I have a SE 300 auto. H reg.. For some reason the car looses power as soon as I try to go over 70mph.
I have taken it to a Mercedes garage but they cannot find anything wrong with it.
It has 35,000 miles on the clock and has been seviced.
I have already paid quite a bit for the service and to Mercedes to check the car.
Does anyone have any pointers please?
Thanks.
|
awasawas
Did they change the fuel filter at that service? Any indications [hissing etc.] that the exhaust may be restricted internally?
|
|
Does the autobox kick down properly, allowing the engine to reach near-max revs in the lower gears? Does the box behave normally in other respects? I have a 300 SE that's done 100k more than yours and it's as sweet as a nut. If you don't solve the problem soon, you may get good value out of the MB Owners Club (£30 sub, £5 joining fee).
|
Merc-Care spent seven hours over a week period but could not find the fault. I stopped work because I felt they had reached end of what they could do without spending weeks indefinitely. They checked OK the following (by trying replacement parts) - Petrol, Fuel Pump, Fuel filter, Fuel divider, Fuel air flow, Fuel injectors, Accumulator, Betterfly throttle switch, over-volt protection relay, ECU, engine wireing harness, plugs, rotor arm and distributor, coil, HT leads, alarm, all vacuums.
Car struggles uphill and to do over 60mph.garage think it is something to do with fuel starvation.
The only hope I have is that someone somewhere has had a similer problem.
Regards.
|
One of the tuning or Merc experts will be along shortly, but when they swopped the fuel pump etc did they actually check flow rate and pressure?
Silly question, but did they check for a blocked cat?
|
I suspect that this car doesn't have a cat.
You need to get it checked by someone with good KE-Jetronic expertise.
They need to check the metering head function - in particular primary pressure and differential pressure. Simply replacing parts like injectors is a bad way to go ('poke and hope').
Also the CO and HC should be measured through the rev range and the functioning of the EHA (elecro-hydrualic actuator) should be checked. This is a current-driven fuel control valve on the side of the metering head.
|
Sorry Aprilla. I saw "35000" but not "H reg"
I said an expert would be along shortly!!!
|
|
If the injection system is "K" it won't have a cat but if it is "KE" it may well do.
|
awasawas
You didn't answer my question, which I asked because at one point my 300 SE was struggling to get to high revs, the autobox was not behaving normally and the cruise control had stopped working. Why? Because some spanner controller or other had bent a throttle-linkage rod when trying to undo the oil filter, which is a bit awkward to deal with unless you have the correct tool (which costs a princely £8). Thus, the travel of the throttle mechanism was impeded. My mechanic straightened it out and everything was fine. It was as simple as that, but the symptoms were alarming and not a world away from yours.
So, putting it another way, does the engine rev freely up to max in neutral?
|
Thank you all for all this advice!
The throttle linkage sounds close.
I have been given another theory and will let you know if it is the right one!
If the Merc idles and drives normally in low gears but has trouble overtaking, high speeds and on hills it could be the torque converter. [I know this is a low milage car, but things can happen]. Apparently even if the torque converter has siezed- up or broken the car can still be driven,but the full torque cannot be delivered to the engine because of this fault.
Will let you know.
Thanks again
|
|
Unlikely to be TC. At high speeds stator free-wheels (its on a Spragg clutch) and the TC acts as a straight 1:1 coupling. TC is usually seen as inability to pull away from rest when torque multiplication is at a maximum (about 2.5:1 on this car). Could be some other transmission fault though - hence need to establish mixture is correct at all rpm.
|
|
Thank you all for your help and advice.
It now appears that there is a fault with the timing chain and valves. The valves do not open enough to allow air/petrol mix to burn correctly hence the loss of power.
I hope this helps others.
Thanks again.
Awasawas
|
|
|
|
If the injection system is "K" it won't have a cat but if it is "KE" it may well do.
>>
No. The 'E' means its electronically-enhanced (has the EHA) - nothing to do with whether it has a cat or not.
|
I don't know 'Merc-Care' but judging from the post above they are not much good at diagnostics.
This is the way I would do it:
Book a session on a rolling road (£60 in my part of the work).
Have pressure gauge and 4-gas analyser at the read.
Run car with air cleaner removed.
Operate car with modest load up to WOT and observe movement of throttle spindle and metering plate (checking for binding and obstructions).
Observe primary pressure at WOT and check it is above the minimum spec.
Read CO and HC and check they are correct.
If mixture is weak and primary pressue is OK then you have a fault in the metering head.
If primary pressure is low then you have a problem with fuel delivery - possibly pressure regulator or pump or pump supply voltage.
If mixture is OK then you have some other problem (ignition - check with strobe whilst on RR; or brakes binding, transmission fault).
If the metering head appears to be at fault then remove the electrical connector to the EHA (careful not to snap the clips) and see what happens. If mixture then looks OK (or better) it could be a fault with the EHA or the driver circuit for the EHA inside the ECU.
I reckon I could do the above during a 1 hour session on a rolling road. Much better than aimlessly guessing and replacing parts.
|
|
one of the reasons for the EHA was to trim the calibation to send a stoichmetric fuel/air ratio to the catalyst-the F/A ratio controlled by an EGO(lambda) sensor.If you read what I said,I said a KE equipped car may have a cat and one that was sold in Germany or Scandinavia at this date would certainly have one fitted and they were offered as options in other European countries.
|
|
For what it's worth, my 1991 300 SE is one of the last to be built and it has no cat. They were indeed optional, but if I recall correctly they entered the mainstream only in the early-mid 1990s; my 1989 Audi 100 didn't have one either, but my 1996 Golf VR6 has, as does my 1996 E320 Coupé.
|
Excuse the repetition, but I'd be interested in an answer to this question:
"So, putting it another way, does the engine rev freely up to max in neutral?"
And do keep us posted. I'm particularly interested in the problems that develop in cars that haven't been used enough.
|
|
Between 1985 & 1992,Germany and a number of other countries offered reduced or zero car-tax to to catalyst equipped vehicles tho' not a legal requirement and a fair number were sold to green-minded purchasers in other countries who were prepared to pay a price premium just to feel "good".
|
Between 1985 & 1992,Germany and a number of other countries offered reduced or zero car-tax to to catalyst equipped vehicles tho' not a legal requirement and a fair number were sold to green-minded purchasers in other countries who were prepared to pay a price premium just to feel "good".
What you say is correct, but it is irrelevant to this discussion because the car in question is a UK market car. I've never seen a UK W126 with a cat. Also, no 300SE's were produced with K-Jetronic.
|
awasawas
Any news? We always like a story to have a happy ending.
|
Thanks for reporting back - much appreciated.
A timing problem on a 35k car? If you find out any more about why and how it happened, that will be of interest too.
|
|
|
