5.7L GM Engine w/Problems

[marine_man]

Not a fishing related question, but you guys have been really good with vehicle questions so I thought I'd throw it out there...

Here's the deal...

1996 GMC Sierra w/5.7L (Vortec) with approx. 135k miles.

I first detected a hint of gas in the exhaust of my pickup on Sunday. I drove it on Tuesday with no problems and did not notice a gas smell from the exhaust on Tuesday after letting it warm up.

This morning I was headed to Fargo. After driving 15 miles I coasted to a stop sign and the engine died while coasting to the stop sign. I restarted the pickup (no problem there) and drove another 100 yards and probably got up to about 40 mph when it died on me again (this time while I was accelerating). It took a little while longer to get it started this time (perhaps like it was flooded). I got it started, got up to speed (70 mph) and the engine hesitated twice within a couple of seconds with each other - the engine didn't die during this hesitation, but acted like it lost power and then it came back.

About that time I was coming into a small town. Since I was at about a 1/2 tank I filled up and put a bottle of heat in to rule out any water in the fuel issues. I then drove back home (not wanting to chance it) and the pickup performed normally for the 15 miles I drove it home. At no point during this drive did I sense a loss of power or did the SES light come on.

I took the wife's van to Fargo. She called and said that while she was letting the pickup warm up in the garage that the exhaust smelled strongly like gas and the engine was idling rough and that the SES light came on. This is the second time the rough idling has happend... the last time was about 6 months ago and I shrugged it off since it never did it again.

She drove it to work (1.5 miles) and the pickup ran fine the rest of the time. On the way home she coasted down a hill and the engine died again then. She got it restarted without a problem.

I had the oil changed on Monday, and checked the oil tonight and I'm a 1/2 quart over on oil and it smells like gas.

I've got an appointment to get it in on Friday for a cursory look, but they won't be able to dive into it unil closer to the end of the month, which isn't a huge deal...

Any rough ideas / stabs at what's going on and what to expect for a bill? My preliminary theory is that an injector is not functioning correctly and is just dumping gas into the cylinder... hopefully it hasn't been doing it long enough to wash the oil off the cylinder wall and score the cylinder...

I also thought about the possibility that the downstream O2 sensor isn't working consistently and the engine is running rich, but I would guess that it wouldn't dump 1/2 quart of oil into the pan in 30 miles.

One other question... I've sort of suspected that I could have a stuck lifter. I've had it checked out and the mechanic (different one that where I'm taking it in this time) told me that it was just piston slap. It sounds like a ticking noise and is more pronounced when it's cold outside and only noticeable at idle. So, follow me here for a minute, if I did have a stuck lifter, which I'm guessing would burn the lobe off the cam shaft, could that be the cause of this problem?

I appreciate any info you can offer!

Thanks!

marine_man

[vizsla01]

Hey I have a co-worker that has a Tahoe with the same engine, and the problems sound somewhat the same. It ended up being the fuel pump and filter. The mechanic had him try to blow thru the filter and he could barely get any air thru. He thinks that he could of gotten by with just a filter. Hope this helps.

[Macgyver55]

I'd suspect the fuel pressure regulator. A fuel pressure test can quickly verify if thats the problem. 75 to 85 bucks average cost for the part. Depends on who does it what the labor cost would be.

[Sutty]

I have a buddy (mechanic) that told me to change my fuel filter every year in my truck. I have the same truck as you (98 GMC-K1500) I don't know if it is overkill or not but it is real easy to get at and change yourself. If it turns out that was the problem. I end up going it about every other year.

[Jeremy airjer W]

O2 sensors will not cause a vehicle to run so rich or so lean as to cause a missfire or serious driveability issue. The downstream O2's only function is to monitor catalytic efficiency. The upstream O2's are responsible for fuel trim. One of the tests we use to do is backprobe the 02 and then grab the test lead with one hand while touching the battery + (full rich)or - (full lean) with the other hand and monitor the scanned values of the O2. If the went up while touching + and down with - then we could conclude that the computer was able to receive the correct information. This never caused any noticeable difference in idle.

I would also suspect something under the intake plentum, fuel pressure regulator or fuel injector. Since it happens intermittently it seems more likely a fule injector. The good news is these are both serviceable items with this CPI unit.

