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Old 03-09-2010, 09:02 PM   #1 (permalink)
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Exclamation Help! ML320 looses acceleration at all speeds

My 1988 ML320 looses power at all speeds (175k miles). While driving straight at highway speeds, the engine rpm drops all of a sudden slowing down the vehicle from 65 mph to 40mph within several seconds. Pressing the accelerator paddle does not have any effect. However most of the time power comes back. Car speeds up, but again looses power. When engine power and RPM comes backs, it thumps and jerks the car. Sometimes, a little tap on the brake helps restore power. This issue gets worse with each passing day. It happens more often and now happens at lower speed. I have no codes. I checked with Carsoft. Nothing. I suspected ABS and traction control. I disconnected a speed sensor to disable ABS ETS. Same problem persisted. I do not have ESP. I checked brake rotors. They were not hot after driving. I replaced fuel filter. I cleaned intake with seafoam through vacuum line. Changed engine oil (0W40), changed transmission fluid and filter (shell ATF134). Erased adaptive learning using carsoft. No improvement. The previous owner replaced mass airflow sensor. My next guesses will be CPS, fuel pump, throttle position/paddle transducer or throttle actuator. Any guesses? I will borrow a fuel pressure gauge and check the car out. Any suggestions? Please help.
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Old 03-09-2010, 09:38 PM   #2 (permalink)
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when you lose power, does the vehicle behave as though you turned the key ie dash lights turn on?

EDIT: wait nevermind, the engine doesn't completely stop does it? does it just idle, causing the slow down?
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Old 03-09-2010, 09:41 PM   #3 (permalink)
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First off, you might want to upgrade to a newer model, the 1988's are known to have many issues.

That being said, when you reach 65, do you notice what gear it is in? count it up when you go up to that speed next time. Just a start.
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Old 03-10-2010, 01:53 AM   #4 (permalink)
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I don't know what Carsoft is capable of, but it would be a good idea to have the truck scanned with something that has the capability of reading M/B codes. There are many M/B codes that do not have a generic Pxxx code attached to it.

The pdf below shows Cxxx codes in the Traction System and again I suggest getting it properly scanned to save you and you pocket from rebuilding the entire truck. It's going to get real expensive.

You don't mention it, but have you considered replacing the brake light switch ($15) before you go on to CKP sensor and fuel pump.
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Old 03-10-2010, 07:40 AM   #5 (permalink)
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Quote:
Originally Posted by teqvexed View Post
when you lose power, does the vehicle behave as though you turned the key ie dash lights turn on?

EDIT: wait nevermind, the engine doesn't completely stop does it? does it just idle, causing the slow down?
No, car still had power but much less. RPM drops as if I took my foot off of gas. However, this RPM drop is more abrupt compared to taking my foot of the gas paddle. Feels like that transmission was still engaged and sudden drop of RPM was bogging the vehicle down. Vehicle slows much faster as if engine low RPM is working as brakes. I touch brake rotors and they seemed just warm, not hot.
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Old 03-10-2010, 07:49 AM   #6 (permalink)
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Quote:
Originally Posted by 43sqd View Post
I don't know what Carsoft is capable of, but it would be a good idea to have the truck scanned with something that has the capability of reading M/B codes. There are many M/B codes that do not have a generic Pxxx code attached to it.

The pdf below shows Cxxx codes in the Traction System and again I suggest getting it properly scanned to save you and you pocket from rebuilding the entire truck. It's going to get real expensive.

You don't mention it, but have you considered replacing the brake light switch ($15) before you go on to CKP sensor and fuel pump.
Carsoft 7.4 multiplex specially designed for MB, reads all engine, transmission, abs, ets, and many others. It can also show live data. I have not tried the live data yet. Maybe I should drive and monitor what’s wrong. It’s a two person job, one watching data on laptop and other driving. This morning, I saw check engine light. Maybe I got something. When I go home I will hook up carsoft interface and my computer. I already changed brake light switch 2 months ago. I should change the CPS anyway. Its time. I need two cranks to start
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Old 03-10-2010, 08:24 AM   #7 (permalink)
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How's your fuel pump/fuel pressure?
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Old 03-10-2010, 11:15 AM   #8 (permalink)
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You must be anti-Toyota! Sorry, couldn't pass on that after news of more Toyota problems today.
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Old 03-10-2010, 01:52 PM   #9 (permalink)
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Fuel pressure

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Originally Posted by FAR888 View Post
How's your fuel pump/fuel pressure?
I have not checked it yet. I will get a tester and check it this week.
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Old 03-15-2010, 06:31 PM   #10 (permalink)
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53-56 psig

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Originally Posted by FAR888 View Post
How's your fuel pump/fuel pressure?
I borrowed a fuel gauge and connected to the fuel injector rail valve. Read ~55 psig. Needle was vibrating a bit. Drove around with gauge taped to windscreen. 53-56 psig. I had several episodes of rpm dropping off, as if the car was choking, speed dropping, light tapping of brake and pressing gas brought rpm back with thumps (I guess at transfer case). All the time the pressure did not drop below 53 psig. I parked ML320 with gauge connected. Went away for an hour. Came back and saw that the pressure bled to 20 psig. This might explain the second crank for starting. I dont know what else can be wrong.
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