1998 C1500 Fuel Issues

[95chev-w/t-guy]

Hey guys, need some help with this one before I pull my hair out and set the truck on fire. I bought a 1998 c1500, in good shape but not running, for $600. Was told it needed a fuel pump (it did, I'll get to that in a minute), but it started with gas down the intake. Changed the pump and it still wouldn't start. So here's a list of what I've tested so far. I've used a good multimeter and and pressure gauge for testing, and I have a good battery in the truck.
Checked all fuses/relays
Checked grounds
Checked voltage where harness plugs in to pump (over 12 volts)
Checked for spark
Changed fuel filter

Then I changed the pump and figured it'd start right up.

Here's where I got stumped...
If I check the pressure anywhere in the system with a pressure guage it only goes to 25 psi and holds. Truck obviously won't start.

So I made a jumper harness to the pump and ran it directly off of another battery. Now the pump builds up to 70 psi, and when I take power away from the pump it drops to about 60-65 psi and holds. Power the pump again, crank it over and it fires right up, but will only run for 5-10 seconds and quits.

I'm completely stumped on this. Anyone have any ideas? If I can't get this working soon I'm doing a carb swap.

[95chev-w/t-guy]

Also there's 1 engine code on for the crank/cam sensor but I believe this came on because it backfired once trying to start it with gas down the intake. May end up changing those too just to eliminate them as problems.

[95 S_Trucker]

I would check the ground for the fuel pump. On a 98, I think its at the left rear frame rail behind the tire.

There may be some corrosion you cant see. You may need to put a new terminal on it.

[speedygonzales]

When pressure is low, it could be from the pump or other things. Although your ground could be crappy, I highly doubt it's causing a low pressure issue.

First of course, you need to rule out external leaks visually.

Next check the pressure of the system with the return line pinched. If the pressure comes up, you know the problem is with the return (regulator) side of the system. If the pressure does NOT come up, the problem is at the pump or before the regulator.

In the original Vortec engine, the fuel pressure regulator is under the plastic plenum on the side of the spider injector assembly.

If you have to replace the regulator but still have the original style injectors, replace the entire unit (with regulator) from Standard Motor Products.

8 cyl
https://www.summitracing.com/parts/s...et/model/c1500

6 cyl
https://www.summitracing.com/parts/s...et/model/c1500

FYI all units made are from SMP regardless of who's name is on them.

One other point. Usually when the Vortec regulator goes out, the fuel runs into the cylinders in the middle of the bank. I think the regulator is on the right bank side. The point is, check the oil for a fuel smell.

Don't throw parts at it like a CKP. You know the pressure is wrong, fix that issue first. Might as well say this as well. I have seen way too many fuel pressure gauges that were wrong. If you don't know for sure it's perfect, put it on a good running engine to see it's showing you the correct pressure for that engine.

[95 S_Trucker]

It sounds just like a corroded ground to me. I don't know about your area, Speedy, but up here where there is rust, it happens all the time.

A corroded ground will act like a load and use voltage. Since its in series instead of parallel, a corroded ground would rob some voltage, We can take a guess and say the pump is getting 8 volts and the ground is consuming 4.

I see it all of the time on these C/K trucks and astro vans.

If there was a leak with the injector/FPR, it would not hold pressure over time. We can rule those out.

[95chev-w/t-guy]

Thanks for the responses, I'll be double checking all of the grounds and go from there. I think I'll also add better bonding straps between the frame, body and engine to rule that out as well. If that doesn't fix it I'll look into the regulat or. I'll post an update with how that goes.

[95 S_Trucker]

Originally Posted by 95chev-w/t-guy

Thanks for the responses, I'll be double checking all of the grounds and go from there. I think I'll also add better bonding straps between the frame, body and engine to rule that out as well. If that doesn't fix it I'll look into the regulat or. I'll post an update with how that goes.

Specifically the ground for the fuel pump. It's not between the cab/frame/engine.

Its a dedicated ground for the fuel pump. Its not shared with anything else.

[speedygonzales]

Originally Posted by 95chev-w/t-guy

If I check the pressure anywhere in the system with a pressure guage it only goes to 25 psi and holds.

Originally Posted by 95 S_Trucker

If there was a leak with the injector/FPR, it would not hold pressure over time. We can rule those out.

You read "and holds" as in when the engine shuts off.

I read it as "as long as it's running".

Big difference. He never said if it holds after shut down.

And if the ground were bad, as you mentioned, it causes a load. With the same amount of current trying to go through the corrosion, it would cause heat. The connection would quickly disappear from melting if it were causing the pump to only come up to 25PSI.

We will see when he checks the grounds and it doesn't change. But since he just bought the truck, he has no history on it. Likely it sat for a long time and the FPR diaphragm dried out.

Now if he tests the pressure AFTER shut down, that is a different story. But that is only part of the story since the check ball in the tank is probably bad and allows the pressure to bleed off. Again likely since it more than likely, sat for a long time.

[95 S_Trucker]

Originally Posted by speedygonzales

You read "and holds" as in when the engine shuts off.

I read it as "as long as it's running".

Big difference. He never said if it holds after shut down.

Here he says it holds pressure and didn't run.

Originally Posted by 95chev-w/t-guy

Here's where I got stumped...
If I check the pressure anywhere in the system with a pressure guage it only goes to 25 psi and holds. Truck obviously won't start.

I am not trying to start an argument. I see this all the time in my shop. I just fixed a 96 astro last week. It came in and had 34 PSI at the rail. I actually use an infrared thermal imager to visually see the ground getting hot.

This is what I use(except its got a yellow case so I don't loose it).

https://www.snapon.com/diagnostics/us/thermal

[95chev-w/t-guy]

Okay just to clear this up, it maintains pressure with the engine off. As I said, it only runs for a few seconds and quits. I did just get the truck and it sat for at least a year. I haven't been home to check the ground, but that's my next step (it's on top of the frame and clearly visable, I cut an access hole in the box). I do recall that the wire had electrical tape on it, so I suspect someone was at it before. I also figure I'm having multiple issues, since it quits after a few seconds whether I leave power hooked up to the pump or not. Again thanks for the suggestions, I'm willing to have a look at anything at this point.

[what66]

It's a good thing to check the ground.
The Vortec engine used popets, not injectors it will not operate below 55 psi.
I would check your spider it's where the big plug going into the intake you will have to take off the plastic intake your spider might be leaking it's also where the fuel pressure regulator is.
I had a similar problem it would run on carb but would not without it after I took off the intake I saw gas puddling inside replaced the spider and I'm still driving it today.

[95 S_Trucker]

Originally Posted by what66

It's a good thing to check the ground.
The Vortec engine used popets, not injectors it will not operate below 55 psi.
I would check your spider it's where the big plug going into the intake you will have to take off the plastic intake your spider might be leaking it's also where the fuel pressure regulator is.
I had a similar problem it would run on carb but would not without it after I took off the intake I saw gas puddling inside replaced the spider and I'm still driving it today.

Every car that has fuel injection has injectors.

From the factory, the injector is at the center and there are individual poppets at the end. The poppets are operated by fuel pressure. It still has an injector.

The upgrade gives you 6 little injectors at the end of each spider leg.