Fuel pump run time

LarryW

LarryW

Well-known member
Mar 28, 2002
5,968
688
113
Menomonie, WI.
I am using the Dynamic EFI P-4 software and TunerPro. Does anyone know if there is a way of changing the switch on pump run time. I have found that when turning the switch on, that the fuel pump (which is suppose to bring the fuel pressure up for starting) only runs for 2 seconds which only brings the pressure up to 18lbs. I need 42lbs for normal operation. As a result, I need to crank for an longer period of time than would be necessary while fuel pressure is coming up.
Thanks
Larry :-)
 
Unfortunately, I find no reference to this in BobR’s documentation. Perhaps it is hidden deeper and Randy will know.
As a result, I need to crank for an longer period of time than would be necessary while fuel pressure is coming up.
----
Best Wishes,
George
http://www.pggp.com
 
Who would have thought, a motorhome problem. In case the software
fix isn't forthcoming, it doesn't take much power to keep a fuel pump
relay on once it has pulled in. I can think of using resistors, a cap,
and a couple diodes to stretch the hold time of the relay some
seconds.
Bruce Roe
+++++++++++++++++++++++++++++++++++++++++++++++++++
From: Larry Weidner 23 May 15
I am using the Dynamic EFI P-4 software and TunerPro. Does
anyone know if there is a way of changing the switch on pump run
time. I have found that when turning the switch on, that the fuel pump
(which is suppose to bring the fuel pressure up for starting) only
runs for 2 seconds which only brings the pressure up to 18lbs. I
need 42lbs for normal operation. As a result, I need to crank for a
longer period of time than would be necessary while fuel pressure
is coming up.
Thanks
Larry
 
Larry,
A search of the bin doesn't show that as an available parameter. You MAY
be able to extend the relay hold time by installing a large capacitor
across its coil. At some small risk of overheating the driver in the ECU.
A better option would be to insert a little delay circuit, probably based
on a 555 timer, to give you another second or two of pumping.
On second thought, do an eBay search on "time delay". The prices for
various delay devices are so absurdly low that it makes no sense to build
something -- at least until you know exactly what you need and perhaps want
a more compact, encapsulated, device. $5 for experimentation ain't too bad.
Ken H.
 
Larry,
What I do is turn off the key after the first and wait for a full minute
and key on again.
I had one of the 8 injector stuck open and gilled the crankcase with so
much fuel, that the engine starter could not crank.
It shold hold pressure for sometime.
On Sat, May 23, 2015 at 4:09 PM, Ken Henderson
wrote:
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Don't connect a big cap across the relay coil; that would require a
possibly damaging surge from the driver. Connect a resistor in series
with the cap across the coil, so the cap will be some 90% charged at
your timeout. If that resistor won't supply sufficient current to hold the
relay till half discharged, parallel the resistor with a second resistor and
series diode, so it will only add current on discharge. A typical DC relay
might hold till the coil voltage drops below 20%. Checking relay
sensitivity might bring down the scale of everything.
Adding a prebuilt timer circuit will bring the added complication of
power & ground wiring, good to avoid. I use 4541 CMOS circuitry
for this sort of thing, that family can run on a few microamps down
to 3V, provide start and output polarity options, easily does long
intervals, has rail to rail signals.
The 555 is available as a CMOS C555, don't see any advantage.
Bruce Roe
++++++++++++++++++++++++++++++++++++++++++++++++++++++
From: Ken Henderson 23 May 15
Larry,
A search of the bin doesn't show that as an available parameter. You MAY
be able to extend the relay hold time by installing a large capacitor across
its coil. At some small risk of overheating the driver in the ECU. A better
option would be to insert a little delay circuit, probably based on a 555
timer, to give you another second or two of pumping.
 
This is a good point and I suppose why the timer is on the system. It is curious that the pressure does not build in the timed shutoff. Are you sure (Larry) that there is no leaking injector causing the slow buildup? It would be good to check WOT in 2nd gear above 3000 RPMs just to be sure the pump is keeping up.
I had one of the 8 injector stuck open and gilled the crankcase with so much fuel, that the engine starter could not crank.
----
Best Wishes,
George
http://www.pggp.com
 
