Poor running 280ge

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ErnestTBass
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I am having problems with intermittent bad running - will start easily but fails to rev beyond 1000 rpm. If the Air meter flap is pushed down at the same time it revs fine. I have done a fuel pressure test and it was within limits but its intermittent and sometimes drives with no problem, I have replaced the fuel filter and cleaned the air flap and housing - it operates smoothly and does not stick. So the options are fuel distributor, fuel pump or fuel pump relay. All the electrics have been checked and are good.

Where is the fuel pump relay? - there is a relay above the small fuse box under the drivers side panel. its visible, just, from the the hole left by removing the panel next to the steering wheel. Is this it? and does it just pull out as its in there really tight. The contacts to this cant be seen without removing the fuse box. Cant really see to short the relevant pins to bypass the relay.

Any suggestions as to prob causes for this problem would be welcomed as I don't want to take it off for an expensive fishing trip at a garage that has no idea what to do with old k-jetronics

fixwin38
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Re: Poor running 280ge

Hi Ernest

start your diagnosis with the first cold start.of the day ...turn ignition to start  position NO accelerator/ throttle ..engine should start on the second/third turn of the starter and rev NO accelerator/throttle to 11/1200 rpm smooth with no black exhaust smoke ( lots of steam) as the engine gets warmer "one to six minutes" depending on the ambient temperature...slowly the rpm will drop to 7/800rpm  smooth idle. no smoke...when engine is hot it should start   NO accelerator/throttle rev to 1200 rpm for two seconds and drop back to 700rpm..  smooth and no smoke.....come back to the forum with the results of the action before any other checls....

Pistonhead
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Re: Poor running 280ge

Hello Ernest,
The fuel relay is where you describe it to be.

My money is on false air leak from the rubber hose of the idle circuit.  These are difficult to see, they run under the inlet manifold, close to the head.  From the big plastic screw, that is the idle speed adjuster, follow the rubber hose directly underneath; runing along the head to the head and joins to a protruding pipe in the middle of the head, between No: 3 and 4 cylinder.

Feeling with your hand directly underneath the plenum chamber, the hoses also connect to vacuum chamber (I can not think at this moment what the unit is called).  There is another hose from the warm up regulator (near-side of engine block) to the inlet manifold, this can dislodge very easily, the rubber hose can deteriorate.
A quick way to check is if you have an aerosol can of brake and clutch cleaner, sprayingly spray near the inlet manifold along the path of the rubber hose, should there be a false air leak, the sraying will improve runing of the engine.  CAUTION - do not spray near the electrics, mixture is highly flammable, keep a fire extinguisher handy!  Take care checking the leaks, the engine needs to be runing, so do use your senses inspecting the leaks.

Cheers

prwales
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Re: Poor running 280ge

you don't say how old you truck is. The fuel pump can fail if it has been exposed to salt spray, the aluminium casings literally disolve. Try the test 1st though before you splash out on one of these as they are pricey.

ErnestTBass
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Re: Poor running 280ge

Thanks guys, its an 88 swb auto. The cold start seems to be fine, maybe a tad rich but nothing I cant live with if the way to cure it is new cold start thing on the bock!! It always starts easily. It just frequently wont rev above 1000rpm - gives all the indications of not enough fuel - does it hot as well as cold.

I'll check for air leaks and if I can get at the pump relay I can check the fuel pressure properly but that relay is in very tight and force might pull the lid off it leaving it in place. Is there an easy way to get at the pins on the relay to test the pump?

fixwin38
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Re: Poor running 280ge

