My stock 91 (454, the one in my signature) is having problems staying running. Just at random it dies but will not stay running for more than 5 minutes. I can turn the key back for a minute or two to off, then it usually restarts.
I already replaced the intank fuel pump, strainer and fuel filter, it has a fairly new throttle sensor on the TBI and the injectors look like they're giving good pressure (when it runs).
A friend talked to his dad who is a master mechanic and he suggested the fuel pump relay but I am not sure where that is on this beast...

any other ideas?

The fuel pump relay should be located on the firewall (passenger side), next to the indentation in the firewall for the motor.

Are you noticing any voltage dips?

My opinion is, most likely it is not the fuel pump relay causing the problem.

When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through one of the oil pressure sensors. If a fuel pump relay does not make contact prior to the system getting oil pressure a code 54 will get set.

It would be a good idea to see if the ECM has any stored codes in it. If you need instruction on pulling codes, without a scan tool, let me know.

Here is a link for a truck different then what you have but will give you an idea what the relay looks like and where it is located: (many trucks only have one relay in this location, and it’s the fuel pump relay)
http://autorepair.about.com/library/illustrations/bl433lib.htm

My first guess, by what you described, would be a failing ignition module in the distributor.

I saw the relay after I bought it, was easy as hell finding it.. right there on the top back firewall behind the air cleaner... took 30 seconds to replace... but still no difference. It is the ONLY relay there so no question on what or where once I saw it.
I will be checking the codes when it is warm enough for me to do it and I am not working (this weekend hopefully). With it being 70 all day while I'm working and 30-40s when I am home in the evenings...

As for the code, I understand a simple wire jumper between pin 1&2 will make the check engine light blink the codes...

After I get the codes, I will be checking electrical to ensure the injectors are getting voltage, then check the fuel line to ensure gas is being pumped... if both check out then I am thinking the injectors themselves.

Another idea might be the oil pressure switch/sensor?

guess I will check the codes first...

As for the failing ignition module, would that control the power going to the injectors and stop gas from coming out at all, even when the pedal is depressed? or since it is an electrical system and not manual pump, pumping the gas pedal without power wouldn't do anything...??? Basically when it won't start, there is absolutely NO gas coming from the injectors but there is a light gas smell (and it wasn't the burritos.... this time).

As for the code, I understand a simple wire jumper between pin 1&2 will make the check engine light blink the codes...
Here are some web sites with the basics on retrieving codes without a scan tool or code reader.

Poor drawing of ALDL but ok instruction + codes
http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

OBDI terminal identification
http://robertpowersmotorsports.freeservers.com/images/ALDL_plug.jpg

OBDI illustration and instructions
http://www.troublecodes.net/GM/

Another idea might be the oil pressure switch/sensor? As I stated earlier, there is a redundant circuit supplying power to the fuel pump, meaning two circuits supply power to the pump. One circuit through the oil sender/switch, and the other circuit through the fuel pump relay. If either circuit is ok the truck will have power on the fuel pump circuit, once the truck is running and has oil pressure.

As for the failing ignition module, would that control the power going to the injectors and stop gas from coming out at all, even when the pedal is depressed? or since it is an electrical system and not manual pump, pumping the gas pedal without power wouldn't do anything...??? Basically when it won't start, there is absolutely NO gas coming from the injectors but there is a light gas smell (and it wasn't the burritos.... this time). The computer needs to receive a distributor reference pulse from the distributor module to trigger the injectors.
It is possible for the module to produce spark without the computer getting a reference pulse. A bad distributor module or wiring between the module and the ECM can cause this.

With the key on there should always be power at the injectors. The ECM does not supply power to the injectors, it supplies the ground. The ECM grounds the other side of the injector, to make the injectors open.

A "Noid Light" can be used to see if the injectors are getting power and being triggered by the ECM.

Edit:
If the only problem is dying at idle or starting problems, it is also possible that the distributor upper bushing is getting so loose that the reluctor points on the distributor shaft are coming in contact with the points on the pole piece of the pickup coil. See if the distributor shaft can more sideways.

Oil coming up the distributor and leaking on the distributor pickup coil can also cause distributor reference pulse issues.

much appreciated

edit: ok checked the codes and notta... only flashed code 12 the whole time

also to answer the last question, it dies anytime... right now it is not starting at all but previously I could be going 55mph down the road and it would die

Does it have spark now when cranking?

Is fuel coming out of the injectors when the engine is cranking?

no fuel when engine is cranking

last I checked it did have spark but I may check again tomorrow to be sure

Best guess at this point - It sounds like the distributor module may be bad.

NAPA stores in my area will test distributor modules for free. Make sure you put heat sink grease under the module when you reinstall it.

ok got it replaced, $39 after tax
so far so good, took it out for a 5 mile test drive, seems to be back up to full power and hasn't died (yet)

The real test will be this week as I go to work

thanks for the help so far guys!

Excellent!

so far so good, drove it the past 2 days to and from work and around town, it still feels as if it is heasitating a little at low RPMs (like 1000-1200 or lower) but otherwise it is doing good, even with our colder weather.

Thanks for the feedback.

If you did not move the distributor changing the timing, my first guess would be that possibly it is the EGR causing the hesitation. You may want to check the timing and make sure it correct.

If the hesitation bothers you, the first test I suggest is a test drive with the hose to the EGR disconnected and plugged.

so if it disappears with the EGR line plugged then it is bad EGR...

I know I didn't do anything to the timing since all I did was replace the module and the cap only screws down one way directly into the base.. not like my old 76 where it had a L base that just held onto the bottom but could get twisted easily

so if it disappears with the EGR line plugged then it is bad EGR... It’s a good possibility, but another problem can cause excess EGR flow, such as restricted exhaust. Disconnecting the EGR can also help if it is a lean condition causing the sag/hesitation, making it appear the EGR is the cause, when it is not.

If disconnecting and plugging the EGR helped, first step is to identify which type of EGR valve/system your truck has.

There are multiple types of EGR valves.
Port EGR Valves – The EGR solenoid pulses like a mixture control solenoid/fuel injector to control vacuum supply.

Positive back pressure EGR valves - Should have a “P” after the last numbers on the valve. The pressure in the exhaust system effects (modulates) how much the valve opens.

Negative pressure EGR valves - Should have an “N” after the last numbers on the valve. The pressure in the exhaust system effects (modulates) how much the valve opens.

This is a site that has a photo and an illustration about EGR vale numbers
http://shbox.com/1/EGR_ID.jpg

TBI trucks are generally Negative pressure EGR or Port EGR systems.

EGR valves have a spring in them that can get weak causing the valve to open to much or to easily.

I would suggest only using a general motors replacement EGR valve, if you decide to put a new valve on it.

If you want a longer post with more information on EGR, let me know.

I will get that replaced this weekend then (hopefully)
as I do not have $100 to place on parts like this for now, I will get a cheaper one and get a better one later down the road

I ran out and looked and it currently has a generic one on there with no OEM #s

been so busy hauling girl scout cookies (filled by burb twice now) that I haven't had a chance to get any further with it, it is slowly getting worse but seems to be sporadic.... at low RPMs say around 10-25mph it surges sometimes... seems to be slightly worse when more power is being drawn (like at night) but that could be my imagination... hopefully I get some time later this week to do more troubleshooting. Again it is very random.

I have also had the spring in an egr valve get weak and cause a hesitation. I have cured it temporarily by placing a socket on top of the EGR valve and dimpling the top in a little to tighten the spring. It is definately not the correct way to fix it, but it will work until you buy a new one, if that is the problem.