Are these signs of a plugged filter and/or failing feul pump?
 

For about a month or so I didn't start my car (1986 300E W124). I was away on business. It was running fine when I left, when I got back it initially started fine. I went to the bank without any problems. After stopping by 7-11 I started the car and it began to miss. Both at idle and while pressing on the gas. I figured maybe the line got some air so I let it go.

Today the problem persisted. It even died out at a stoplight. It sounded like it was trying to suck some gas. After getting a haircut, I had a hard time starting the car. When it finally started, it missed for a while, then suddenly it cleard up. I made it home without any problems.

I have a very important business to attend to next Sunday. I cannot afford to get stuck. Are these signs of a plugged fuel filter and/or a failing fuel pump?

hmmmmmm.....

too short of time for gas to go bad......

you got me!

did a little research...I think I'll try changing the fuel filter (might be plugged) and probably replace the fuel pump relay (malfunctioning)

The OVP has be replaced before (to correct a rough idle) so I'm familar with that problem.

This problem is more of a hesitation, lack of gas. I initially suspected the fuel pump, but my dad said the car wouldn't start if it was. The pump either works or don't work.

Can anyone give me their opinions?

stalling, hesitation and bucking
 

feels like a filter problem. It is a fact that the car will start with a clogged filter! (gas pools aftershutting down) If you need constant gas pedal pressure to keep going and it bucks (or stalls) probably clogged filter. good luck Abe G

yeahm and with that age, I am sure that a $21 filter will benefit alot and still be relatively cheap insurance!

A fuel filter is a good place to start. Needs to be replaced every 30,000 miles or so. The fuel relay is another thing to be looked at. you could remove and bridge it (terminal 30>87 I think) to see if the problem remains. Distributer cap & Rotor as well as spark plug & wires can all do the things you describe. The fuel pump can actually continue working and still not produce enough pressure, so put that too on your check list if it is older than three years. You can also remove the pump and clean it's insides (with care - diesel fuel) by powering it externally and reversing the polarity, thus having it work backwards spewing out crud.
I had to do all the above to fix my car.good luck

abe g
I agree, that's what it initially felt like. I've got a fuel filter already. Just doing some research on RR. I can't get to until Sunday. I'll have to make alternative arrangements to make an importantant meeting Sat. I can't afford to get stuck on that peculiar day.

Rahulio1989300E
Yeah, I'm hoping this is the problem. But the more I research about this problem on this forum, the more I cringe. I'd hate to replace things if they are not needed.

gidpor
I've got my fingers crossed. I'll start with the filter (it's been about 30,000 anyway), if that doesn't work I'll check the relay. If I can find a relatively cheap one, I'll just replace it. The distributer cap, rotor, spark plugs, and wires were all changed a few months ago (all new). There were done when I was trying to locate a rough idle problem. Ended up being a loose vaccuum and the OVP relay. I already bought a new Bosch fuel pump last month. I just need to install it. The last time my mechanic worked on my car he recommended that I change my fuel pump. He said a noisy working fuel pump is a sign of near failure. He was going to replace it, but I told him I'll do it myself. Are The fuel pumps really replaced every 3 years? They are kind of expensive. I paid something like $200 for the fuel pump.

DOes your 86' have a single or dual pump setup?


No, I don't think 3 years is the normal service life of a fuel pump- don't sweat it.


Michael

If this is a problem that presist at idel, then a fuel pressure test will at least rule out anything in the fuel delivery system.

1) Have correct fuel pressure while engine is running AND MISSING: No fuel delivery problem. Could be air flow sensor on down, ignition or compression.

2) Dont have correct pressure: start with filter first, its cheepest.

John Roncallo

Well , since you've done some of the items that are on the regular - to check first - list, then you are a step ahead in the elimination game already. That's good.
The fuel pump (I have one on my 126) should last much longer than three years though sometimes they don't. Cleaning mine kept it going for another three years. You might want to change the filter first, while at the same time checking the fuel pump relay, both DIY items and follow that with a fuel pressure test. Good Luck

Gidpor: Concerning cleaning of the fuel pump you mentioned, did you just do this on the bench making the pump run backwards using diesel fuel? How long did you let it run?
Thanks
Doug

I've always found that fuel pumps are a binary thing. They operate, or the do not. Never experienced partial operation condition.

