Mercedes 2.7 diesel engine: Lumpy idle
Discussion
I've got a 2003 Grand Cherokee 2.7crd that used the Mercedes engine. (as in the sprinter vans)
Its got a lumpy idle, the engine idle speed is pretty constant, but the engine shakes a little and you can feel it in the cabin.
But soon as you touch the throttle and move away it smooths out and the Jeep drives perfectly.
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
Lastly I'm reading about the harmonic balancer. I've no experience of these devices, but if it was starting to fail, would it not cause vibration across the entire rev range instead of just at idle ?
Cheers
Its got a lumpy idle, the engine idle speed is pretty constant, but the engine shakes a little and you can feel it in the cabin.
But soon as you touch the throttle and move away it smooths out and the Jeep drives perfectly.
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
Lastly I'm reading about the harmonic balancer. I've no experience of these devices, but if it was starting to fail, would it not cause vibration across the entire rev range instead of just at idle ?
Cheers
pcn1 said:
I've got a 2003 Grand Cherokee 2.7crd that used the Mercedes engine. (as in the sprinter vans)
Its got a lumpy idle, the engine idle speed is pretty constant, but the engine shakes a little and you can feel it in the cabin.
But soon as you touch the throttle and move away it smooths out and the Jeep drives perfectly.
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
Lastly I'm reading about the harmonic balancer. I've no experience of these devices, but if it was starting to fail, would it not cause vibration across the entire rev range instead of just at idle ?
Cheers
Don't bother looking for air bubbles in the fuel, it would be worse at higher revs.Its got a lumpy idle, the engine idle speed is pretty constant, but the engine shakes a little and you can feel it in the cabin.
But soon as you touch the throttle and move away it smooths out and the Jeep drives perfectly.
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
Lastly I'm reading about the harmonic balancer. I've no experience of these devices, but if it was starting to fail, would it not cause vibration across the entire rev range instead of just at idle ?
Cheers
The other things you mention are also equally unlikely IMHO.
My thinking would be that it is a big 4-pot lump & will never be smooth at low revs, but engine/gearbox mounts will take some hammer.
Is there any evidence of uneven power delivery through the rev range?
What is the idle speed?
How many miles?
pcn1 said:
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Where is this wisdom coming from, because all of those issues would worsen at higher revs, and/or throw fault codes?These all seems good so far.
pcn1 said:
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
If you're not doing the work yourself and are directing a mechanic, personally I'd leave them to it. Also, they have the advantage of having the car there, they can listen to it, visually inspect it, plug into it, etc etc. I appreciate you want some reassurance from the internet but your mechanic is much better placed to actually diagnose this.So, I'd check you're not getting in the way of the mechanic, or making his job a PITA. Just let him get on with it
Sounds like poor injector spray pattern to me, but I don't have the benefits of looking at the car like your mechanic (or yourself), so its a wild guess.
pcn1 said:
Its a 5 cylinder
Idle speed approx 750rpm
Smooth power thru the rev range.
90K miles
OOPS!Idle speed approx 750rpm
Smooth power thru the rev range.
90K miles
My bad, I thought they were a 4-pot, I stand corrected.
I would still be thinking engine/gearbox mounts or even have the injectors been checked/tested/cleaned?
ETA.
Sorry, didn't read the later post before replying.
Good point, if you are not the one doing the job, don't get in the way & anyway it is unlikely to be an injector leaking, could indeed be not delivering fuel efficiently, but unlikely to be a leaking injector.
Edited by E-bmw on Wednesday 25th June 11:37
paul_c123 said:
pcn1 said:
Current wisdom says check for air bubbles in the fuel line, check operation of EGR, check turbo waste gate and check injector seals are not blowing by.
These all seems good so far.
Where is this wisdom coming from, because all of those issues would worsen at higher revs, and/or throw fault codes?These all seems good so far.
pcn1 said:
Next check to do would be a injector leak off test which I'll ask my mechanic to do asap. Any other checks I should do ?
If you're not doing the work yourself and are directing a mechanic, personally I'd leave them to it. Also, they have the advantage of having the car there, they can listen to it, visually inspect it, plug into it, etc etc. I appreciate you want some reassurance from the internet but your mechanic is much better placed to actually diagnose this.So, I'd check you're not getting in the way of the mechanic, or making his job a PITA. Just let him get on with it
Sounds like poor injector spray pattern to me, but I don't have the benefits of looking at the car like your mechanic (or yourself), so its a wild guess.
