M103 Vacuum Issues
04-14-2008, 10:55 PM
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190E 2.6 + 560SL
Need help with M103 Vacuum Issues
Greetings
I've finished Replacing the head of a ('93) M103 in a 190E and am in the process of getting the Rough Idle to stabilize.
Stats :
Fuel pressure in lower chamber is 75psi @ idle, 72Psi under acceleration.
IAC valve operates (tested with 9V battery as another poster suggested).
MAF Sensor Tests OK as per MB Manual tests.
EHA current checks out.
Lambda test shows 42% - 48% on an oscilliscope.
No Fault codes.
Coolant temp sensor resistance OK - didn't check continuity to CIS-E Controls
Plug Wires are all 1300 Ohms (replaced #1 wire at 10K Ohms,Smoothed a bit)
Plugs are New
Note: Before Head replacement, the engine ran fine (but had oil in the coolant). However, somebody DID mess with the adjustment screw in the "tower" (Mixture ?) since the anti tamper stuff was missing.
All hose leaks have been cleared up and brake vacuum has no sign of leaks. EGR seems OK as well. The engine idles at anout 1000 with 15 in hg vacuum in Park, and 650 with 13 in hg in Drive/Reverse. Although to me this seems low, I have an identical '89 which shows the same characteristics but with a silk smooth Idle through 5000 RPM. What is a reasonable level of vacuum once the leaks are resolved ?
Im also in the process of replacing the rest of the rubber "breather" (IAC) hoses and the one beneath the air mass meter. In doing so I noticed that there is a large vacuum connection between the intake manifold and the valve cover. As I understand it, there is no valve here, just the oil separator, so it appears that the valve cover chamber and crankcase are under vacuum as well ?
If this is true, then the other breather (PCV) from the valve cover to the air filter must need a good seal to preserve vacuum. Also, wouldn't any crankcase leaks (gaskets, timing chain tensioner ?) lead to vacuum leaks ?
Since the car is a '93 but only has < 60K Miles, I'd like to replace as much brittle rubber as is necessary, and drive it happily for another 100K.
Any help is greatly appreciated.
I've finished Replacing the head of a ('93) M103 in a 190E and am in the process of getting the Rough Idle to stabilize.
Stats :
Fuel pressure in lower chamber is 75psi @ idle, 72Psi under acceleration.
IAC valve operates (tested with 9V battery as another poster suggested).
MAF Sensor Tests OK as per MB Manual tests.
EHA current checks out.
Lambda test shows 42% - 48% on an oscilliscope.
No Fault codes.
Coolant temp sensor resistance OK - didn't check continuity to CIS-E Controls
Plug Wires are all 1300 Ohms (replaced #1 wire at 10K Ohms,Smoothed a bit)
Plugs are New
Note: Before Head replacement, the engine ran fine (but had oil in the coolant). However, somebody DID mess with the adjustment screw in the "tower" (Mixture ?) since the anti tamper stuff was missing.
All hose leaks have been cleared up and brake vacuum has no sign of leaks. EGR seems OK as well. The engine idles at anout 1000 with 15 in hg vacuum in Park, and 650 with 13 in hg in Drive/Reverse. Although to me this seems low, I have an identical '89 which shows the same characteristics but with a silk smooth Idle through 5000 RPM. What is a reasonable level of vacuum once the leaks are resolved ?
Im also in the process of replacing the rest of the rubber "breather" (IAC) hoses and the one beneath the air mass meter. In doing so I noticed that there is a large vacuum connection between the intake manifold and the valve cover. As I understand it, there is no valve here, just the oil separator, so it appears that the valve cover chamber and crankcase are under vacuum as well ?
If this is true, then the other breather (PCV) from the valve cover to the air filter must need a good seal to preserve vacuum. Also, wouldn't any crankcase leaks (gaskets, timing chain tensioner ?) lead to vacuum leaks ?
Since the car is a '93 but only has < 60K Miles, I'd like to replace as much brittle rubber as is necessary, and drive it happily for another 100K.
Any help is greatly appreciated.
Last edited by jjkuhnjr; 04-15-2008 at 07:57 PM. Reason: Misleading title
04-22-2008, 04:39 PM
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190E 2.6 + 560SL
OK,
Here's a lesson for everyone with mysterious rough acceleration in the low end. Even if your plug wires check out with an ohm-meter, they may be causing cross-firing and misfiring.
I thought that my troubles were vacuum and fuel injection related, since the car ran great > 2500 RPM. So the plan to fix the rough low end was:
1) replace all rubber vacuum connectors (the car IS 15 years old)
2) Replace Fuel Filter
3) Replace rotor and wires Plugs and cap already new, and it looked as if the original wires with cylinder number tags were still in at 55K miles, although it WAS dealer only serviced in the past.
4) Replace injectors, seals, o-rings and nylon insulators. Hopefully this might cure an injector vacuum leak or injector problem, and I can use any of the still good injectors on my (soon to be my kid's) '89 with LOTS more miles.
5) Replace the rubber hoses to/from the IAC and replace the rubber piece at the bottom of the Air Mass Meter. (Why do they list these under "Breather Hoses" in the online parts ?)
When the parts came in, I started attacking the least filthy jobs first. Did the vacuum hoses without any significant improvement. Replaced the rotor and wires....PROBLEM SOLVED !
Now I've got injectors, insulators, rubber seals and filters laying around that I'll probably need for the '89....
Hope this helps someone else with similar woes.
Here's a lesson for everyone with mysterious rough acceleration in the low end. Even if your plug wires check out with an ohm-meter, they may be causing cross-firing and misfiring.
I thought that my troubles were vacuum and fuel injection related, since the car ran great > 2500 RPM. So the plan to fix the rough low end was:
1) replace all rubber vacuum connectors (the car IS 15 years old)
2) Replace Fuel Filter
3) Replace rotor and wires Plugs and cap already new, and it looked as if the original wires with cylinder number tags were still in at 55K miles, although it WAS dealer only serviced in the past.
4) Replace injectors, seals, o-rings and nylon insulators. Hopefully this might cure an injector vacuum leak or injector problem, and I can use any of the still good injectors on my (soon to be my kid's) '89 with LOTS more miles.
5) Replace the rubber hoses to/from the IAC and replace the rubber piece at the bottom of the Air Mass Meter. (Why do they list these under "Breather Hoses" in the online parts ?)
When the parts came in, I started attacking the least filthy jobs first. Did the vacuum hoses without any significant improvement. Replaced the rotor and wires....PROBLEM SOLVED !
Now I've got injectors, insulators, rubber seals and filters laying around that I'll probably need for the '89....
Hope this helps someone else with similar woes.