Hi Ernest
 I asked for the specific rpm indications to give me a clue as to  the fuel/air mixture .and  as the basis for further diagnosis ....Vacuum system integrity is paramount with the Cis Jetronic fuel management....your limited revs  (1000 rpm) would indicate a vacuum leak causing the air mass sensor plate  to have limited response.too  much fuel and not enough air makes for black smoke.....there are many areas that a vacuum leak can occur..the thin grey pipes from the EGR valve on the exhaust manifold into the distributor / air mass sensor junction .the same sort of pipe runs to the gearbox modulator valve...the other pipes Rakesh has mentioned are all vacuum related problem areas... a major vacuum leak will reduce brake servo efficiency...the fuel pump should run for 2/3 seconds to pressurise the system after you turn the ignition on and before moving to the starter position...if there is a loud droning noise from the fuel pump with engine at idle you could have a a failing pump /  choked fuel filter ...intermittent fuel pump relay action could be corroded pins as the result of water ingress from leaking wiper spindles.this could make the relay hard to remove...

ErnestTBass
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Re: Poor running 280ge

I have just started it and it fired first time running about 1200 rpm but the tach is a little fast when checked against my Snapon strobe. It was fine for five mins then stalled, (i suspect the fuel pump circuit as when the ignition was switched off and on to restart there was no short whir from the fuel pump) then a few mins later started first turn and revved fine no smoke then idles at about 800 and reduces rpm if you restrict the airflow by blocking the air intake a bit but the idle is still smooth but slower. The problem is intermittent and could be many things from a bad earth onwards - the only way forward is to eliminate all the prob causes. Its pissing down here at the moment so cant do much more and its almost dark too. And I have not tried driving it as when it goes bad it will only drive at about 3mph or so.

So far I have removed the vacuum pipe off the head near the egr - no difference - so could that indicate a leak? The one off then air manifold to the rear of the fuel distributor - increase in revs about 150 ish
Not been able to do anything with the hidden pipes tho
I still cant get the fuel relay out. There is a huge birdnest of cables over the relay making it difficult to see and the relay is buried under them. the manual says to short two pins but there is very little chance of getting to them without removing the fuse box which is directly underneath the relay. I need to find away to remove the relay so that I check for dry joints etc.
Thanks for the help!

fixwin38
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Re: Poor running 280ge

Hi Ernest
if you remove the two screws at the bottom of the fuse board/fascia  you can then lower the carrier down to access the relays....also check the wiring connections to the fuel pump for corrosion (pump located forward of the fuel tank under a deflector plate secured with two screws)  It could also be the cold start sensing probe in the cylinder head. there are two probes. one for the water temp guage and the other for the cold start  system (above the egr valve) if this is not working (can become erratic if you have ever overheated the engine) it will shut the cold start system down early.. reducing the fuel supply and stopping the engine. sometimes the fuel pump will not whirr at all  if you try to start the engine right after switching off.....due to the system being pressurised to capacity...

ErnestTBass
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Re: Poor running 280ge

thanks for your reply:

Do you mean removing the panel that covers the main fuse rack at the bottom edge of the fascia? There are 2 screws one at either end of the fuse panel. Removing them does not release the panel. Is there another screw say underneath the small covered fuse box which is situated under the relay? My Mercedes manual is October 1982 and does not show anything that looks like mine. There is nothing in the WIS and now my epc has decided to forget its serial no :(

fixwin38
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Re: Poor running 280ge

Hi Ernest
once you remove the long strip  (bottom of fascia with 3  Dzus "T" slotted screws (one in the door jamb) you will see two star headed screws  one at each end of the fuse carrier ..remove these screws and drop the complete carrier / fuse board to access the relays.....

ErnestTBass
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Re: Poor running 280ge

Thanks -  I did take those out but it didn't want to come down and didnt wan't to force it, which is why I thought there might be other screws. Will try again in the light.

ErnestTBass
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Re: Poor running 280ge

Well after hanging upsidedown and undoing the relay carrier exposing a  bunch - well 4 relays, what I thought was the Fuel pump relay turned out to be the wiper delay relay - infact one of the others was the indicator and two are unidentified but none was the fuel pump relay!!!  With them all removed it still started ran.

So now the  hunt is on for the location of the fuel pump relay in a 88 280ge auto.