I get what you say about the mechanic, but he's a friend and we get along fine.
Lasty, should have said the lumpy idle is not erratic, its kinda very rhythmic, like its in time on every cycle of the engine.
Not sure if thats a clue ?
I have a wj 2.7. I say a. I've got a breaker, another breaker and my daily driver. Along with a few spares and engines.
They are a funny old beast. Utterly worthless, quite expensive to fix sometimes and mostly very reliable. Unfortunately the bit that tends to go wrong isn't the American bit, it's the mercedes bits.
What you really want is to find someone near you with wjdiag. Or do a diesel leak off test. Worth doing the key jiggle dance (Google it) to see if any fault codes. My guess is you have an injector issue, either an injector that's worn, a copper washer that's let go or possibly a wire cracked on the wiring loom which hardens with age (probably not that though). Could potentially be an issue with swirl flaps but they tend to be fairly reliable individually and only fairly rarely does the actuator go down knocking them all out together (wouldn't cause that problem).
Take the top engine cover off, if you hear a chuffing noise with the engine running, and/or the top of the engines covered in black carbon like coal deposits, it's an injector washer that's failed. If your lucky it's no 1,2 or 3. 4s more of a pain and 5s an arse of a job. Same goes for if leak off test shows an injector down (despite the cost I'd suggest you get all 5 refurbed if you need to get one done so they match).
Hopefully some of that helps. Generally great things, bit prone to rust but you can deal with it/protect them.
Injectors a pain, but they can be sorted.
Head gaskets go, all will suffer at some point. As it's head off and expensive get injectors and glow plugs sorted at same time and properly bottom the job.
Gearboxes can be a bit of a pain.
That all sounds doom and gloom but honestly we've been all over Europe in ours, our old one waded through rivers, it's towed huge weights, climbed up hills that you would struggle to walk up, yet been comfy and relaxing to drive and returned surprisingly good mpg. My old one is incredibly broken but still drags itself around, it drove 300 miles with a very broken engine to collect a spare engine for itself before I found a replacement vehicle in better condition.
Persist, it's worth it
They are a funny old beast. Utterly worthless, quite expensive to fix sometimes and mostly very reliable. Unfortunately the bit that tends to go wrong isn't the American bit, it's the mercedes bits.
What you really want is to find someone near you with wjdiag. Or do a diesel leak off test. Worth doing the key jiggle dance (Google it) to see if any fault codes. My guess is you have an injector issue, either an injector that's worn, a copper washer that's let go or possibly a wire cracked on the wiring loom which hardens with age (probably not that though). Could potentially be an issue with swirl flaps but they tend to be fairly reliable individually and only fairly rarely does the actuator go down knocking them all out together (wouldn't cause that problem).
Take the top engine cover off, if you hear a chuffing noise with the engine running, and/or the top of the engines covered in black carbon like coal deposits, it's an injector washer that's failed. If your lucky it's no 1,2 or 3. 4s more of a pain and 5s an arse of a job. Same goes for if leak off test shows an injector down (despite the cost I'd suggest you get all 5 refurbed if you need to get one done so they match).
Hopefully some of that helps. Generally great things, bit prone to rust but you can deal with it/protect them.
Injectors a pain, but they can be sorted.
Head gaskets go, all will suffer at some point. As it's head off and expensive get injectors and glow plugs sorted at same time and properly bottom the job.
Gearboxes can be a bit of a pain.
That all sounds doom and gloom but honestly we've been all over Europe in ours, our old one waded through rivers, it's towed huge weights, climbed up hills that you would struggle to walk up, yet been comfy and relaxing to drive and returned surprisingly good mpg. My old one is incredibly broken but still drags itself around, it drove 300 miles with a very broken engine to collect a spare engine for itself before I found a replacement vehicle in better condition.
Persist, it's worth it
I had that engine in a 2005 C Class. Had it from 5K miles to 100K and the idle did become more noticeable as the mileage went up.
You could feel it through the seat and in the steering wheel.
Mostly is was suggested it was engine mounts softening, and (in the C Class) it was recommended to change both the engine mounts and the gearbox mount. I never did it as Covid happened and I pretty well stopped using the car, then sold it.
Another thing I recall is if the air filter housing is removed and isn't refitted properly on its rubber mounts then that can transmit idle vibrations into the car.
You could feel it through the seat and in the steering wheel.
