If I read your original post correctly you state that the problem happened as you were pulling away from the service station. There is a considerable volume of fuel in your car's plumbing that would need to be burned through before the bad gas/water would reach the injectors. If it was several minutes after driving away from the station that the shudder started then I might consider bad gas, but immediately when pulling away from the pump? I just can't see the gas causing that.

Robert

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Actually, the fuel pump delivers far more fuel to the injectors than is injected, and the excess is returned to the tank. It will not take long for fuel at the inlet strainer to travel through the inlet tubing to the pump, to the inector rail, and back to the tank.

Best Regards,
Jim

You got a load of water and sediments with your gas. Gasoline travels from refineries to terminals via pipelines. A refinery puts a barrel of gasoline in the pipe in Texas and can immedaitely take a barrel out in NY. All gasoline is essentially the same, varying only in octane. The differences are in the additive packages that are mixed in at the terminals. Some are better than others, but all have some detergents that keep injectors clean. If you have blended winter fuel that uses ethanol or other alcohols, then be advised that this is mixed at the refinery or intermediate points. If it flows through pipelines then you should understand that it is a powerful solvent and "hygroscopic," which means it will pick up all the moisture in the pipeline and will scrub out all the pipeline crud as it passes through on its way to the terminal/mixing point. This ends up in the station tanks and then in your tank.

Alcohol is also used as a gas dryer when normal condensation occurs in the fuel tank, or when suspended water settles from the gasoline and causes the stalling and mis-firing you described. Always carry some gas dryer in your trunk, Heet or another brand would be good. Also, the Techron contains alcohols which will allow the water to stay suspended in the gas, so, yes, it will help to remove the water as you noticed. Check the Techron bottle, it lists this as a benefit of its use. Try to avoid fueling at stations where the tanker is off-loading. This does stir up the crud.

Modern fuel injectors are finely made precision parts that can be easily fouled by contaminated fuels.

Finally, it may be wise to change your fuel filter: Add another bottle of alcohol and another of Techron and drive the contamination out by driving the car.

Like a bad meal, this too will pass.

FWIW,

230/8

There's at least 4 ounces of fuel in the distributor and tubing to the injectors. This is after the fuel return line. To make the math easy lets say the car gets 20 mpg. So 128 ounces gets 20 miles, or 6.4 ounces per mile. So if he was 2/3 mile away from the fuel station when the problem started I'd believe it.

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Good points, thank you. May I continue the math? When accelerating away from the station, I'd expect less economy, maybe 10 mpg or less until he was up to speed, so it could be a bit less than the 2/3 mile. With a heavy foot, maybe half of that, 2/6 or 1/3 of a mile, not including any fuel added by idling until pull away? Not quite immediate, but closer to it...

Best Regards,
Jim

97diesel and 230/8 are both correct in their desc. of fuel delivery/sales practices -though most people just do not realize what goes on. The marketing people from he various companies are selling the name, and the credit card. They are not selling their "brand" of fuel. So, you really never know what it is that you are buying when it comes to gasoline. Even rhe most "honest" of station owners will, occasionally, buy a known lesser-grade of fuel and sell it at the most markup that he can get. The station owners are not the ones making money on fuel in the last 15 years that I have seen the business. The profit goes to the oil jobbers, brand name holder, and the inflated taxes.

easiest way to check how "good" the gas is to to determine how long it takes to fill up. gas stations with slow pumps have old/ clogged filters. faster fillups mean the filters are changed more frequently.

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I should add that the car was RUNNING at idle while I filled it up. This would undoubtedly account for the rapid reaction.

All theorizing aside, I wanted to bump this thread because the problem appears to have returned. This time it just started occurring after I got into the car to drive home from work. And I did not fill the car up that day (several days ago). The tank was about 1/2 full. And just when I thought the problem was gone.

Same symptoms - at idle in D, occasional massive jerk that feels as if it would kill the car if it continued - but it doesn't. It's the weirdest thing. It's not like an ignition misfire, more like someone flashed the ignition key to the "off" position for a fraction of a second and then turned it back to "run." And yet the car never dies. When the car is first started and this is occurring, putting it into gear will kill it. It only stays alive once the car is hot. But only sometimes. Other times, it doesn't occur at all, even at a cold start. I just put it in gear cold this morning and backed out of the garage and driveway with no problems. It only started the jerk / shudder about 20 minutes into my drive. I should also mention that at speed (i.e. 5 mph and up) the problem is not noticeable, if it is occurring at all.

