Mercedes-Benz Forum banner

1973 Mercedes benz 450SL Running Rich after replacing Fuel pump

33K views 85 replies 14 participants last post by  6punkt3 
#1 ·
I recently replaced the fuel pump on the 450SL and now its burning 30$ worth of gas in 1 day, does anyone know what could be the problem?

this is the exact fuel pump I replaced it with
 
See less See more
1
#2 ·
I recently replaced the fuel pump on the 450SL and now its burning 30$ worth of gas in 1 day, does anyone know what could be the problem?

this is the exact fuel pump I replaced it with
$ per day means nothing, but it must be higher than you were experiencing before.

How many miles/day? It wouldn't take but about 70 miles to eat that much gas in a typical 450SL around town, and maybe 105 miles on the highway...

Have you ruled out leaks associated with replacing the pump?
 
#3 ·
Before replacing the fuel pump, it wasn't burning that much fuel. I drive about 25-30 miles on highway speed.

I was thinking if it leaks, it would've been the old hose that I crimped off on the hose from the tank to the fuel cluster? but if it leaks, you would still smell it, when I replaced the fuel pump, I checked for leaks and there wasn't any leak coming from any of the hoses.

could it be the wrong fuel pump?

is there anyway to adjust the fuel output?
 
#7 ·
Before replacing the fuel pump, it wasn't burning that much fuel. I drive about 25-30 miles on highway speed.
Since you have not filled in your profile, I have no way of knowing what gas prices might be in your area. Given a guess of $4.00/gal, it would take 7 or so gallons to equal your estimate of $30/day. At 10mpg (typical for poor tune 450Sl around town), that would be about 70 miles. Since you drive only 30, it would mean you are burning at a rate of less than 5mpg, and I don't think that is possible without copious amounts of black smoke, fouling plugs, etc... Most likely a leak, or the metrics I used that you reported are way wrong...

Start 'er up and look underneath the right side rear to see if leaks... I'm betting yes!
 
#4 ·
If the fuel pump had been dyng over time, (putting out less and less pressure/fuel), the mixture might have ben adjusted to compensate. It might just need to be checked and adjusted. Unfortunately, I don't know enough about K-Jets to say if that's an easy or difficult job or what equipment is needed.
 
#15 ·
I seriously doubt this, as the amount of increased usage he is reporting is over double what it was prior to the repairs... Without reports of overly rich running, ie excessive smoking and fouling of plugs, I doubt he is running rich due to the pump change.

Of course, I could be very wrong...

Don't rule out hose(s) rupturing further downstream. The new pump may have compromised old lines with its possibly higher pressure...
 
#5 ·
could a leak caused it to make the gas gone that quick? I know fuel leaks are hard to detect because it leaks out in a form of vapor if its small, I was wondering if it could be the hose from the tank out line to the dampener could be the culprit because I crimped that line before i replaced the fuel pump and I know those lines are brittle and old and could cause a crack with hard pressure crimping. anyone know if that could be possible?
 
#39 ·
I am sure you know that you will have to drain the tank to replace that line. The OE line has a crimped fitting at the upper end and required the threaded fitting to be unscrewed from the tank. I have not done this, but others have and there are some posts somewhere here. It is apparently hard to get at and needs a special wrench. But it provides an opportunity to clean the in-tank screen.

On my '72 car, someone had replaced that line and had installed clamps at top end. This made it a lot easier to replace when I did it.

PS: With that aftermarket pump (what type is it?) I would definitely check the pressure and flow - I never ever found an aftermarket pump that had the right specs for the d-jet. And be aware that the pump most likely does not have an integral relief valve, so if for any reason the fuel pressure regulator or the return line to the tank was blocked, you could have rubber hose connector leak in the injection piping. (This info came directly from Bosch who now do have a replacement pump $$$)
 
#8 · (Edited)
Newbie ?

Hi
First , it would be nice to know, where the person is, that I am writing to/for, maybe you could add that to your profile.

Second, with a bunch of fuel lost and unaccounted for, I always look under the car thoroughly to detect leaks !
However:
It may be your whole fuel system needs a check up.
(Not as bad as it sounds.)
in 1973 they used the fuel pressure pump to aid in the injection, meaning, that the pump is providing the fuel pressure and the injectors are opened electronically.
It all is regulated by an electronic brain and the injectors are open by a signal from the "Trigger" points (located in the bottom portion of the distributor).
If you don't see a (green) wire leading to the bottom of the distributor, then you have a newer engine installed.
It is not uncommon that 1 or MORE injectors are stuck open and dumping fuel constantly in your cylinders while the car is running.
Check you oil level and how thinned out the oil is.
It will have an effect on your camshafts eventually....
Given a new Pump with more vigor, you might just be blowing that fuel right through..........

Sorry, that was the short version\. Ask if you need more detail.

Good Luck
 
#9 ·
Thank you for all your input, and I'm sorry I didn't have time to update my profile.