The computer codes will help identify the cylinder effected. The engine light flashing tells me that the computer is seeing a dead cylinder and is trying to tell you to not drive it in order to preserve the integrity of the catalytic converter. The code should be any one of or several of these, P0301 - P0308 (P0301 - missfire #1 cylinder, P0302 missfire #2 cylinder, etc.) If it is a P0300 I would be more likely to suspect the pressure regulator. Pulling off the upper plentum and visually checking will confirm this.

As far as the ticking noise its probably lifter tick. Piston slap is more of a hollow noise with a cold engine under exceleration. I would try a half a can of seafoam in the oil right before an oil change. Let it run for 15 - 20 minutes and then change the oil. Add the other half to the new oil. I have fixed numerous GM's with this problem with this product. Good Stuff!!

A fuel injector will run you about a $100 a piece, pressure reguolator about the same. A couple hundred for labor. Don't forget the plenum gasket, around $30.

Good luck marine_man

[Guest]

Im with McGyver on this one, the fuel injection pressure regulator. Sometimes for a really quick test you can take the vaccum line off the regulator.. if you get a drop of gas, or an odor of gas.. its out for sure. I have had to do 6 of them in the last 3 years on different vehicles we owned.. I got the drop of gas on 4 of them.

Another think it could be is a bad fuel injector, or bad fuel injector O ring. I have also had this problem where the inner O ring fails and gas literally pours into one of the cylanders at the fuel injector. Its easy to notice when an outer seal goes out when gas is leaking externally ont he engine,but when it leaks into the engine.. you dont notice until its pouring excess gas into the cylander.

Have the fuel pressure tested at the fuel rail.. You will likely find your problem.

[BIG DS]

It is a leaking fuel pressure regulator. Common problem. The diaphragm in the regulator will develop a leak in hot conditions or cold conditions. The rough idle 6 months ago could have been an EGR valve stuck open. Also another common problem. Your SES trouble code will more than likely be rich exhaust and will be on all O2 banks. Not too scary

[marine_man]

Quote:

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The engine light flashing tells me that the computer is seeing a dead cylinder and is trying to tell you to not drive it in order to preserve the integrity of the catalytic converter.

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Thanks for the help guys... one clarification here.. the ses light is not blinking... it just came on (and stays on until it times out) when the rough idle occured (for the second time).

If this is the case... why does the engine kill / hesitate? Too much fuel in the cylinders?

Oh, and I'll try the sticky lifter remedy soon once this is squared away...

Thanks!

marine_man

[Jeremy airjer W]

Quote:

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Im with McGyver on this one, the fuel injection pressure regulator. Sometimes for a really quick test you can take the vaccum line off the regulator

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The regulator is under the intake plentum on these vehicles. There is no easy access. The only way to find out for sure if it is leaking is to pull off the intake plenum.

[Jeremy airjer W]

Quote:

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Thanks for the help guys... one clarification here.. the ses light is not blinking... it just came on (and stays on until it times out) when the rough idle occured (for the second time).

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My bad, I could of swore you said flashing?

The thing that puzzles me is that it looks like it will have the problem when its cold and when its hot and it just goes away when it feels like it. If a regulator is leaking its leaking. sometimes they will be more pronounced when they are hot sometimes when they are cold.

The other thing is you never metioned an extended crank. this would be more pronounced after a hot soak (drive it for a half hour shut it off, run into the store for 10 minutes come out and the vehicle takes a long time to start.

Scratch everything I just said in the previous post. I think you need a major tune-up. Something in the ignition system is worn out or leaking. This would explain not only the fuel smell, stalling, running ruff and why the symptom disappears at random. Do you notice it more when its wet out?? You also mentioned that it stalled as you where accelerating (i miss spelled that in my other post didn't I ), an ignition system problem will more likely show up under load or acceleration. If it where an egr problem the sympton would improve under acceration as this is when the EGR is more likely to be commanded on anyways!

If the regulator was leaking that bad to make it stall it would do it all the time and not intermittently.

Rob, Ill send you an email (yahoo account) with my phone number. I'd like to get a few more details.

[ice_it_06]

marine_man:

We have two 98 Tahoes and two 93 S10 Blazers in our family and all have had the "fuel pressure regulator" replaced under the same symptons you have.

You can have a pressure leak down test done at the plenum area and back through the pump. If you are getting long starts and sputtereing when it does because its loaded up on fuel, I'd all but assure its the regulator that these things go through.

You can also just pull the lines at the black junction on the drivers side top/rear of the plenunm. Shine a flash light in there looking towards the passenger rear (regulator location)and simply look for wet gas or soot laying around inside the plenum.

