5.7 vortec sluggish, loss power. so far can't figure it out (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

88chevota

88chevota

Joined
Jun 5, 2006
Threads
145
Messages
1,644
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:
Its odd since it happened when you ran out of gas but the lean code a lot of times is a vacuum leak.

Does the engine have the retrofit to mpfi? the original injector design was sort of problematic and the csfi system clogs easily. Running out of fuel could do it. check this out a lot of people have issues with it and swap to mpfi instead of replacing the stock system since its relatively cheap.

CSFI to MPFI - Vortec Engine Fueling Fix - Fuel Injection - Off-Road Magazine
 
Hmm by chance done a fuel volume test? Just because pressure is good does not mean it has good volume. if ya ran out of fuel theres a good chance you smoked the fuel pump. its supposed to be something like 10 ounces of fuel for ten seconds of cranking. that is a pretty universal spec. but see if you can get a spec from an fsm first.
 
just started it up and moved it out of the way tonight and noticed it smelled of gas real bad. GRRRRRRRR. I'll be checking all the plugs and ignition stuff in the next few days.
 
check the fuel pump, that's probably the cause. Our old Silverado would burn up a pump if you got into the final gallon of fuel.
 
Is this a swapped in motor or a factory setup? I thought it was in your FJ62, but your sig says TBI.

There's nine kinds of speculation on the internet about common causes for a 0300 code. Everything from stripped distributors to bad poppet spiders to clogged cats (I didn't say it, the interwebz did).

Misfires mean firing out of time, right? I'd start there. You can't jack with the timing on this motor, so you can only check components. The distributor, the cam sensor, the crank sensor, and the ignition control module all have their hands in it. If you're smelling fuel, you likely have a lack of spark somewhere, and, once again, these components play in that. If you have a tech manual, look for ways to test these pieces and go through them one by one.

The lean code is confusing as hell. Maybe residual from you running the thing out of fuel? You are smelling gas, so it is in abundance. I'd clear the computer and see if that one comes back once you get it running again.

I just went through this with my Vortec swap and troubleshot by throwing parts at it. Don't do what I did, please. My problem turned out to be a bad crank sensor that doesn't throw codes. My symptoms were different than yours. In fact, they are in no way related, but my problem caused me to get VERY intimate with the ignition and fuel systems. This is why I point you in the direction of the components I listed above.

Good luck. I probably won't be of much use, but I'll be glad to help if I can.

EDIT: I never mentioned that I think your problem is coincidental with regard to running out of fuel and that they are unrelated. It sounds like two different issues to my untrained ears, and I would treat them as such until I found a reason to think otherwise.

EDIT 2 D EDIT: Be careful running your rig with this "rich" problem! I made the mistake of continuing to drive mine while I had issues and burned up 2 catalytic converters in the process. A $730 mistake here in good old CA.
 
Jon,

good advice. actually great advice! I don't have $$$ to just throw at this thing. It is a stock set up in a 99 burb. I was going to transplant it but decided to daily drive it. good thing i did cause I can still drive the cruiser.

I am confused as all get out too. I have cleared all codes twice and they still come up the same.

weird.

idles rough, smells of gas, complete loss of power, bogs down under load, backfires, fuel pressure is over 50.... this is so frustrating!
 
Do you have a pressure gauge? If you do, you can buy an adapter that screws into the forward O2 sensor port that allows you to patch the gauge to it via a silicone hose allowing you to check the back pressure in the exhaust between the manifold and cat. If you have greater than about 5 psi (I think that's what my mechanic friend told me), it is an indication of a clogged cat. A clogged cat will cause all of those symptoms if severe enough. I ended up blowing one of mine completely out the tailpipe before I learned about the gauge. It is a cheap thing to check at ~$15 for the adapter. If you don't have a gauge, I'll send you my Craftsman one as they can be a little pricier. I'm not using it right now...

If the cat proves to be clogged, the next thing you'll need to worry about is what caused the problem. Rich running clogs cats! I found out the hard way that unburned fuel gets into the exhaust and ignites causing the cat to melt down into a brick. My crank sensor going ape s*** caused excess fuel to do its damage. If your truck is running rough at idle, I'd pull the distributor and check the teeth to ensure they are not damaged. If the distributor is slipping out of time, it could easily cause your issues. Checking it is monetarily free, although it may be a headache to align it for re-insertion what with where it sits in the engine bay. If there's an o ring on it, it may need replaced. One thing to keep in mind is that the cap has the screws that need replaced since they have the lock-tite stuff on them and tend to work themselves out once they've been re-used. They are a Torx head that can be frustrating if you don't know they're there.

I also assume you have an automatic transmission in the 'burban. Is the air injection working?
 
Last edited:
These are good thoughts Jon. I'll check those things. I still have the fuel pressure gauge. will that work? my brother in law has a compression tester.

I am definitely leaning toward some type of timing issue or the cat.

Since I have excess fuel (hence the smell of gas and the backfiring which indicates gas igniting sometime after the piston chamber) I don't think it is my fuel pump or injectors.

The question is, "What would make my PCM tell the injectors to "spit" fuel early or late causing the misfire?

or if it is a clogged cat is it sending enough back pressure into the engine to mess with the timing???

the first question makes more sense to me. I am just trying to think logically here.
 