Has anyone removed this relay - the manual I have is oct 82 and shows a nice photo of the relay plug socket and which terminals to bridge!! Very good but where is it???

peter perfect
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Re: Poor running 280ge

 If I remember the fuel pump relay is behind the fuse panel, you can unscrew the fuse panel and it drops down, my relay, on my 230 was located behind that, I remember as mine was converted to lpg as mine packed up once.

ErnestTBass
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Re: Poor running 280ge

Well thanks for the help guys, the relay has been found!! its lurks, hidden on the rear of the fuse panel plate so you have to take it right down to get to it. Unfortunately is seems to be fine.

Now the task is to check why there is too litle fuel.

Cold start is fine at first turn BUT won't rev just dies if you try.

fixwin38
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Re: Poor running 280ge

Hi Ernest
either vacuum or electrical related...the cold start fuel supply is activated by the temp sensor in the cylinder head which activates a bi-metal strip in the the cold start regulator that increases the fuel supply via the seventh injector... (1200 rpm)if you do not get that extra fuel the engine will not rev out when cold....over a water temperature sensed period the voltage is reduced to the bi-metal strip and the fuel decreases reducing the revs to 700/800rpm at hot idle.... ANY  reduction in vacuum will affect the air mass sensor opening and result in no revs or complete shut down....talkto Kaiserhnf@googlemail.com who had exactly the same problems on a LWB 280GE

ErnestTBass
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Re: Poor running 280ge

Thanks - I'll check these out - is a bit cold at the moment!!

One strange thing is that its not just during cold running - it did it hot after 30mis driving. Only magaged 8mph -BUT got me home!!

I'l lhave to check the vacuum and fuel pressures - I hope its not a bad WUR

ErnestTBass
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Re: Poor running 280ge

Update for anyone else with these problems!

tested the fuel pressures - first place to start on injection problems on these k-jetronic things!
The Control pressure all screwed up way too high! - the problem - warm up regulator was knackered. Removing and replacing is a pig but is possible.
Solution re-built one - sent it off to ATP Electronic Developments Ltd - (they rebuild fuel distributors too)
Working fine now!

peter perfect
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Re: Poor running 280ge

 Better late than never !

ErnestTBass
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Re: Poor running 280ge

Well I spoke too soon!!

thought it was ok but nah back to its old trick - starts great idles well but dies on acceleration. Have even changed the injectors

Pistonhead
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Re: Poor running 280ge

Hello ErnestTBass,

Does the engine die when accelerating hard or even accelerating slowly?  Will the engine run as you push down the air mass sensor plate, just like you did in your earlier threads?

How does it starts; when it does, will it keep runing without any interference to the accelerator pedal?  How long will run, if it does, if left alone?  
 
Should you want to talk to me, call me on:Tel. 01509 212721, I am available until 21:00 hrs.  If, I remember correctly, was it you who reported a low compression in one of the cylinders?  What resolve of that finding?

Cheers,

ErnestTBass
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Re: Poor running 280ge

thanks

the story so far.......

It was originally was a bit reluctant to start cold and ran rough for a while - got worse over the years

finally it would start ok even on cold winter day BUT would not rev just died or popped and banged a bit then died BUT after a few mins was ok
I checked all I could - air leaks with propane and brake cleaner but couldn't find any
I attempted to check the fuel pressure with made up kit that leaked a bit and the control pressure was too high which was re done by someone with the right kit - WUR suspect
Fuel pump relay was checked Fuel pump out put OK - fuel filter changed

I had the WUR rebuilt by ATP - I hoped to new standards
Put it back and it ran fine
Next time I started it cold it was exhibiting the same symptoms - starts first turn - idles very well BUT wants to die on acceleration for about 3-5 mins then runs perfectly - at all speeeds
Next I put in new injectors and seals
NO change apart from very smooth running - so much that I thought it had stalled at lights
So now its just the first 5 mins of poor running

If just started and left it runs fine and idles smoothy after a few mins will accelerate as normal

Yes it it better if I move the air flap manually (suspecting WUR still giving to higher pressure or bad Fuel distributor (but it runs perfectly apart from the initial few mins)
I really need to check the fuel pressures again as the whole system is dependent on the correct pressures at the relevant temperature. I either need to find the right gauges or some connectors for my gauge.

