Poor running 280ge
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
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....
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
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.
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...
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...
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.....
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.
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
Better late than never !
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,
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
Strooth. Almost four years to sort out a running issue, I've got to admire your doggedness.
gordon
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
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.
Can I buy the remaining pipe of you please
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.
So Guys after all the dogged work on eliminating the loss of power was there also an increase in fuel economy?
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?