Your dumping major fuel in to the oil the way it sounds.

Not good, I fixed the last two myself (Tahoes) and dumped the oil out of them twice within a few operating hours to get the fuel out of there. Ridiculous GM design to tear off the upper half to push in a new regulator but it is what it is.

Check it out quick by looking and keep us posted, my $$$ on that regulator.

[marine_man]

Thank you to all for the help... and thanks airjer for the phone call... I've got some things to look at tonight and I'll let you know what I find...

marine_man

[Splake]

I have a 95 Silverado and a 2000 Jimmy they both acted as you described. Fuel pumps were bad. Have your fuel pressure tested.

Splake

[marine_man]

Quote:

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I have a 95 Silverado and a 2000 Jimmy they both acted as you described. Fuel pumps were bad.

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A question to everyone who's suggested fuel regulators / pumps / filters - did your vehicle also exhibit gas in the oil after a short drive (1/2 quart in 30 miles)?

Thanks!

marine_man

[ice_it_06]

The thing is rich with fuel and dumping it everywhere. (ie. oil & exhaust) Supply is definately there but regulation and pressure at the engine is a definate issue. There is a regulator leak or injector problem.

But @ 135,000 and if on the original fuel pump that cant be far behind. (sorry marine_guy)

In any equation the pressure test is still a must to see where the leak down is originated. But I'll bet if he pulls the lines at the junction on the plenum he'll see wet gas and soot sitting inside and smell of gas.

[ice_it_06]

One of my Tahoes was dumping it badly and at a high leak rate oil will get contaminated very fast. It pours down the cylinder and the regulator side of my plenum was totaly cleaned and shiney new from the leak area.

If its in the oil and exhaust I would not run it until diagnosed and fixed, and the oil changed out asap afterwards. Mine ran a week before I discovered (out ice fishing) it in 04 truck idle was bad, exhaust tail pipe was black. I went out to look at it and could smell the raw fuel comming from the tail pipe. Took it right home and shut her down until fixed a couple days later. Mine had been leaking long before the day of discovery though. The hard starts I had I thought were just a bad cap/rotor but was wrong there.

[marine_man]

Thanks for the info ice it...

The only driving I'm going to do with it is to the service shop when they can get it in... unless I get lucky tonight.

marine_man

[Guest]

Quote:

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A question to everyone who's suggested fuel regulators / pumps / filters - did your vehicle also exhibit gas in the oil after a short drive (1/2 quart in 30 miles)?

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Yes on the gas in the oil on one.. I didnt check for the exact amount but it was a lot... when checking the fuel pressure it decided to do something new.. It started pouring gas out of the air cleaner when running! I have no idea how it managed to start going there, but it did.

The only other time I got the serious gas in the oil issue is when I had a very bad O ring on an injector. The symptoms sound similar to some of yours.. the very stinky, gas smell, or excessive exhaust smell and a grey color to the exhaust(raw gas in the exhaust) that would diminish as the vehicle warmed up and burned off the excess.

I dont think its a injector issue, but it could be. My money is still on the pressure regulator.. and I'm as broke as it comes, and every penny counts! I am certain its one or the other unless your distributer cap is about to fal off, your plugs are worn to nothing, and your plug wires are shooting lighning bolts!

[ice_it_06]

That Guy:

LOL to that post description. Sounds like your betting is that of mine. Not much to bet with but the .99 I have I'll still put on the regulator. Don't lose my a!! that way Your electrical component description is very comical but could be accurate as well. This all takes a toll on the strating components if left unaddressed to long.

Marine_man should check cap/rotor and I'd replace the plugs as well. I'm sure there is a gas soaked plug or two in her.

**Side note my son Blazer had so much fuel leaking it came out of the plenum leaking on the ground and had his oil level two quarts over fill. His CPI unit blew a hose to the regulator. So the gas will travel anywhere it can.

[marine_man]

The ignition components are something airjer mentioned I should check.. and I'll be doing that tonight hopefully...

I'll let you know what I find...

marine_man

[ice_it_06]

It all goes hand in hand with the ignition and such.

You have good direction in which to look for your fix. airjer is full of good knowledge and help from his posts.

The cost and process to replace a $40 regulator is crazy on these 5.7 Vortecs. I know a mecahnic that did mine for $100 but he can do them in his sleep he's done so many. I believe the original shop quote was over $300.

