om617 jeep cherokee bad miss /idle - PeachParts Mercedes-Benz Forum

1chrisapple · #1 03-13-2015, 09:14 PM

ok everybody i have a 96 jeep cherokee with a om617 turbo motor.when i first picked it up it ran pretty decent but now its getting tougher to start and it has a engine miss that seems to be getting a little worse. it has an external elcectric fuel feed pump which i have no idea what pressure it puts out but flow is good.i have adjusted the valves and it didnt help. i have not checked timing yet.but i did notice the rack dampener bolt was screwed all the way in so i loosened it and no matter what location its at it dont help.the alda has been removed but wasnt done by me.im curious if the rack has been removed as well?how would i check for that.the dampener bolt is the old style and i can push the little pin in by hand.but the miss seems to be the worst just barely off idle maybe 1500/200 rpms.just wondering if u guys could point me in a direction of where to start.the motor i have not check compression on but when it was swapped supposedly had 425-450 psi on all 5 cylinders.
anyone that cares heres a pic

1chrisapple · #2 03-13-2015, 09:16 PM

upon further inspection i have 3-4 degrees of chain stretch and i cracked all injector lines and no change.i pulled the rack bolt and the rack it is still in the pump.i also took a 4 ft long wood rod and held to all the injectors which turned up a slight knock noise on #4 then i did the same on the pump delivery valves which turned up a even louder knock from the #4 delivery valve.i dont know what to make of it can someone enlighten me?do i have bad delivery valve?

jsain86 · #3 03-13-2015, 09:41 PM

Always check compression first, then go from there.

eatont9999 · #4 03-14-2015, 10:00 AM

Air intrusion check, compression check, injector pop test, delivery valves and valve adjustment. In that order.

Unrealted to current issue: You have a California or 1985 emissions engine in the Jeep. You may want to address the EGR system for longer life of the engine. The fuel lines are not what MB specifies, so you should replace them with the correct hose to avoid air intrusion.

1chrisapple · #5 03-14-2015, 11:23 AM

not sure how air is gonna intrude brand new fuel line.all the way to tank is steel line with rubber where it connects to engine and the tank?

eatont9999 · #6 03-16-2015, 12:32 AM

Quote:

Originally Posted by 1chrisapple

not sure how air is gonna intrude brand new fuel line.all the way to tank is steel line with rubber where it connects to engine and the tank?

The return lines do not look to be OEM spec. Air intrusion can happen once the car is shut off and the fuel returns to the tank via gravity.

1chrisapple · #7 03-18-2015, 10:17 PM

well i got the compression check on a warm angine and came up with
1 425
2 390
3 400
4 300
5 400

then i tried a wet test on #4 and thats when the schrader valve in the compression tester went crazy so i changed it then did the complete dry retest with cold engine and got
1 425
2 415
3 400
4 390
5 400

i pulled the rack damper the other day and noticed its screwed all the way in and no adjustment helps at all also i can push the pin in with my fingers should i be able to? its not a crazy miss seems to be worse when the engine gets up to operating temp.as for the hard starts i found that only 3 glow plugs are working.

Maxbumpo · #8 03-19-2015, 08:21 AM

Sounds like your engine miss problem is related to either injector #4 or delivery valve #4 or pre-chamber #4.

If you have some spare heat shields (which go under each injector) you could try moving #4 injector to another position to see if the noise follows. When you pull the injector, visually check the pre-chamber to makes sure the ball pin is still present and complete. If the noise follows the injector, bad injector. If it does not follow and the pre-chamber appears intact, you can try rebuilding #4 delivery valve.

If all the above are negative, then you have a choice of either pulling the pre-chamber to inspect or replacing the injection pump with a known good pump (either used or rebuilt).

Maxbumpo · #9 03-19-2015, 08:23 AM

The purpose of the rack damper pin is reduce a harmonic in the pump which causes a looping idle, not a miss. If you have doubts about this part, replace with a new damper pin (the new updated pins are gold and have a stronger spring) and carefully research the proper installation method. Incorrect installation will result in hard start / no start condition.

eatont9999 · #10 03-19-2015, 08:31 AM

I had a situation in my second 300SD where the idle got rough once it warmed up a little; rocking from side to side like a dead cylinder was present. I had to go through all of the usual troubleshooting before replacing the delivery valves. Please describe your compression check process in detail. I got 420-450 across all cylinders. I have seen strong running engines read 320-350 but that is getting low. If anyone has run WVO in the engine, you might have a long journey ahead.

1chrisapple · #11 03-19-2015, 02:21 PM

almost certian its injectors as when i reinstalled them back in the engine there is some serious injector nailing on #2 and smokes pretty heavy of unburnt fuel.i did inspect all ball pintles and they were good shape and clean.i can loosen #2 injector line and the nailing goes away.this engine has over 200k and never had nozzles so i think its way overdue.and obviously needs glow plugs.my compression check consisted of removing all injectors and reuse the heat shields.install tester then crank engine till gauge stopped but the first try on hot engine schrader valve in the cheap ass harbor frieght tester gave up so i had to change it and try agian and it was better.

eatont9999 · #12 03-25-2015, 10:06 PM

I wonder if someone replaced #2 injector with a NA spec injector. I have seen that done by oblivious people in the past. The pop pressure is lower than the turbo spec injectors. Or you could just have a bad nozzle in the injector. Pull them and pop test them - either do it yourself or have a shop do it. The nozzles are probably due for replacement but people often blame injectors at the first sign of trouble. The truth is, they have to be REALLY bad for most people to notice. Often times there is some other issue at hand.

biopete · #13 03-26-2015, 12:38 AM

Quote:

Originally Posted by eatont9999

The return lines do not look to be OEM spec. Air intrusion can happen once the car is shut off and the fuel returns to the tank via gravity.

Those are viton return lines. Best you can get.

biopete · #14 03-26-2015, 12:45 AM

Quote:

Originally Posted by 1chrisapple

almost certian its injectors as when i reinstalled them back in the engine there is some serious injector nailing on #2 and smokes pretty heavy of unburnt fuel.i did inspect all ball pintles and they were good shape and clean.i can loosen #2 injector line and the nailing goes away.this engine has over 200k and never had nozzles so i think its way overdue.and obviously needs glow plugs.my compression check consisted of removing all injectors and reuse the heat shields.install tester then crank engine till gauge stopped but the first try on hot engine schrader valve in the cheap ass harbor frieght tester gave up so i had to change it and try agian and it was better.

Hey Chris. Looks like your getting some where. I had that same Damn problem with harbor freight tester. They are total junk. The adapters are good though.
You should make a pop tester. We made one with a bottle jack and a injector line, compression fitting and a little welding real cheap. Jake did it. But it doesn't hold pressure now. The seals went out. I need to fix it.

So what were your accurate compression numbers?
You could maybe try a diesel purge. Also is the fuel good? You probably checked that. But if there is no filter before the electric pump it may have got a clog? Are you gonna go with monarch or Bosch nozzles?

biopete · #15 03-26-2015, 12:47 AM

Also, I wouldn't be surprised if that egr is blocked off.