Can anyone please provide suggestions on what to look for?

The cap/rotor/wires/plugs and air filter were replaced last September, roughly 15K miles ago. I used all OEM parts. So I don't suspect them. What could cause this to just start happening one day? Was the occurrence at fillup just a coincidence?

I had a Ford station wagon with a clogged fuel filter once, and it behaved differently - loss of power at mid to higher speeds, going up hills, etc. but at idle the problem was not apparent (probably because clogged filters limit maximum volume throughput?). Anyway, I don't suspect the fuel filter.

Should I try running a couple cans of Heet through there when the tank is almost empty?

Any help or suggestions would be greatly appreciated! Thanks.

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It's a shame you still have this problem. But, I would not abandon the belief that fuel contaminants are causing your trouble, yet. I would add some Techron, toss in a bottle of Heet and drive. If you note a positive benefit from this as you drive, then you are likely looking at a recurrent contamination problem and should change gas stations. Also, if you are mechanically inclined, look at the plugs, check your electrical connectors for corrosion and tight fit, do all those cheap check-outs that help rule out little glitches.

I once owned a nice Toyota Corolla FX16 that was a wonderful car (wish I still had it). However, during the winter (lived in Colorado) it became a little snot to drive. Bucking and snorting all the time. We had to use the alcohol blended gas after November until March and every year between November and March the car bucked and stalled and was miserable to drive because the alcohol blend carried so much crud and water into the fuel system. Once Spring was sprung everything returned to normal, the car ran fine again and gas mileage went back to normal. During the deep parts of winter we would get some warm days, also regular as clockwork, in January. On those days the car was the most rotten little beast on the road because the fuel was contaminated and also was vaporizing so fast (higher temps) it would stall every time I let out the clutch.

Just a thought, hope it helps,

230/8

Techron and your average "cleaners" are little better than snake oil.....

Dump a can of BG44K in the tank.....it costs about $15 a can, but it works....something that the cheaper ones barely do.

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OK, my tank was nearly empty (light was on for about 5 miles) so at lunch time I got a bottle of Heet and threw it in there, then added 5 gallons of gas. The Heet bottle says it treats up to 10 gallons, so I should be OK. On the way back to the office, it still did the occasional jerk, but I don't expect the Heet to work immediately (if at all, depending on the cause). I'll drive this tank empty and report back if there is any improvement.

Interestingly, I had to go to WalMart to get the Heet, since the gas station was out of it. But the station attendant told me that if I couldn't find Heet, I could just use a capful of isopropyl alcohol and it would be just as good. Anyone know if that's accurate?

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85 W126 380SE Silver
85 W126 380SE Cranberry
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75 W114 280

Yes, you can use it without concern. There are two types of gas dryer out there, one uses methyl alcohol and the other is isopropyl. Of the two the isopropyl alcohol version is usually the most costly. I'd get it at the pharmacy section of wallyworld where it is dirt cheap, and try to get the 100% strength. The most common is 70% which means it is diluted with 30% water.

230/8

All alcohols act as a co-solvent that allows water to mix with gasoline rather than separating out and dropping the to bottom of the tank.

The trouble with most store-bought alcohols is that they already have water in them. Read the label. If it's 80 percent isopropyl alcohol, it already has 20 percent water, so you're better off using a product that has little or no water in it. Heet is mostly alcohol, and it should be "dry" (read the label).

Oxygenated fuel already has 5-10 percent by volume ethanol, so any water will have a greater propensity to dissolve into the solution rather than separating out. In CA we have oxygenated fuel year-round. In many parts of the country oxygenated fuel is only supplied during the winter months.

Duke

Important Question: Does it seem to be worse if the car has been sitting for two days?

I'd inspect the wires, cap, rotor, coil, etc for a loose connection. Trace the wire from the cap to the coil for shorts. I could see how a sloppy installation of this wire 15k ago would begin to cause problems if the insulation was getting scraped off. And the symptom could be the bucking too, since all cylinders would be momentarily effected and the buck would move the shorting wire.

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I really doubt it's any of those since they are all nearly new, but you never know. I'll check and report back.

I threw a couple bottles of Heet in there and filled up. Overall, the car *seems* to idle more smoothly, but I still get the occasional jerk and the car will still die backing out of a parking space or the garage if it isn't warmed up for a few minutes first.

I'm beginning to think my whole theory of this being related to fuel system is not correct. The occurrence at time of fillup may have just been a coincidence. I will be doing a full inspection sometime in the next week; hopefully I'll find something obvious.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280