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Discussion Starter #1
A week ago i replaced the fuel pump on my 87 2.8 FI, manual, 4x4 s10... We changed it like normal, reinstalled.. nothing... this is kinda hard to grasp but just go with me on this... at the end of the power wire for the pump there is 11.81 volts with the key on.. that's good.. but as soon as you give it a ground or put it on the pump, nothing. Black magic or something, the voltage disapears.. then i ran a wire from the battery ground to be reassured i had a good ground.. when you brush a wire with 12 volts with a ground, shouldnt there be a spark??? I'd think so... well anyway, nothing.. so I went up front and found a pink and black wire out of the same relay that is only hot when the key is on and hooked it up to that... worked good enough to get it home from the shop. Last night i had some time, and hooked it up to the ecm through some wires from a neighboring relay. When it was hooked up on the pink and black wire it started quickly, like it should, but when i hooked it back up through the ecm, it's back to starting hard, just like it did before i ever touched the pump. It's still throwin a code 54... i was told that is low pressure. Hmm.. feels like a waste of $50.. with no improvement. When i let it out of first, it likes to want to stall too when it's not revved pretty high. So what's the deal? How do i get my truck starting like it should? Why did my voltage dissappear when i hooked up that wire? Thanks A LOT! Jared
 

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When it is wired normally, if you let it crank for a LONG time, will it start?

Code 54 could be bad quad driver in the ECM, fuel pump relay, or any of the wiring involved (low pump voltage). It doesn't actually measure pressure directly, though it could indicate low pressure.

I'd be thinking relay or quad driver at this point, but I certainly wouldn't throw a new ECM at it without waiting for more experenced people to reply. Off ebay, or from a friendly wrecking yard, you maybe able to find a ECM cheap if it comes to that.


On my truck (87, 2.8, Auto, A/C), the fuel pump is only energized for a a couple seconds when you turn the key on, so it is possible that you are missing the window where voltage shows up when you try to measure/ get sparks. Also, there seems to be a built in ~30 delay, so if you turn the key on-off-on, you only get voltage on the first "on" unless you wait long enough.

Off the top of my head, I don't remember which relay is which, and what the wire colors are. I did get code 54's when I had a relay get corroded into its connector...eventually got long crank times until the oil pressure built up enough to close the switch.
 

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I agree with the above.. the relay on the 4.3s is on the driverside fender and i presume the 2.8 is the same... probably at least two relays there........ all the stuff about the ECM timer and stuff is true... if you dont catch it right you wont get anything at the pump.

i didn't understand what you did with the neighboring relay? what i would do is try a good relay and see if that makes anything better. Make sure all the connections are good, especially at the relay. I would also check your grounds, especially the ones dealling with the fuel pump relay.. if it isn't grounded properly it could be tripping in and out rather than run solid once started.

if all those are good... then unplug the relay and jump the pump with 12v off the battery at pump side of the relay (12v directly to the pump from the relay plug). this will ensure the integrity of the wiring to the pump and the pumps ground

then plug the relay in and feed 12v from the battery to the ignitor wire of the relay (normally gets 12v from the ecm). the pump should run fine also. this will ensure the relay is good

I would then check the relays ECM ignitor source for 12v exactly when the key is turned on or while cranking. Make sure its been a min or two befor doing this since the last cranking otherwise it wont show 12v.

I would also check the relays ground and relays 12v constant power or ignition power, its probably 12v ignition on.

from the sounds of it, it seems to me to be the relay ground or relay itself... if it was anything else it wouldn't run at all
 

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Discussion Starter #4
I know where the relay is, so that isnt an issue, but i dont know where it is grounded. The pump's ground is good because i hooked the pump up to a wire out of the same relay that was only hot when the key was on. This was a pink and black wire. I think it could have been something to do with the fuel gauge or temp gauge because neither has worked since. And yes, it does start, but after a lot of cranking, some times it gets to the point where you can here it cranking slower due to the battery dieing out...So where is the ground and ignitor wire for that relay? Thanks for the replys.
 

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its probably the one in the back of the head or on the front of the intake...... they splice them together in the harness behind the driver side head..... and it later bolts on in one of the two spots i mentioned......

maybe the easiest way to make sure its grounded properly is to ground the relay's ground wire directly to the battery with a test lead and see if that helps

you know the relay is good then?

when you wire the pump directly to the battery and the pump turns on, the truck starts and runs fine, right? it should
 

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Discussion Starter #6
yes, the truck starts amazingly instantly when the pump is direct to the battery.
 

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well then keep working your way back from the pump if you dont find a problem and cant find a ecm cheap i would just wire the relay ignitor wire (currently goes to the ecm) to an ignition source.


probably not the most recommended thing todo but it will work
 

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Ok, in keeping posting from the oldest topics to the most recent ones ;). Yes, the "disappearing" voltage to the fuel pump power wire is normal when you turn the key to the "on" position. That is to prime the fuel pump and is powered through the ECMB fuse in your fuse block. First thing to check if your truck dies and you can't hear the pump kick on for a second or two when you put you ear by the tank BTW...

On the 2.8's the Fuel pump relay and the A/C relay and side by side on the driver's side firewall. The fuel pump relay is towards the master cylinder and the A/C relay is towards the fender (on 4.3's it is reversed). These relays are interchangable so, you can swap them out to see if one is bad or not.

