[D.Snutz]

I'm in the middle of an LT1 rebuild and install, but I want the 4.3 running well when I sell it.

It's a 1996 Vin X 4.3L (the non-Vortec), with an RPO code LF6. When the truck sits overnight, it is very difficult to start. With a good starting circuit and multiple crank overs, the engine won't start until I crank it 6-8 times. Once the engine has run for 30 seconds or more, I can shut it down and refire it without a problem.

Since it's only a problem with a cold motor, I don't think it's the fuel pump.

I've replaced the fuel filter, and have just finished cleaning out the EGR and replacing both the ECT and CTS (both of the coolant temp sensors; one is on the drivers side near the exhaust manifold and the other is on the front of the motor by the EGR; one is grounded through the block, the other has a 2 terminal connector).

I've got a replacement fuel pressure regulator, but don't want to tear the entire top off the engine unless I have to.

So, any thoughts? Do I go with the FPR, or should I look elsewhere first?

Thanks in advance.

 

[s10xtremist]

The FPR could be leaking over the course of a couple hours (over night) and flooding the intake. This usually just causes a bit of a rough start. I don't think this is your problem, though. The fuel pump itself seems to be fine, like you said, but it still may have a problem. The fuel pump has a built-in valve that keeps the fuel system primed with pressure, and it has probably failed. As the truck sits, the fuel system leaks it's pressurized fuel back in to the tank. When you crank the engine, it's like you have just replaced the fuel filter or pump and it has to build up fuel pressure in the system before it can squeeze it through the injectors. After the truck has sat for a few hours or over night, turn the key to "ON" (not all the way to start) for about 3 seconds, then turn it all the way "OFF" (as you would if you wanted to remove the key). Repeat this once or twice more. Then, turn the key as you normally would to start the engine. If it starts much quicker, then you need to change your fuel pump because this valve is built in and not serviceable. Or, you could just do the "key on/key off" trick every time you go to start the truck. Sometimes, it may stumble a bit when the engine fires up. On a side note, my '02 has been doing this for about 3 years now. I usually just do the key on/key off trick once and it starts. It's a pain to drop the tank since it's lowered so much, and I only drive it on the weekends, so I'm not in a rush to fix it right now.

 

[Bill Wheats]

Before replacing the FPR, make sure that the fuel pump primer relay is working propperly. When you turn the key to run the primer relay needs to kick on for at least 3 full seconds. A lot of the relays will get sticky and take a second or so to kick on.
There is a fuel pump test lead on the pass side fire wall. You can connect a test light to it. The test lead will have +12v when the pump has + 12v. If you apply + 12volts to that wire the pump will run.

If the relay works well and the ground on the pump is good then testing the fuel preassure and bleed down time, then replacing the FPR is the next simple step.

 

[lesterl]

95 was the last year for the TBI and the CPI, the 96 should have Vortec heads. I would suspect the priming relay first, it can be swapped with a different relay....

 

[D.Snutz]

Sorry, I should have included that. Fuel pump prime works great, spins for 2-3 seconds when I turn the key on. If I turn it off and then back on immediately, I don't get any priming, but if I leave the key off for 5-10 seconds, it'll prime again. This SOMETIMES, MARGINALLY helps, but not a significant amount recently. And it seems to be worse than it was last summer.

Lesterl, I definitely don't have the Vortec heads; I'm pretty sure I've got the CSEFI setup. It seems to be somewhat rare. Third one down, and of course, the one without the picture:
http://forums.s-series.org/viewtopic.php?f=13&t=12717

So...how do I decide whether it's the leak-by valve in the fuel pump or the FPR?

 

[lesterl]

Sorry, I should have included that. Fuel pump prime works great, spins for 2-3 seconds when I turn the key on. If I turn it off and then back on immediately, I don't get any priming, but if I leave the key off for 5-10 seconds, it'll prime again. This SOMETIMES, MARGINALLY helps, but not a significant amount recently. And it seems to be worse than it was last summer.

Lesterl, I definitely don't have the Vortec heads; I'm pretty sure I've got the CSEFI setup. It seems to be somewhat rare. Third one down, and of course, the one without the picture:
http://forums.s-series.org/viewtopic.php?f=13&t=12717

So...how do I decide whether it's the leak-by valve in the fuel pump or the FPR?