I am not good enough in my understanding of electronics to do any of these kind of things. With my luck I'd damage the computer...then what?? It just seems like there should be a timer built into the software where one could just change the fuel pump "power up" time from the defaulted 2 seconds to say 8 seconds or what ever it takes. I played with the start switch some yesterday while watching the FP gauge. If I just go to switch on, and as soon as the pump hits the 2 second mark i turn the switch to start, the pump will continue to build pressure and start time is shorter. Seems to work without a whole lot of cranking.
I think I will write BobR a note and see if he knows of a way to work with the software on this.
Larry :-)
 
Well aren’t you the clever guy. Simple solution. You should try for a job in electronics!
The prime button will get us ready for when we are all running Manny diesels and need to run the glow plugs.
You could just add a "prime". Push button switch like we do for the fuel pump on the Onan. Press the switch to pull the relay in for a few seconds then start'r up.
----
Best Wishes,
George
http://www.pggp.com
 
If I was doing it, I'd likely use a PIC or some such nonsense, just because I can.
Bruce Hislop
Perth Communications
Sent from my BlackBerry Classic with a real keypad!
From: George BeckmanSent: Sunday, May 24, 2015 10:07 AMTo: EFI GoogleListReply To: gmcmh-efi[-b]Subject: [/b]Re: [GMCMH-EFI] Fuel pump run time
Well aren’t you the clever guy. Simple solution. You should try for a job in electronics!
The prime button will get us ready for when we are all running Manny diesels and need to run the glow plugs.
You could just add a "prime". Push button switch like we do for the fuel pump on the Onan. Press the switch to pull the relay in for a few seconds then start'r up.
-Best Wishes,
George
http://www.pggp.com"]http://www.pggp.com]http://www.pggp.com[/url][/url][/url]
 
Gorden, your right.
It should not happened, but mine is 8 injectors and with the turbo so at 0
vac. the pressure runs around 60 psi.
Also I had a friend playing wih reprograming the fuel map and turning on
and off.
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Don't know if this is at all useful to you, but on the stock GM 454 tbi
harness, there's a thing called a "fuel module" aka "hot fuel handling
module".
It increases the time the pump runs at key on from the typical 2 seconds to
around 10 seconds. It's a small black box that plugs into the harness
near the ecm
and ties into the fuel pump relay circuit. I found one in a junkyard
truck, located near the ecm behind the glovebox. Haven't had to use it so
far, but carry it along just in case.
Karen
1975 26'
 
Here is an image that shows the connections
747ecm3.jpg
"]http://www.wedgeparts.com/images/747ecm3.jpg[/IMG][/url]
Google ACDelco 10052973 you will find lots of info.
Dave
Subject: [Maybe Spam] Re: [GMCMH-EFI] Re: Fuel pump run time
Clever, where did you find the identifier, description and specifications?
Thanks,
 
Ok, if I do that, what am I looking for?
After shut down, I have noticed that FP goes from 40+ lbs to 20 or less in about 5 seconds. Not surprising to me when you consider that a liquid under pressure will fall off quite quickly with ANY kind of minor leak...liquids do not compress, so fall of of pressure with even the most minor of a leak will be fast. Gotta have a pretty tight system to keep pressure up. Is my thinking on this right?
As I said, at key on, if I wait for the pump to finish it's 2 sec prime and immediately go to start, the pump continues to build pressure and starts then pretty fast.
Got an answer to question from BobR. Similar to Karens and other suggestions. Below is his response.
Larry :-)
BobR's response below
Larry,
The fuel pump timeout is in the ECM hardware. Can't really change it. You can use what is known as a 'hot fuel module.'
This module operates the fuel pump for 20 seconds at key-on. GM used them in many trucks due to the heat build up under the hood. It gets wired in parallel to the fuel pump relay. The only issue with them is the transistor that drives the pump will burn out with anything that draws more current then the stock pump.
However, that transistor can be upgraded with a heat sink added. Then wired in the same way GM did it.
Or, the hot fuel module can be used along with the ECM to turn on the fuel pump relay. This may be the best way to go.
The module is in a black plastic box, about the size of a pack of cigarettes. Even has a flip lid like the Marlboro's.
Attached picture shows how it is wired in. They are usually located near the ECM.
Regards,
BobR.
Dynamic EFI
Pic is the same one that Dave Murmet posted for us.
 
One thing to look for is the duty cycle of the injectors. This will not help your pressure problems, but we need to be sure we are no where near 100 percent. I think you have done this in the past.
Then, look at the pressure as we don't want much fall when you are using lots of gas. If it holds at WOT at say 3300 I think your pump is keeping up.
Best Wishes,
George
Sent from my iPad
 
Applied GMC
Get your shine on at www.cruzingear.co

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