Fuel pump electronics

Trucks not starting... Well it will,,,, just got to kinda let it crank, then stop, then let the

pump prime a few times..

I don't think the fuel pump is working right..

It'll start sometimes idle up to around 1000 rpm, like a normal start then while its idling down

just keep going down till it stops running.

Then you can start it right up after that. No problems...

It takes it forever tuning over to start, but I swear I hear the pump turn on (sorta a roar) and she'll

fire right up...

Here's what I know.. (not much but.......)

Ign switch powers up one side of fuel pump relay coil. ECU supplies the ground of coil, which

switches the fuel pump on.

How does the ballast resistor come into the system?

All I know is it switches to run through the resistor after startup so it runs quieter.

If it's grumbling, then I bet a bearing in the pump is dying and you need to replace it ASAP.

All I know is it switches to run through the resistor after startup so it runs quieter.

 

If it's grumbling, then I bet a bearing in the pump is dying and you need to replace it ASAP.

I just replaced the pump 2 weeks ago.. Runs good after it's started.

The ballast resistor is by-passed at start-up, so starting has nothing to do with that...however, since you say it starts and then slowly dies, you may want to try eliminating the resistor with a jumper and see if anything changes.

I was thinking about doing that too Brent, just havent had any time to wrench.. Hopefully this weekend.. If rain doesnt stop me from it. I can hear the pump prime, but not when turning over.

Knowing all what you tossed into this the past month........the only thing I can think of is the pressure regulator :hmm:

Sounds like low pressure in the rail before the start, then getting a rush of pressure when it starts, and it dwindles down and stalls out.

Hows the EGR valve??? still hooked up???.......take the vacuum line off it, and plug it, and see if that makes any difference on how it starts and dies......ah er.....runs.

Knowing all what you tossed into this the past month........the only thing I can think of is the pressure regulator :hmm:

 

Sounds like low pressure in the rail before the start, then getting a rush of pressure when it starts, and it dwindles down and stalls out.

 

Hows the EGR valve??? still hooked up???.......take the vacuum line off it, and plug it, and see if that makes any difference on how it starts and dies......ah er.....runs.

:thumbsup:

I just don't get it... Hooked the fuel pressure tester up to it and did some digging.. felt the ballast resistor getting pretty warm pretty quick.. I jumped the resistor and she fires right up every time.. unhook it, it won't crank, or have any pressure at all. Hook it up and its like a hit or miss if it cranks or not... I thought the fuel pump bypasses that resistor on starting.. What gives?????

I just don't get it... Hooked the fuel pressure tester up to it and did some digging.. felt the ballast resistor getting pretty warm pretty quick.. I jumped the resistor and she fires right up every time.. unhook it, it won't crank, or have any pressure at all. Hook it up and its like a hit or miss if it cranks or not... I thought the fuel pump bypasses that resistor on starting.. What gives?????

The ballast resistor is bypassed at startup unless some PO altered the original circuit. Once running, the ECU immediately sends a signal to the ballast resistor relay and it's latched into the fuel pump voltage supply circuit. The resistance value on the ballast is critical; some of the "universal" ones are not the correct value and drop the voltage too much or not enough to the pump. I'd pick up a new one from the dealer (p/n 33000682, about $7.00), reterminate the spade connectors on the wires, and install a new resistor.

I just don't get it... Hooked the fuel pressure tester up to it and did some digging.. felt the ballast resistor getting pretty warm pretty quick.. I jumped the resistor and she fires right up every time.. unhook it, it won't crank, or have any pressure at all. Hook it up and its like a hit or miss if it cranks or not... I thought the fuel pump bypasses that resistor on starting.. What gives?????

 

The ballast resistor is bypassed at startup unless some PO altered the original circuit. Once running, the ECU immediately sends a signal to the ballast resistor relay and it's latched into the fuel pump voltage supply circuit. The resistance value on the ballast is critical; some of the "universal" ones are not the correct value and drop the voltage too much or not enough to the pump. I'd pick up a new one from the dealer (p/n 33000682, about $7.00), reterminate the spade connectors on the wires, and install a new resistor.

Yeah I know thats the thing,, it won't start with the resistor unhooked.. But it will hooked up.. I omhed it out at just a tad under 1 ohm. I'm guessing Ill get another one, but still isnt working like y'all say it should, by bypassing at start-up.

WAIT,,, ballast resistor relay...... where is that???

One ohm is a bit low JT. Mine measures about 1.3 ohms (just checked it). The resistors were the same from 84-94. The HOs have both a fuel pump relay and a ballast resistor relay; probably the Renix has only the fuel pump relay to do the ballast switching.

One ohm is a bit low JT. Mine measures about 2.3 ohms. The resistors were the same from 84-94. The HOs have both a fuel pump relay and a ballast resistor relay; probably the Renix has only the fuel pump relay to do the ballast switching.

OK that makes alot of sense.. I'm still searching through the wiring diagrams trying to find the ballast and switching circuit...

Found this... Still looking for the wiring diagram

Still don't see any way the resistor is switched in the system..

I think you need the next sheet as the "RESISTOR PACK" I believe is the ballast resistor.

I was going to ask about that resistor pack.. I found it (the ballast resistor) in a 93 FSM but still not in the 88... :wall:

The ballast resistor didn't come in the '87, it was "added" in the '88+, so the '88 FSM might not show it, the '89 FSM shows it.

The ballast resistor didn't come in the '87, it was "added" in the '88+, so the '88 FSM might not show it, the '89 FSM shows it.

Hey Wildman could you scan me a copy of the wiring diagram??

Yea, tomorrow.......getting too late tonight :(

Yea, tomorrow.......getting too late tonight :(

Roger that.. :thumbsup:

Yea, tomorrow.......getting too late tonight :(

Roger that.. :thumbsup:

Who's Roger???? :hmm:

Check your PM's JT :D

Check your PM's JT :D

No.. Check your PM's...... :doh:

In my best CA gov's voice...... I'll be back....

Another topic about the same for future reference http://www.comancheclub.com/forums/viewtopic.php?f=2&t=16008&start=0