300E with no acceleration - engine will not rev past 4500RPM
Ian Chamberlain
I have a problem with a 1992 Mercedes 300E. The car has done 43000 miles,
and runs very smoothly, but will not achieve more than 4500RPM. Even with it
in PARK, I can only manage to get just over 5000 RPM. When you bury the
throttle peddle ( with the car in PARK), it quickly revs to about 2500RPM,
then the revs take a little longer to 3500RPM, then really struggle to get
up to the 5000RPM. When Driving, kicking it down often slows the car down,
as you are calling for more revs than the engine will easily deliver. Also
when you set off, with the throttle half pressed, it changes up with a jerk,
obviously as the gearbox is expecting much more power at that throttle
position.
I have tried and tested the following to try to correct it.
1. Checked the air filter, which looked clean, and tried revving the car
with the air filter removed. No noticeable change
2. Replaced the fuel filter, with no noticeable change
3. Changed the spark plugs. Managed to get from 4500RPM to about 4750RPM
4. Checked the cylinder compression - all OK.
5. Checked the timing (dealers checked on computer, advances OK to about 40
degrees BTDC)
6. Checked timing chain to make sure it had not jumped a tooth or
stretched - Chain installed correctly
7. Check fuel pump delivery flows and pressures with the engine OFF, and are
as follows. Open ended flow (no restriction), gives 2400 litters per minute.
5 bar pressure gives a flow of 1860 liters per minute, 7 bar pressure gives
a flow of 1620 liters per minute, 9 bar pressure gives a flow of 1140 liters
per minute, 11 bar pressure gives a flow of 600 liters per minute. These
according to MB dealer are all OK.
8. Tested the fuel supply pressure with the engine running to make sure the
fuel regulator was working OK. The delivery pressure held at 5.5 bar
regardless of REVS. Suggests it is OK.
9. Tested the air flow sensor, and found the resistance to be none linear.
Around the middle of the range, it did not really go up, but jumped around,
then at the bottom end of the range went linear again. Tried a resistance
box onto the sensor plug, to emulate the sensor output resistance, this made
no noticeable change to the engine revs. When the plug was removed from the
resistance box, or from the sensor when the engine was running, the engine
revs changes for a fraction of a second, then recovered to normal.
10. Lastly, the only thing I could then think of was the catalyst was
blocked, cut this out, and welded new pipe in place, and still no change
(well very little about an extra 200-400 RPM). Even tried revving with no
exhaust at all, with no change.
I have now run out of Ideas, has any one got any clues????
This should be quite straight forward for the dealers to solve as it is NOT
an intermittent problem it is like this all the time, but the dealers
solution to all the problems is throw enough money at it and they will solve
the problem
T.G. Lambach
very analytically and much more thoughtfully than any dealer shop that I know
of. You can work on my car anytime!
Item #9 - the air flow sensor. Out of ignorance I ask if this device shouldn't
provide the engine computer a linear reading? How else can the computer adjust
the air / fuel ratio?
The jumping around in the middle of the engine's speed range is, in my
technically uninformed opinion, the cause of the problem. The engine's computer
isn't receiving an appropriate air flow input for the engine's speed (known to
the CPU from other inputs) and so the CPU reduces the fuel and the engine can't
achieve greater speed.
Suggest you ask the dealer or, if they refuse, an independent repair shop, to
TRY a different air flow sensor and to restore the original if the problem
isn't cured. You've done the hard work so let the shop do the simple remove and
replace work - but only if they are willing to undertake it on a TRY IT basis
instead of the usual "you bought it" basis.
Ian Chamberlain
The air flow sensor, I have heard should have a linear increase in
resistance from about 4K ohm upto about 10K ohm. I actually measured the
resistance for each millimetre the air damper flap was open (measured from
the centre beam across the air intake to the canter of the damper flap using
verneer gauges), ( have the results if any one is really interested - about
50 of them). The resistance increased very steadily about 100 ohm for the
first 5 mm of flap opening, then the next 15mm the resistance either dropped
off by 100 ohms, stayed the same, or moved up by 100 ohm. Then at around
20mm open, the resistance jumped to about 6K, then increase nicely in 200 -
500 ohm steps per mm upto the maximum. As I say, I tried connecting a
resistance box to the air flow sensor plug to emulate the air flow sensor.
