5.7 vortec sluggish, loss power. need help w/ diagnosis....

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88chevota

88chevota

10 Year 15 Year
Joined
Jun 5, 2006
Threads
146
Messages
1,646
Location
Colorado Springs, CO
Hey so I need some help on diagnosing this thing. The guys here seem to be the most knowledgeable about most things so I thought I'd bounce it off you guys.

I ran out of gas last week.:bang:
Put gas in ran fine for about 3-4days then just started getting sluggish, loss power, some backfiring when you try to jump on it. so I started with the simple and cheap tricks.

1. ran about 1/4 tank through with injector cleaner.
2. replaced fuel filter
3. tested fuel pressure - steady at 55 at idle, goes up a little with initial pedal, steady then at 55 again, drops with release of pedal, then steady at 55 again. never drops below 50
4. I have tried 1/2 can seafoam and let it set for about 20 minutes. started it up and idled it up to around 2500 to blow it out. still runs like crap.
5. trying seafoam again and I am letting it set overnight now.

My codes are:
P0300 misfire
P0174 lean fuel
then a bunch of other non coed stuff that also makes sense since it is running rough.


but any help would be great.

thanks!
 
Last edited:
Your fuel pump is gone. If you let those high pressure fuel pumps run out of gas, the pump runs dry and burns up the vanes. You will be able to idle, but getting off from stop signs, and loading the engine will show lean and backfire.
 
Just saw Luke's post. Hopefully it's an externally mounted pump and you can swap one out to check easily. I've checked injector function with a 9 volt to make sure they are opening. Maybe check distributer for crack and moisture.
 
So should my PSI reading be above 60 then? It idles a little rough too. definitely worse as it gets under load though.

If I put in an external pump can I leave the old one in the tank? shouldn't the external just pull the fuel right through the old one? I did that in my Landcruiser when I put my tbi350 in. I know it is different pressure though.
 
What about the fuel pressure regulater and the fuel injectors? I am tempted to go to the pull yard and get a TBI system and drop it on. so much less trouble.
 
Don't do that. I run TBI on my vortec v6 and it's pretty inconsistent. The computer doesn't know what to do with all the air that flows through a vortec cylinder head and intake. I have yet to get mine tuned because I'm cheap and lazy.

My suggestion: go to vatozone and rent the fuel pressure tester. doesn't cost you a thing unless you don't bring it back. I bet when you load up the engine, you'll see that pressure drop to almost nothing. I would replace the in tank pump, it's really not that hard unless you just filled up. If it's a truck, it's supposedly easier to take the bed off.
 
in Tank pumps are the best! They run Cooler, quieter, and last longer than an external pump.

if you can somehow hook up a Fuel Pressure guage so that it can be read while driving.. then i bet you will see it dipping below 50 on hard accelleration.

Im Happy to Swap you motors if you wish! ;)
 
I have a fuel pressure gauge you can borrow, with a long hose so you can monitor while driving. Not sure of the fitting size. I like external fuel pumps, easier to replace, I don't buy that they don't last as long as an internal so long as it is sized properly nor do I think they are categorically quieter. Based on my limited experience. I wouldn't put an external in front of a bad in tank pump, if that's what your problem is.

It just hit me, I had a similar problem years ago and mine was an old clogged in tank fuel screen. I'd still check the distributer.
 
Pretty sure my '97 p/u did.
 
black95 said:
Don't do that. I run TBI on my vortec v6 and it's pretty inconsistent. The computer doesn't know what to do with all the air that flows through a vortec cylinder head and intake. I have yet to get mine tuned because I'm cheap and lazy.

My suggestion: go to vatozone and rent the fuel pressure tester. doesn't cost you a thing unless you don't bring it back. I bet when you load up the engine, you'll see that pressure drop to almost nothing. I would replace the in tank pump, it's really not that hard unless you just filled up. If it's a truck, it's supposedly easier to take the bed off.
Click to expand...

Already went to vatozone. also put it under load and the pressure stayed above 50psi. but never went about 60. I just started it and moved it out of the way for the night. smelled of gasoline bad.

Isotel said:
in Tank pumps are the best! They run Cooler, quieter, and last longer than an external pump.

if you can somehow hook up a Fuel Pressure guage so that it can be read while driving.. then i bet you will see it dipping below 50 on hard accelleration.

Im Happy to Swap you motors if you wish! ;)
Click to expand...

I have had an external on my cruiser for 8+ years with no problems.

I'll try hooking it up again and putz around my neighborhood. I have enough hills to get it to load down.

I bet you would love to trade. ;p
 
ok so I changed the cap, rotor, plugs, and wires. Bingo! fixed. runs like a champ and the codes are all gone!
 
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