1999 gmc sierra head scratcher

headhunter · May 5, 2013

(1999 gmc sierra 1/2 ton 2x4 with 4.8l) so im driving home and truck starts to misfire, check engine light flashing, lookin for a spot to pull over and it stalls roll to the side of the road, grab handy little code reader and comes up with #4 cylinder mechanical failure/fuel error on #4/ spark error on #4, so pop the hood and #4 plug wire is hanging on the spark plug, fell off of coil, so call a friend, he comes to help, connect #4 wire back onto coil try to start and it just turns over no fire, hhmm #4 now has spark lets check for fuel in the rail, no pressure, fuel pump not running, hot wire and get the fuel pump runnin, still no go, unplug egr and truck runs, so we go back to local auto parts get a set of plug wires and carb cleaner for egr,(friend says egr is plugged thats why it wont run with egr plugged in, so clean egr) so i get home, this morning i go out and pull egr to clean and its spotless, well clean for 256k, so i plug in the egr and it wont start unplug egr and it runs, with the fuel pump relay plugged in pump wont run, so hot wire the pump and it runs. error codes that came up this morning are po102,230,405 and p1870, please help only set of wheels and in the middle of nowhere. so just scanned it again and getting po230 (fuel pump relay; Fuel Pump Relay Control Circuit Malfunction , and po405 which is egr circuit problem, its unplugged because it wont run when plugged in. any help at all is greatly appreciated, is it something with the ecu or what, fixed the problem with the misfire and now the fuel pump wont run and there's a problem with the egr

aflesch · May 5, 2013

It sounds like the PCM shut the fuel pump off when it set the Cyl #4 mechanical failure. Try disconnecting the battery for a few minutes to reset the PCM.

The other option is that when the spark plug wire came off it shorted to something and fried it or blew a fuse. That could be why you have to unplug the EGR to get it to run. One of the EGR wires may be shorted.

headhunter · May 7, 2013

how do i check the egr wires, and thanks for the reply, i have a multimeter with ac/dc, ohms, and i think its called continuity, i also disconnected the neg battery cable for over 24 hrs and the fuel pump still wont activate, everything checks out good with the egr, my money is on the pcm being bad

aflesch · May 9, 2013

You will need to get a wiring diagram. You can visually inspect the wires all the way back to the PCM though.

bossier62guy · May 9, 2013

Here's the wiring for the EGR system. It by no means has any connection w/ the fuel pump not running. For curiousity's sake......why do you think a plug wire fell off? Most people have issues just removing the things to replace spark plugs or wires. Did you swap the fuel pump relay w/ another like relay to verify that you don't have a bad relay? How did you hot wire the fuel pump to get it to come on? The P0405 is probably due to the fact that you had the plug off of the EGR valve. I'd focus on the fuel pump issue first.

BTW....one of the codes you listed was in reference to the MAF and another to the tranny. Check your battery cables and grounds. I don't know where you are located but you might have corrosion issues.

EGR.pdf

headhunter · May 10, 2013

thanks for the diagram, plug wire?, well after the truck stalled i grabbed my code reader and scanned the dtc, called a friend and had her check the codes i got online and the first code was #4 cylinder had fuel, spark, or mechanical error, got out to look and #4 spark wire was hanging off the spark plug, fell off of the coil but still on the spark plug, yes swapped relay for another one in the fuse box and still nothing, the pcm isnt sending a signal to turn on the relay, the maf code, i just replaced the maf because it was bad and still had the old one in the truck so once the spark plug wire was replaced and it still wouldn't start i put the old maf back on to see if that was the issue, other then the maf sensor issue previously and then replacing it i have had no issues with the truck until the plug wire came off. now i have no fuel pump, issues with the egr, and the trans shifts hard between 1-2 and 2-3, fuel pump hot wire? went from pin 30 on fuel pump relay(which is full time 12v) to pin 87(which is power feed to fuel pump) in power box under the hood where the fuel pump relay is supposed to be. i have an aftermarket set of driving lights on my truck that i took the power wire from and inserted into the #87 fuel pump relay in the power box, this is all done thru the 4 sockets for the fuel pump relay where it sits in the under hood power box behind the battery, the sockets are, full time 12v, ground, signal wire from pcm, and feed to pump. thats why i am thinkin its the pcm because of the problems with the egr, no signal from pcm to turn on the fuel pump relay and the issues with the trans all of a sudden. i checked the pinouts in the power box for the fuel pump, and when the key is turned on there is supposed to be a prime pulse sent from the pcm to the fuel pump relay, and then when the engine is cranked over there is a signal sent to turn on the relay and neither time does the pcm send the signal. i hope this novel i've typed here makes sense

bossier62guy · May 10, 2013

You've got some problems....pin 38 is 12V for the FPR, not 30 from what I'm seeing in the schematics but nonetheless I get all that you're saying. There just may be an underlying reason the PCM is not commanding the fuel pump on. If you have access to another PCM give it a try.

headhunter · May 10, 2013

im going by the pins on the bottom of the relay, on the relay there are pins 30,85,86,87, if you stand on the drivers side of the truck looking across the engine compartment towards the passengers side where the fuel pump relay sits the 12v pin is in the upper right corner of the 4 pins

bossier62guy · May 10, 2013

im going by the pins on the bottom of the relay, on the relay there are pins 30,85,86,87, if you stand on the drivers side of the truck looking across the engine compartment towards the passengers side where the fuel pump relay sits the 12v pin is in the upper right corner of the 4 pins

And this is what I'm going by....not that it makes any difference at this time.

fuelsch.pdf

headhunter · May 12, 2013

with the neg cable off the battery and the ignition turned on, when i place the neg cable on the battery should the egr pop open or should it stay closed till the pcm tells it to open

bossier62guy · May 12, 2013

Here's a little info on the EGR valve operation.

EGR.pdf

headhunter · May 12, 2013

thanks Bossier

headhunter · May 31, 2013

UPDATE: so spark plug wire fell off of coil, truck stalls,new spark plug wires installed, issues afterwards, fuel pump doesn't run when key is turned on or when cranking, egr error, so unplug egr, hot wire fuel pump, truck runs, shifts really hard into second, hard into 3, drive and o-drive. so now the update picked up a used pcm today, now fuel pump runs when key is turned on(prime pulse?), tried to start now message center says security. what to do now ?