Help diagnosing 87 TBI fuel pump problem

[p7387]

hello:
i could use help diagnosing the problem.
87 350 TBI short step

today motor attempted to start and after about 10 seconds of "rough start" just gave up.
never had this problem before, truck always started.
i popped the hood removed the air cleaner and did smell some gas, i also checked for blown fuses there were none.
when i first put the key in the ignition and turn it to it's first position i always hear the hum of the fuel pump, now i don't.
is there a fuse or relay for the fuel pump somewhere other than the fuse box? i replaced the tank,sending unit,and fuel pump just 3 years ago. i am hoping it's something that won't require tank removal again.

any advice would be appreciated.
i

[Irish_Alley]

sounds like a pump problem. try hitting the tank with a hammer and see if that helps. if it does then its prob the pump. you could slide the bed back a couple feet, its easier than dropping the tank

[p7387]

do you think the relay could be bad? or are there any other fuses to check?
i did it last time by dropping the tank on the ground, on earth, not again.
how many bed bolts on a short fleet?
also the last time i got the fuel pump from rock auto, non brand name, any advice on a better pump less likely to fail after 3 years?

thanks

[Irish_Alley]

i think its 8 bolts on lwb and swb. you have the tail light wire plug and ground strap to take car of also
http://forum.73-87chevytrucks.com/smforum/index.php/topic,22894.msg189512.html#msg189512
http://forum.73-87chevytrucks.com/smforum/index.php/topic,15708.msg122905.html#msg122905
but capt did a write up on the gas tank removal, so its kind of a toss up on which is better. for one you might strip out some bolts on the bed since you havnt dont that before they might be rusty and weak. you know how to drop the tank. but back to the bolts imo electric parts are kind of a toss up cause more than likely they are "made in china" so its probably the same plant that make most of them.

[p7387]

found some good instruction on checking the pump......

instructions
---------------------------------------
 Unplug the fuel pump connector by the tank and check for power with a test light while someone turns the key to on. The pink wire should be the fuel pump wire, the tan/white wire is for the sending unit, ground the test light to a good clean section of the frame (grind it shiney to be sure you have a good ground so you get an accurate test). The test light should come on for just two seconds each time the key is cycled to on. There is only a two second prime until the truck starts, then once oil pressure is up, the computer will send constant power to the fuel pump. Sometimes just unplugging, cleaning and re-connecting the connector will fix the problem. If you do have power, I would suspect the fuel pump quit. Sometimes hitting the tank with your fist or a rubber mallet while someone is cycling the key will start the pump again if it's starting to go bad. If no power at the connector, try to listen for the pump relay clicking when the key is cycled, it should be on the firewall on the passenger side I think?
----------------------------------------------------------------------------------------
*anybody know where the relay is specifically?
also i dropped the tank once when i did the job 3 years ago, not something i ever care to repeat on my back on earth.
i was even tempted to cut a hatch in the bed for access. got the idea on you tube.
based on your experiences how likely to fail/whats the life expectancy of aftermarket fuel pumps?

[p7387]

hey

my fuel pump might be bad but i want to check the relay before i write it off.
does any know where it is located? picture?
thanks

[bd]

The relay is mounted at the top of the firewall, just right (passenger side) of the engine.  Look at the lowermost image here...
http://forum.73-87chevytrucks.com/smforum/index.php/topic,9072.msg198713.html#msg198713

To test:  With the ignition OFF, temporarily jumper battery power to the 3" long red pigtail coming from the relay.  This will bypass the relay and feed power directly to the fuel pump circuit (via the tank selector valve, if you have dual tanks) and the pump should run.  If the pump doesn't run, you have wiring/ground problems or a faulty pump.  Don't forget to check your relay connections.

AC Delco markets the OEM pump.  With ethanol enriched fuels, pump life (regardless of brand) is a 'roll of the dice....'

[p7387]

thanks bd
btw-where would the jumper be inserted for the test?

however.........
1)apparently i was wrong about not hearing the pump coming on, with my ear up to the tank i distinctly heard the pump hum
when my neighbor moved the key to pos #1
2)i distinctly heard the relay click
3)with the breather/cover off i DID NOT notice any fuel being sprayed into the "carb"

what would the next logical step be?

thanks

[bd]

...where would the jumper be inserted for the test?

...temporarily jumper battery power to the 3" long red pigtail coming from the relay.

...what would the next logical step be?

