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Discussion Starter #1
OK gents...Please read, I know it is long, but needs to be for a good background.
I have written about this issue in a previous thread, but decided to start a thread for this specific topic.

Car: 1991 300CE, 158,000, very good condition, but....

My car when warmed up and a stop light, jerks.
It's as if the fuel is being cut off for about 1/2 a second. The car almost seems like it has the hiccups. There is no particular interval between the hiccups (for a lack of a better word), but it seems like it happens about every 2-10 seconds.
Upon acceleration, if the acceleration happens to fall in the interval of the hiccup, it will show the symptoms for a about a second or two. Accelerates, but I can feel the hesitation.
Once the car is on it's way, it does not do it, or at least I can recognize the symptom. Not saying that it does not occur.
This is fairly new symptom and happened out of nowhere.

What I have done to the car so far.
New Fuel accumulator (old was good)
New fuel filter (old was good, but needed changing due to age)
New seals etc for injectors (the injectors have been changed at some point of the cars life, as they are coper colored) No difference.
No vacuum leaks. I have replaced many vacuum hoses and have tested for leaks.
New EHA o rings, and no leaks at the EHA.
New cap, rotor, correct plugs, etc etc. Needed to be changed.
The car runs very, very smooth!!! I love it!!! It has good power, no complaints there, and economy falls in the 17+/- mpg range city drivings.

The only things I have not touched are the fuel pumps, the fuel pres. regulator, and other less prone to failure stuff that exhibit no failure symptoms.

The fuel pumps (I have 2), have check valves. Has anyone experienced failure with these? Could they be the culprit?

Could the fuel pumps cause this issue?

Is there a fuel pump relay? (I have seen it mentioned a couple of times) but I have not seen the part listed for my car.

My car also has a "two key twist to start" issue. Some might have read about this in a previous thread, but I think that this could be a separate issue.
I get code for the crank position sensor although I have changed that as well with a new one. Not sure why I still get the code. Testing shows the CPS as working as it should.
Could the bad fuel delivery issue (if it is indeed that) be causing the CPS code as the engine does not start properly and causes "confusion"?

I am ready to buy fuel pumps and see what happens, but they are pricey and I do not want to spend money for nothing.

Any ideas?
Any suggested tests?

I appreciate any suggestions, thanks.
 

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Discussion Starter #3
Yes, this is the only controller for fuel in my car. Apparently 91-93 CEs and R129 had only this system. No relay.
It is the ECU for the fuel system and AC. My AC does not work, but due to the well known fault.

MERCEDES=FUEL&A/C RELAY 300SL AND 300CE 011-545-83-32 | eBay

Not looking to buy this used one, posting as reference.

I can't believe I missed Kevin's thread!!!

Thanks cbc atl.

Other help is welcome ofcourse.
 

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Semis,

I have a similar issue on my 300ce. It does take 2 cranks to start generally. Not super long cranks. Also, the hesitation. It is not periodic like yours, but it shows up once in a while. Generally, when you most need the power (ie: merging into the throughway etc). If I keep the rpms, high, then the response is definitely better. It was worse before I changed the fuel filter. Sometimes, if I floor it and it feels like it is about to die-but does not...Do tell if you resolve your issue. Good luck!
 

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Discussion Starter #6
OK, I just got my fuel pumps. I bought a pair from fuelpumps.com for $90 shipped.
They have 1 year warranty, great feedback and at that price, worth the experiment.
I will be updating once I change them, probably by Sunday night or Monday morning.
Wish me luck, at the hiccup situation is getting worse. It now does it upon acceleration.
My start issue is about the same, but when first starting in the morning, it will always fire up the first time. After that start, it will fire up on the second Short crank.
We shall see soon enough.
 

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OK, I just got my fuel pumps. I bought a pair from fuelpumps.com for $90 shipped.
They have 1 year warranty, great feedback and at that price, worth the experiment.
I will be updating once I change them, probably by Sunday night or Monday morning.
Wish me luck, at the hiccup situation is getting worse. It now does it upon acceleration.
My start issue is about the same, but when first starting in the morning, it will always fire up the first time. After that start, it will fire up on the second Short crank.
We shall see soon enough.
Anxious to see what happens with the new pumps! Do you have a way to test pressure...it would be nice to see the 'before' & 'after' readings? I don't consider installing new pumps 'throwing' parts at a problem. Old, high mileage pumps need to be replaced anyway.

Best of luck! Make sure the pumps have NEW check valves.;)

Kevin
 

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OK, I think I see what you did, because I put in my car and it returned one US made Walbro pump for $135.:eek: You must have speced out with the US made Hayg for $44.99?

I hate decisions like that.:( You would ASSume on the surface, that the Walbro has to be a 'better' pump, but necessarily so in the field.:confused:

Kevin
 

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Discussion Starter #9 (Edited)
Kevin you are right. I accidentally spaced the address.
The reason I went with these pumps, it will show me if the pumps are the problem.
They should work as a diagnostic tool. So for $90, for me it is worth it. Will they last as long? We shall see, but I do not plan on keeping the car for another 20 years.
My car has 2 pumps, so I could not justify spending $280 on a hunch.
I do have a fuel pressure gauge, but I have not researched on where to hook it up on my engine. I used it for other engine builds in the past.
If someone can give me that info, I will try and hook it up and post numbers.