1996-2003 was CSFI IIRC. They do use the higher flowing Vortec heads CSFI was all that was available durring the years listed, after 2003 they went to MPFI. There is a kit available for the 1996-2003 to convert to the MPFI.

The delay in priming is programmed in, you need to cycle the power several times, might try to start it with another vehicle hooked up as jump start of your vehicle to boost the battery voltage to 14.4Vdc which will spin the pump faster and thus increase pressure, if it starts better, you can then suspect the pump, might throw a fuel pressure guage on it to see what it is at and if it bleeds off.

 

[Bill Wheats]

Then I say; replace the FPR.

 

[D.Snutz]

1996-2003 was CSFI IIRC. They do use the higher flowing Vortec heads CSFI was all that was available durring the years listed, after 2003 they went to MPFI. There is a kit available for the 1996-2003 to convert to the MPFI.

The delay in priming is programmed in, you need to cycle the power several times, might try to start it with another vehicle hooked up as jump start of your vehicle to boost the battery voltage to 14.4Vdc which will spin the pump faster and thus increase pressure, if it starts better, you can then suspect the pump, might throw a fuel pressure guage on it to see what it is at and if it bleeds off.

Lesterl, thanks for the head lesson. No wait, that didn't come out right...

Anyway, I've never quite figured out this VIN X, it seems to be a bit of a bastard configuration. So the VORTEC heads were available and worked with the TBI-appearing intake manifold? I don't have the LT1-imitation crossover intake runner upper intake, just a top mounted TB.

I guess it's not really that important; the FPR is still inside the upper intake assembly. I'm pretty sure it's not the fuel pump, since I don't get any lean running issues, even at high RPM.

Even with priming four or five times, the vehicle is still hard to start. I suppose it's still possible for it to be the supply line check valve in the fuel pump assembly. Do you know of a check valve I could install, say, near the fuel filter at the frame rail that would do the same thing and would be easier to deal with than dropping the tank?

I'm really leaning toward the FPR, I'm just whining about having to pull the manifold off. Cleaning and gaskets and all the sensors and blargh. :rant::rant: I've considered buying a fuel pressure gauge (auto parts store doesn't rent them here), but if it leaks down, that still won't indicate whether it's the fuel pump check valve or the FPR (down through the supply line, or down through the FI return line...does it matter?).

Then again, I'll probably have to go to a higher flow pump when I get the LT1 in, so maybe I should start there? But that's a REAL pain to do.

 

[s10xtremist]

...Do you know of a check valve I could install, say, near the fuel filter at the frame rail that would do the same thing and would be easier to deal with than dropping the tank?

Hmmm. I never thought about that. I'm now wondering the same.

I'm really leaning toward the FPR, I'm just whining about having to pull the manifold off. Cleaning and gaskets and all the sensors and blargh. :rant::rant: I've considered buying a fuel pressure gauge (auto parts store doesn't rent them here), but if it leaks down, that still won't indicate whether it's the fuel pump check valve or the FPR (down through the supply line, or down through the FI return line...does it matter?).

Then again, I'll probably have to go to a higher flow pump when I get the LT1 in, so maybe I should start there? But that's a REAL pain to do.

Opening up the intake manifold is a pain, but I'd say dropping the tank is a bit less of a pain. At least, it is for me since I've done it 3 times on my lowered Xtreme. If you don't have a sprayed-in liner, remove the bed bolts and slide the bed back to get to the top of the tank.

 

[D.Snutz]

xtremist, I started on pulling the intake manifold. Not because I don't value your input or opinion, but because I'm a stubborn fool.

Turns out it cannot be done without a 10mm deepwell. I picked one up last night. I hope to finish it up this weekend, but we'll see. I'll be sure to post up what I find out, along with pictures.

Holy crap, I hope I can figure out where all those electrical connectors go. Two to the alternator, two to the IAC & TPS, the fuel meter body of course, the two throttle/cruise cables, EGR, EVAP... I guess I'm stubborn and also too impatient to label stuff like I should have. DOH!

