Archived Help..I'm in trouble..Fuel pump

[IMunro]

I decided to install a pusher pump at the tank to try and preserve my new lift pump, installed last month. It was working okay, with 15-16 psi at idle and mostly 12 at cruise.



I had been following the method used by Steve St. Laurent and Gary - KJ6Q and purchased the Carter 4600 pump from Summit Racing. I had a fuel filter head from another application and got a new cartridge for it.



So I broke into the fuel line just fwd of the tank and installed the filter. I then installed the new pusher pump, just fwd of the filter. I had cracked open the banjo to allow the fuel to drain into the tank, so I fed 12 volts to the new pump to prime the filter and purge the line of air. All well so far.



Rather than a relay I planned to use a solonoid that I had from the boat. I had to find out which of the wires to the liftpump was positive, as they seemed to be different to Steves. There was a yellow and a black. I figured the yellow was the positive and inserted the probes from the multimeter and turned on the ignition key. The multimeter went to 12. 2 volts, or thereabouts, and then dropped back to 8 and a bit. Which is what its supposed to do, I gather. I double-checked this and then went ahead and scabbed on the wire that was to go to the solonoid. When I checked the voltage at the end of the new wire I had nuffin. Plugged in the plug to the lift-pump and turned on ignition and there was 0 pressure on the guage. Tried to start engine and it ran for a few seconds and then stopped. Checked the voltage at the liftpump and it was 8 or so. What the heck?? I decided to see what happened if I applied 12 volts to the pusher pump. I had about 6 or 7 psi, as one would expect. With the plug plugged into the liftpump I started the engine and I had 20-22 psi on the guage. Great, I thought, problem has gone away. I pulled the wire off the pusher pump and the pressure went to 0 again. When the engine was running at the 20 psi I noticed a check engine lite on the dash. I don't think 8 volts is enough to activate the solonoid so I am in a quandry.



I decided to reset the computer and dis-connected the grounds, which is where it is now. If anyone has any ideas as to what's going on I'd appreciate your input. I guess I could figure out some way to activate the solonoid without using the circuit of the liftpump but I'm not sure if that would be the ideal way.



Thanks for listening, and I'm sure I have left something out of my explanation.



Ian





I am at a friend's computer, so a resonse to this thread would be best, or a PM or an email to -- email address removed --

 

[ToolManTimTaylor]

When you applied the 12 Volt power source was the OEM Lift Pump wire still connected? If so It sounds like you backfed the ECM as the ecm supplies power to the L. P if memory serves me right. Just goin' off a hunch.

 

[IMunro]

Lift pump still connected?

Its possible, but not initially. I took a wire straight from the battery to the pos side of the new pump to prime the system. At that time the liftpump was not connected, nor was the ign. on. But later, yes the lift pump was connected.



What would that mean, if the ECM was backflashed? Toast? Reflash? Is it possible that there was enough voltage in the digital volmeter to mess up the ECM? That would be the only time that voltage could have gone up it, as I had one probe to the yellow and one to the black pins? As I said initially, it was OK to begin with.



Thanks for the thought,



Ian

 

[Bob4x4]

The ECM gives a very short duration power on to the pump with just key on,it varies depending on model. If you bump the starter it will run about 25 seconds this is normal. The power to the pump is pwm-pulse width modulated.

I would not use a high draw solenoid to run a low current pump. Hopefully you did not fry the ECM by trying to run too many amps through it.



Bob

 

[JoshPeters]

I would take the power supply signal to the lift pump, and install a relay. Use good clean 12v to your new pusher pump with that relay and see what happens. I have been told that the ECM can change the ammount of voltage the lift pump sees depending on how much "demand" the ECM thinks it needs. Putting a relay in that loop should eliminate that problem, effectivly giving you 12v to your lift pump and pusher pump.



Josh

 

[IMunro]

Yes, since the installation of the fuel pressure guage, I was aware that there was a short duration burst from the pump and also the longer one if the starter was bumped. Those are what went away, but if I connected the pusher pump the pressure would rise to 21-22 psi after a couple of seconds. So decided that things could not be as bad as I thought. I was afraid that the liftpump was getting only 8 volts all the time and would burn up the motor. That didn't make sense since I was getting 22 psi, so the 12 volts must have been getting there. All seems to be well now.



Thanks for the response and the input.



