Help!!!!Engine stumbling as though it is starving

Problem:
Yesterday I was driving about 95 when the car stumbled a bit. I made it home but the engine was suddenly stumbling between 3k and 4k rpms. I looked at the fuel through the translusent tube and it appeared to have more air in the line than I had ever seen before. I tightened the fuel filter lines to ensure it wasn't sucking air. I have read the FAQ's and it doesn't have the same symptoms of a MAF. This morning I got up to seventy and it started to stumble again even when pulling away from a stoplight at around 2k RPMs. I disconneceted the MAF and it was still stumbling.

Background:
I have a 2003 Jetta Wagon with 76k on the odometer. I was upsoluted 50k miles ago, ventectomy, mufflerectomey,2" lift.
I changed the fuel filter,air filters,oil filter and oil 6k miles ago. I have been running b-99 for the past 2 months and have used amsoil since the car was new.

Any suggestions?????????

I forgot to note that no check enfine light has come on.

Thanks

Did you change the filter before you started using B99? It's possible that it's clogged. I've heard that biodiesel has a cleaning affect.

I'm changing the filter right now, I'll let you know if that was it.

If you've had air in your fuel line you might also have to purge air from the injectors.

I don't think so if it runs.
Could also be the fuel pickup I guess.
I hope it's not the fuel pump.

Thanks for all the help, I think it may have been enough restriction in the filter to cause air to possibly by-pass the o-rings on the filter. I have only driven it two or three miles but it seems to be OK now with no air in the translucent fuel lines. I'm a few hours late to work so I now will give it a 150 mile test drive to work and home tonight. If I don't get back to you tonight, that means I'm on the side of the road somewhere. But God willing, it's fixed.

This web site is invaluable,

Re: Help!!!!Engine stumbling as though it is starv

NO YOU DON'T!

DO NOT OPEN THOSE INJECTOR LINES unless you are changing the injectors / nozzles! The air you are seeing is most likely from fuel starvation from a plugged filter. THAT AIR DOES NOT ENTER THE INJECTORS!

Think of the injector pump as a big "holding area" for fuel. The inside of the pump is completely filled with fuel, surrounding and lubricating the parts. For the outgoing fuel to the engine, only a tiny amount of that fuel bath is taken on each turn of the engine, and it comes directly from the pump itself. The air you see from the filter to the pump body is because the pump generates a powerful suction (separate from the delivery to the engine) that pulls fuel from the tank, through the filter, and into the pump body. This primary flow is many times faster than the need of the engine, and the excess flows BACK to the tank to start again. So where is that air going? Mostly to sit at the very top of the inside of the pump, since there is not enough flow to keep the entire pump filled with fuel. The engine stumbles because it is draining the rest of that fuel bath from the inside of the pump, and the fuel is not being replaced fast enough.

Do not ask more of your engine than it is capable of delivering right now, or you WILL stall it out and it will be a pain to restart. You won't do damage, but it takes a LOT of wear on your starter to get it going again. In my personal opinion, I think this is a bad design, not having a positive-flow fuel pump in the tank to keep fuel flowing all the time through the injector pump. But that's just my opinion.

Run your engine slowly until you have a filter ready to install. Get it SOON. TODAY. Once you do, also have a bottle of Power Service to pre-fill the filter with, it makes your engine's job a lot easier. Shut off the car, change the filter, prefill through the temp valve hole in the filter, and then restart the car. Since the injector pump is still full of fuel (because you ran the engine SLOWLY, right?) The car should fire right up. It will then rapidly purge the air from the line, while it IDLES. DO NOT DRIVE OR HIT THE PEDAL FOR AT LEAST 5 MINUTES!!!! Let the engine idle and have plenty of time to re-fill the fuel lines and that fuel bath in the pump, and purge the air itself. As long as your engine is running, you are in a good place. If it stalls out, because you didn't get the filter fast enough, or whatever... Then change the filter, pre-fill again... And have a spare battery or jumper car nearby. It WILL take several minutes of cranking to get it restarted.

Trust me on this stuff, I know from too many experiences exactly where the bottom of my tank is, and how to quick-change a filter on the side of the highway.

--Jim

I experienced something similar recently after disconnecting my lines from the fuel filter to run a can of diesel purge. When I hooked everything back up it seemed like there were more bubbles than normal in the clear line, but the car had started right up and ran OK so I figured it would work itself out.

A few hours later I go to restart the car and it takes a decent amount of cranking to get it to fire. Then I noticed there were still many bubbles in the fuel line. I checked the spring clamp on the feed line from the filter to the pump, and it looked a little bent out of shape. I fortunately had a couple spare clamps on hand, so I replaced it and voila, everything was fine. The clamp I took off was indeed "stressed out"!

So, if you've gone through a few filter changes and are having starting problems it's always possible that your clamps are weak.

Re: Help!!!!Engine stumbling as though it is starv

You kept using those cheap retard clamps?

Yea, I guess those could contribute to air in the lines, but I don't have those anymore, I pulled them the first time I changed the filter and replaced them with solid screw-drive hoseclamps. Much more reliable.

--Jim

Re: Help!!!!Engine stumbling as though it is starv

Freds TDI CClub,

Thanks for the help, it was a clogged fuel filter after all, and in less than 7k miles. I changed the filter and drove 150 miles to work and back like a madman. The b-99 must have clogged the filter in no time flat, if this happens again, I'm back to dino diesel. I appreciate everyones timely response. And if you see this again, pass the information along.

CharlesTDI

Re: Help!!!!Engine stumbling as though it is starv

It shouldn't happen again, as your tank's sludge-covered walls are now shiny clean again.

It's the dino-D that cruds up the tank, then the cleaning power of biodiesel scours it off... and right into the filter. A good addition to your car would be a pre-filter from your local parts store, Purolator fuel filter model #20011. $2, small paper-in-plastic filter that you can SEE when it turns dark and cruddy. I swear by these, they have saved me several filters. I very good investment.

--Jim

Re: Help!!!!Engine stumbling as though it is starv

Geordi, Where did you install that Purolator? Just upstream from the main filter?

Sounds like a pretty good idea.