Clogged Fuel Filter / Start Problems

[vicmason]

I use biodiesel in my '83 Maxima sedan (and have done so since buying it two years ago). I think I got a bad batch in the tank because I started having fuel delivery problems whenever I put a load on the engine (going fast, or uphill). It starts to choke, temporarily loses power, then takes off again. This has happened to me on occasion in other vehicles and it has meant a clogged fuel filter (so far has never happened in the Maxima, though). As I've been driving it I've continued to fill it with petrodiesel every few gallons so as to gradually dilute then replace the bad bio with new fuel. It's probably at about half and half now.

While I've been out of town this week my boyfriend changed out the fuel filter. Now the car doesn't want to start at all. He's been able to get it going a couple of times but it dies. I think it may be that there's air in the fuel lines, so I asked him to try and work the pump at the top of the filter. He says that the pump doesn't respond so well. Without me being there I can't really tell what's going on. Any ideas from you all?

BTW, I've run out of fuel before in this car and have worked that pump myself (and it seemed to solve the air purge problem). However, in my Mazda pickup there is a valve that allows fuel to escape; which tells you when you're done. But in the Maxima I've not seen anything like that that allows the fuel to run out. Am I missing something?

[goglio704]

Have a look at this thread. I think it will help. http://nissandiesel.dyndns.org/viewtopic.php?t=1182

Feel free to ask further questions, but that thread has some pictures. I've heard they're worth thousand of words.

[vicmason]

Thanks, goglio704! You're right -- seeing the picture is very helpful. I have forwarded the referred thread to my boyfriend so he can try loosening that vent screw and trying the priming pump again for up to at least 50 pumps. I had never done it that much before, it's good to know. He did already fill the new filter with fuel before installing it; so hopefully that will do the trick and we won't have to try the workaround solution of pulling the IP return line.

[goglio704]

If you're still having trouble after taking the steps mentioned in that thread, it may be necessary to bleed a couple of the high pressure lines at the injector. This is not complicated, you loosen the line at the injector and crank the engine until fuel shows up. Just remember to keep cranking times short so the starter doesn't overheat. I can't think of a thread that illustrates this procedure. If anybody else can, please link to it and I'll also add it to the LD section index

[asavage]

I've never had to bleed the injector lines. The system used on the LD28 is self-bleeding on the high-pressure side.

The priming pump on the fuel filter housing is known to fail. Mine's bad on my '82 Wagon. I use a vacuum pump tool on the return line instead.

Never pre-fill a diesel fuel filter. It is very easy to introduce un-filtered fuel to the "clean" side of the filter, and thereby get contaminants into the injection pump. Contaminants are anything larger than ten microns in size -- you are not going to see these with the nekkid eye.

[davehoos]

i often have trouble bleeding injector lines if the car has been standing for some time or its a new intall.

the non return valve at the outlet of the IP can stick and not let the small amount of air/contamination through that in the end of the plunger.

i find if a crack a injector line and or the non return valve holder at the top of the pump the rest of the cyl's join in.

[vicmason]

Okay, so we opened the vent screw on the fuel filter and pumped and pumped until fuel came out. Then we tried starting the car. First, it wouldn't start. Then, it started but died right away. Next, it started and continued running for about 30 seconds before dying; the next time for 60 seconds. Finally, I was able to get the car to run and idle smoothly for several minutes and thought 'aha!'

I did not have time to test drive it then, but later my boyfriend did. He said it started, idled and ran fine -- that is, until he got it up to about 30 mph. It did not want to go any faster. Same symptoms as before, acting as though it was not getting fuel (though we had just changed the fuel filter). Could it be the fuel injection pump? It's leaked ever since I bought it but has not just pooped out. Is it still the biodiesel in the tank? It's now about 50/50 bio and petro. Anyway, he drove the car back home and it died as he was pulling into the driveway. He coasted to a stop in its parking place.

What to do?

[rlaggren]

Same symptoms as before, acting as though it was not getting fuel (though we had just changed the fuel filter). Could it be the fuel injection pump? It's leaked ever since I bought it but has not just pooped out.