 

[lesterl]

I guess you could have pulled the 3 bolts holding on the Throttle body and looked down inside.

 

[s10xtremist]

xtremist, I started on pulling the intake manifold. Not because I don't value your input or opinion, but because I'm a stubborn fool.

Hey man, you're not gonna offend me. I'm just sharing my experiences with similar symptoms in hopes that it'll help you get this problem whupped. (Yes, I meant to say "whupped"!)

...I'll be sure to post up what I find out, along with pictures.

Do that. I, for one, am definitely interested.

 

[D.Snutz]

PIDDERS!!!

Those are all taken from my LT1 rebuild blog; some unrelated pics are also up there on the LT1, the Bourbon resurrection, and the Sopping Stratus.

I'll get back to this next week. Tonight is the Nutcracker with the girl, and I've got a reserve weekend Sat & Sun. I did pick up the deepwell, so that's a small step.

 

[Bill Wheats]

The FPR is in the top of the TBI, and only takes a few minutes to replace. I think it runs about $18 - $25 with all the gaskets.

 

[s10xtremist]

...Tonight is the Nutcracker with the girl...

Damn, let's keep your freak sex life out of this and stay on subject!

 

[lesterl]

Coil looks aftermarket as well....

 

[D.Snutz]

xtremist-- SHADDUP...dat's nunya foo!

Lester: Right on; ACCEL tune up kit. First thing that went on, right after the exhaust came off.

SOOOOoooo....I got the new FPR in there. Pictures below. When I reinstalled the Upper Intake Manifold (UIM?), I ripped up the seal around the fuel meter body. She fired up, but it took a good ten or fifteen cranks. No improvement, and now the idle was HORRIBLE...hunting up and all most all the way down to a stall, followed by a huge gasp, and then it'd fire back up. So I knew something was wrong.

So tonight, I ripped it ALL back off again, and there was a bunch of seal PIECES lying in the intake runners. Crap. I fished everything out, but it didn't make a full oval. I'm hoping everything else either flies through or is chopped up...I was only missing about 1/8" of seal. I HOPE???

Ran to O'Reilley's, got a FelPro kit. Yes, it was thirty bucks vice the 10 I probably could have spent, but I got a TB gasket and a UIM gasket and tossed those in as well. Got it all put back together.

I only primed it twice, and it tried to turn over on the first turn. It didn't quite make until the fourth crank, but it fired right up and idled smoothly! Granted, I had run it for a minute or so earlier in the evening, but I'd also relieved the fuel pressure from pulling the fuel lines. So, I'm not 100% sure, but I feel a LOT better about it than I have in a couple months! We'll see tomorrow. Keep you guys updated!

Nom nom nom....rebuild fuel:

 

[s10xtremist]

Congrats (I think/hope)!

 

[D.Snutz]

Congrats (I think/hope)!

Fired her up yesterday, and it was still a bit difficult of a start. Four or five cranks. ALTHOUGH, I still hadn't run it any distance, just idled in the garage. I got her out and drove her for about half an hour yesterday (and found the radiator fan electrical problem, FINALLY--stupid installer didn't know what the hell they were...crap, that's me). Sat for three hours, and fired right up to move it back into the garage. It's been sitting overnight; I'll try it this evening when I get home.

After the (lesser) trouble starting yesterday, I may have to listen to your voices of reason and pull the pump.

Is there a wahlbro or other aftermarket option for an S10? Summit just has OEM replacements. I think I'll eventually need more flow for the LT1 if I decide to put in a blower or nitrous. Any suggestions if I go that route? How much flow? 55gph or more?

 

[s10xtremist]

I had a Walbro 255 in mine for a little while. It's slightly larger in diameter than the stock pump, so it's a really tight squeeze to fit it into the rubber isolators. Other than that, it's a direct plug-and-play swap. Also, if the one you get is in a kit that comes with it's own piece of "EFI" rated fuel line, don't use it. Reattach your stock "umbilical cord" fuel hose. I installed my Walbro and it worked great until that "EFI" rated hose that came with it in the kit deteriorated inside my gas tank and clogged up my filter and pump. I don't have any model numbers, but a quick search here or on Google should find you something, as this is a common swap.