Well, lesson number one. If you need to change your fuel pump, buy a genuine GM pump. The aftermarket one lasted me a whopping 5 months. I just got done dropping the tank for the second time that I've owned this truck (grr..........) to change the pump. This time I put in a genuine GM pump. Pressure went back up to where I had read it before (14 psi) and the truck started up. The old one is now sitting in the truck, so that I can drive to the auto parts store to return it.

However, it appears my pressure regulator isn't regulating correctly. When I increase throttle (i.e. fuel going to the engine) the fuel pressure drops slowly and linearly with the amount of fuel I'm requesting. If I jab the throttle, it drops a good sum. I am fairly certain this is NOT how my truck is supposed to operate, so would it seem a fairly safe bet that something is screwed up with my pressure regulator? Possibly, I screwed something up with my pressure regulator when I installed it? I never tried moving the throttle the first time I checked it right after the TBI rebuild. So, it seems possible to me that this problem has always been present.

It seems to me that the next thing I have to do is try bumping up the pressure on the regulator, confirm that it corresponds with an increase in pressure, and see how that works. The spring was not broken and didn't seem to be having problems.

Ideas, anyone? :(

UM, isn't the 454 normal fuel pressure is 26-32psi?????

You need to go way up, OR they gave you the wrong pump that can't go that high.

They gave me the right pump, I worked with them to make sure it was correct, and my online GM parts sources confirm.

This has been an issue for me since I started checking the fuel pressure. I stated the first time I checked the fuel pressure that I was having a severe "WTF?!" moment. I think I'll try jacking up the fuel pressure as high as I can, see what it goes to and how the truck runs.

I still say you have the 350 TBI pump, it runs on 9 psi, you need 30 psi for the 454.

That's probably why the first pump burned up so quickly, trying to feed that beast.

The first pump I got was from Advance. Upon looking into it, they supply the same pump for all TBIs. So, I am certain this is why the first one died. This second one I actually got from the dealership, and they had to order it.

The part number is EP377. I cross referenced this back and confirmed that this is the correct pump for my truck, and it is for the 454 and not the 350. So, unless they actually put the wrong pump in the box, it is the correct pump. My pump WAS dead. But there definitely also appears to be a problem with my pressure regulator.

Tomorrow or Saturday (depending on when I have time) I am going to rip into the TBI unit itself some more, and see if I can find the cause. I wonder if maybe there is some debris stuck in the pressure regulator causing it to stay at a constant open? I will investigate further tomorrow.

When did you last change your fuel filter? ARe you sure all of your lines are straight and not kinked after the TBI rebuild? Your describing a fuel supply problem more so than a fuel pressure problem. What is your fuel pressure with the key on engine off?

ON EDIT: Your 95 454 should have 28-30 PSI of fuel pressure, 14 is for the small blocks and 93- 454's. Try pinching the fuel return line for a moment to see what your fuel pressure does. You can pinch the line with a pair of needle nose pliers at the drivers side rear of the engine over the bellhousing where it turns to rubber line. If pressure shoots way up, you probably have a ruptured diaphram in the regulator.

Ted, I'm not trying to be a PITA, I'm just trying to help, really.

But I just looked at the Autozone website and they list different numbers for the 454 and 350, 95 2500 suburbans.

E3212 454 pump
E3902 350 pump
E3567 350 pump (old number, while stock lasts)

And Advanced offers two as well.

E3902 350
E3212 454

Ted, I'm not trying to be a PITA, I'm just trying to help, really.

I know, I'm sorry if I came off sounding agitated. :)

But I just looked at the Autozone website and they list different numbers for the 454 and 350, 95 2500 suburbans.

E3212 454 pump
E3902 350 pump
E3567 350 pump (old number, while stock lasts)

And Advanced offers two as well.

E3902 350
E3212 454

Hmm. Well, either way now I have a GM pump which is showing to be better than whatever was in there. If nothing else, the truck actually now runs and drives.

Fermanator, with the key off my fuel pressure is 14 psi. I will try pinching the return hose tomorrow and see what that does for the pressure and report back. That will definitely help me tell if the problem exists within the regulator or where exactly. I changed the fuel filter last week (first thing I did when this problem arose), but before that I had changed it about 9,000 miles ago, so definitely within reasonable time.

More news tomorrow...

You didn't at all, I just wanted to make sure I wasn't trying to be one. :D

Good luck, I'm watching with interest.

I know it's probably not the solution you're after, but a mallory 3 port regultor on the return side of the TBI with a nice gauge is how I set my old suburban up. It costs less than a $100 and makes tinkering with fuel pressure a sinch.

It sounds like you have a few other gremlins worth tracking down first, but it's worth a mention.

Nick

I drove the truck to work. I am now confident that I had something in addition to the fuel pump occur, because past a ceratin throttle point (where the fuel pressure decreases too much) there's no more power. This does seem indicative of a supply issue.

