thanks

 

[410Fortune]

Don Hold on a second, let me get my wiring books (at home now...)

PIn 8 at the PCM is a DG/Y (dark Green with yellow tracer) wire.
This wire is the fuel pump monitor

PIN 22 is LB/O (light blue with orange tracer)
This is the FUel pump enable output
CIrcuit 926
This wire actually splits and goes directly to your Data link connector (near blower motor, where you test codes) At the connector it is LG/O
You can test it right there!
This will tell you if the computer is telling the fuel pump relay to turn the pump on.

Youcan test this with a 12V test light.
Have somebody turn the key to on. You should hear the fuel pump come on and the relay click for a couple seconds.
Your test light should light up if you connect one end of it to this wire (at data link connector, LG/O) and the other to the + side of the battery

The PCM sends - signals in most cases.

the other end of the LB/O wire (circuit 926) goes directly to the fuel pump relay.


From the fuel pump relay the signal wire to the pump leaves as DG/Y (238) it goes directly to the inertia switch. From the inertia switch the wire is pink/black and goes directly to the fuel pump.

Remember this is a - wire.

The DG/Y wire also splits and goes back to the computer as the fuel pump monitor.

hope that helps.......

 

[DonM]

Originally posted by 410Fortune
Don Hold on a second, let me get my wiring books (at home now...)

PIn 8 at the PCM is a DG/Y (dark Green with yellow tracer) wire.
This wire is the fuel pump monitor

PIN 22 is LB/O (light blue with orange tracer)
This is the FUel pump enable output
CIrcuit 926
This wire actually splits and goes directly to your Data link connector (near blower motor, where you test codes) At the connector it is LG/O
You can test it right there!
This will tell you if the computer is telling the fuel pump relay to turn the pump on.

Thanks, but I have a few questions...

First, Pin 8 at the PCM. Where is that? Whould I find the test spot on the wire harness that plugs into the PCM itself? Im not really familar at all with the wiring of this vehicle. So Finding these test spots might not be all that easy for me.

So a 12v test light is all I need to diagnose this problem? Nothing more?

It would be nice if my Chilton had these wiring diagrams.

Thanks again

Oh, I replaced the PCM relay today. I hope this will do the trick? But I doubt it will be this easy...