The gas over here in California is around 3.89$ a gallon.

I did a little of searching on the forum, it is a D-jet series, and I've seen a tutorial of how to fix the old fuel pump, but I ended up buying a new one already. I'm thinking of fixing the old fuel pump as well. But I think the problem isn't the fuel pump, but it might be the hoses since their pretty old and I might have over pinched them with my tool, since the first hose from the dampener to the fuel pump was cracked once I crimped it with the tool, or maybe I didn't tighten the hose clamps.

I got a quote from the dealer for the fuel tank out line hose for 19.38$. I will check this week if its leaking or smelling gas underneath the car.

Is there any other way to check if there's a fuel leak other than smelling it? is there a fuel leak tester?

Thank you for all your inputs and help. I really appreciate the fast response as well from this forum! I'm starting to love this forum already :)
 
#14 ·
Is there any other way to check if there's a fuel leak other than smelling it? is there a fuel leak tester?
I became aware of a very large leak under my car (in the dealer's driveway) when a frightened lady rapped on my window and said, "Your car is sitting in a big puddle of gas." It was. Fuel line (improperly installed, crimped - prior owner) had broken, and fuel had pumped out as I tried repeatedly to start it.

The aggravating part was, when the dealer installed a new line, he installed it exactly the same (improper) way, and the crimped new line broke again in 2 weeks.

That won't help with your problem, but the pump, accumulator, fuel filter, dampener, and connecting lines are easy to see. Do check them for obvious leaks. However, RadioTek's suggestion that your system may have been adjusted in the past to account for low pressure (lean condition) is well worth considering.
 
#13 ·
Generic hose

That hose , if not mistaken is a generic , by the foot, fuel line hose (3/8 inner diameter) going for about $1 or 2.
if the other end, the screwed on fuel pressure line is bad , you're better of at the dealer.
As the name says the second has (a lot of) pressure on it......
I am in so Cal,

Good Luck
 
#16 ·
That does not look like the proper pump for the car. It is obviously an aftermarket pump and there are few, if any, of those that are correct for the D-Jet.

If it is one that is intended for the later K-jet cars, it will be capable of much higher pressure and it will not have an internal relief valve as the D-jet pump does.

I don't know the exact discharge pressure for the OE K-jets, but I believe that those pumps could reach 80 or 90 psig if deadheaded. The D-jet pump is limited to a max of about 45psig by the internal relief valve to safeguard the injection piping (rubber hose & clamps).

If that pump has a higher capacity and is used with a D-jet without readjusting the fuel pressure regulator, the rubber hose connectors throughout the fuel system could see higher pressure than they are designed for and sooner or later leak and the car would run rich

Have you checked the fuel pressure in the injector rails? It should be about 30 +/- 1 psig. That is the first thing I would do after checking for leaks. No need to start car. Just turn key on & off a few times while checking pressure.

Once you have pressure under control at 30 psig, you should do a flow test by disconnecting the return line from the pressure regulator and collecting the gas for 30 sec. You will have to jumper the fuel pump regulator to get the pump to run for that long (it is designed to cut off after a few sec if the engine is not running) Pump should put out 1 Litre/30 sec. Method of checking this should be in engine manual.

If you are still rich with proper pressure, I would suspect the trigger points, but it could also be cold start valve or injectors stuck open. I think I posted here or perhaps on Peachparts Vintage forum on how I tested the trigger points when I had a rich running situation. The MB test in the manual doesn't tell you everything.

Finally, you will need to check the mixture and only way is with some type of exhaust analyzer - MB specify numbers for %CO (I posted full official MB mixture specs here some time back and they are in Stickies (EG) under Lfedje's name.)
 
#17 ·
I tried installing that short hoses with the 3/8 fuel line, but it was so tight I couldn't install it. So I got a bigger hose to fit it in there smoothly, does it matter if it's bigger in size? And with a regular rubber hose? Or does it have to be a high pressure fuel line with braided on the outside?

As for the car running rich, the car wasn't running like that before, so I'm suspecting there's a leak by the hose cause the car was running fine and wasnt using that much fuel as it is now. I might assume there is a leak. I car maintenance has been kept up to date.

I'll take some more recent pictures for you guys this weekend. Thank you all.

I hope to find the culprit before the car is driven.
 
#18 ·
That hose is the suction hose and has little or no internal pressure. It is an odd metric size, not 3/8" and is different on early D-jets than on later cars. So long as the hose fits over the barbs and doesn't collapse under vacuum it should be OK.

Let us know the fuel pressure.
 
#23 ·
Given his question is indicative of lack of familiarity with the 117, the volume required to answer these and ensuing follow-up questions are best not rehashed in another set of posts... Especially when they have already been addressed in full in other threads.