As I slowly revved the engine, my helper slowly increased the resistance
from the base level of 4K ohms up to 9K ohms. Unfortunately, this seamed to
have little effect on the RPM I could get out of the engine.
Is it possible that is the computer does not receive the resistance it is
expecting for the RPM range it ignores it. Surly though if this were the
case, the engine would not run smoothly, but pop, and miss fire all the way
up to its rev limit..
Could it be the REV limiter that could be causing a problem. Has it actually
got a rev limiter on this model.
Every ones comments would be much appreciated.
Thanks
Ian
T.G. Lambach <tlam...@home.com> wrote in message
news:39736F59...@home.com...
Mick J
performance suffers from a wrongly adjusted throttle cable. It's so obvious
that many people overlook it.
--
Blake, Tony [NC1:3199:EXCH]
This might be something you have checked already but could it be dirty fuel
injectors/throttle body?
My 91 300 SE (185,000 miles) will exhibit performance problems similar to,
but not nearly as severe as you describe when driven around town for extended
periods of time - this happens about every two years. My solution; a tank full
of fuel with Techron added, and a good 1/2 hour highway speed drive. (A good off
the engine throttle body cleaning in the near future is in order, but time
constrains are the limiting factor)
Ian Chamberlain wrote:
> I`m Quite shocked that some one should reply so soon. Thanks!!
>
> The air flow sensor, I have heard should have a linear increase in
> resistance from about 4K ohm upto about 10K ohm.
<deletia>
T.G. Lambach
proceeding further.
If not the cable, I believe the problem is due to a fuel limitation; the task
is to learn why.
This 300E engine is a 12 valve engine not a 24 valve engine. I own the 24 valve
version which has a definite step to its acceleration when one really pushes
the accelerator. This would account for the sudden sharp rise in the air flow
sensor's ohms that you describe:
"Then at around 20mm open, the resistance jumped to about 6K, then increased
nicely in 200 - 500 ohm steps per mm up to the maximum."
But as this engine is a 12 valve engine there should be no reason for an ohm
jump for the air flow into the engine will be linear. But I have to respect
your emulation of the air flow sensor's resistance and that nothing was gained.
Was the air flow sensor ever replaced? If so was the correct part used? I still
vote for the air flow sensor being the culprit.
A speculative thought: Could the engine's speed be limited by the computer if
it received a false temperature input. That the program doesn't allow the
engine to rev while cold? You might check the engine temperature sensors if
only to eliminate the possibility.
Ian Chamberlain
you operate the throttle from under the bonnet. The throttle arm goes right
over until it can travel no more.
The air flow sensor has never been replaced, well not to my knowledge (just
bought the car from an auction, so don't know its history) The sensor, from
what I have read in the past is not a replaceable part. The whole of the air
flow unit i.e. flap and body comes with it, and s very expensive.
I really need to know how the computer works. What does the computer operate
on the fuel side. Does the computer assist the mechanical linkages to the
accelerator peddle, or take an input from it and send an output to the fuel
injection unit based on all the corresponding factors like engine
temperature, Lambda sensor (oxygen) air flow, throttle position engine speed
etc.
Does any one know what the computer actually controls??? (probably
everything, but HOW??)
Please keep your comments coming, I am still listening all the advice helps.
Many thanks
Ian
T.G. Lambach <tlam...@home.com> wrote in message
news:3973989E...@home.com...
> The other reply about the throttle cable is a good one to check before
> proceeding further.
> If not the cable, I believe the problem is due to a fuel limitation; the
task
> is to learn why.
>
> This 300E engine is a 12 valve engine not a 24 valve engine. I own the 24
valve
> version which has a definite step to its acceleration when one really
pushes
> the accelerator. This would account for the sudden sharp rise in the air
flow
> sensor's ohms that you describe:
>
> "Then at around 20mm open, the resistance jumped to about 6K, then
increased
> nicely in 200 - 500 ohm steps per mm up to the maximum."
