Long starts, fuel odor, poor mileage

[FknMaxum]

Good afternoon fellas, new here but not to these trucks. I’m looking for input on my 1997 k2500 suburban 7.4l Got it couple years ago from original owner which is a helicopter pilot & sells helicopter parts worldwide. Included that so if you know conditions of my truck. Helicopter pilots are notoriously **** & meticulous about their vehicles. With just over 100k miles on it it’s been running amazing mileage was what it was as I got it to tow my boat and it does not hesitate to haul anything.
Recently it started taking forever to start and when it did start it would idle rough and stumble for a minute then she’d be alright. Now it almost drains th battery cranking over. Changed the plugs oil , filters and battery last weekend. Still cranks Long n finally fires up almost draining the battery. And while driving I smell fuel yet haven’t found any leaks and my mileage seems to get worse. I checked the fuel pump which I found is bad due to 45 psi at first then leak down to 0 in a minute after off.
I plan on changing the fuel pump this weekend and wondering what else need to go. It being Christmas and 3 kids birthdays on and around christmas leaves me on a buget for now eventually ill change everything but as for now im looking for opinions.
Im thinking the lack of pressure is what keeping it from starting and rough idle or if the pump is good but leaking unable to build up pressure,,, still cant seem to find where the smell is coming from but at times its strong as if i spilled gas inside the cab. i have a scanner that is capable of live data and tests of different kinds just not sure what to look for any help would be very usefull. ive been turning wrenches since a kid so i know my way around the truck just not the computer parts. thank you

 

[someotherguy]

Welcome,

That strong fuel smell would have me concerned you might actually have a leak somewhere.

The 45psi reading is a bit low so yes, the pump is suspect, but it's also very common on higher mileage Vortec 7.4's for the fuel pressure regulator to be bad.

Another sore spot on these engines are the original Multec injectors which aren't the greatest and will tend to leak. Swapping these out for something else has been discussed a lot here; check out the Vortec 7.4 info thread in the subforum at the top of this one.

Here's a direct link to the thread, but warning, it's grown to a million or so pages at this point.. covering all types of relevant subjects https://www.gmt400.com/threads/the-official-vortec-454-info-thread.50576/

Richard

 

[Keeper]

I'd check again for any fuel leaks between tank and engine with key on engine off

the 7.4 "injectors and a fpr" is almost a scheduled maintenance

edit: what Richard said

 

[movietvet]

What @someotherguy said. Sounds like you shut off the vehicle and the fuel system is not holding pressure and when it does build pressure, is low. May have fuel leak at the injectors and even at top of tank where the seal could be leaking. I suspect the injectors though. I would meticulously have the vehicle running at idle and look with a very bright light from tank to where the lines get to back of engine and then snake up to the fuel injection system and all around the top. Look for any sign of leakage, wet spots. Another sign of leakage is where the lines are and you find a very clean spot because the wet fuel cleans the area. If is all dry, then is likely the injectors or worse case, the top of tank.

 

[RichLo]

x2 to what everyone else said to check first.

But I just bought the injectors linked below for my 97 7.4, but I havent installed them yet, being winter and all. They seem to be the best upgrade for these engines. They will run slightly rich for the first few drives until the LTFT catches up to the slightly higher flow rate. They were flowed 19lb/hr at 3-bar while OEM injectors flowed 19psi at 4-bar.

19lb 5.0 D3 Camaro Firebird 305 TPI SouthBay Fuel Injectors

CONTACT US IF YOU HAVE AN AFTER MARKET INTAKE.19lb Bosch D3 Camaro 5.0/305 TPI Fuel Injectors. The Bosch Design 3 fuel injectors are .125 inch shorter than the stock TPI fuel injectors. To solve all fitment issues we designed an adapter (see video) that

www.southbayfuelinjectors.com

Here is the thread discussing different injector options if you dont want to deal with that slightly different flow rate...

Bosch injectors

I’m having to put a new motor in my 99’ K2500 7.4. Long story short it also needs injectors. I would like to do the 5.0 Bosch upgrades but honestly can’t afford the cost right now. After a full day of cross referencing part numbers in their site and several others I think I have a solution. 50...

www.gmt400.com

 

[FknMaxum]

first Thank you guys for responses. I’ve checked underneath the truck n tank for any sign of leaks . The 7.4 has just over 100k and everything well cared for and original. Every document included also the dealer gift that I’ve never seen before which is a medium size Chevrolet Suburban duffle bag with flashlight first aid kit umbrella and a coffee mug, all stuffed in the spare tire.

 

[FknMaxum]

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[FknMaxum]

Got a question I got injectors, fuel pressure regulator and a pump now when I dropped the tan this is the crap I found some white plumbers putty type stuff all on and around the pump. What and why is this there or reason to put this unless this is factory but I doubt it. Pump I got was just the pump no lines some I’m gonna have to use these well maybe I’ll try n return and het th whole unit f I could. Any thoughts

 

[FknMaxum]

Hello fellas sorry for delay on post , it’s been raining in so cal and we don’t know what to do or how to act when it rains so I’ve been busy anywho. Couple questions I changed the pump , injectors and a fuel pressure regulator. Pressure went up to bout 60 then when k shut the power it drops to zero almost instantly although it did fire right up . I figured as long as she starts and not effecting my I wouldn’t worry about pressure drop. So when I hoped in the truck my check engine light was on. P1345 cam and crank correlation ? I’m thinking I pulled the distributor and marked it. When I went to install it checking my marks afterwards it wasn’t tdc to number 1. I was puzzled and have messed up before so not to take chances i pulled the distributor and put it at tdc no. 1. Now I have the code p1345. Wondering if im supposed to drop in advance or retarded since tdc gives me the code. Also when power off I can hear the fuel regulator make noise as in gas passing through it…is that normal or is that where I would still will be leaking pressure? Thank you

 

[Schurkey]

1. The "plumber's putty" stuff on the fuel tank is just a sealant to prevent moisture from accumulating in the depression of the sending unit and causing rust. Clean it out, replace the fuel pump items, and then either get more plumber's putty, or the wax from a toilet sealing ring, or play-doh, or whatever you feel like using.

2. If the pressure is dropping to zero, and quickly, either your gauge isn't connected properly or there's a major fuel leak--probably past the regulator or the pump, since if it was an injector leaking you'd have starting problems. If you're hearing noise at the regulator...that'd be my first choice.

3. You need a scan tool to set the cam sensor/crank sensor correlation to fix your code. Turning the distributor doesn't change timing, so it's not a matter of advance/retard.