Is going to be a real pain to drive it to get the pressures checked as it has to be left overnight

The last time I tested the cylinder pressures they were within limits

Thanks again

oh just remembered I have set the advance at 34 tdc rather than the recommended 30 _ always seemed to run better with a bit more advance

ErnestTBass
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Re: Poor running 280ge UPDATE!

Update!!!

Finally finished the injection rebuild

New injectors
Rebuilt warm up regulator rebuilt - I can recommend http://www.kmipetrolinjection.co.uk/ the guy there understands K-Jetronic and tested my fuel distributor which was within the spec just a little dirty. It also seems that those injection cleaners that you put in the fuel tank can release crud which ends up in the Fuel Distributor and wrecks it – so be warned. Also attempting to rebuild a WUR or fuel distributor without the proper test gear etc is a waste of time and the likelihood is more damage will be done!

All the air pipes under the inlet manifold were replaced – takes an age to get from Germany and some seem to be unavailable!
There is a pipe on my 88 from the WUR to the fuel damper under the manifold ( the larger of the two metal pipes attached to the WUR. Inside it is a piece of nylon? tube which can be taken out . I took it out and cleaned the pipe and put it back. It’s very strange and no-one I spoke too had see it before. If it gets clogged then the fuel pressures will be all screwed up.

Remember, K-Jetronic is all about fuel pressure – hot and cold – so the first thing to do is check the fuel pressure!!
Secondly – Vacuum and air leaks!! Eliminate them or it will not run correctly
I disconnected the EGR – firstly because you have to undo it to remove the inlet manifold (needed to renew all the pipes to be found hiding there!! The hole in the air intake can be blocked with a oil drain plug from local motor factors.

The Aux Air valve – attached to the block under there was cleaned and reset to be fully closed at 65c which is the temp marked on it. This was done by hitting the center top of the valve – but be careful not to close it too much – I am told that you can also set it by pinching the brass bulb on the other end to compress it a bit more.

Seems to be running well now smoother than ever and idles well at about 780 although the mixture was only guessed at – richend until rough running then backed off till smooth.

John757
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Re: Poor running 280ge

Had a horrible experience a few days ago... having changed and serviced my G to what i think is top condition , but with a slight hesitation as i pull away i decided to give her a treat and have a tune up... My Trusty guy at Paul P&R Autos obliged by checking the timing (all good) and the air/fuel mix and tickover... his gas analyzer was telling him i was running so lean it was as good as a modern cat equipped car... puzzled he adjusted the mixture and tickover until she was purring... very pleased i paid him and left... a few days later whilst on a longer journey around the M25  i pulled off at a slip road and when i came to a stop the engine just died... puzzled (and blaming poor Paul) i restarted and found a lay-by... no amount of coaxing i could give it would let it idle...it just died instantly as soon as my foot was off the accelerator pedal... even in N it did this....so I abandoned my trip and set off on a 30 mile journey to find my mechanic and ask him to put it right... the journey was awful... as heavy traffic  was at a crawl for 5 miles...(1 hour) slipping it in and out of neutral and using my right foot to brake.. i managed to avoid stalling  more than 5 or 6 times...  when I got to his garage he was as mystified as me... and climbed all over it..after setting the idle to tick-over on its own... he surmised there must be an air leak... and sprayed brake cleaner in various possible locations without any noticeable change to the engine... then just as a last resort he sprayed his magic liquid at the brake master cylinder vacuum hose...and wow! the engine picked up noticeably... several more tests showed the hose was loose... but no amount of tightening of the jubilee clip on it would solve the problem... so i took the car home and removed the hose (which im told was of the wrong type and not genuine MB) and sure enough...the vacuum hose had hardened so much it was no longer making a good seal on the fitting.(and had to be cut off!).. so consiquently...too much air in the mix into the inlet manifold Vs fuel...causing over lean running... have ordered the correct vacuum pipe from MB for Monday... (£7.50 per meter)

 

so if you are having poor running issues... this could be the cause.. !!

