Brain storming (engine randomly dies)

[dyeager535]

So yeah. Back to this. Didn't fix it.

After the February debacle, replaced the defective (new Delco, maybe 5 years/30k on it) oil pressure switch, re-mounted the relays more securely, and re-did some questionable wires. Quite convinced I had solved the problem.

Last week driving, repeat of California trip. The problem had not returned in over 6 months of driving, although under 5K miles. This time however, I was not in a hurry and could sit and think about it. After stalling on me, it would fire, sputter, and immediately stall. Sometimes I could get it to sputter for longer by varying the throttle. Eventually it wouldn't fire at all, just crank. I noticed I wasn't hearing the fuel pump prime, so I ran 12V to the pump wire, and the pump wouldn't run. So it's either the pump, or the wiring to the tank. I'll verify. FWIW before this last trip, I even borrowed the fuel pressure tester and took a test drive. No issues with the pressure.

IF this is a bad fuel pump, I'm going to begin to question the quality of Delco products. This pump is also maybe 5yrs old and has 30K miles on it. As an aside, the first oil pressure switch/sender failing was unusual, as they should last far longer IMO. This BRAND NEW switch/sender however, has also already failed (stuck closed, which runs the pump even with the key off). I don't see any reason these would be failing based on the location they are mounted. Far away from the headers, the connector, wires, nor sensor body show ANY sign of heat exposure above normal underhood temps.

Much of this at this point is cautionary, in case anyone else happens to run across these symptoms. I'm going to verify the pump issue, but I hope now whatever has failed, has completely failed, and isn't intermittent. So I KNOW it's fixed this time.

 

[1-ton]

You could check the wires that run along side the frame under the driver floor pan. Those wires rub against the frame, and can wear through. Those wires run to the fuel pump. When those wires rub through on the frame they cause an intermittent problem. The problem will happen often when making a turn or braking because the wires are moving around while turning or braking. I had those same wires rub through on my truck, and when one of those hot wires would ground on the frame the check engine light would come on intermittently. This only happened when I was turning or braking.

 

[dyeager535]

Yeah, that's where I hope the intermittent is no longer intermittent. If the pump won't run, I can check continuity on the pump wire, then check the tank ground. If both of those check out, it's either the wiring in the tank, or the pump itself.

The wiring to the rear of the vehicle, if routed OEM, is very difficult to check for damage. I try to do a very good job in routing wiring and protecting it, but doesn't mean something couldn't have come loose, been pinched or chafed, etc.

 

[1-ton]

Intermittent problems are 90% of the time electrical because a single unit part on a vehicle most of the time will have a consistent partial functioning condition, or consistent 100% non-functioning condition. Some where in the fuel system is a wire that is making no contact intermittently or making partial contact intermittently.

 

[diesel4me]

The wire(s) that power the fuel pump are noted for corroding inside and the connector at the pump also does too,many new pumps come with a new connector and the warranty is void if you don't use it..but if the wire is faulty anywhere from the fuse box to the pump,you'll have intermittent power delivery issues that will drive you nuts..

My friend's method of diagnosing power to the fuel pump used to consist of just using a test light --he soon learned a test light,especially the newer LED ones,do not draw enough current to tell just how much current the wire can supply,without it's "bad spot" breaking down...he now uses a sealed beam headlamp or something like an old blower motor to hook to the wire and lets the lamp stay on or the motor running several minutes--on several vehicles,the light began to dim ,or the motor slow down or shut off,once the wire's bad spot heated up enough to break the connection..
The oil pressure switch can cause this also if the portion that controls the fuel pump goes south..

Running a new wire to the fuel pump from the fuse box cured the problem on most of the vehicles--many of these vehicles had fairly new pumps "go bad" shortly after being replaced,he thinks low voltage smoked them..of course they were ones that replacing the pump was a very difficult procedure..

 

[dyeager535]

Dragging this up because I'm bored, and not too much more time before I'll finally be able to work on it.

It finally become relatively consistent in not being able to be started, although randomly it would still start.

Pretty much verified its the pump or tank wiring, since it became consistent long enough for me to test properly. Before I had to stop working on it in December, I was able to check the condition/continuity of the entire fuel pump circuitry while it was not starting, check power, and check grounds. All checked out. The tank is grounded, and power is getting to at least the sending unit connector. Going to have to drop the tank (yes, I'm stubborn and refuse to cut a hole in the bed) to inspect the wiring that goes to the sending unit, and the pump internally, but given the failure of multiple new GM oil pressure senders, I'm solidly convinced the new-ish Delco pump is going to be found to be the issue. I have a known good pump I took out when the hose that came with it split, I will throw that pump in regardless of whether the pump in there now is operating correctly when the time comes to drop the tank.

If I can verify it's the pump, I'm probably done with Delco parts that aren't just body and trim, outside of the spares I have. I'll wait until I absolutely know the issue before I make that judgment. But there is no way this pump should be dead. Whatever this issue is, it's cost me well over $1000 in towing and rentals, completely ignoring the amount of time it has consumed.

 

[rampage]

Sorry, haven’t re-read the entire thread.
Have you tried hooking power up directly to the pump at the harness by the tank? You can even use a 9V battery if you don’t feel like running a wire back there. Grey wire is power to the pump and ground is any bare metal spot on the tank.