* Check the 3-amp INJ fuse and the 10-amp ECMB and ECMI fuses located near the bottom of the fuse block. 
* Measure the fuel pressure.  For ~2 seconds after the ignition is switched ON the fuel pressure should be constant and unvarying between 9-13 PSI, typically ~11 PSI.  When the fuel pump cycles OFF, pressure should drop to about 6 PSI and hold.
* Check for spark.

[p7387]

thanks bd

checked the fuses mentioned and they are all ok.
don't have the gauge to ck pressure, if i were to buy one, where are the tbi fuel supply lines? are they apparent or hidden?if multiple lines in that area which hose?

thanks

[bd]

Remove the fuel filter inside the right frame rail next to the transmission and purchase/rent a gauge that will connect in-line using the factory fuel filter tube & o-ring hoses.  While you're there, replace the fuel filter - f/filters on these trucks are notorious for plugging up and limiting fuel delivery, because they have a finer micron rating than conventional filters used with carburetion.

[p7387]

thanks bd, here is my update

had nobody to help me today so i sprayed carb cleaner into the TB and rushed over to crank the motor, i "Thought"?? i heard a weak attempt to fire and without checking the spark went to look at the fuel filter, it looked ancient so i thought it should be replaced anyway. after the usual opening a can of rust/worms i managed to get the new fuel filter in, the nuts were of course stripped by the time i finished. the filter did not solve the problem.

next
i pulled the fuel supply from the TB and observed a healthy flow.
(note- i also cranked while the filter was off  to see if fuel was coming out, it was and the flow looked good, i have no pressure gauge so this was just visual observation)

next
pulled the wire from the ignition coil and the post was completely covered with crud, i thought for sure that was the problem but after thorough cleaning still no start

next
pulled the cap and noticed all the inner contacts were covered in the same scaly crud, i will for sure replace the cap and rotor.

the ecm and crank fuses are all good

next step?
i guess ill need to check for spark but i will buy a spark tester as i am working alone
would the two remaining choices be bad coil? or bad computer?

also-
is the fuel relay linked in with the oil pressure relay as a backup system?

didn't have any new small circular rubber gaskets for new fuel filter or reconnect of the TB supply so i used the same ones, will this be a problem?

thanks

[bd]

...i sprayed carb cleaner into the TB and rushed over to crank the motor, i "Thought"?? i heard a weak attempt to fire...

Be very conscious of the potential for fire while testing the fuel and ignition systems.  Keep a fire extinguisher available and know how to use it!  Don't let fuel puddle on the manifold.

In your attempt to start the motor try using a conservative amount of "starter fluid" instead of carb spray.  With a helper, you can also check for fuel spray from the injectors while cranking.  Or, you can purchase a TBI NOID light and check for injector signal from the ECM.  Follow this link to see a short description of how to use a NOID light... http://www.noidlight.com/checking-you-cars-fuel-injection-system-with-a-noid-light/

...didn't have any new small circular rubber gaskets for new fuel filter or reconnect of the TB supply so i used the same ones, will this be a problem?

Not an issue as long as the o-rings weren't torn.  If there are no leaks from the hose connections to the f/filter, you should be okay until next time the filter is removed.  When you replace them use Viton o-rings (typically brown in color and available from many auto parts stores and Harbor Freight).

...pulled the wire from the ignition coil and the post was completely covered with crud, i thought for sure that was the problem but after thorough cleaning still no start...

The gray 'crud' is conductive ash and/or aluminum oxide from the cap terminal(s). 

Inspect deep inside the coil wire terminal for evidence of "black soot."  If you see any soot, the wire is burning back internally and needs to be replaced.

...i guess ill need to check for spark but i will buy a spark tester as i am working alone
would the two remaining choices be bad coil? or bad computer?

For a good HEI spark tester see the attached image.  Don't jump ahead of your diagnosis - first verify whether or not you have spark.  Be systematic.

...is the fuel relay linked in with the oil pressure relay as a backup system?

The fuel pump relay is wired in parallel with the oil pressure switch located adjacent to the distributor.  The oil pressure switch is a redundant, fail-safe backup should the relay fail.

[p7387]

thanks bd

i will get the tester and check for spark next. i thought i would also replace the cap/rotor while at it.
i did see evidence of fuel in the tbi so i figure injectors are ok

will report details

[p7387]

hey guys
here's my update, still no luck starting

so far i have................

confirmed fuel spray into the tbi, i visually confirmed this.

got a basic in line spark tester with the enclosed bulb, not sure if this is "hei" but i tested for spark and its positive as the light does flicker but given the type of tester i cant check the size of the spark.

replaced the cap and rotor, double checked the coil wire for continuity

still not starting, any ideas on the next step in diagnosis?

thanks