Ian

 

[IMunro]

would take the power supply signal to the lift pump, and install a relay. Use good clean 12v to your new pusher pump with that relay and see what happens. I have been told that the ECM can change the ammount of voltage the lift pump sees depending on how much "demand" the ECM thinks it needs. Putting a relay in that loop should eliminate that problem, effectivly giving you 12v to your lift pump and pusher pump.



This is what I tried to do initially, take the signal from the liftpump to activate the relay, but as it seemed to be only 8 volts, it would not activate it, I thought.



What I ended up doing was taking a switched source of 12 volts which was controlled by the ignition switch, too, to activate the relay(solonoid). And a "clean" source of 12 volts straight from the battery, through the solonoid and into the pusher pump. The funny thing is that all seems to be back to normal. I get the pulse when the ignition is turned on, 14-15 psi with no pusher on, and 21-22 when the pusher is swithed on!! So this is how the system was advertised and it beats the heck out of me as to what was going on before. Perhaps dis-connecting the the batteries allowed everything to normalise.



I may go back to my first intention, of having the lift pump control the pusher, but for the moment I am going to leave a "Working system" alone in case I really screw something up!!



Thanks again for your input,



Ian

 

[bavrit]

Lift pump

Could it be that when the grid heaters come on, it is dropping your voltage to 8 volts?

 

[IMunro]

Could it be that when the grid heaters come on, it is dropping your voltage to 8 volts?

Quote

Could it be that when the grid heaters come on, it is dropping your voltage to 8 volts?



Yes, I expect it could be. I didn't think of that. But there was still no pressure at the guage. I ran around today and the truck runs fine but I'm not out of the woods yet, I'm afraid. Will post more tomorrow.



Ian

 

[RT66DOC]

Ian - Did you use the P4600HP (8 psi/100gph) or P4601HP (18 psi/100 gph)?

 

[IMunro]

Ian - Did you use the P4600HP (8 psi/100gph) or P4601HP (18 psi/100 gph)?

yes, I used the Carter P4600HP from Summit Racing. I have been doing a lot of thinking about this... it is destroying my beauty sleep!!



I had planned on using the setup that Gary-KJ6Q used, where he had a shunt with a check-valve in case of pusher-pump failure. I was, however, unable to obtain one and Summit has them back-ordered. I prepared for the addition af the shunt at a later date by plugging the holes.



Everything seems to OK when the pusher-pump is switched on... pressure up at 21-22 psi at idle, voltage at the lift-pump is 13. 6 or so, and the pressure drops a little when accelerating. (Have not determined by how much, yet) What was bothering me was that the lift-pump didn't seem to be working on its own, and I was concerned about what would happen if the pusher went toes-up. I think I know what the deal is now:



Without the pusher-pump switched on the lift-pump cannot draw fuel through the pusher-pump and the filter, that I installed just after the tank and before the P-P. The filter did not seem to have much of a restriction, as when I blew through it, a not very scientific test, I agree, it was pretty easy, whereas when I tried to blow through the pusher-pump I got very little air through it. All of which validates Gary-KJ6Q's system for a check-valve and a shunt, in case of Pusher-pump failure.



So, I think I am OK on this now, and I want to thank all of you for your input, each suggestion was valuable and sent me down another path, each of which converged at the conclusion above.



I see in your sig, Tom, that your wife has a '78 XJ6L. I used to have a Series I XJ6 that I dearly loved. I built up from boxes of parts, completely rebuilding the engine. One of the biggest thrills of my life was when the engine fired up for the very first time. I feel the same way about this truck... it seems to do everything so well it a pleasure to drive, and listen to, especially the swoosh of the turbo as it comes on. As someone else on this Register said "I look for opportunities to drive it all the time". With the sorting out of the transmission, the replacement of the lift-pump, the re-arrangment of the boost hoses and now the addition of the pusher-pump all should be well. I seem to be averaging around 20 mpg which I find amazing for a vehicle that is close to 7000#, as my previous car was a Mercury Mountaineer, IT weighed a little over 4000# and the best mileage I ever got from it was just under 17 mpg. How do they do it??!!



One note on the Carter P4600HP. The fittings that come with the pump are 1/2" and the stock lines on the truck are 3/8". I retained the stock sizes and the input/output fittings on the pump are 3/8" also. This must effect the output of the pump because the volume of fuel passed by a 1/2" hole is significantly more that that of a 3/8" hole. Perhaps as much as 2:1? Maybe not that much. Does anything happen to the pressure? Perhaps someone who is more knowlegable about fluid dynamics than I can chime in.



Thanks again guys, once more the TDR rules.



Ian