>
> But as this engine is a 12 valve engine there should be no reason for an
ohm
> jump for the air flow into the engine will be linear. But I ha~e to
pelleplutt
swap to if something is wrong.
Try to RESET the system by leaving the battery cable disconnected for a
while (over the night)
Just a hunch!
Ian Chamberlain skrev i meddelandet <8kvhud$2ua$2...@supernews.com>...
>no noticeable change to the engine revs. When the plug was removed from the
T.G. Lambach
timing. It can't regulate anything else!
Having written that, is there any way to check the spark advance? Although I
continue to believe the air flow sensor the culprit perhaps the ignition timing
is being severely retarded causing the rpms to max out at 4,500. A thought, if
only to eliminate this possibility - before its air flow sensor time!
Ian Chamberlain
advanced from the correct idle of about 8 BTDC upto 40 BTDC at full RPM.
Again I really cant see the air sensor, as I have had a resistance box onto
the plug to emulate the sensor out put. No matter what resistance was input
to the plug, the RPM stayed the same.
I have been told that the computer can only make fine adjustments to the
fuel supply, as the injection unit is basically a mechanical system with a
few minor electronic enhancements. I take the point about the timing though,
but as I say, this has been checked OK.
Some one suggested that it could be the ignition coil not producing enough
voltage, limiting the revs. Has any one any views on this.???
Anyone know how I can test it?????
The ignition setting on the timing plug is set to the N mark. The book says
for fuel with an octane rating of RON 95 (which is the rating of British
standard grade unleaded) the plug should be in the S position. If I try
this, the engine PINKS quite badly. Changing it to the N position makes it
much better, but under hard acceleration ( yes what acceleration I know!!!!)
it starts to pink. Also when revving hard, i.e. at its max 4500RPM you can
hear the engine popping as though it is missing, or back firing. The popping
is very fast, with no pattern to it. Any clues??????????
Every ones comments are very welcome, please keep them coming, I`m still
listening.
Thanks
Ian
T.G. Lambach <tlam...@home.com> wrote in message
news:39764B73...@home.com...
Ian Chamberlain
300E??,
The engine is a single cam version with the distributor at the front
(directly in front of the cam). The system does have the EZL ignition module
on the wheel arch, but also has a black box of tricks mounted behind the
battery. I am assuming the one on the wheel arch is solely for the ignition,
and the one behind the battery is for the fine tuning of the fuel side of
things. Can anyone confirm this????????
As for swapping things around, I don't know any one with a 300E. My uncle
has a 1990 560 SEL (V8 engine). Are there any components that are
interchangeable on the 2 engines like the coil for example. I would not have
thought the ignition module would be as the 560 is a 8 cylinder and the 300
is a 6 cylinder.
Has any one got any views on the pinking of the engine with the timing plug
set to the S mark. It is much better with it in the N position
Mick J <mixs...@cwcom.net> wrote in message
news:Bbde5.4666$K06.43259@news2-hme0...
> When you mention 'popping & misfiring' at the maximum revs this suggests
the
> ingition module may be limiting the revs at the wrong speed. I am assuming
> you have the single cam engine with a distributor on the front of the head
> and EZL ignition module mounted on the wheel arch, not the HFM combined
> fuel/ignition management system which is mounted behind the battery
although
> either system could do this I think.
>
> Maybe worth getting together with another owner with the same car and
> swapping a few things round to find what is faulty. Unfortunately mine is
a
> 230 and nearly everything is different!
>
> If it is EZL the comment about the fuel computer being an 'aid' to a
> mechanical system is correct and the car should run without it. Most of
its
> work affects idle and cruise by operating an auxiliary air valve and
> hydraulic control on the fuel distributor to give fine control over the
> mixture and idle speed. You can easily disable it by pulling the fuse from
> the voltage protection relay which is also behind the battery to see its
> effects which include idle speed compensation when gears are selected from
> Neutral (if auto transmission) and when the a/c compressor engages. I had
an
> intermittently faulty voltage protection relay at one time which mainly
> manifested itself by preventing the ABS from working and illuminating the
> warning light. I did not notice any deterioration in performance and it
was
> only when I associated the light with rough idling that I made the
> connection (no pun intended!)