 

hopefully it will be sorted after that... stressful journey without idle!

 

John

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Re: Poor running 280ge

Strooth. Almost four years to sort out a running issue, I've got to admire your doggedness.

gordon

John757
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Re: Poor running 280ge

Gordon i think perhaps you are confusing me with the original author of the post... i am just adding to it to assist other 280GE owners with similar issues..

 2 months into ownership..

i have also discovered with the help of my MB parts guru that my limit valve is missing from my current brake booster vacuum setup.. not sure of the impact of the previous owners omission... part ordered and to be fitted with the new Vacuum pipe tomorrow.. was pure luck that i discovered the missing valve... whilst looking at the set-up on dealers computer parts illustration.

lucky... !

  running problems like this can cause no end of headaches.. especially when you dont know what the issue is... will post picks tomorrow for those who dont know what im talking about!!

as each issue rears its head... the more i learn about my G and its engine!

John

ErnestTBass
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Re: Poor running 280ge

I'll second that sentiment! vacuum  leaks on the Bosch mechanical injection are a pain. Mine was an intermittent running problem  mostly it ran well enough not to make me fork out to fix it. Finally it packed up and would only drive at 2 mph - but did get me home!

Secondly, there is virtually no-one left who really understands the CSI system so its going to be an expensive fishing trip and you end up spending a fortune with no results - replace fuel distributor - warm up regulator etc etc plus time fitting etc.

I took everything of mine - not simple as the inlet manifold or inner and outer fender needs to come off the access the vacuum pipes under the inlet manifold.

Understanding the the fuel pressures at cold and hot is paramount but then its quite simple to work out what the problem is.

Fuel distributor and warm up regulator can come off and be tested for proper operation.

DONT use injection cleaning stuff in the fuel as it will allow bits of crap to get into the fuel distributor an wreck it! You can get the injectors cleaned but its not worth the cost just get new ones. The guy I recommend above was excellent for rebuilds of the major bits.

 So its correct fuel pressures and NO vacuum leaks.

 

John757
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Re: Poor running 280ge -now velvet smooth

Further update...  i replaced the knackered looking limit valve (pic 1 angled connector) on the brake booster... along with the vacuum pipe... which was not correct (rubber) for a MB replacement pipe (oddly softish rigid plastic) and started her up... a few crude adjustments to the air fuel mix and OMG!! 

I now have a beautifully idling, responsive G Wagen 280... and sooooo smooth... all the lumpy tick-over has disappeared...to be replaced with a velvet smooth idle... in fact when i drove it i came to a stop and thought it must have stalled... but no... it was still running!!

... for the first time since i bought my G in May ... i can now appreciate a quiet smooth and very refined six cylinder 280 petrol Mercedes Benz engine... the actual reason i bought it was for that smooth six cylinder engine... but have been dogged by small air leaks in the fuel injection system... it actually surpasses my expectations of refinement... when i bought it... all the indications were good... absolutely no rust... only 3 owners... almost full service history on 102k miles... original condition... just a few minor imperfections... and now..apart from a few small dents...she's finally revealed her swan like qualities!!... i'm chuffed!!

if you have idling issues its worth checking the brake servo vacuum pipe for air leaks.... valve and pipe (still have loads of pipe spare) less than 20 quid from MB.

3gtf
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Re: Poor running 280ge

Can I buy the remaining pipe of you please

John757
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Re: Poor running 280ge

Its only £5 a metre (one is all you need)  not easy to post to you as its hard plastic..and wont bent so much to go in a small circle... easier to get from MB direct to be honest.

Zeng
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Re: Poor running 280ge

So Guys after all the dogged work on eliminating the loss of power was there also an increase in fuel economy?