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

[marine_man]

ice it - thanks for the tip... I saw the area you mentioned and figured that's where the fuel lines went in I'll have to try that on Monday night - we're headed out of town for the weekend.

Anyway, here's a little update.. I didn't get much time to work on it tonight, but did manage to pull the plugs...

I didn't find any smoking gun, that's for sure. They certainly could be replaced, but didn't look terrible and looked consistent with each other. The tips were all consitently colored kind of a off white powdered color. All the gaps were similar, were slightly larger than spec, but not by much.

The only thing of interest I found was that on the spark plugs on the drivers side of the engine, from front to back, the first, third and fourth spark plugs smelled of gas more, and the threads on those three were wet and also smelled like gas.

The second spark plug on the drivers side did not nor did any of the plugs on the passenger side of the engine.

One other thing - I tried wiggling the wire from the coil to the distributor and the spark plug wires while it was running and sprayed the wires with soapy water per Airjer's reccomendation and didn't find anything... I also powerbraked it a little to see if it would develop a miss after spraying the soapy water on the wires and the engine didn't hesitate at all.

I'll have to try ice-it's trick on Monday night and will let you know what I find...

Thanks for all the help!

marine_man

[Jeremy airjer W]

Time for the fuel pressure gauge, and a little experience!

[Sutty]

I had to change my fuel pump about 2 years ago. I had a buddy help me I didn't want to tackle it myself. I put in a napa one and it was real loud right away, as the year went on it would take longer and longer to start, before the year was up I used the warranty to get a new one from napa they said they fixed the problem with them. I don't know if that is true or not but it has worked for 9 months or so now.

If you decide to do a tune up yourself ie new plugs cap, rotor, wires I can offer a little advice. I am halfway handy but certainly no expert. I did mine last summer and it wasn't bad. The thing I remembered having problems with were the little plastic guides that the hold the plug wires in place. I think they open up real easy but I needed (and didn't have a third hand to get a couple of them back in place. I think the one that gave me fits was passenger side.

I was also told that ngk spark plugs were the best for fuel milage (I had already bought a differant brand so I can't confirm that or not.)

[Guest]

I had my fuel pump replaced on my chev van last year just before a trip to MO.. I was literally backing up to the boat to hitch it when it went out! Pressed for time I had the shop replace it with the better of the 2 napa pumps.. drove to MO, went fishing for a few hours, backed the van up to load the boat... pulled it out of the water and was securing everything and the van died again.. the new fuel pump was faulty!

Napa exchanged the pump no problem.. but I wish they would have paid the $380 middle of nowhere labor/tow cost!

My experience with these in-tank gm fuel pumps.. when they die, they die. They dont keep running, they just stop dead until you have it towed to a shop and then they work briefly from being jarred around on the tow truck.

[BIG DS]

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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 when the regulator goes out and no on the fuel pump. When the regulator leaks, it dumps fuel into the intake and it then runs past the valves, around the rings and into the oil pan.

[marine_man]

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and a little experience!

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I think this is the route I'm going to take... just wait until the mechanic can take a look at it instead of damaging something else...

Thank you to everyone who provided input on this... you've put me more at ease and I have a better understanding of what it could be so I'm armed when I go to the mechanic.

I'll let you know what it ends up being...

marine_man

[Jeremy airjer W]

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My experience with these in-tank gm fuel pumps.. when they die, they die. They dont keep running, they just stop dead until you have it towed to a shop and then they work briefly from being jarred around on the tow truck.

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Guys, don't be afraid to wack these gm pumps with a mallet or crow bar ore whatever is handy, 9 times out of 10 the commutator is worn out (or the brushes are stuck) tapping on the fuel tank right below the pump while somebody is cranking it over will usually get it going again. This will work for just about any GM vehicle, jeeps, and dodges. The Fords actually melt and lock temselves into place, at least the taurus, contour, escort, etc. Its been a while since I have done a pump in a ford truck so I cant recall what the deal is with them. I'll post some pics of what I'm talking about tonight.

[ice_it_06]

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Guys, don't be afraid to wack these gm pumps

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Thats a good little reminder and has been done before.

If you change out a pump replace the wire harness as well. They corrode bad and cause all kinds of issues.

All this 5.7 talk had me feeling pretty good about mine as they have been good to me for about five months now.

Until this morning I decided to pop hoods and just snoop around and found my sons water pump weeping on his Tahoe.

So much for sticking my nose in things.

