'99 Vortec power loss and CSFI questions

[Lawnman23]

I replaced the pump yesterday with GM Genuine, complete with their fancy blue GM tape -- I almost feel like I'm breaking the law opening the box!

Anyway, not much useful info because I didn't have time to dead head the new pump.

The existing pump was a Carter, so yeah, it's been done before. But judging by the amount of rusty dirt on top of the tank, it's been a long time.

I know it's not an accurate indicator of pump health, but when the pump primes it's virtually silent. The old Carter had a distinct whine. On initial start I thought I had somehow screwed up wiring the provided 4-flat replacement electrical connector, but no -- it's just really quiet

You had to attach that 4 wire plug that came with the new pump? If the old pump didn't already have that installed then its very old. GM updated the electrical connector design with that new plug due to the old design not being insulated enough and burning out/shorting the connections.

Also, I would advise you strongly remind the owner that its VERY important to not let the tank get below 25% before filling up. These pumps do not like heat at all and waiting for the gas needle to drop down to the red zone before filling up will prematurely wear out the pump due to it not being cooled properly with the surrounding gas. People forget that in-tank fuel pumps are "liquid cooled" by the gas and when that's not there, they heat up.

And yeah, the signature whine of the pump lets me know its working Apparently they have gotten much quieter over the years. Glad to hear you were able to get it done

 

[D60]

You had to attach that 4 wire plug that came with the new pump? If the old pump didn't already have that installed then its very old. GM updated the electrical connector design with that new plug due to the old design not being insulated enough and burning out/shorting the connections.

Also, I would advise you strongly remind the owner that its VERY important to not let the tank get below 25% before filling up. These pumps do not like heat at all and waiting for the gas needle to drop down to the red zone before filling up will prematurely wear out the pump due to it not being cooled properly with the surrounding gas. People forget that in-tank fuel pumps are "liquid cooled" by the gas and when that's not there, they heat up.

And yeah, the signature whine of the pump lets me know its working Apparently they have gotten much quieter over the years. Glad to hear you were able to get it done

Yeah his fuel gauge doesn't seem to work. It seemed more "stable" after pump replacement but since it was completely unpredictable before, I may have just caught it during a brief period of stability.

It read E but there was very little fuel in the tank (I got lucky there).

When you turn the key the fuel gauge does an Exorcist type thing of twitching and going upside down briefly -- were the 400's also plagued with stepper motor problems?

And yeah, it had the old 4-square connector. I had to wire on the 4-flat. I found the correct combo in the instructions (it was scenario #2) and wired accordingly.

 

[Lawnman23]

Yeah his fuel gauge doesn't seem to work. It seemed more "stable" after pump replacement but since it was completely unpredictable before, I may have just caught it during a brief period of stability.

It read E but there was very little fuel in the tank (I got lucky there).

When you turn the key the fuel gauge does an Exorcist type thing of twitching and going upside down briefly -- were the 400's also plagued with stepper motor problems?

And yeah, it had the old 4-square connector. I had to wire on the 4-flat. I found the correct combo in the instructions (it was scenario #2) and wired accordingly.

Yeah, the fuel gauge most commonly(although the other three can do it as well) gets the shakes. Mine flutters like a hummingbird wing constantly and has worked fine for 15+ years. Some guys replace them as they don't like the flutter. Since the fuel level sender is now new, if it doesn't accurately show level (after a fill up) its either the fuel gauge in the cluster that's totally shot or its wiring from back to front.

Yep, the square plug is the old style so we are talking ~20 years old. Had a good run. When I replaced my pump the first time(2006-ish?), both styles were still offered. I went with the square plug as that's what the truck had and though all would be well. That Napa pump lasted ~3 years and was toast. When I replaced that one, I went with a genuine GM unit that had the new flat connector. That's still working in the truck to this day, ~15 years later.

My dad and I had to drop the tank in the driveway for the first one. Tank was mostly full. We ended up using his tranny jack to lower it down. PITA of a afternoon that was.

 

[D60]

Also, I didn't mean for this to turn into tech on GMT400 SUV fuel pump R&R, but I had the opportunity to use some tools that really helped.

First, I've come to despise the emissions lines with the opposing "windows", but the uber-cheap ebay special red-handled pliers really helped there.

The way the Carter pump was designed I had to use my low profile fuel line disconnect (upper right). I saw one vid where he used the standard, deeper aluminum disco but there was NO way that was fitting here.

Finally, for the first time ever I used the disconnect pliers. They hook over the bell end of the fuel line and behind your disco, then squeeze to force it in further to disengage all the teeth. This was a game changer because I just couldn't force it in by hand enough, even after lubing and cleaning with compressed air.

I actually wanted the disconnect pliers to close up a touch more so I've ordered a second import set to cut and weld to adjust the jaw spacing.

 

[wtd]

Marginal at best, I like to see 95-100 PSI.

87A is for the "Fuel Pump Prime Connector", You've probably seen a taped down red wire & a Packard 56 series female spade connector near the fuse box....Which is likely the only Packard 56 series connector used on a late GMT400's.

Used to prime the fuel system or drain the tank with a fused jumper.

I have owned my 98 K1500 Chevy truck since it was new and have never noticed the fuel pump prime connector. I'm now going to have to go look for it. My 92 Cavaliers have this connector near the strut tower on the driver's side.

 

[D60]

Edelmann 24003 16mm O-ring Fitting, Remove the front/forward line off the fuel filter, Screw in the 24003 with some 300 psi fuel injection hose adapted to your FP gauge, Bleed the air out by pulsing the FP Relay a couple times while depressing the bleed , Run the pump @ 10 seconds.

My Cornwell master FP set has 16mm adapters.

Top Engine Cleaner is "HOT" & will destroy a fuel pump, I use a regulated air powered pressure vessel, Before coming across the Snap-on one I have now, HERE. I had a modified paint pressure pot.

I modified a factory L31 intake fuel pipe assembly, I'll snap some pic's tomorrow.

Thanks for the tip on the Edelmann fitting. I think this issue is closed for me on this vehicle and I had other ways to adapt 16mm, but I decided to grab the Edelmann piece just to have in my arsenal. Cost me $13 on ebay and will be worth 100x that if I ever need it on a Saturday night.....

 

[FTTSHO]

Fellow Vortec owner here. I own the 3/4 Vortec, the 4.3!

If the truck still have the original spider poppet style CSFI, it should get the spider MPFI with individual injectors. It’s a direct install, zero modifications needed.

Did the MPFI swap to my 4.3 Vortec about a year ago, and she runs smoother and overall better than it did with the poppet spider system.

at each oil change, run some Techron fuel system cleaner through the tank at 1/4 tank every time, and drive it until it really needs to be filled up. Those poppets love to stick and cause lots of weird issues. The MPFI ones do not really have this issue, at least nowhere near as frequent as the poppets.

Also, do a very thorough intake system cleaning. Clean the IAC, throttle body and maybe the EGR if your truck has one.

These older GM’s are known to not tell everything even though it’s OBD2, until you get stranded on the side of the road lol. Ask me how I know!

But to me, it seems like a fuel system issue, definitely a pump that’s getting tired. It sounds like it’s getting weak, and it’s getting hot, so when you pull over and let it cool off for a couple minutes, it starts working again.