96 Vortec fuel pressure

[dirtautoguy]

I swear my truck must be on it’s time of the month for this whole month!!

long story short my wife and I got in the truck to go hunting one evening and it wouldn’t start. I couldn’t hear the pump so i said some bad words and we took the Jeep instead.

when we got home I looked at it some more and tried swapping in a relay from my dads truck and it started right up hurray!!

I gave the relay back and put my old one back in untill I could go get a new one. And for kicks I tried starting it and it started right up!

I’m sure I’m driving on borrowed time but Iv been driving it to work and has been driving funny once in a while it will have a hiccup like it ran out of gas but it comes right back. I also noticed sometimes when I turn the key on the pump is really loud and sometimes it’s really quiet but it’s always sounds the same with the truck running.

just now I had time to put my fuel pressure tester on it and I got 55 psi engine off and 52 psi idling. I can’t find a solid spec on what it should be but if memory serves me right from last time I had issues it should be closer to 60 does that sound right?

it does have the upgraded injectors from the poppet valves I’m not sure if that changes what it needs or not but what do you guys think?

 

[Carlaisle]

Which Vortec engine do you have?

 

[dirtautoguy]

I guess that’s kinda important huh? My bad. It’s a 1996 k1500 with a 350

 

[stutaeng]

So the first time it happened when going hunting...it would not start, right? Did it just crank and not fire?

There's some iffy situations on these distributers when damp/humid/raining. Was it by any chance like that then? And when you came back and it started? What were the conditions? Distributer original? However, this is only a starting problem, which does not explain the hiccup issue you describe.

It does sound a bit low on the fuel pressure side though for the original spider injectors, but should not be a problem on the mpfi upgrade.

Do you have any SES codes?

 

[dirtautoguy]

I guess I shouldn’t say it wouldn’t start. It did start and it died when I put it in reverse and then it would not start just crank no fire and I couldn’t hear the pump.

the weather was about 45 degrees dry we haven’t seen much rain lately. The distributor has been replaced about 45-50000 miles ago, the cap,rotor, plugs, and plug wires were done 35-40000 miles ago. The motor was new about 20000 miles ago. The mpfi upgrade was done about 40000 miles ago.

The weather was about the same when we got back. The pump only sounds loud and abnormal engine off key on. After it starts it sounds normal.

 

[96-2D-Hoe]

Change fuel filter if it's not been changed recently. Check and clean up battery terminals and grounds, there's also a ground at the fuel pump. Marvel mystery oil with the gas quietened my fuel pump right down.

My 96 shows around 55psi and runs fine. Spec is 60-65psi.


But I've had a similar episode where the truck wouldn't fire up properly, and read others having the same issue. I think mine was bad voltage. I hope anyway because that was a couple years ago, it hasn't come back and all I did was to clean up ALL electrical.


"
The pump only sounds loud and abnormal engine off key on. After it starts it sounds normal.
"
That sounds like your battery may have issues also. Get it tested

 

[dirtautoguy]

The fuel filter was replaced maybe 15000 miles ago.

the battery issue would make sense. The truck has had “the big 3 upgrade” 3 or 4 years ago and they haven’t given me any issues but I haven’t looked back either.

I’ll check those out this week as well as the ground near the wires near the tank.

the battery is probably about due for replacement as it was done about the same time as the big 3 upgrade.

I’m not sure why some of these things didn’t cross my mind, I’ll get these things checked out

 

[Schurkey]

Given how many diagnostic tools are sold by bottom-feeder companies sourcing crap from Communist China, and the fact that even good tools can go out-of-calibration; it makes sense to TEST THE GAUGES of pressure-sensing tools now and then.

It's easy enough to connect fuel pressure testers, cranking compression testers, etc. to a regulated compressed-air source in a way that allows you to compare a couple of gauges--or three or four--to see if they all agree.

For that matter, I've been known to compare voltmeters, ohmmeters, etc. with one another for the same reason.

There's nothing worse than spending all day trying to "fix" a problem with a vehicle, only to find out the real problem was with the testing tool all along.


Yes, fully-charged batteries can solve a lot of weird issues.

 

[tinfoil_hat]

Keep in mind, testing the pressure at the rail isn't just testing the pump. It is also testing how well the regulator holds that pressure.
I have been chasing a similar problem. I was getting a steadily declining fuel pressure reading over the last several months. When it just flat out refused to start the gauge was reading 52psi. My fuel pump has always been VERY loud so I went ahead and swapped the pump and filter. The fuel in the filter was dark brown.
The truck starts every time now but a few times I have still had to crank a little. The fuel pressure gauge now says 56 psi which could mean a bad guage or a weak pump. I think the fuel pressure regulator might be the real culprit. If the regulator is just letting fuel cycle back to the tank then you will never reach 65 psi even with a new pump. I think a good regulator will somewhat compensate for a weak pump and a strong pump can somewhat compensate for a weak regulator. When both components get tired you are in trouble. I need to do the lower intake anyway so I am probably going to do the MPFI spider upgrade while I am in there. Alternatively, the regulator alone is like $65. I don't know if it is possible to test the regulator by itself.

 

[Pinger]

Funny that you mention the regulator - I was just thinking about the same a couple of days back. Because, when I had no fuel pressure, I never actually tested the rail pressure with a gauge. Just tried to have the pump prime the rail (including bypassing the relay) and when pump switched off, opened the pintle on the schrader to see if fuel was there. With a stuck open regulator the pump could have primed the rail and then the rail drained by the time I disconnected my jumper lead and opened the pintle. (I never opened the pintle with the pump connected due to fire risk).
Fuel supply lately hasn't been a problem for a while now. It all sorted itself out after an (LPG induced) inlet backfire. Just the kind of sharp pressure rise to close a stuck regulator.
I'm guessing this is what might have happened of course but it is at least plausible.