>
> I think the air flow sensor on your system is a potentiometer operated by
> the air flow flap. The flap controls fuel flow mechanically and the
> potentiometer signals the computer. This has to be carefully calibrated so
> be very careful if you are tempted to remove it.
>
> Sorry I can't be more helpful, this is getting everyone quite intrigued!
>
> --
>
>
> Ian Chamberlain <Ichamb...@lineone.net> wrote in message
> news:8l7kii$6kv$1...@supernews.com...
Mick J
--
lianne chamberlain
on the fuel side) can not limit the RPM this much. The fuel injection system
is basically a mechanical system with electronic optimization.
I have run the engine with all the plugs removed from this injection
distributor body, with no noticeable difference in performance
I have also run the engine with one of the fuel injectors removed, and still
get identical performance as when all injectors are in. This suggests that
there is plenty of fuel available.
I have renewed the spark plugs, rotor arm and distributor cap, with little
difference. I have also tried a different coil, with no change in
performance.
Can any one think of anything that can effect to ignition system that wold
cause the engine to max out at between 4000 and 5000 RPM??????
To recap, on the symptoms and what has been done.
The engine runs smoothly upto 4000RPM. The revs quickly increase upto about
2500 RPM then struggle the rest of the way.
With the timing adjustment plug in the S position ( should be for fuel with
a RON of 95 or above which is the case for British unleaded petrol) the
engine starts to ping under hard acceleration. With it in the N position,
the pinging is less apparent. Under no load i.e. with the engine in park at
the top end of the revs range (4500 RPM) there is muffled popping coming
from the inlet manifold (sounds a bit like back fire)
The car will achieve about 26 -30 MPG at 80 mph on a constant run, but has
no power at all on the hills, can only maintain 60 - 70 mph.
kicking the gears down generally slows the car down as it can get the revs.
I have tried the following
1. Replaced sparks, rotor arm, and distributor cap and tried a different
coil.
2. Had the timing checked at the Mercedes dealer, which showed it advancing
to about 40 BTDC
3. Checked timing chain is fitted correctly
4. Checked fuel supply pressure which remains constant at 5.5 bar all
through the revs
5. Changed fuel filter (first thing I did
6. run the engine without the exhaust on to check that a blockage was not
the problem
7. Tried the engine with the lambda sensor disconnected - no change
8. Tried the engine with the airflow sensor disconnected - no change
9. Tried the engine with the throttle position sensor disconnected - no
change - checked that this was working, it switches at idle and full power
10. Pulled the plug on the fuel distributor (presume it is the output from
computer to the fuel system) - no change
"Ray Jordan" <rwjo...@telerama.com> wrote in message
news:so3jo3m...@corp.supernews.com...
> Could be that the signal from the throttle plate position indicator is not
> being received by the ECU. Assuming the car is equipped with J-Jetronic
> fuel injection, the device in question is what Mercedes terms the M16
motor.
> It is essentially a potentiometer that indicates actual throttle position.
> Lack of a signal will cause the symptoms described. It could be a faulty
> potentiometer or simply worn or dirty contacts inside it. If present and
> possible, remove the access panel and apply contact clean while cycling
the
> throttle plate. Also check all electrical connectors leading to the ECU.
> Repair, clean, tighten them as required. Good luck!
>
>
>
>
>
>
Ray Jordan
Mick J
before as I think this has a built in rev limiter which may be faulty. Could
the car have been fitted with a module for a 4 cylinder car which should
limit the revs at 6200, but would be at 2/3rds of this if used with a 6
cylinder engine? Would also explain the 'muffled popping' you mention.
What about the general mechanical condition of the engine? Weak/broken valve
springs? I have also heard that a worn camshaft can cause the hydraulic
tappets to 'pump up' at high revs. This might cause loss of compression at
these speeds and subsequent misfiring.
--
lianne chamberlain <lia...@lchamberlain77.fsnet.co.uk> wrote in message
news:8m1h9p$ect$1...@newsg2.svr.pol.co.uk...