You want the compression gauge. You want to check that back pressure at both of the forward O2 ports. You should be able to pick up the O2 bung adapter at a parts store with diagnostic tools, but if you can't, my MAC tool truck had it for $20. While you've got the gauge, check your manifold vacuum at the brake booster hose. If I remember correctly, you'll want vacuum at idle (I can't remember how many inches), and when you step on the gas, you'll want it to temporarily increase to somewhere around 20" before settling back to it's idle level. After settling, you let go of the gas and vacuum should drop and then settle back at its idle level. Clear as mud, right?

I think you are on the right track regarding fuel delivery and timing. Again, I say these things, not claiming to know how to find your problem. I'm simply trying to offer suggestions based on my painful learning experience. I would check the distributor first. It's free and can be the cause of your misfire, which could cause your excess fuel, which could cause your backfire, blah blah blah. The other pieces in the ignition system that the PCM uses to time the engine (ICM, Crank position sensor, Cam position sensor, MAF) are a bit harder to check without GM test tools (they have a computer with connectors for all these things that diagnose their operation). The distributor is made out of plastic and is known to strip its teeth. My GM parts guy always keeps one on the shelf since they are a commonly replaced item on this engine.
 
How difficult would it be to go to the junk yard and find a TBI set up with a PCM, grab a 454 throttle body, a normal distributor, have someone burn a chip for it, get rid of air injection and throw some shorty headers on it and make this thing run awesome with easy maintenance? anyone done this?

The vortec injection system seems to be a pile of crap!
 
:lol:

The engine runs nice when it has all the input it needs. Please realize that I'm saying this to help quell my own urge to yank the irritating Vortec out and put in a diesel of some sort. I need to convince myself...

Anyway, I think you better pull that distributor out and check it tomorrow. Let me know if I can "help" any further. :D
 
I am tempted to try and trade this thing for a diesel tow rig once I fix this.

It ran awesome when it was working! I like engines that are simple. I love my 350 TBI. sooooooo easy to work on.

I'll try and get to the distr tomorrow. I am not driving it now so no big deal at the moment.
 
when it ran out of fuel did you happen to see if the temp gauge went up ? check O2 sensors and the lean condition may have melted the cat as well. If the injectors picked up crap from the fuel the seafoam prolly won't clear it, you should remove and clean them or get reman. ones.
 
changed cap, rotor, plugs, wires. Fixed it! rotor and plugs looked awful. I bought it with 35k on the new motor. I had assumed they had just done a tune up. they definitely had the signs of 40K+ miles on them.
 
That's great news! I'm glad your fix came easy. I will say to pay attention to the power and take a peek at the cats for discoloration. There should be plenty of pics out there to show you what an overheated cat (from running rich due to poor ignition performance) looks like. There could be damage in them that's already done.

Congrats on the ignition repair, and I'm truly happy it worked out for you!
 
Glad you got it fixed. My motor is essentially what you were considering, a Vortec motor, (first generation roller lifter block with Vortec heads) and TBI. I have both a bored 350 throttle body that should flow about 600 CFM and a 454 TB that should flow over 750 CFM. (I'm running the big one at the moment) The cam is a Comp Cams LT1 unit, the chip is custom from Brian at www.tbichips.com The intake is Edelbrock for a carb with an adapter form a 454 TBI engine. Its a very strong engine, lots of poop and super simple, runs better than any stock Vortec I ever drove.
 
lehiguy said:
Glad you got it fixed. My motor is essentially what you were considering, a Vortec motor, (first generation roller lifter block with Vortec heads) and TBI. I have both a bored 350 throttle body that should flow about 600 CFM and a 454 TB that should flow over 750 CFM. (I'm running the big one at the moment) The cam is a Comp Cams LT1 unit, the chip is custom from Brian at www.tbichips.com The intake is Edelbrock for a carb with an adapter form a 454 TBI engine. Its a very strong engine, lots of poop and super simple, runs better than any stock Vortec I ever drove.
Click to expand...

I would really like to know more about this set up. Running this thing on a simpler system sounds like a lot less headache when I am trying to work on it. What computer do you use? I could get rid of all that air injection stuff too and put some shorty headers on it. The drivers side exhaust manifold is starting to leak too. In the six years I have had my shorty headers they have yet to leak.
 
88chevota said:
I would really like to know more about this set up. Running this thing on a simpler system sounds like a lot less headache when I am trying to work on it. What computer do you use? I could get rid of all that air injection stuff too and put some shorty headers on it. The drivers side exhaust manifold is starting to leak too. In the six years I have had my shorty headers they have yet to leak.
Click to expand...

I have the super common 14477 something or other. I run shorty headers too. The cam and the chip are responsible for the HP and torque. I downloaded Comp Cams software (a proprietary desktop dyno) and it actually reccomended the cam I selected (gen 1 motors can run an LT-1 cam, they still have the distributor drive gear on the rear of the cam). Their software indicated something like 420 pounds of torque (stock Vortec is 330) and 380 horse (stock Vortec is 260). While I think their numbers might be a bit optimistic, I'll bet the farm it's 400 pounds of torque and 350 horse and it comes on strong right off idle. I usually get around 15 MPG with 4.56 gears and 35" tires using an NV4500 trans. (Saying its an aerodynamic barn door is offensive to barn doors.) I'm considering going to 37" tires as it feels a bit under-geared. Do check out that website I put in the previous post. I REALLY like the performance of this chip and they are super great to deal with and the whole system has been very good to me. I'm an electronic moron, so if I can do it, anybody can. The question for you is, is it worth it? You can certainly tweak the Vortec setup. I have never owned a Vortec, but I am of the opinion that TBI is probably more reliable and certainly more simple.
 
Last edited:
You must log in or register to reply here.

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)

Share this page

Back
Top Bottom