Mostly is was suggested it was engine mounts softening, and (in the C Class) it was recommended to change both the engine mounts and the gearbox mount. I never did it as Covid happened and I pretty well stopped using the car, then sold it.
Another thing I recall is if the air filter housing is removed and isn't refitted properly on its rubber mounts then that can transmit idle vibrations into the car.
wildoliver said:
I have a wj 2.7. I say a. I've got a breaker, another breaker and my daily driver. Along with a few spares and engines.
They are a funny old beast. Utterly worthless, quite expensive to fix sometimes and mostly very reliable. Unfortunately the bit that tends to go wrong isn't the American bit, it's the mercedes bits.
What you really want is to find someone near you with wjdiag. Or do a diesel leak off test. Worth doing the key jiggle dance (Google it) to see if any fault codes. My guess is you have an injector issue, either an injector that's worn, a copper washer that's let go or possibly a wire cracked on the wiring loom which hardens with age (probably not that though). Could potentially be an issue with swirl flaps but they tend to be fairly reliable individually and only fairly rarely does the actuator go down knocking them all out together (wouldn't cause that problem).
Take the top engine cover off, if you hear a chuffing noise with the engine running, and/or the top of the engines covered in black carbon like coal deposits, it's an injector washer that's failed. If your lucky it's no 1,2 or 3. 4s more of a pain and 5s an arse of a job. Same goes for if leak off test shows an injector down (despite the cost I'd suggest you get all 5 refurbed if you need to get one done so they match).
Hopefully some of that helps. Generally great things, bit prone to rust but you can deal with it/protect them.
Injectors a pain, but they can be sorted.
Head gaskets go, all will suffer at some point. As it's head off and expensive get injectors and glow plugs sorted at same time and properly bottom the job.
Gearboxes can be a bit of a pain.
That all sounds doom and gloom but honestly we've been all over Europe in ours, our old one waded through rivers, it's towed huge weights, climbed up hills that you would struggle to walk up, yet been comfy and relaxing to drive and returned surprisingly good mpg. My old one is incredibly broken but still drags itself around, it drove 300 miles with a very broken engine to collect a spare engine for itself before I found a replacement vehicle in better condition.
Persist, it's worth it
Hear what your saying, this is my second WJ 2.7crd. Took the first (a 2004 Overland) from 55K to 120K over 7 years and learnt to do many jobs along the way.They are a funny old beast. Utterly worthless, quite expensive to fix sometimes and mostly very reliable. Unfortunately the bit that tends to go wrong isn't the American bit, it's the mercedes bits.
What you really want is to find someone near you with wjdiag. Or do a diesel leak off test. Worth doing the key jiggle dance (Google it) to see if any fault codes. My guess is you have an injector issue, either an injector that's worn, a copper washer that's let go or possibly a wire cracked on the wiring loom which hardens with age (probably not that though). Could potentially be an issue with swirl flaps but they tend to be fairly reliable individually and only fairly rarely does the actuator go down knocking them all out together (wouldn't cause that problem).
Take the top engine cover off, if you hear a chuffing noise with the engine running, and/or the top of the engines covered in black carbon like coal deposits, it's an injector washer that's failed. If your lucky it's no 1,2 or 3. 4s more of a pain and 5s an arse of a job. Same goes for if leak off test shows an injector down (despite the cost I'd suggest you get all 5 refurbed if you need to get one done so they match).
Hopefully some of that helps. Generally great things, bit prone to rust but you can deal with it/protect them.
Injectors a pain, but they can be sorted.
Head gaskets go, all will suffer at some point. As it's head off and expensive get injectors and glow plugs sorted at same time and properly bottom the job.
Gearboxes can be a bit of a pain.
That all sounds doom and gloom but honestly we've been all over Europe in ours, our old one waded through rivers, it's towed huge weights, climbed up hills that you would struggle to walk up, yet been comfy and relaxing to drive and returned surprisingly good mpg. My old one is incredibly broken but still drags itself around, it drove 300 miles with a very broken engine to collect a spare engine for itself before I found a replacement vehicle in better condition.
Persist, it's worth it
Sold it, then a few years later missed it so I bought another (2003 Overland) 3 years ago with a low 68K on the clock and a near full Jeep history.
No signs of black death on either fortunately.
My mechanic has a decent code reader that talks to the Jeep, but he's not about for another week.
Like you say, it isn't worth hardly anything on the market, but its worth a lot to me. Real old school 4x4, maintenance heavy at this age now so you need to be able to do most of the work yourself or it will bankrupt you !
