Hello all!

I am having a slight hesitation under heavy to WOT acceleration. This happens in the upper RPM range, above 3900 RPM. The car will stumble for a maybe a 1/4 to 1/2 second and then power comes back on.

Today, I left the trans in 3rd and accelerated onto the highway. At about 110, the engine stumbled up to about 120, then I shifted into 4th and from 120 to 130 all was fine.

I also tried a high RPM run in 2nd, took the car to 80 mph in 2nd, and felt the stumble as well, but not as bad as when in the 100+ range.

Plugs are new, cap/rotor only have 20k miles on them. Fuel filter is new with only 10k miles. Car has 82k miles on it. Had the engine wiring harness replaced less than 6 months ago.

I think it may be the fuel pump going out on me. Can anyone tell me what the fuel pressure is on a '92 400e at idle and under load? I try and connect a gauge to monitor the pressure while under load.

Thanks!

-David

I have this same problem on my 400E to a tee. Can anyone out there suggest a starting place?

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

I have had a similar problem with my 92 '400E
in rpms above 3K. Fuel filter has been changed out, plugs and rotors and harness checks out....What else should I look at?

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Matt
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92 400E 128K
99 GMC YUKON 88K

A very cheaper first check would be the fuel pressure regulator before replacing the fuel pump. Look for my thread on my 400E. The generic pressure would be 38PSI at idle and 45 PSI with high vaccum (low pressure) on the fuel pressure regulator that sits on the fuel rail near the fire wall under the air filter housing. My car runs like a champ now.

It takes a lot of fuel rate to move a car at 130 mph, and it will be about the same rate whether in 3rd or 4th. The difference is the engine speed, and missing at high rpm might be a coil or HV problem.

If the problem only shows up in acceleration tests, try to keep the variables from confusing the issue. E.g., try to keep apparent acceleration the same as you pass a given speed in different gears. This can isolate between fuel delivery and ignition problems. a vacuum gauge connected above the throttle valve can also isolate an airflow meter problem.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Thanks Rafi & Steve....Good starting points and will report back when I have zero'ed in on the cause.

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Matt
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92 400E 128K
99 GMC YUKON 88K

Hi Rafi,

I have the same symptoms on ny 206E ,1988, could you explain how you checked the fuel pressure? any pictures?

thanks

At idle, my 92 400E measured 50-60 PSI at the fuel rail

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99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.

CC260E I did not have the tools to check the fuel pressure. I changed the regulator without checking the pressure. I was quoting a book about Bosch fuel injection LH jetronic. That is why I said generic. There is a nipple with Shrader valve (sp) (similar to tire valve) and cap on the fuel rail of M119 engine that is the place to check the pressure. Since that would be the same pressure that the fuel injectors see.
I wonder where Carman850 tested his pressure and what equipment he used.

I used a fuel pressure guage and measured it at fuel rail.

Fuel pressure guage cost me about 40$ Cdn from autopart store.

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99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.

Over the weekend I could not replicate hesitation at >3K rpm if in 3rd or 2nd. I did not get a chance to go buy a fuel pressure gauge so pressure at fuel rail at idle remains a mystery but if you read below I think it will probably be within range.

Then, yesterday it started stalling only if I bump the pedal from a standing start and takes a few cranks to get it running again. The engine turns over fine but will not catch like it usually does. If I push the accelerator slowly it does not stall and accelerates smoothly.

Engine continues to idle smooth as silk and will rev up to 3K (did not go beyond that) in neutral without conking out.

My inexperience pushes me in the direction that this is the fuel system acting up as I just changed the fuel filter and this stalling out phenomenon emerged (high speed hesitation pre-existed prior to fuel filter change) BUT the engine seems to be getting fuel all right while in neutral and that seems to contradict the fuel system problem theory.

The problem does seem to occur when fuel flow is increased at a rapid rate i.e harder acceleration.

Any thoughts?

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Matt
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92 400E 128K
99 GMC YUKON 88K

Checked fuel pressure and that holds at 50psi at idle.....continued to hold at 50psi after I shut the car off for 1/2 hour. So I think that the fuel pumps, check valve and fuel injectors are OK.

Since I had the new fuel pressure regulator handy I decided to pop the old one out....that went well....except I cannot press in the new one far enough to get the circlip into its groove so that it secure the FPR tightly....Is there a special tool to get the Fuel Pressure Regulator pressed into its "seat" ? Or do I need to start looking for a bionic upgrade for my thumb and index finger...???

Rafi, how did you get that thing in there?

Anyone else? Someone must have insight........

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Matt
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92 400E 128K
99 GMC YUKON 88K

400E_FAN Try moving the regulator side to side (not too far) using the nipple for manifold vacuum while pushing it down into the housing.

Rafi,
Thanks...I was pushing straight down and
did not want to mash the 'o-rings' in the
process. Will try what you recommend
and see if it works.

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Matt
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92 400E 128K
99 GMC YUKON 88K

400E_FAN do not forget to add a dab of oil to the 2 O-rings to ease it into place and make sure you are pushing squarely no off on an angle.