So when you add the new plugs needed, oil change, cap/rotor/ have wires checked etc it turned in to a find a mechanic on the side.

I watched him closely and educated myself so when the next one went (six months later) I tackled it myself.

Oh by the way it was the "same" one that went bad as I got a faulty regulator from NAPA that lasted less then six months. I was informed these things are not good at times out of the box even

If you know some people or friends who know of a cheaper labor rate (experienced) seek them out after the diagnose is certain. My first one ended up over $300 without a shop.

After I replaced all ignition parts such as plugs,wires,cap,rotor, and then oil,oil filter,and fuel filter.

**have them check your intake for leak signs when there as these are a very common problem as well and @135,000 if original you are on borrowed time. Look for leaks or consider doing that job as well seeing its torn down to that degree if it turns out to be the regulator.

[woodman]

I have had the same problems with my 5.7. It ended up being the fuil pump inside the tank. Very expensive. I also did a complete tune up for the cost of around $650 Six months later the pump went again and they warrantied it out for me including labor. Last winter the pump went again so I went to another mechanic and he said that I was charged for the expensive one, but they put in the cheap one!

My NEW mechanic fixed it right and has not given me a problem in over a year. I probably should not be typing that, because I may jinx myself.

Good luck and best wishes!

[ice_it_06]

I've replaced numerous fuel pumps and on both of my 5.7 Vortecs. Marine_mans symptoms are of excessive raw fuel somewhere in the plenum fuel area as oppossed to a starvation of fuel which would indicate a filter or pump or relay maybe.Have even seen a loose fuel cap cause pressure issues where someone was taken for a pump that was never put in.

I've seen far to many people get hosed for a pump job and a regulator job together because they knew no better but to believe the entire fuel delivery system went south on them.The pumps are easily heard to engage at key "on" position and are loud when running so I'm sure he must have connection seeing nothing was mentioned.

Mentioned before his pump (if original) is at its time as well but I know of no bad pump issues that over supply the system. These pumps are very sensative to bad filters as well and get diagnosed as a bad pump when its just the filter. You have a 5.7 Vortec change the filter every year to spare the bad pumps. Aftermarket pumps are a dump shoot as well if not getting a OEM. Delphi is the only pumps I've had luck with if I went on the cheap an opted out of OEM.

These darn things have so many issues I cant believe there are so many on the road. (lol) Mine were after purchase discoveries so I'm kind of stuck with mine

We'll find out soon what the issue is, but I'm sticking to a regulator which he can find out for himself in (5) minutes tonite!!

Hate to see people get stabbed for big $$$$ on parts and misdiagnosis. (some intentional)

[marine_man]

Quote:

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have them check your intake for leak signs when there as these are a very common problem as well and @135,000 if original you are on borrowed time.

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Thanks for the help everyone...

I have had the intake gasket replaced... had it replaced under the extended warranty and haven't noticed any missing coolant since thankfully.

I'm headed out to the garage right now... but thought I'd check in on all the advice that's been offered...

As far as the fuel pump goes.. it's been loud, but the same loudness ever since I got it 60,000 miles ago... so I don't think that's it... as far as I can tell it's still functioning normally and the sporadic nature of the problem seems to lend itself more to an ignition problem than perhaps a fuel problem - or, if I'm really lucky a combination of both...

We'll see how it goes.. I'm a little hesitant to remove the intake plenum (as that's where the fuel regulator resides) but we'll see how it looks and how it goes.

Thanks!

marine_man

[ice_it_06]

Marine_man:

Dont need to remove the plenum.. Just carefully pull the aluminum lines out of the junction center and unscrew the the two little nuts and pop off the center piece. Shine a light down in the hole looking in to the plenum and look for wet, gas or smell of gas.

Your plastic Vortec box on top of throttle body, lower front corner (drivers side) of it is where you will see these two lines sitting atop the plenum next to each other. They pull out kind of hard but is a easy cheater way to see whats going on inside there.

Heading to work, good luck !!

[hondavxr]

GM's with fuel pressure regulator and fuel pump problems are common. I use to have a 00 Silverado and I replaced the fuel pumps two times with OEM pumps and then I traded the truck for a 4runner. Check to see if you are getting any pressure from the pump itself. If you see that the pump is building pressure but the truck is still not running, it mostly likely your fuel pressure regulator. This is very common so I am sure others here can help you more.