I'm not saying it's not possible, just never seen it myself.

You may have developed some condensation water in the fuel, in which case it will clear itself up, or you can hasten with drygas. Found out with the 300E that water in the fuel will be evident after you park nose down but not nose up. Presents as a baffling intermittent problem (like yours).

Got my water from contaminated gas station tanks.

Spoke with my mechanic over the phone and described the problem.

He said it sounded like a fuel pump problem. While changing the fuel pump, he said I might as well change the fuel filter too. If that doesn't clear it up, he wants me to bring it in.

I asked him about the fuel pump relay. He said it either works or doesn't work. Since my car still starts, he doubts it's the fuel pump relay. I've read different experience in this forum.

Comments?

Sounds like my 560....It got so it would only do it (not start) when hot. After a fuel filter, new fuel lines, and an accumulator, they now tell me it's the relay. Shuts down the fuel pumps when it gets hot... we'll see.

yes, I ran the pump backwards on a bench a couple times for just a few seconds or so while it was sucking (from the "wrong" side) on some diesel fuel. It immediately spewed ugly stuff out.
I am no expert , but was told that the pump was not binary in behaviour. So I just mentioned that.
The fuel pump relay too is not necessarily a yes or no relay. It can be intermittent because of temp changes. The solder points expand and shrink.
That is why it is good to either jump it or borrow a good relay for a test.

I don't know if they are the same, however the relay for my 75 450 SL was really inexpensive from Fastlane. Since I am having similar problems I also replaced the fuel filter and as a new fuel pump is over $600.00 I didn't want to just try it to be trying it. I have to be able to afford the gas also.

Same deal with relay as for pump. Tends to operate or not. May operate for a few tries, than not operate for a few tries, but I have not seen a partial situation here either.

Could be the filter or the fuel accumulator, or an induction problem, or an electrical problem.

If you do replace the fuel pump (only 1 pump for you), get a Bosch. Do not be tempted to get the 'made in Taiwan' pump that many parts stores stock. Will be loud, and will not last long. Been there.

I like the sound of experience, as it sure helps. I did find a pump at NAPA for about half price and after what you said I'll bet it is not a Bosch but a knockoff.
Thanks

UPDATE:

Well, after changing my fuel pump and filter, the car still ran rough. In fact, after starting it, it ran fine for a few minutes then started hesitating again! I don't mind changing the fuel pump (it was noisy anyway...sign of failure) and the fuel filter (first change in 3 years) but I didn't want to go on a "fishing trip" and start changing parts randomly. I was going to change the fuel pump relay next before taking it to my mechanic, but I decided against it because I figured at approximately $130, I would be better off taking this in to my mechanic and spend that money on a complete diagnostic and just change what needs to be changed.

When I brought the car in, it started fine and ran great for a few minutes. I thought "Great, it'll run fine here, and start messing up later when I get the car home" I was kind of pissed off because I had towed it pretty far. Luckily the problem reproduced itself a few minutes later. The mechanic first checked to make sure I installed the new pump and filter correctly, he then checked the coil (working), then replaced the fuel pump relay (no change in performance). At that point he told me I could leave and he'll run a complete check on the car.

The next day he said my car was ready. He ended up cleaning out the fuel injectors and replacing the temperature sensor. He told me that the fuel pressure was fine. After replacing the temperature sensor, the car seems to run fine. He warned me that this may not have fixed the problem, but after changing the temperature sensor, the car ran good the whole day that he was testing it. He said sometimes the temperature sensor causes the car to run poorly and have a hard start. I paid him $118 for his work (sensor was $60, parts cleaner $2, rest was labor to clean out the fuel injectors and to clean around the coil and the distributor) and went home. I hope this solved the problem. I'll update this post if my car still runs poorly. If you don't see another post by me on this thread, the problem has been solved.

Comments anyone?