I'm not in the business of hand-holding nor spoon feeding, when the information is so well presented in other formats, ie the EGv107. Our Mods and members have done an outstanding job of organizing the reference material, backed up by real-world member experiences... If one does not have the time to peruse them first for answers, I have no patience to suffer their questions ad infinitum... No offense intended to any one, just a statement of my position.

Yeah, I'm an old fart...
 
#22 ·
Oh Crap, My Bad!! :eek:

Sorry, for some reason I read his as a '78.

I had a much similar problem with mine when the fuel pump was going. It was leaking from the pump itself. I replaced the pump, and the place I got the pump from had the special size hose in stock, so I bought enough to replace both pieces.

There is a high likelihood of a leak in the hose, from what is described. But I would also check under the hood for possible leaks along the fuel rails and attendant hoses. I had a few leaks from old hoses that were remedied by replacement.

Just remember that these are the high pressure lines under the hood for the injection system, so you need to get the high pressure hose.

This damn head cold is messing up my life, if I can't note the existence of another D-Jet when a question is asked. Grrrrr :eek:
 
#35 ·
Old rubber things don't like to be disturbed. They're set in their places and get grumpy when fiddled with. They crack and break and leak at random.

Take enough time time to be thorough in your check-out of the fuel system. Have a good light source handy, to get underneath the car. There is a safety aspect to this, so use the common-sense precautions. I'd hate to see an article about a 107 going up in flames due to a fuel leak.

Scott
 
#36 ·
I've had lots of leaks in the old hoses where they connect to rails and injectors. As a temporary fix, I've tightened down all the clamps and added clamps on the tops of all my injectors. It seems to have stopped the several fuel leaks I've had in my rails and injectors. My hose is old and hard, but seems to be holding up. I guess the rubber shrinks or the clamps loosen with age. The hose on my car is probably older than me.
 
#37 ·
So I checked under the vehicle and sure enough, the hose connecting to from the fuel tank to the dampener is leaking in the back.



and this is the new fuel pump and hose I replaced, but the other hose is damaged so I'll have to order it next monday and install it on wednesday. Hose might be too long, but does it matter?



As for checking the Fuel pressure, I haven't gotten the chance to get the fuel gauge, I'll have to do all that next week and rent it from autozone. As for now, I'll replace the hose first and check the fuel pressure afterwards. Thank you all for your input.
 
#38 ·
As for checking the Fuel pressure, I haven't gotten the chance to get the fuel gauge, I'll have to do all that next week and rent it from autozone. As for now, I'll replace the hose first and check the fuel pressure afterwards. Thank you all for your input.
Well... No surprises there.
After you insure all leaks are repaired, you probably won't need the the pressure check, unless rough running conditions indicate. I'm betting you return to previous conditions, unless the replaced pump is the incorrect one...
 
#44 ·
The E8145 spec says it has a range of 25-35 gph which is 1.57 to 2.19 l/min, but they never replied when I asked them at what pressures the flow was measured. You need 2l/min at 30 psig at about 12.5V. The Airtex pump probably does not have the relief valve, but seeing they specify it for use on the D-jets, it probably has the capacity needed. Nevertheless, I would check your fuel pressure setting because it is ultra important in ensuring proper injection and mixtures.
 
#45 · (Edited)
^^^ I think all the advice about checking pressures is good and proper, if you are still having operational concerns. Firstly, have you found and repaired all the leaks? When yes, then you can assess the operation of the car, and decide if you need to go further. If you had proper function before the pump change, then likely, you will afterward, if the pump is the appropriate unit for the car. You can drive yourself crazy, and broke, chasing issues with these cars, especially if you don't follow a methodology which includes realistic expectations and evaluation. Sometimes, you can be chasing something that is not a problem (how many threads have started by, "... my car is running hot at 100-105C, what do I need to do..."

How is the car running since you have the leaks repaired? Are you truly running rich, or was this diagnosis solely from the increased consumption you experienced, ie the leak(s)...
What other symptoms do you experience that indicate to you the car is running too rich? Starting issues? Smoking? Fouling plugs? Stumbling/poor power? Expect 10-12mpg around town from reports I have read on the D-Jet cars, and not much better on the highway... Can you locate a shop that can check the mixture for you by gas analysis from the exhaust? Tuners at dynos can do this, and I have seen them in action at the local "hot Rod" shops that would open their dyno up to clubs on select weekends.

Take things one step at a time, and determine if any improvement at each step...
1. Insure all leaks are repaired, then evaluate the cars operation...
2. Check the fuel pressure/delivery, affect any repairs, then evaluate...
3. Check basic tune, trigger points, plugs, etc; affect repairs indicated, then evaluate...

Good luck, and be sure to report back when you have the leaks repaired, and evaluate whether the fuel consumption issue changed any...
 
#46 ·
Internal relief valve

I visited Airtex's site, and captured the following cutaway dwg of their rollervane pumps. They purport to have internal pressure relief valves incorporated into their design. Now whether that applies to this particular pump or not is unknown...
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top