Stubborn Check Engine Light 4.0
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New User
Joined: Jan 2006
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Stubborn Check Engine Light 4.0
97 AWD. Purchased used. Many issues, however the latest one does not go away and my local shop probably does not want to see me again. New O2 sensor, idle control valve, purge solenoid (second one in 20K), numerous vacuum lines and EGR connection gasket according to the shop. Finally got it to go 800 miles without check engine light. Now I hear what sounds like a big air leak behind the compressor. Of course you know how easy it is to get to. Sprayed starting fluid near idle control valve and engine revs up. Resealed idle control valve - no luck. Any thoughts on what could be sucking air behind compressor? Also, I have been a backyard mechanic in the past, but not much besides brakes on this. Can you lift the body to get better access to the engine?
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
My 90 Aero 4.0 blew the vacumn plug off the block on the back driver side of the engine, I could see it from the dog house cover openning,looking at top driver side around the valve cover. Just some thing to look at, I guess this has happened to a few Aero's before.
Postmaster
Joined: Sep 2003
Posts: 4,452
Likes: 1
From: Southern California
You probably have the 4.0L since it's an AWD model. Right behind the compressor, on the throttle body is a vacuum line that connects the PCV valve to the throttle body. Check to see if that has popped loose. Another possibility is the Canister Purge Solenoid Valve, which is also in the vicinity.
The "Check Engine Light" going on doesn't tell us much. You need to tell us what code(s) it's throwing. Until then, everything we say is just a shot in the dark.
The "Check Engine Light" going on doesn't tell us much. You need to tell us what code(s) it's throwing. Until then, everything we say is just a shot in the dark.
Post Fiend
Joined: Apr 2005
Posts: 5,720
Likes: 5
From: Washington state
may also be vibration loosened plenum/intake manifold bolts, gaskets can fail if bolts loosen also....tighten bolts and spray again
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Senior User
Joined: Sep 2004
Posts: 391
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From: brooksville, florida
Now I know I am going to upset alot of you tecnical guys out there but I have run my 1991 4.0 v6 aero with the cel on for over two years without any adverse efects, it runs perfect good gas mileage, tranny shift ok and she drives fine and I have heard all the stores about how running it with cel on will seriosly efect the way the engine and tranny runs but honestly mine runs just fine and believe me I have tried many time to put out that cel with no luck.
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Post Fiend
Joined: Apr 2005
Posts: 5,720
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From: Washington state
some CEL codes and corresponding failures have little effect on engine performance
some CEL codes lock ECU/PCM into open loop operation with no torque converter lockup, not good for tranny....cylinder walls and rings get washed down in extra rich fuel drenching that drains into oil
many codes will not even set the CEL
CEL/MIL is just an Idiot Byte Mechanic telling us something is not right..
betcha if is was a just off warrantee Mercedes you wouldn't be driving it around with a continous CEL
some CEL codes lock ECU/PCM into open loop operation with no torque converter lockup, not good for tranny....cylinder walls and rings get washed down in extra rich fuel drenching that drains into oil
many codes will not even set the CEL
CEL/MIL is just an Idiot Byte Mechanic telling us something is not right..
betcha if is was a just off warrantee Mercedes you wouldn't be driving it around with a continous CEL
Former ******
Joined: Nov 2004
Posts: 4,901
Likes: 2
From: Salt Lake City, Utah
A CEL light is telling you something. Now it is possible that the light is for some really little thing, that may be meaningless, eg, our '92 Clubwagon has a code stored for faulty EGR valve position sensor. Doesn't seem to really hurt anything immediately, as far as power, economy and other appart stuff goes. But the failure has lead to the destruction of a 600 catalytic converter. Now if you live in an area where emissions testing is required, this is a very big deal. The sensor is a lot cheaper than that, and canbe replaced yourself. The converter is expensive, and should be installed by a professional.
Senior User
Joined: Sep 2004
Posts: 391
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From: brooksville, florida
Hi again 96-wdr, fat chance of me running a mercedes even with a cel on and if I could afford one and it had a cel on and was running ok then I guess I would run it like that, manly because I could not afford to have mercedes look at it. I guess I am just a cheep basted at heart. I really like to read your inputs though 96-wrd you seem a very knowledgeable chap.
Posting Guru
Joined: Jul 2004
Posts: 2,416
Likes: 1
From: Mitchell, SD
Go to Autozone, CSK, or any auto parts store that pulls codes for free and bring them here. We will go from there.
CBR, sense you have your mind made up about the CEL, there is no point arguing with you.
For tbuchal, it is very important to get this issue solved, OBD-II is alot more finikey than OBD-I because it is more high tech.
CBR, sense you have your mind made up about the CEL, there is no point arguing with you.
For tbuchal, it is very important to get this issue solved, OBD-II is alot more finikey than OBD-I because it is more high tech.
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