So tomorrow we will have a little water pump 101 class.

Better found now then @ 20 below I guess but I was in hope we were good on all of them through the winter

[Guest]

I would consider the 5.7(350) chev motors to be extremely reliable.. The only weak link seems to be the fuel delivery system, or the fuel pumps and pressure regulators for some reason.

All vehicles have their quirks. Some come sooner, some come later.. but they eventually come! I will give GM one thing.. its usually easier to diagnose a problem than it is with other manufacturers!

[Jeremy airjer W]

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I will give GM one thing.. its usually easier to diagnose a problem than it is with other manufacturers!

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That all depends on what your familiar with. Personnally I find it easier to diagnose "asian", but I can usually figure out just about anything on other manufacturers vehicles just as easily. On the other hand I can't stand working on VW, SAAB, Audi, BMW, or Mercedes. Forget diesels, thats a whole nother ball game!

[Guest]

Airjer.. If you want something really difficult.. try to diagnose this AMC sitting in my back yard! Hmmm... which ignition part is it with no way to test it?

[federline]

Air, I had a diesel passat for 250,000 miles, two of your list of hates combined into one. Aside from all the electrical gremlins and crappy hardware, nothing ever had to be done to that diesel drivetrain, and I traded it off on my pickup for a decent amount of credit. There must be 50 miles of wire in those things. If you can appreciate bulletproof drivetrains, and dont mind electrical gremlins and door and window hardware that wears out 3 times over the life of a vehicle, a diesel kraut-mobile is the perfect car. I have vowed to never own another one, tho. I'm much happier with my rattly Chevy truck, now.

[Jeremy airjer W]

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Airjer.. If you want something really difficult.. try to diagnose this AMC sitting in my back yard! Hmmm... which ignition part is it with no way to test it?

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Thats an easy fix! Most salvage yards have a big yellow machine that will crush it into a little cube. Problem solved!! Probably should have been done years ago!!!

[Macgyver55]

I fully concur and back up Airjers fix. That would be my preferred method for fixing this problem too. It would work best though if I were allowed to push the start button on the machine!

[Guest]

Its not all that bad.. and it will keep me from pushing the significant other out of a snow bank this winter... more or less a small station wagon body on a jeep drive train.

It must not be that terrible.. it was a DNR vehicle for the grand rapids area for most of its life... at least I know it was well maintained for most of its life until the last 10,000 miles with the last tree-hugging owner with a *cheap mechanic*... his words, not mine

The only other DNR vehicle I have owner was a early 90's K5 blazer(full size) that still didnt leak a drop of oil at 250,000 miles.

[Sutty]

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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!!

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I was thinking of trying this. When you do this do you wait the typicall 3000 before you do the next oil change? I assume all the seafoam in the oil gets burned up pretty quick.

Thanks,

Sutty

[Jeremy airjer W]

The direction are on the back of the can. Half a can of seafoam motor tune in the oil let it run for 10-15 minutes (longer if its cold out) until the engine is warm. Change the oil/filter. Add the other half to the new oil.

Basically this stuff has five properties. 1 - Moisture dispersant, 2 - Fuel stabalizer, 3 - decorbanizer, 4 - solvent cleaner, 5 - lubricant

[marine_man]

Well, my mechanic suprised me with an early christmas present of sorts - my pickup got done early.

He pulled the code and found it to be a misfire on the 3rd cylinder. He replaced the plug and the plug wire on that cylinder and it resolved the problem. So, he put a new cap & rotor, plugs and plug wires. He checked the fuel pressure and found that it was fine...

The pickup runs good... I pretty much drove it home and parked it since we're out of town for the weekend, but it seems like it runs good.

Total bill - $300

Thanks again everyone for the help!

marine_man

[ice_it_06]

Ignition is the first place to start on them misfires or rough running. Cap/rotor plugs and wires I check regularly on my Chevs.

With the gas smell you described I was sure it was a fuel pressure regulator. Have had various Tahoes and Blazers with plug/wire issues but never loading them up on fuel ?

Glad you got it figured out, I'd get a new set of plugs and wires on it... My Tahoe just [PoorWordUsage]ed a intake this weekend. Heck of a Christmas present

[Jeremy airjer W]

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Scratch everything I just said in the previous post. I think you need a major tune-up.

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(airjer pats himself on the back for a job well done!)

[marine_man]

You hit the nail on the head airjer... thanks again for your help!

marine_man