Need help interpreting fuel pressure test

[mudpie]

There are no safety features built into Optima batteries. The safety features are in most of the consumer level battery chargers built in the last decade or so, they simply won't turn on if the measured voltage of the battery is too low.

I think we're both saying the same thing, but differently. I have one battery charger that is brand new, and my trickle charger is about 2 years old. Those two chargers are presumably going to have whatever safety features that won't allow them to charge a battery that's down to 1.5v, hence the trick with 2 batteries in parallel. I'll be looking around at yard sales in the spring for an old charger with a basic on/off switch and no safety features.
Stupid safety. Gotta ask yourself sometimes, what would Homer Simpson do?

So I got the battery back reading 12v, and put it on my trickle charger overnight just to make sure, and put it in the truck. I'm back to where I left off... my 2 month old Delphi pump in the tank, upper intake off, questioning if the pressure regulator is good.

I reconnected the fuel lines at the spider assembly and jumped the fuel pump by bypassing the relay (jumper wire between pin #30 and 87). Up under the hood, I can hear the pump running. Check for leaks and don't see anything. Check the Autozone loan-a-tool fuel pressure gauge I'm using and it shows zero. Swap the fuel pressure regulator, and still nothing. So at this point, it's gotta be the pump, right? Pulled the pump, returned it as defective, put another brand new Delphi pump in, and still zero fuel pressure with the jumper wire in the relay. No pressure with the relay jumper wire in place, no pressure with the key turned "on", no pressure with the engine cranking. I can hear the pump running, and when I unscrew the gauge from the fuel rail there's fuel under pressure spraying out.

The tank looked clean when I had the pump out. The in-tank wiring harness and strainer were new 2 months ago when I replaced the fuel pump, and the fuel filter on the frame was replaced when I did the pump 2 years ago. Not new, but not more than about 10k on it. Shouldn't be an issue I wouldn't think, or at least not enough of an issue to cause a drop to 0 psi.

Only thing I can think of is a bad gauge, but it seemed to be working when I started checking into all this last week. I'm going to get another gauge and see what happens. In the meantime, any thoughts appreciated.

 

[df2x4]

I think we're both saying the same thing, but differently.

Pretty much. My only point was that the safety features built into modern chargers apply to AGM batteries just like they do standard lead acid batteries. If the voltage is too low, they won't charge. Really just doing a bad job of pointing out that the issue isn't specific to AGMs.

Glad your battery wasn't toasted! Good luck figuring out the issue.

 

[east302]

If you have fuel spraying out of the schrader valve but a gauge that reads zero, then it's the gauge or the fitting/adapter in the gauge kit.




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[mudpie]

That's what I've found. I went to a different Autozone and got another gauge, hooked it up and got vastly different numbers. Moral of the story...you can't always trust rented or borrowed tools.

I've got a used, but known to be good fuel pressure regulator from a friend. I've been using that for testing, and I've now got a brand new Delphi pump in it. Put the 2nd gauge on the rail, turned the key, and it jumps to 60 psi in about 2 seconds. Holds pressure at about 53 psi with the key off. I swapped my original FPR back in, turned the key, and the gauge reads 10 psi. Pretty sure I found the problem, which kinda sucks because it probably means I pulled the fuel pump and returned it for no reason other than that 1st gauge was not working.

I'm headed out to get a new FPR, rather than run with this used one, which leads me to my last (hopefully) question. Since it's been updated to the MPFI spider assembly, should I get a FPR for the year of the truck ('96) or one from a newer model with the newer spider assembly? Are there different pressure requirements? I looked it up and I'm pretty sure it was a different part number. Does it matter? The FPR I've been using, and got 60 psi with, is from an older CSFI spider assembly.

I appreciate all the input. It's been a huge help.

 

[east302]

Hmm...good question. Is there any kind of part number on the MPFI regulator?

You could ask a dealer, the right parts guy may be able to help you figure it out.

I would have guessed that both relieved or opened at the same pressure.


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[mudpie]

In the process of searching I found a thread where somebody mentioned that they think, maybe, the newer spider has a lower pressure requirement. Hardly a definitive answer though, and really, how do you define "lower"? From what I've read, they all require at least 50 psi, and generally 52-54 is where it should be. So if one is 52, and one is maybe 55, no big deal, right?

My local O'Reilly's had a regulator that was listed for '99-00 C2500 trucks with the 5.7, and they list the '00 as having the MPFI spider. Borg Warner, 50 bucks, lifetime warranty. Hopefully this will do it.

 

[shamrock246]

i'm curious to because the pressure rating on the regulator on upgraded spider is lower than the pressure spec in the book (61psi vs spec 60-66psi KOEO). During the 2 second prime i get 60psi and when the pump shuts off it stays at 58psi at idle its 52psi and takes about 6 hours before i start to loose any pressure. I wish there was a adjustable unit that went in the place of the original one.

 

[mudpie]

Ok, this thing is stressing my last nerve now.

I've got plenty of fuel pressure, all day long. Crank and crank and crank and nothing. Checked and rechecked all the plugs I had to pull to get the upper intake off. Check all the grounds, multiple times. I thought I had it figured out when I realized I had missed the two wires on the back of the right side head, by the transmission dipstick tube. Cleaned them and bolted them down and nothing. Checked the order of the plug wires, multiple times. Pulled a spark plug and it was wet with fuel. I cleaned it and checked for spark and it appeared to be good.

I scanned for codes and got a PO122. Replaced the TPS, because I figured that had to be it. It wasn't, and I've got 5v going to the sensor.

So now I don't know if I ever really had a fuel problem in the first place, or just got locked on to that because that's the direction the faulty gauge pointed me. Or maybe I did, and I've screwed up something else in the process of taking everything apart.

It's pumping out a foul smell from the exhaust that is obviously unburned fuel. About all I can think of now is an ignition module. I suppose it would make sense, given that it just all of a sudden wouldn't start, but I'm just guessing at this point.

 

[shamrock246]

Do you have a nice blue spark or orange on the spark tester, Put #1 cyl on compression stroke and verify that it's pointing to the #8 pointer in the distributor. I had a Toyota Camry that had an orange spark on the tester but the engine wouldn't fire got a new coil had blue spark engine fired right up. The crank sensors on these engine were know to have different kinds of issues with starting and running there is a TSB on it.

 

[east302]

I scanned for codes and got a PO122. Replaced the TPS, because I figured that had to be it. It wasn't, and I've got 5v going to the sensor.

Here are the diagnostics for P0122...

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