After I did my 2.8 to 3.4 swap, I had electrical problems big time. It might be a long shoot but, you might want to check the condition of the bulkhead connector that is by the windwasher reservoir. On my truck, somehow it became loose and was creating all kinds of headaches. There is a 1/4" bolt in the center to hold it in place under a plastic cover that snaps on. Mine was very loose.

I pulled my bed off and took out my pump in additon to buying a ECM out of a truck at a junkyard trying the track down my problems... I know the ECM works because after I got the truck running, I put it in to make sure it was good. I would not think that it is an ECM problem if the truck ran fine before the fuel pump replacement however.

Your truck is a year older than mine. Corrosion is a BIG problem in vehicles as old as ours are. Mine only has 62K on it too (5K less than my syclone :()... Double and triple check ALL your connections and get a tube of dielectric grease from NAPA or the like and coat eveything electrical with it. I use a toothpick to smear it in the plugs. Makes good electrical contact and prevents corrosion from forming in the future. HTH's

Mike Campbell
 

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Discussion Starter #9
The truck didnt start good though before the fuel pump, thats what prompted me to change the pump... after a tune-up it was the only thing i could come up with. So when we had a problem with the disappearing voltage, we hooked the pump up off another wire out of that relay which caused the truck to start very quickly, i think this is because it wasn't being controlled by the ecm there; it was a pink and black wire that i hooked into. and the pump ran very loud, i believe this could have been due to too high of voltage, though i'm really not sure. Then i rehooked it up the way it was and it's starting hard again... so the ecm makes sense... could it be the fuel pressure regulator? I didnt think i had one but autozone lists one for $23. Thanks again for the replys...Jared
 

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it could be fuel pressure but I highly doubt it, check the pressure to make sure with a gauge befor going and buying a new regulator.

the pump shouldnt get louder, it only get 12v and upto 14 volts when its running. you said your gauge wasnt working, well i had to reground my pump to get my gauge to work, i dont know but that might be the problem... you should have found a problem by now if you checked everything we told you to check and if you checked it properly. I still think its in the area of the relay back to the ecm, SY had a point with the bulk head connector, the relay ignitor wire that comes from the ecm goes into and directly back out of the bulk head connector, i dont know why gm did this. It seems like a waste, I know because I traced it out when I did my 4.3 swap.
 

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Discussion Starter #11
Meeh350.. could you explain this in greater detail?


I would then check the relays ECM ignitor source for 12v exactly when the key is turned on or while cranking. Make sure its been a min or two befor doing this since the last cranking otherwise it wont show 12v. ............is this the only yellow wire comming out of it???

I would also check the relays ground and relays 12v constant power or ignition power, its probably 12v ignition on.... black?
 

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i dont remember what colors are what, black is probably ground.. check it with a test light to the pos. battery terminal.... Then check it with an ohm meter, it should have little resistance when connected to the neg. battery terminal.

one should be 12v when the key is on, ALL THE TIME. That is your relay power source that feeds the pump when the relay is kicked on by the ecm via the ignitor wire.

one should be the ignitor wire, it comes from the ECM, goes into the bulk head connector and then back out again to the the relay. It should read 12v with the key on for only a few seconds (10 seconds roundabouts) or 12v while cranking and or the truck is running. This wire turns on the fuel pump via the relay or in otherwords turns on the switch (relay).

Then the last wire is your pump supply wire, it gets the 12v when the relay is on and goes to the fuel pump

thats all there is, if all those check out then there has to be a problem with the pump, the pump ground, or something isn't keeping the values that they are supposed to........ ground circuit not grounding properly and building voltage ....... relay kicking in and out...... or ecm not providing 12v to the relay all the time for whatever reason.

ECMb fuse feeds the ecm's fuel pump ignitor wire as mentioned earlier too.......12v ignition on or all the time i cant remember

that is basically the whole fuel pumps electrical system pretty much, the problem should be in there
 

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wow, im really getting discouraged here, this is pretty aggrevating.... yeah he is right...... THATS A SHITTY GROUND..... pardon my language but it makes me mad i wasted my time helping when you had that for a ground
 

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Discussion Starter #15
no,no,no dont be discouraged. that is not the problem. i'm sorry if i was misleading but i DID NOT ground to a fuel line. I grounded to the top of the sending until then that wire goes to the frame. Dont think you've wasted you time, you havent. I cant thank you enough for everything you've helped with.
 

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well regardless..... there is more than enough info above to figure out the problem... good luck feel free to ask again
 

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Discussion Starter #17
one more question, then i'll leave everyone alone on this topic, does the fuel pump run constantly or does it shut off and run lower while its being driven? or is it constantly on from the time you start it until you shut it off?
 

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Older ones like ours turn on, then stay on solid.

Some later model vehicles can modulate the voltage to the pump.
 

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Discussion Starter #19
so i'd be all good if i just hooked it up to a wire that was always hot and left it like that right? Thanks a lot.
 

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you mean, ignition on 12v not 12v ALL the time, it would never shut off.... that would be fine.. not the best thing in the world if your in an accident but it will be fine
 
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