wj 2.7 cherokee blowing smoke

[haywj1]

hi guys,

new to this forum, have been doing a lot of reading up with many good write ups coming from this forum.

i have searched as much as i can regarding my issue and thought id just start a thread so maybe could get some help.

my newly acquired wj cherokee, which is a 2.7 crd is blowing black smoke.

i will start by saying i am both a light vehicle mechanic and diesel mechanic. not saying i know all - as i know very well that if you do not know the specific machine/vehicle very well you practically know nothing, more so just saying that i have a fairly broad range of knowledge with this kind of thing.

I Have removed the inlet manifold, cleaned out the swirl flaps and made sure they operate correctly ( i personally wanted to keep these in) and blanked off egr using the method of tricking the ecm to thinking there is still normal egr operation (found this info on this site so thank you)

the smoke is present almost all the time. the smoke is definitely black - unburnt fuel, and it is heavy under load. seems to clear up once you go wide open throttle a few times and then if you let idle for a little while and go wide open throttle again it comes back heavy so on and so forth.

all injectors have been replaced by previous owner which was carried out due to this issue and an attempt to fix problem. which didn't fix and the reason i purchased the car as i thought apart from injectors it must be something to do with egr or swirl flaps.

car is in amazing condition, drives fairly well besides from the smoke and maybe a little underpowered or slightly choking (but as i have not driven another vehicle of the same type I'm not sure if i can comment on power) full service history and only 130000kms which i understand is nothing for the mercedes engine comparatively speaking.

it is seeming more to me like one or more injector may be faulty. i am about to perform injector leak back test but just wanted to post on here to see if anyone else has any info on any different things i should be investigating.

i am curious to whether the maf sensor could be the culprit? any help would be much appreciated!!!

[haywj1]

i should also say, no trouble codes!

[almc3]

Air restriction of some kind ?
Turbo weak ,intercooler half blocked ,turbo wastegate stuck open.? Air filter hose cavitating /blocked.
Electrics - turbo pressure switch allowing full fuel before full boost ?
Few suggestion - but you need to know how much boost first up.
Did the previous owner put the correct injectors in ,as a couple of numbers different in the Bosch range can make a huge difference . Maybe ECU needs re flashing. Suggest you post on the WJ site not the technical site.

[silycr]

I'd assume you do not have a scan tool and getting no check engine lights.
I would still obtain a bluetooth OBD2 module, and get hold of both torquePro lite(free) and a program specifically for this car, JeepDiag
http://jeepswj.com/software/
The software can read and clear both engine and gearbox codes consistently.

Few things to check
Leak back test(as you're about to)
If you're cheeky, you can use a ball bearing to block the injector fuel feed between the rail and injector. Unplugging the injector harness will only result in a code relating to that injector and the engine shutting down.

Check the injectors have actually been sealed. If an additional washer has been left in there, it will create the exact same symptoms(personal experience from crap mechanics). It will smoke at idle and accelerating, occasionally clearing up at full throttle. Otherwise it just leaves clouds of smoke
I wouldn't expect this to be the problem if that is the reason the injectors were replaced to start with.

You can disconnect the MAF sensor to test. It should be gutless(no turbo) but not much difference otherwise. If the smoke clears, this is the problem.

You can also check the MAP sensor. This is done easiest with the TorquePro app. You can also check if the turbo is pushing the boost it should. Mine sits about 17psi for reference.
you can also check the AIT while you're in the TorquePro app.

If you want to get into checking your fuel pressures let me know.

[ren0vator]

Hey haywj1

Black smoke is partially burnt fuel
White smoke is unburnt fuel

Three things needed to run a Direct Injection Engine
Fuel, Air, Compression

Assuming your fuel supply is all good there are only two faults left.
Lack of air, or lack of compression.

Cheers

[haywj1]

Hi everyone, thanks for the response! I wasn't actually expecting much feedback and didn't really check up! I must appologise for the assumption!

First up, should I be posting in the wj forum instead?

I have access to a snap on solus machine, here is where I viewed previous codes, cleared stored and started fresh. No current or active codes.

As the snap on tool doesn't communicate very fast and fails to give reliable sensor feedback in some areas I used obd doctor on my phone to obtain boost pressure - showing roughly 32 psi under full load, I gather this is taking into affect atmospheric pressure due to at idle it sits at around 15psi so I'd say around 17psi boost pressure.

I performed leak back test, I am unsure of the actual specs but all injectors were showing roughly the same leakage and wasn't very much.

I am still under the impression that the nozzles themselves could have issues and be pouring to much fuel into the cylinders and showing no faults at a leak back test? Also as silycr stated some possible issues with injector fitment?

Maf sensor has been disconnected to check for change, no change in smoke, only very slight change in running condition. Not sure of the range this should be showing on scanner but it didn't look erratic or out of ordinary?

I did notice that cyl 4 and 5 were incorrectly matched so I changed to correct matching but no difference. Seemed as though smoke was slightly worse but I am really not sure as I have been looking into smoke clouds for the past few days so losing my perception of what is reality 😂

I would like to smoke bomb the inlet and check for any leaks that I have not been able to find visually because otherwise I'm stumped.

Anything I have missed? Any more suggestions?

I have to fly up to work today for a week and will continue to investigate when I get home. In the meantime I am going to order some injector seals etc so I can pull them out and inspect and get injectors tested.

Any other suggestions or help would be much appreciated. Need to get to the bottom of this.

Re compression test - I will try and order a compression test kit also. I really hope I don't need this as I purchased the car under full hopes that due to the engine having only low kms and full service history that compression wouldn't be an issue. As I said earlier close to no blow by so hopefully no issues with the valves or anything.

Once again thanks for any help at all!!!

[haywj1]

Could we also talk about fuel pressure? I was getting some readings that I thought were quite low for a common rail? But both set point for rail pressure which I gather is ecm's request and actual rail pressure were both around the same, this was only 29000kpa at idle? Around 5000psi?

I have not been able to get any specs for pressure, including in the service manual, but have noticed in some of the U.K. Merc forums that readings of only around 400bar, around the 5000psi is what I should be getting?

Is this true? I thought this was ridiculously low for crd! Please if anyone can confirm that would be great. As I said the set point was around what the rail pressure was and no codes are coming up so not sure with this one?