miss/rough idle problem identified - Page 2 - PeachParts Mercedes-Benz Forum

greythunder · #1 02-22-2015, 05:03 PM

what I have done: nozzles pop tested to within 50 psi, delivery valve seals and crush washers, all filters fuel and air except tank screen, I run stanadyne with every fill up, just recently started using biokleen, glow plugs with holes reamed, all fuel hoses under the hood, vacuum actuator swap, egr and flap valves removed.

what car does: after starting initially, starts fine, the car misfires and idles rough. the power output is fine. 13-15 psi of boost per gauge plumbed into alda. when driving and you let off the accelerator the car shakes and is VERY rough for a few seconds when returning to idle. a misfire can be heard while listening to the exhaust. Thud- thud- thud.

vstech · #2 02-22-2015, 05:04 PM

Quote:

Originally Posted by greythunder

ok, today when i got home from work and pulled the valve cover and turned the engine by hand. i lined up the timing marks through the cam sprocket and looked at the crank pointer. not good.

had i bothered to clean the sludge off the pointer you could see exactly how far stretched it its, but its safe to say it's somewhere between 7 and 8 degrees. dammit.

i would def. agree about the comments about this mechanic/shop and $103
per hr they should know this stuff.

still need to find a place around CLT that has a good reputation and knows our cars.

What side of charlotte are you on?

vstech · #3 02-22-2015, 05:11 PM

Boost pressure is higher than I'm used to... maybe the over boost is cutting out?

Have you cracked the injector line nuts one at a time to see if thud stopped?

greythunder · #4 02-22-2015, 06:08 PM

im in Matthews, and yes I tried the cracking fuel lines, even used stethoscope, nothing. all the injectors being cracked just made it REALLY miss and didn't "sync" with the misfire.

to my knowledge, the 92 was the first year without the overboost cutout, which is why I installed the boost guage

vstech · #5 02-22-2015, 07:41 PM

Nope, all the turbocharged diesels have an overboost cutout.

sixto · #6 02-25-2015, 11:23 PM

John, 92-93 2.5s don't have overboost swtich per se since boost is controlled by EDS and monitored by a MAP sensor. A plastic line tee'd into the ALDA line leads to the MAP sensor by the ECU. 90-91 2.5s have a MAP sensor but also have the conventional pressure switch in the manifold that triggers a switchover valve interrupt.

Agreed, 8* of stretch shouldn't cause a rough idling engine. When the engine idles rough, does disconnecting the ELR actuator (red round thing on the aft end of the IP) make idle even worse or cause the engine to stall? If not, you might have a bad signal from the ECU to the ELR actuator. Does disconnecting the vacuum line to the shutoff actuator help things? Could someone have mucked up a delivery valve reseal?

Sixto
MB-less

Maxbumpo · #7 02-26-2015, 12:35 PM

Quote:

Originally Posted by sixto

When the engine idles rough, does disconnecting the ELR actuator (red round thing on the aft end of the IP) make idle even worse or cause the engine to stall? If not, you might have a bad signal from the ECU to the ELR actuator. Does disconnecting the vacuum line to the shutoff actuator help things? Could someone have mucked up a delivery valve reseal?

I like these ideas.

My '87 wagon had a very rough idle when I got it, chased if for awhile just like you, finally disconnected the ELR at the back of the injection pump, and had smooth but very low idle. Manually increased the idle back to about 750 rpm, never looked back.

greythunder · #8 03-11-2015, 05:59 PM

definitely was the timing chain. I had it and the tensioner replaced about 2 weeks ago, and they retimed the injection pump. doesn't even sound like a diesel anymore. very smooth. they said the guides looked fine, and for only 136K miles he said it was one of the "youngest" engines he has seen to be stretched that far.

Maxbumpo · #9 03-12-2015, 10:07 AM

Quote:

Originally Posted by greythunder

definitely was the timing chain. I had it and the tensioner replaced about 2 weeks ago, and they retimed the injection pump. doesn't even sound like a diesel anymore. very smooth. they said the guides looked fine, and for only 136K miles he said it was one of the "youngest" engines he has seen to be stretched that far.

That's great news!

Maxbumpo · #10 02-26-2015, 12:33 PM

I'd replace the chain as your next step. On the OM60x, 5 degrees of stretch is the allowable upper limit.

Who did your injector work? You may want to send them to Greazzer to have them checked.