The other reason that I went with the Hayg pumps vs. Walbro (besides cost) was that I really do not believe that the Walbro could be that much better. Everything nowadays is outsourced or made elsewhere than the original equipment which was superior in theory.
All of this is a guess, but a realistic guess nowadays.
Well, I guess this is an experiment that might be worth the effort if the pumps turn out to work good.
Plus made in the U.S. for Hayg must count for something right? I hope so...
 

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Kevin you are right. I accidentally spaced the address.
The reason I went with these pumps, it will show me if the pumps are the problem.
They should work as a diagnostic tool. So for $90, for me it is worth it. Will they last as long? We shall see, but I do not plan on keeping the car for another 20 years.
My car has 2 pumps, so I could not justify spending $280 on a hunch.
I do have a fuel pressure gauge, but I have not researched on where to hook it up on my engine. I used it for other engine builds in the past.
If someone can give me that info, I will try and hook it up and post numbers.

The other reason that I went with the Hayg pumps vs. Walbro (besides cost) was that I really do not believe that the Walbro could be that much better. Everything nowadays is outsourced or made elsewhere than the original equipment which was superior in theory.
All of this is a guess, but a realistic guess nowadays.
Well, I guess this is an experiment that might be worth the effort if the pumps turn out to work good.
Plus made in the U.S. for Hayg must count for something right? I hope so...
Yeah, I understand...that was my thinking on the pumps as well. I've searched and searched for feedback on Walbro versus Hayg versus Bosh. I can't really find anything outstanding....which would indicate that all three are very serviceable in actual use and maybe the best option is the best price. Like you said though, sans the Chinese and crap products.

The ports are on the fuel distributor itself...MB suggest using two gauges so you can see the difference between the lower port and upper port at the same time. Not necessary, but very handy. I think ps2cho has this pictured on his site.

Kevin
 

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From what I've read,if fuel pumps are bad or going bad,you will hear it.high pitch sounds, mine has issues also,plan to look into mas unit ,control's pumps ,a/c comp, Idle control valve ICV,sounds like you've replaced almost all!
cold solder joints failing in most of the relays in these cars after 20 years,hell seems the mechanicals last a long time in MB but the electronics don't
so many relays ,so little time ! luck!
 

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Thanks Kevin, I will search a bit on the fuel pressure gauge placement.
Oh and the pumps do come with check valves.
Forgot to answer earlier.
Sam...Robert's site (ps2cho) is:http://w124-zone.com/

If you scroll down in his DIY for engines, you'll see his dual gauge set-up. I was wrong about the factory method; they use one gauge, but a switchover valve to read upper and lower chambers alternately.

Kevin
 

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Discussion Starter #14 (Edited)
lowesguy,
yup the pumps will be loud when failing or about to, although mine are not real loud (I can hear the buzzing when close to a wall while driving), for the cost, it is worth exploring. The MAS is more expensive than both of my pumps and I have no other sign of it failing. My AC does not work anyway, never did since I bought the car. Idle etc is good.

Thanks Kevin,
I took a look and it is way too much work for now. I barely have time to R&R the new pumps.
Hope that will be it, but...not very sure.
 

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Discussion Starter #15
Interesting twist this midmorning...
Early this morning the car starts fine with about a second or two of extra cranking.
Usual when temps are cold. Idle fine and moves fine until the engine warms up, then back to the hiccup situation.

I stopped by the new restaurant construction, was there for about 2 hours, around 9 I get in the car to leave for my other restaurant and the car starts up but dies immediately. This happened about 4-5 times until I decide to keep the gas pedal slightly depressed until it idles.
That worked, idled fine and took off.
On the way, the hiccups are gone!!!
The car idles and accelerates beautifully, like before.
I am crossing my fingers that it stays that way.
I am not sure what could have caused this change. I have NOT changed the pumps yet as I had no time. I am wondering if the MAS had wigged out, reset it self with the extra cranking. Well, I really have no clue. We will see on the upcoming days what happens.
Have a good one.
 

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Interesting twist this midmorning...
Early this morning the car starts fine with about a second or two of extra cranking.
Usual when temps are cold. Idle fine and moves fine until the engine warms up, then back to the hiccup situation.

I stopped by the new restaurant construction, was there for about 2 hours, around 9 I get in the car to leave for my other restaurant and the car starts up but dies immediately. This happened about 4-5 times until I decide to keep the gas pedal slightly depressed until it idles.
That worked, idled fine and took off.
On the way, the hiccups are gone!!!
The car idles and accelerates beautifully, like before.
I am crossing my fingers that it stays that way.
I am not sure what could have caused this change. I have NOT changed the pumps yet as I had no time. I am wondering if the MAS had wigged out, reset it self with the extra cranking. Well, I really have no clue. We will see on the upcoming days what happens.
Have a good one.
Do you have fly-by-wire that year or the mechanical linkage?

Kevin
 

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Discussion Starter #19
I will report back tomorrow and keep you updated. I hope it is fixed.
It just seems weird. A hard start situation fixed the hiccups. (Not the 2 key turns to stay on situation).
But why and how? Who the heck knows....
 
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