fuel pressure problem

[driceaz]

I have a 97 4.3. I started off having a harder time starting it in the morning. At first it would take 2-3 cranks before it would fire. Lately I have had more trouble starting it. 15-20 cranks or more. If I put some gas / choke cleaner in the throttle body it starts right up. Once it is started, it runs fine. Once it has been running I can turn it off and restart it no problem. From reading posts on here I suspected either the injectors, the pressure regulator or the fuel pump. I will be changing the fuel filter first to see if that helps at all, but it isn't that old.

I checked the fuel pressure. With the key on / engine off the pressure is about 58-60 psi (pretty much where it should be) after I have had it running for a while and turn it back off. The pressure seems to hold okay. So far so good. However, if I let it sit overnight and come back and turn the key on, the pressure will only go to about 48-50 psi. I can prime it several times and it never seems to go higher. This is when I can't start it. I assume that the pressure isn't high enough for the fuel injector. Still holds pressure okay.

Based on these results I think I can rule out the fuel injector / poppets as the main problem. That leaves the regulator and pump. What could be causing the pressure to be different if it is hot or cold? Is there anything else I can do to narrow it down? Any other ideas. I was thinking about trying a new fuel pressure regulator to see if it helps because I hate the idea of dropping the gas tank. But if this is clearly a fuel pump problem I will just go ahead and do it.

Would it be worthwhile to do a volume test of the fuel pump? Does anyone know how to check the direct pressure from the pump? (Should be like 75 psi I think).

Sorry for all the questions,

Any help would be appreciated.

[old_master]

Fuel pressure spec is 60psi to 66psi, so your 58 to 60 is borderline below spec. The big clue here is that it holds pressure but will only build 48 to 50 psi when you have trouble starting. Cycling the key several times, and adding carb cleaner with positive results, is a classic symptom of low fuel pressure. Holding pressure indicates the regulator and the check valve in the pump are sealing and not leaking. The pump should be able to create a maximum pressure of 108psi, the fuel pressure regulator, which is located downstream of the injectors, is most likely ok, because it does regulate near 60psi, which is probably all the pump can build. To determine if the pump is weak, check maximum output at the fuel filter by connecting the fuel pressure tester directly to pump output. Make sure there is battery voltage and a good ground at the fuel pump module. If the max output is less than 108psi, it's time for a new pump. Do yourself a huge favor and stay away from aftermarket pumps. Spend the extra money and install an AC Delco.

[mixin]

^^^^^2X - he is the master for a reason - helped me many times!

Also, get your battery tested. If your truck starts fine with a jump, your batt may not have enough voltage to energize the pump properly on its own. - this happened to me.

If you end up replacing the FP, do not buy anything else except AC! I installed an Airtex and it crapped out 40k later - not to mention my fuel gauge NEVER worked. Now that I've got an AC back in it, the gas gauge magically works again and the truck starts and runs awesome. Rock solid 58-60 psi ALL the time.