First thing to do is to check you haven't got a knackered engine mount.
You'll need a helper to stand next to the car (NOT IN FRONT) or a camera set up to watch the engine.
Pop the bonnet up, keep your left foot hard on the brake pedal and put it in D. Press the throttle enough that the engine is fighting the brakes. Do the same in R. If the engine looks like it's trying to climb out of the car (instead of some limited restrained movement) you've got a knackered mount.
When they are failing, engine mounts tend to smooth out as revs increase.
(If it's manual, you need to trust your parking brake or use your left foot across two pedals)
You'll need a helper to stand next to the car (NOT IN FRONT) or a camera set up to watch the engine.
Pop the bonnet up, keep your left foot hard on the brake pedal and put it in D. Press the throttle enough that the engine is fighting the brakes. Do the same in R. If the engine looks like it's trying to climb out of the car (instead of some limited restrained movement) you've got a knackered mount.
When they are failing, engine mounts tend to smooth out as revs increase.
(If it's manual, you need to trust your parking brake or use your left foot across two pedals)
Finally got around to buying a injector leak test kit and these are the results.
There were no instructions so I did a timed 3 min run at idle.
I don't have the technical info to hand to say what are the acceptable tolerations.
From you diesel guys, what does this result tell me about the state of my injectors ? Could this difference cause the slightly lumpy idle ?
Cylinders 1 to 5 from left to right.
There were no instructions so I did a timed 3 min run at idle.
I don't have the technical info to hand to say what are the acceptable tolerations.
From you diesel guys, what does this result tell me about the state of my injectors ? Could this difference cause the slightly lumpy idle ?
Cylinders 1 to 5 from left to right.
pcn1 said:
So 2 of them are passing nearly twice as much as thew others...... In answer to your question, yes it could be the cause.
I have used these guys before for injectors & they were excellent.
https://www.ebay.co.uk/str/wtdiesel
pcn1 said:
Finally got around to buying a injector leak test kit and these are the results.
There were no instructions so I did a timed 3 min run at idle.
I don't have the technical info to hand to say what are the acceptable tolerations.
From you diesel guys, what does this result tell me about the state of my injectors ? Could this difference cause the slightly lumpy idle ?
Cylinders 1 to 5 from left to right.
MaybeThere were no instructions so I did a timed 3 min run at idle.
I don't have the technical info to hand to say what are the acceptable tolerations.
From you diesel guys, what does this result tell me about the state of my injectors ? Could this difference cause the slightly lumpy idle ?
Cylinders 1 to 5 from left to right.
A leak test shows a related value, not the "Gold Standard" actual thing you want to check for - which is atomisation of fuel, spray pattern and volume of fuel delivered.
Correct me if I'm wrong, but this ISN'T a common rail? So it could also be the fuel pump delivering inconsistent pressure to each injector?
Also correct me if I'm wrong, but there isn't any coding/adaption of the injectors to the pump/car on these style - they are just injectors which are expected to perform to certain parameters, and it would be newer stuff which has adaption.
Anyway, given the price of fuel injectors, and the fact it might be the pump, it would be worth doing further testing before condemning those and buying new ones.
pcn1 said:
Its CRD model, so Common rail diesel.
The injectors are not coded as far as I'm aware
Aaah in a way that's good news, the pump is far simpler - and its an easy check to see that fuel rail pressure is within tolerances (you'd need to look it up for yours, but 300-350 bar at idle is a good start).The injectors are not coded as far as I'm aware
paul_c123 said:
Aaah in a way that's good news, the pump is far simpler - and its an easy check to see that fuel rail pressure is within tolerances (you'd need to look it up for yours, but 300-350 bar at idle is a good start).
No error codes and it runs fine at all other points of the rev rangeI had a Merc’ C270 CDi with the 5 cylinder engine. I can remember the idle was playing up and down.
Took it to my old mate who has this very good diagnostic kit, and knows how to use it.
He replaced this little air flow sensor in the intake trunking. Problem solved.
OP, I can see you are in Berkshire, could be worth a trip to Newbury??
https://www.autosolutions-newbury.co.uk/
Took it to my old mate who has this very good diagnostic kit, and knows how to use it.
He replaced this little air flow sensor in the intake trunking. Problem solved.
OP, I can see you are in Berkshire, could be worth a trip to Newbury??
https://www.autosolutions-newbury.co.uk/
Edited by Old Merc on Wednesday 27th August 09:10
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