KE Jetronic Help Please asap - PeachParts Mercedes-Benz Forum

mmark · #1 10-30-2008, 01:32 PM

I need some experience with this problem, 1988 300 ce, When I force the first gear start the car doesn't accelerate till 2500 rpm then it goes with gusto, If I let the car start in second gear from a dead stop, it is lifeless till 2500 rpm then takes off again.
If I push the gas slowly down from a dead stop it slowly accelerates till the pedal hits the 3/4 mark then the car takes off with the same gusto as a down shift from second to first, even though it's in second gear start, If I force the first gear start from dead stop, again the car feels week till I hit the 3/4 mark with the gas pedal then it takes off again, The last part is the gas pedal is way more linear when the car is cold, there is no snap in acceleration @ the 3/4 mark. If I tap the gas from a dead stop the car will leap forward when cold. This problem with dead gas pedal only occurs when the car is @ operating temperature. I was thinking this could be the airflow sensor (potentiometer) seems like it ???? The car idles great and doesn't misfire, Thanks in advance for any advice you can offer.

Other notable things, I live in central Alberta Canada and winter is on the way. In cold weather the idle is still 550rpm when you start the car cold -2C for now, -30 on the way!. If you don't hold the gas floored it won't start. It does idle nice with no misses. Also the vacum seems low, 3/4 to the left in park when warm & 1/2 when in drive stopped? stays @ 1/2-3/4when cruise is on @ 110kph 65mph whith flat roads, is this about right?

If anyone can provide links to Benz KE Jetronic system and how it works I'd be very greatful, I have a Haynes manual. This is a M103 engine rebuilt with 20,000 km and 4sp auto, I get about 425km to a tank of gas 80% highway@ 110/120kph. I love this car and it is my new hotrod, lol. I have had 11 mustangs over five years, went 4 years with no toys and the wife let me get this car cause I begged! Know what I mean? I have done Plugs wires cap rotor both fuel pumps fuel filter thats it, oh and rims and tires.......

Thanks for any help!!

Mark

mbdoc · #2 10-30-2008, 05:02 PM

The basics of that fuel system are all about fuel pressures. Even good MB technicians can have problems diagnosing that type of problem.

Having a gauge that you can connect to the fuel distributor that reads at least 90psi is a starting point.

mmark · #3 10-30-2008, 05:46 PM

Hey MB Doc,

We did do a test on fuel pressure and found 80 psi after the pump (x2) replacement. It also held pressure for 45 min. engine off! I tested @ the fuel distributor under the air cleaner. There was a 1/4 bolt I have the size wrong for the bolt, but it was the only place availiable I could find to hook up the gauge. Are you saying I should hook up a fuel pressure gauge and drive the car when it's warmed up and compare hot and cold engine fuel pressure?

Thanks DOC

babymog · #4 10-30-2008, 09:36 PM

Spray carefully around the engine intake etc. with (ether) starting fluid, any change in RPM and you've found a vacuum leak. Careful, that stuff burns!

Also, get some RedLine "complete fuel system conditioner". It is the ONLY fuel treatment that I have EVER found to work, my '91 started the soft-pedal thing at 60,000mlies, tried all of the solvent-based treatments, a bottle of RedLine actually made a difference (without causing damage to the engine bearings as Techron et al warn you on the bottle can happen).

Funny thing about the K-jetronic CIS system is that low fuel pressure will cause the engine to run rich, because the fuel pressure is used as counter-pressure against the air-flow meter. Can also be the frequency valve, unplug it and see if there's a difference, ... also, how old is the Oxygen-sensor?

mbdoc · #5 10-31-2008, 07:57 AM

Measuring the system pressure is done at the upper section, ie: cold start injector.

ON a fully warmed up car the lower chamber pressure needs to be 0.4 bar lower that the upper.

So if the upper pressure is 5.2 bar the lower HAS to be 4.8 bar.