86 300E power loss at speed - PeachParts Mercedes-Benz Forum

A264172 · #1 01-29-2006, 12:15 AM

Happened twice today. Car fully warmed up temp (90C+). Both incidents were on highway at aprox.60 mph. Economy gage pegged in red. Oil pressure good (pegged). RPM's responded to pedal but produced no power. As I would pull over and pump the gas to get a little further up the berm I would get slight little bits of power transmission. Let it sit for a couple minutes and it started right up and did not loose power till the next 25mile highway trip. Both times uphill.

Looked for vacuum leaks between the two stalls but the symptoms were not present during testing. Replaced the cracked crankcase to intake manifold hose.

Thinking vacuum leak...

Or crankposition sensor (do rpms stay under control of accelerator pedal during cps related stalling?)

Other possibilitys... coil?... valve cover gasket?... ???

Any suggestions, ideas, or experiences appriciated.

t walgamuth · #2 01-29-2006, 08:19 AM

like fuel starvation to me. are you sure you have fuel? could be a sender failure. also could be junk in your fuel and plugged filter or strainer. air filter is possible but less likely.

good luck

tom w

dave_rose69 · #3 01-29-2006, 09:28 AM

Marty: You have one of those hair pulling intermittant problems which requires some sophisticated diagnostic routines, however if you are really going to try and fix this problem yourself, stay with this forum and be ready to invest in some diag. equipment. Do these things: 1. Check fuel pressure at fuel distributor or spray bar inlet rail, buy or borrow a fuel pressure gauge that goes to at least 100PSI. You need a "T" fitting to do this test, 3/8" on top of the "T" side, 5/16" to the pressure gauge side. You need a steady 75 to 85 lbs. PSI for good running. Also check the volume, its about a 1 quart delivery in 30 seconds. Hose clamp all the fittings, as the 80lbs of pressure will surely pop a test hose off its fitting. If your pressure drops at any time during the loss of power, replace or service the fuel pump relay first. A tell tale test is to run a pair of wires from the pumps and into a VOM, set it for DC volts. you must have 13.XX volts solid at that point, if it drops down during the power loss, its the pump relay. If you have a module on the left side of your battery compartment with a knob marked 0/1 on it, this is the MAS module. This knob actually retracts the module from its socket.The fuel pump relay is inside of this unit. IT CAN BE SERVICED. If you have a seperate relay for the pumps, just find it and change it. If there is no power droppage to the pumps, do an entire fuel sys. overhaul. Clean Pickup screen, (large allen socket plug in middle of tank, you will need a new O-ring), main filter, check fuel accumulator, fuel pressure regulator. If you monitor the fuel pressure directly from the pumps and it fails, its the pump (s) or accumulator. if it drops when hooked between the inlet and pressure regulator, its the regulator. Generally, the fuel sysems are bullet proof, and If you find no faults with pump power and pressure, I would do: Ignition overhaul, plugs cap rotor wires, and coil... Also replace your OVP relay. The MB Ign coils are the worst, especially the older ones with sheet metal stamped center sections. Go look at the color of your spark, it must be whitish blue, not orangy red...... be patient, you'll find something eventually.....
If its the CPS, the tach will drop down even though the engine is running. It tests: 750 to 780 ohms, and .480 to .505 Volts AC during cranking. They do sometimes fail even if they test good with the VOM. If you have no spark at any time, it could be the CPS. Also check the rotor adaptor plate retainer bolt, these adaptors get loose too.

go here to learn where your modules and relays are located
http://mb.braingears.com
Go here for parts: www.***************
http://catalog.peachparts.com/
dave
dave_rose69@yahoo.com

A264172 · #4 01-30-2006, 02:47 PM

Thanks for that guys.

Ill post back when I get some preliminary readings.

Can I buy 10' of regular rubber fuel hose to extend the gage into the cabin to try and recreate the stall? Or will I need a teflon hose for the higher pressure?

Ill buy some fittings and get started when I have a little time.

Thanks again.

dave_rose69 · #5 01-30-2006, 05:39 PM

Go to a parts place where they sell fuel line by the foot. 5/16 to 3/8" ID is good. Gates brand seems the most flexable. You must use hose clamps on every fiitting, dont forget....What system does your car have? Does it have mechanical fuel injection "KE" Hows your electrical systems voltage, at least 13.5 volts? Do you have the original Ign coil in the car? Do the electrical testing first....

Dave.....

#6 01-30-2006, 05:52 PM

I would first replace the fuel filter and see if the problem remains. If it does, disconnect the EHA harness and see if the car drives okay. If it does, then the trouble is in the EHA, very likely related to the O2 sensor.

Is the check engine light on? Check the O2 sensor connector underneath the passenger side front floor mat.

Good luck,

A264172 · #7 01-30-2006, 05:57 PM

It has CIS E

This being an intermitant problem (didn't happen yesterday or today) I am thinking of rigging up the fuel pressure gage as you suggest and taking it out for a 20 mile drive to try and duplicate it. Where would be a logical place for my t fitting?