It does not sound like the IP is the real source of the problem, although it may be gummed up a little with the bad bio. There are threads here on teeing a vacuum gauge into the fuel line before and after the filter to see if the filter is constricting the supply.

Until you get rid of the bad fuel you don't really have a good starting point to begin fixing the performance issues. The tank has a drain plug that may work; mine did. I don't have personal knowledge on whether the pick-up in the tank clogs easily; others may chime in. IAC, drain the tank, put in a little (1-2 gal) petro, slosh it and drain it again. Then put in another gallon of petro, maybe add a strong dose of injector cleaner and get it up to the filter again; if you don't have a strong wrist you can use a cheap electric fuel pump. There is a slight philosophical issue about just leaving it in the line; search the threads here. If you have not changed the hoses in the fuel lines to be bio safe you may have finally disolved them a little have have bits of hose clogging things up too. But getting clean good fuel through the system is the first step and that may be all it takes.

Good luck. Rufus

[asavage]

The starter will be the next item to die. You've really got to let it cool down for at least ten or fifteen minutes between those long cranking sessions.

You said your BF replaced the fuel filter. At this point, rather than guessing, invest in a vacuum gauge and a line tee. They look like the ones I show in this post. Take the line off of the output line of the fuel filter, install a short section of new line, and your tee. Snake the gauge line under the back of the hood and duct-tape it to the windscreen. Start it and watch the gauge. If it only registers one or two inches vacuum, try to drive it.

If the vacuum goes fairly high -- over five inches -- you have a fuel restriction. Usually the fuel filter. If your new filter is now clogged again, you'll want to drain the fuel tank, and there's a handy bolt back there that's a tank drain. Unfortunately, really bad fuel has components that float and/or are too large to get out of the drain. See pics in this post for gory details of how I know this. On the affected rig with that batch of fuel, even after filing/draining four times, I could not get clean fuel out the line, so I eventually dropped the tank and washed it with a strong base mixture and very hot water -- that did the trick.

For other sources of fuel restrictions, read some of my personal amusing fuel system tales.

If, OTOH, you never see more than 2-3" vacuum, but the fuel starvation symptom persists, you may have a bad feed pump -- that's the lift pump built into the back of the IP. There are pics of a bad feed pump ring & vanes that I had to replace, in the long-running and rambling Tom Sigmond's 1986 Toyota PU thread. I haven't seen a totally failed feed pump in an LD28 yet, but it is possible.

Another possibility is that you are picking up air somewhere. Make that short section of fuel line that I mentioned, from clear tubing. The tubing will be eaten by the fuel in a short time but you can watch for air bubbles and KNOW that there is no air being delivered to the IP. But do the vacuum test first, with regular fuel line.

Guessing is going to drive you nuts. Invest under $30 for a vacuum gauge. Buy a few feet of 5/16 fuel line, cheap stuff is fine as you'll only be using it for hours or days. A couple of hose clamps. You might have to build a tee from brass -- figure $15 max (three 5/16" host barbs x 1/8" NPTM, and a brass 3-way tee with 1/8" NPTF holes, a bit of teflon tape). You'll have a tool that you can use over & over. I have diagnosed a couple dozen fuel system problems with mine over the years.

You've already done the obvious stuff. Time to diagnose.

HTH

Oh, if you really don't think you'll need a vacuum gauge again, I can loan you one, but by the time you pay shipping two ways, you'd be close to paying for a new gauge & tee and some hose & clamps. My ZIP is 98368.

[vicmason]

I know it's been awhile, but I wanted to post the resolution of the problem I had earlier this summer in the hopes that the information might help someone else. So, what the problem turned out to be was that the fuel filter HOUSING was still clogged with rust and sediment. When my boyfriend had changed the filter cartridge he didn't check the housing. Once that had been cleaned out the whole fuel starvation problem was solved! I love it when the answers are simple.

[rlaggren]

> answers simple...

Amen. <g> Glad to hear it's running.


Rufus