1998 chevy 350 acting up.

[Tom]

I have a 98 Chevrolet z71 that has been acting up. It has around 170,000 miles on it.
After sitting for a month in Seattle (moderate temperatures with rain), it was hard to start and ran really rough. Treatment with seafoam in the gas seemed to help. Three weeks later, I had to use ether to start it. After getting it running, it smooths out.
Our gas here has ethanol in it. My friend that shares it with me thinks the ethanol is gumming up the fuel system.
Could the gas go bad in only three or four weeks, or does this sound like something else?

 

[CWLONGSHOT]

I know that it KILLS SMALL ENGINES!! Most times vehicles cause the are used regularly its OK.
Its apauling what some folks make ok for the rest of us based upon there own crteria...

CW

 

[JonB]

My first guess is water in the gas.
Sitting for long period of time in humid rainy conditions, moisture could condense in fuel tank as temperature rises above and dips below the dew point. The Ethanol in gas absorbs moisture and brings it to the injectors and if the moisture content is high enough, it'll start rough and run rough, until the engine is up to operating temperature.
disclaimer: Again, that is my first guess...I am not a mechanic and don't play one on TV, LOL...so I surely could be wrong.

 

[RicinYakima]

First thing I would do is clean the Mass Air Flow sensor with that many miles. WA's 10% minimum ethanol makes any oil deposits stick to them.

 

[Tom]

Thanks guys. I do know that alcohol is hygroscopic, so that makes sense. I had to look online to figure out where the mass airflow sensor is and what it looks like. Cleaning or replacing it looks like an easy project.
There are a few places at home that sell non ethanol 91 octane, not sure about over here in the Seattle/Kent area where we keep this vehicle. I hate to pay an extra .50 a gallon, but it might be worth it.

 

[fiver]

IIRC they had a plastic fuel tank too.
get you a couple of bottles of that Heat stuff and run it through the system.

I used to get junk/water in my fuel back in the day, I kind of think it was the fuel station I was using, but it would freeze in my fuel lines.
sometimes the old girl wouldn't start and others it'd suck some ice right into the fuel line,,, you know,, on the freeway.
had to start using Heet to keep things clear every tank full during the winter months.

I never had that problem with it once I moved up here to Idaho even though the temps are a lot lower.

 

[Bret4207]

2nd Fivers suggestion. Even Ethanol fuels can only absorb/bind with a given amount of water. "Dipping the tank" weekly using a stick with a water alerting paste on it was a common thing done at places I worked. There was often 3-4" or more water in the bottom of a fuel tank. Ethanol fuels are going to grab that moisture and be saturated with H2O. If your tank has some water in it, there's nothing there to deal with it. And that doesn't even touch on the crap residue ethanol fuels leave behind as they deteriorate while just sitting there for a couple months.

FWIW, I'm not a Seafoam fan. I like Berrymans B-12 Chemtool. Found beside the Seafoam in many places. Better stuff IMO.

 

[Tom]

Bret, I've never heard of a water detection paste, had to look it up. Looks like a good thing to have, but it says for non ethanol fuel. That makes sense since the ethanol would bind with water. I think I need to find non ethanol and fill up with that a couple times before testing with that. I guess a siphon hose all the way to the bottom of the tank would be the easiest way to deal with an appreciable amount of water if there is any in there.

Fiver, would heet bond with water and help get it out?

 

[RBHarter]

Airplane stuff and old skool .
Run several bottles of heet through it like 1.5x recommended and run it as far down as your comfortable before you pump the "good stuff" in . The good fuel will screw up the balance and if it's under 35° or so the water will fall out and the alcohol will separate from the gas . At 25° it'll slush in the system at 70° it raises caine with sensors , gives you boggy studders , and water in the exhaust almost like a blown head gasket . Once it falls out it takes about an 80° day to stir it back in or Heat about 3/1 .

 

[S Mac]

Don't imagine you would be able to find the bottom of the tank with a siphon hose, many vehicles have a baffle to prevent theft. You could disconnect the line to the engine and use the fuel pump to pull the fuel level down, wouldn't get it all but most of it. Of course the pump only runs for seconds key on engine off. Pain in the butt unless you can jump the pump power wire with B+.

 

[S Mac]

From the sound of your complaint it could be a vacuum leak that seals up after the engine warms up, something to think about.

 

[popper]

Also rusts tanks AND fuel pumps in the tank. Put a pressure gauge on the fuel rail and see what happens. MAF should default to always run but can be rough. Special cleaner for it.

 

[Ian]

Yes, gas goes bad in 3-4 weeks.