I have a known leaking EHA. Would this be able to produce these symptoms?

dave_rose69 · #8 01-30-2006, 10:03 PM

Remove the air cleaner housing assembly, and cover the fuel plate with a plastic bag and a rubber band so you dont accidentally drop something into the intake. DISCONNECT YOUR BATTERY and cover one terminal. You probably wont find any clamps on the fuel inlet line, but be ready to add one later. The OEM fuel line has a hard plasticized over wrap on it, YOU CANNOT generally twist it off. BE READY TO CATCH FUEL WITH A LARGE TOWEL! Wear safety glasses. Cut the hose off at about one inch from the end of the inlet barb, and relieve the hold on the remainder of the cut hose by slowly cutting length wize. Dont cut into the aluminum barb!! Use a good sharp set of jaws on your pliers, to help peel it away from where the cuts are. Be careful not to let any pieces of rubber or plastic migrate into the barbs inlet, and dont bend the metal line. After you whittle it off, put a shorty piece of 3/8 hose on it with small hose clamps. Take a needle nose pliers and twist it into the freshly cut end of the orig hose to stretch it until it fits the other end of the T fitting, add clamps. Hook the gauge to the center T part, and again use clamps on the T side and gauge side. If you leave the needle nose in tight for 3 mins or so, your job will go easier. Before you go through all of this though, do the Ign system overhaul, and if the EHA is leaking, get a new one in with the two new O-rings... Dont forget to check electrical system voltage, you need 13.5 volts or better, inspect spark color, whitish blue, and make sure your battery terms are clean. If you have a weak battery and charge back sys, these can cause power problems too...
dave...

A264172 · #9 02-10-2006, 04:31 PM

So I thought I should replace it before fuel pressure testing began.

Got a lightly used one (1,000 miles on it) from member 'carson356' (thanks Ray) and it cured the problem completely.

Edit: ignore "it cured the problem completely."

PatOne · #10 02-10-2006, 10:30 PM

Had similar symptoms but no increase in rpm. The more the accelerator was depressed the faster the car (1988 190e 2.3) would slow. The mechanic ultimately diagnosed the problem - I never would have guessed as I had replaced the cat only 3 months earlier. He loosened the header to pipe flanges so I could drive it to the muffler shop for a replacement.
Hope this helps. Beware I'm new to group so consider the source.
PatO

neanderthal · #11 02-11-2006, 04:45 AM

i would start with basic tuneup stuff like plugs and wires, cap and rotor.

then id move on to fuel stuff; filter, regulator etc

then id check for vacuum leaks

A264172 · #12 02-12-2006, 03:13 PM

Well I was wrong -fuel filter on order Monday.
The snow and frigid weather has kept me from testing thus far... but I am getting my ducks lined up... will update soon.

Once I get the new fuel filter on I will try to test the upper and lower chambers to see if new EHA is not set correctly...

A264172 · #13 02-13-2006, 02:28 PM

While waiting around for my fuel filter and playing around with my intermitant power loss... I think I am noticing a corolation between the HVAC vacuum switching going on under the dash and the power loss. Can a vac leak in one of the vent control actuators or lines affect the engine preformance?
Thanks.

A264172 · #14 02-13-2006, 06:54 PM

Quote:

Originally Posted by dave_rose69

Marty: ...check fuel accumulator, ... If you monitor the fuel pressure directly from the pumps and it fails, its the pump (s) or accumulator. ...

Dave,
How would accumulator failure manifest itself in power loss?

I ask this because I have read that a secondary function of the accumulator is ti supress pulseing noises of the fuel pump, and I have been hearing pulsing noises under load.

dave_rose69 · #15 02-13-2006, 08:38 PM

The fuel accumulator, acts as a reverse flow check valve, but is more of a reverse pressure regulator. It allows the fuel system to hold pressure, from the delivery side (tank and pumps) and insures quick start ups, by keeping the fuel pressure up, even when the pumps have been off for many hours. If the accumulator is letting go, (leaking down) while driving, the end result is a lowered fuel pump pressure to the fuel distributor and its pressure regulator. The only way to see this, is to drive the car and monitor the fuel pump pressure remotely via a gauge brought into the car. I do suggest a helper friend to watch the gauge, as not to be destracting while you are driving. You can block the return line from the accumulator, but you run the risk of introducing contamination into your fuel system, if you dont do it in surgically clean way. If you havent already checked your ignition coil out, do so, you might be suffering from this power loss due to ignition break down under compression from a weak coil....Check the color of your spark....!!!! Any unusual noise from the pumps can be traced first to a clogged pick up screen in your tank, It makes a sorta slurping sucking noise, like when you pull soda from a straw in an almost empty can, or, a squishing sound, (over pressure) from trying to suction through a very clogged filter. Or, maybe the motors armature bushings in the pump are shot, rare until around 250,000 miles. Usually poor power problems stemming from a clogged fuel filter, lessens when you add more fuel into the tank. The extra fuel now available, via gravity, helps push the fuel better into the pump system.