 

[dyeager535]

No, its ok, its long lol. And went down a few rabbit holes as the inconsistent nature of the problem caused me to try a few different things.

I tested as much as possible without actually hooking a battery up back there. I checked power and ground at the sending unit connector. I got power back there by "bypassing" the fuel pump relay in the engine bay. I don't get so much as a click in the tank when I connect it with incoming power.

I know it's possible to still have wiring problems, but it doesn't seem that likely when I can see the pump wire has 12V, and that wire is run directly to the battery. It's so easy test though, that I will try when I'm back.

 

[rampage]

Also, I’m sure this has already been pointed out, but you can measure 12V at the connector but that doesn’t mean it will run the pump. If any of the wiring is damaged/corroded (either power or ground) then it can have a large resistance when current is running through it thereby making the voltage seen by the pump less. Check the voltage at the connector while a load is placed on it like a headlight.
You can also measure the resistance of the pump windings. You should get a low value, thinking somewhere in the 10’s of ohms range. I can check my pump if you’d like.

 

[dyeager535]

Actually I have a spare known good pump I can test, I can definitely compare. Still awhile before I get to the chance to put my hands on it again but I'll refer back to this thread at that time to refresh my memory lol.

Yes, it is definitely a possibility there is a wiring issue. I don't think it's likely just based on how things are run, but I can't discount it just because I don't think its likely. The way the wiring is run under these things, there could be an issue inside the loom I can't see, or a pinhole in the insulation that caused the wires to corrode, etc. I'll test the pump resistance from the connector, and put 12V to the connector from another source as well. Only thing I dislike about the weatherpack connectors, testing voltage while they connected is impossible unless you want to puncture the insulation, and I don't do that.

 

[dyeager535]

Since I have the other fuel pump thread going, I didn't want to pollute it with something specific to my trucks issues.

Nvrenuf in that thread mentioned a Bosch pump needing hard wired, so I'm hesitant to say my pump has actually failed, vs. a wiring/connector issue. This thing has been giving me intermittent fits for about a year and a half now (I've been home maybe just over half that time, so not all my fault lol) leaving me stranded in southern Oregon back in February 2019, then again 20 miles from the house in November 2019 after having thought I found/fixed the cause. Back to it this month, trucks been sitting since December. Hop in, turn the key, pump runs. The tank is coming down regardless, but cycling the key 4-5 times as I let it empty the tank for me, not once did it stutter. It gave me time to get back to the tank while the pump was running (truck off) and give the wiring a good jostling near the tank...nary an issue. Then I started it with the little bit of fuel left, idled it a few minutes, then re-positioned the truck so I can drop the tank. Wish whatever it is would die already. lol

It would be one thing if this was a briefly intermittent problem. But its gotten up to days where it won't restart, and it will go months without issue. I could swap pumps and think I've fixed it, only to find out in the middle of a snowstorm, that it was something else. I'll be adding a spool of wire to my in vehicle spare parts kit.

 

[dyeager535]

Running update.

Pump I just took out measured 2.8 ohms across the terminals. The Old "good" pump measures ~20 ohms. I'm going to test my spare new out of the box pumps and see what they show.

I noticed some physical differences between the pump I just took out and the known good pump, took some pics and what not, will eventually get those up. The new pumps I have are all "Advantage" (plus the one I think is problematic), the known good pump I have that is definitely different than what I just took out. A few mostly little differences. But I want to see if every pump is identical.

 

[rampage]

Running update.

Pump I just took out measured 2.8 ohms across the terminals. The Old "good" pump measures ~20 ohms. I'm going to test my spare new out of the box pumps and see what they show.

I noticed some physical differences between the pump I just took out and the known good pump, took some pics and what not, will eventually get those up. The new pumps I have are all "Advantage" (plus the one I think is problematic), the known good pump I have that is definitely different than what I just took out. A few mostly little differences. But I want to see if every pump is identical.

20 ohms sounds too high, 2.8 is more what I’d expect.

 

[dyeager535]

~2 is what both the new advantage pumps were as well. I ran the old good pump off a battery to drain the last 5 gallons out of the tank, seemed to be no issues with its operation. I read elsewhere that if the pumps are used and have sat, resistance may be unnaturally high until the motor has turned and any corrosion has been knocked off via the brushes? I'll see what it reads next chance I get to test, now that its run.

 

[dyeager535]

Here are the pics. Definitely differences. I have no idea what the "old, good" pump is, the part number (25163495) doesn't come up anywhere, yet a very similar part number is what is listed for TPI, and should be what I had purchased back then. I assume NOT Delco Advantage at that time. What I've been running is an Advantage EP381 (later Vortec application, often recommended as an upgrade for most GM fuel pumps BGV00381 on pump body). I definitely did not imagine the mismatch in fuel pump tubing diameters.

EP381 Advantage at top, other Delco at bottom

Unknown pump part number(s)

EP381 part number

EP381 on right

EP381 on left

TBI sender fuel tube diameter (~.470" OD)

EP381 and UNK pump outlet diameter (~.371" OD)