Adding seafoam or heet is just adding more alcohol to soak water.

Vortec distributer caps are notorious for holding moisture because the vent screen in the bottom plate plugs up with oily grime. Coil wire at coil end tends to corrode.

The CPI unit's seals bake with time and leak fuel into the intake, causing air intrusion into the fuel system and long crank/initial rough running.

I could go on and on but the most likely culprit is a leaking fuel pressure regulator diaphragm. Ethanol, and especially seafoam, eats these things up.

 

[Petrol & Powder]

I'll second everything Ian wrote.

I have a truck that sits a lot and I've been exclusively running non-ethanol fuel in that truck for several years.
I did the math, and it works out even in terms of money. The non-ethanol fuel costs more but it also delivers slightly fuel mileage (just a smidge over a 2 mpg gain). If I drove the truck daily it wouldn't be worth the hassle to seek out one of the few stations that sells non-ethanol gasoline. As it is, I break even AND have zero fuel problems despite the long down times.

As for ethanol/gasoline blends going bad over the course of just a weeks - it absolutely can.

As for the plastic fuel tanks, it's been my experience they are actually better than the steel ones. They can't rust and they're unbelievably tough. Dodge started using them in their trucks in the 1970's. I've scraped those Dodge gas tanks over rocks that would have split a metal tank wide open. Didn't hurt the plastic tanks at all.

I also agree with the technique of running ALL of the old gas out as much as you dare before putting good fuel in.

 

[Mitty38]

If you have not changed the fuel filter for a while. Now would be a good time. Especially after you are done running all those additives thru it.
Will be directly under the driver's door and would use regular wrenches. No goofy clip things.
Should be like a 15 min job tops.
Since the pump is in the tank it you should not even drain more then a pint of fuel durrng the change.
Just saying.

 

[Petrol & Powder]

And while we're at it;
I completely agree that the OP's problem is likely fuel related BUT.....a 33 year old engine could have some ignition system issues in wet weather.

Ian reminded me of this when he mentioned the Vortec distributor cap problems.
Years ago I was driving a Dodge with a slant six. It was a cold wet day. Started up a mountain and got into slushy snow and about 20 degree temperature drop along with an elevation change. The engine went from running fine to barely running at all. A buddy was riding with me and he told me to stop and cut off the engine.
He pulled the distributor cap off, used a rag to wipe the water out from inside the cap and put it back on. Took 20 seconds. The engine started and ran perfectly! Water had condensed inside the cap and was causing all sorts of problems.

I'm not saying that is the OP's issue but I'll never forget that correct 10 second diagnoses or the 20 second fix.

 

[Ian]

Make certain you get replacement o-rings for the fuel lines when you replace the filter. They are brown Viton and only available from the dealer. The black aftermarket ones are crap.

The ruptured fuel pressure regulator will flood cylinders #5 and #7 due to the lower intake manifold design. This makes for long crank times and rough running for a few minutes after startup. You can determine if this is the problem by removing the throttle body and peering carefully into the plenum on the passenger side of the engine. The regulator is inside, mounted to the side of the CPI unit and has a little tube in the side pointing down to get vacuum. The fuel leaks out of this tube from a ruptured diaphragm and sprays fuel directly onto the aluminum lower intake manifold making a circular clean, shiny spot. Everything else will be covered in dark brown varnish or caked with black carbon from the egr valve. If you see a clean spot of aluminim about 2-3" in diameter back in there even with the side of the CPI unit, on the top of the lower intake, it's regulator time and a good idea to reseal or replace the CPI unit too. Dorman makes a full replacement conversion CPI unit which moves the injector solenoids away from the central unit of the spider and puts them right into the ports, eliminating the solenoid and poppet injector system. Cost is about $400 last I checked and well worth it for the upgrade.....plus it's designed to be ethanol compliant, unlike the original system.

 

[Tomme boy]

Those motors had problem with the distributors drive shaft wearing out the housing and taking out the pickup. Otherwise the regulator and fuel lines under the intake like Ian said.

 

[fiver]

yep like Ian points out it just sucks up more water, but it puts it through the system and out of the tank.
it sucked to dump a bunch of money in the hole then run it all out asap, but I was driving 90 miles one way to work at the time, so getting the tank emptied didn't take long.

 

[Mitty38]

Pretty sure the o ring on the filter and the push and snap stuff did not start till 99.
Should just need a line wrench set, and the filter. Pretty sure 98 's do not use O rings on either side of the filter. Just a line brake line type fitting.
Of course it's been two years since I have done one so I could be wrong.