Maybe the first thing for me to do would be to pull off the fuel line between the fuel filter and the TBI, and inspect that for kinks. Seems likely since I was fiddling around there with the pressure fitting and such. If it is kinked, I can fix that pretty easily. I need to go by the auto parts store anyway to get my refund on my fuel pump, so I should come up with a list of stuff to spend my refund on. :)

Nick, do you have a part number or source on that regulator? I would definitely be interested in doing that if I have regulator issues.

Ok, so now my truck fixed itself. On the way home it made good power and now it's holding at a steady 16 psi. Obviously it's still too low, but it's back to where it was before this problem started. My guess is there was some debris stuck in the regulator that finally got dislodged.

Nick, if you have a source for that pressure regulator I would greatly appreciate it. I would go right ahead and buy it so I could tinker with this. :)

www.summitracing.com

Hate to say it but IIRC the EP377 is a small block pump.... then again I could be wrong.

Some of the TBI big blocks have a "hot soak" pump relay... it keeps the pump running for a minute or two after shut off, they can mess with the pump fer sure.

I've been searching aroundfor a good fuel pressure regulator that I can bolt on back of the TBI and am not having any luck. There's certainly nothing that says it's specific for the TBI, and for prices under $100 the only regulators I'm finding having a minimum setting of 30 psi. Really, I want a regulator that will do 20-40 psi for this. I found a Trick Flow that would do the trick, but that's over $100 and I don't want to spend that much.

I suppose my other option here is to pull the TBI off, drill a hole in the bottom, and then put a screwdriver in and try to adjust the standard pressure regulator and see how high I can get it, but really I should pull the top off. It seems that I will probably break that gasket even though it's new. Maybe I just should order a couple of those gaskets so I can try this by trial and error until I get it right?

When you pulled the pump, how did the line in the tank look? Did it look really rusty/coroded. I have heard (never experienced) those lines corroding through with very tiny, basically microscopic holes. Enough of a hole that would allow air to be sucked into the supply or to leak out depending on where the pump is.

I am happy with my setup as it is, but an adjustable regulator that sits next to the TBI setup that would be easy to adjust sure does sound nice. Especially for under 100 bucks. Mine is by no means easy to adjust and the guage is hard to read when it is facing the firewall.

How are all of your grounds? I don't know a whole lot about electric fuel pumps, but I would assume that they have a positve and a negative feed. It's a DC current afterall! Is it possible that the pump isn't getting the right voltage? When you require more power and the pump works harder and requires more current draw, it just can't do it? Perhaps why it fixed itself for you. It got a little better connection?

Hell, I don't know! Does that help? :D

Del

I wonder if that regulator was the Mallory 4305M? If you google that one you will find out some more info on it.

Well, I don't believe the problem is that the voltage is too low going to the pump. That may have been part of my problem, but this fuel pressure is now rock solid. I think that most likely either there's something wrong with the pressure regulator and it's staying low, or it was set low by someone who thought "WTF?! It's a TBI! It's not supposed to run at this high of pressure!"

Either way, having an external regulator would be nice. That Mallory unit says it's supposed to do 30-100 psi, but my experience with most adjustable regulators is that I can get them to go down pretty low. So, that might be the ticket for me.

i have had nothing but problems with am pumps i always use oem no matter what make im working on jusy my.02

Ted, that very well could be. I talked with a friend that's a GM master tech and he thought they all ran the same psi...

Years ago it was the hot tip to use a 7.4 TBI on a 350, could it be that a PO swapped it out before they sold it?

Nope, it's a 7.4 TBI. It's got the 50mm bores instead of the 46mm. Measured and double-checked when I had thought I'd ordered a 7.4 TBI rebuild but they actually sent me a 350 TBI rebuild saying "Well it was all we had." :)

The older 454 TBI's did run 12 psi. So maybe they put on an older throttle body. I went through this with a boat engine I worked on. All of the marine TBI systems use the larger 454 throttle body(the one without the venturi lip above the butterfly's), but up until 93 they were 12 psi systems with 95 lb/hr injectors @ 12 psi. In 94 on the light duty engines they went to injectors that flowed 45 lb/hr @ 12 psi, but they flowed 105 lb/hr @ 26 psi. This is when the transition was supposed to have taken place.

Right, this is what I understood to be the case. But the more I look at this the more I have reason to believe it's not getting proper fueling. If nothing else, when it was running at 9 psi it was barely running at all. I have observed that, with no changes besides fuel pressure, there is a remarkable range that an engine will tolerate running, both hgih and low. So, I'm pretty sure it's a 26 psi system, it is just set improperly for whatever reason.

You need to measure the spring inside the fuel pressure regulator. I measured the one I have for the 30 psi system and it measures just shy of 2 inches tall, and .920" in diameter. This is the measurement for a 98 regulator spring which is the same as the 94+(GM continued to use the TBI for off-highway use until around 2001).

Yep, that's about what mine was. I will double check if I disassemble the system again.