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1994 E320 Sedan
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41 Posts
Discussion Starter · #1 ·
Hi guys,

I just picked up a 94 E320 a couple months ago. It's had extensive work done and performs great at 121k miles apart from a starting issue.

It's been preferring a bit of throttle to start quickly, which won't occur until the oil pressure gauge rises. This can take several seconds, and an open throttle hastens the start. The car has no visible leaks.

Any idea where I should start?

Thanks,

Doug

And because pictures:
 

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2016 E350 wagon; **1994 E320 wagon SOLD**
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like any FI car, it should start right up with no throttle at all.

what do the spark plugs look like? when was the ignition system last refreshed (new coil-overs and plug wires+boots, and new plugs) ?

if the ignition system is in good shape, then I'd wonder what the fuel pressure is right after turning the key on, before cranking, and how long does it take to drop off? the pumps should run about 1 second when you turn the key on to prime the pressure, and a one-way valve in the fuel line should hold that pressure until the pumps start again when the car is cranked over.

also, whats the date code on the main engine wiring harness (should be on a cloth tag near the ECU in the compartment aft of the battery), and whats the date code on the throttle body (shoulod be able to see it peering down between the intake manifold runners just forward of the throttle). if either of these isn't 1998 or newer, you likely still have ecojunk wiring issues.
 

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1994 E320 Sedan
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41 Posts
Discussion Starter · #3 ·
I'll have to check the plugs myself later today.

The ignition system was last checked in May 2015 at 100k miles (121k now). One coil was found faulty and replaced, the spark plugs, coils and wires, and wiring harness were all checked and found ok.

This was two years and 20k miles ago, so I assume well worth another look.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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19,778 Posts
A couple of very important things to keep in mind

1) The only proper plug for that engine is Bosch F8DC4. No exceptions

2) The ENTIRE ignition system is disposable and needs to be replaced around 100-125K miles with plugs every 25K miles. The ignition system consists of 6 plugs, 3 coil to plug boots, 3 spark plug cables, and 3 coils.

If they replaced one coil, the other 2 are probably at or near the failing point as well. Think of it like headlight bulbs, no point in just replacing the one when the other(s) have just as many hours on them.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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19,778 Posts
A diagnostic error code reader would be an invaluable tool to get an idea of any electrical faults.
Only if and when the OP has verified eco junk wiring is not at play, meaning engine harness and throttle body are 1998 vintage or newer.

Otherwise, all bets are off
 

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1994 E320 Sedan
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41 Posts
Discussion Starter · #7 ·
Only if and when the OP has verified eco junk wiring is not at play, meaning engine harness and throttle body are 1998 vintage or newer.

Otherwise, all bets are off

I didn't remove the battery to check the date, but I did check out the wiring harness connections. New-ish looking thick black insulation, no exposed metal whatsoever, and the previous owner showed me the previous rotting engine harness he'd kept for some reason, so I assume it's been been replaced.

I found documentation of the transmission's wiring harness getting replaced about 7 years ago.

Don't have a date yet, but let's assume the harness is good. Not sure about the throttle body.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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19,778 Posts
When it comes to eco junk, you're better off not assuming anything until you know for sure.

But assuming your engine harness was replaced as you say, the primary suspect is throttle body IMO
 

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89 190E2.6- 5-speed Manual - 200K miles, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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4,549 Posts
Nice car, you did not mention if the car has difficulty starting without some throttle:

(1) When engine is cold, first thing in the morning?
(2) When engine is hot, right after you turn off the engine?
(3) When engine is warm, 1 hour after engine is turned off?
(4) All 3 above
 

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1989 W124 260E
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8,423 Posts
I have the same hot start .But cold is right away . Yesterday i went to start up after 5 weeks standing in hot weather [well over here ] She started once , stoped , started twice, sroped , started the 3rd times and keep running.Its like as if she dont like the hot temperature Just about to go and look to see if i can find a problem.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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19,778 Posts
I have the same hot start .But cold is right away . Yesterday i went to start up after 5 weeks standing in hot weather [well over here ] She started once , stoped , started twice, sroped , started the 3rd times and keep running.Its like as if she dont like the hot temperature Just about to go and look to see if i can find a problem.
OP has a car with HFM injection. Your car has CIS-E injection. The only common thread is that they are supplied by Bosch, and nothing more.

Apples and oranges. Completely different approach in troubleshooting.

Let's not confuse the issue by just guessing at it.
 

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1994 E320 Sedan
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41 Posts
Discussion Starter · #13 ·
So from this picture I believe the engine harness is 24-1-03, however I can't tell the throttle body.

I'm out on the road with it so I won't be able to get to the spark plugs or deeper in for a couple days since I didn't bring tools.

However! One big question. When I was looking at the harness connections the piece of engine trim broke one of its connector tabs and I had to remove it. Is this a serious issue (serious question lol)?
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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I took a very close look at the pic of that throttle body and it appears to read 94M02. Which means it is a eco junk unit. I'd start looking for a replacement unit made in 1998 or newer along with a new gasket.

The black cover is kinda important, but not critical. That part is easy and cheap to replace.

Make sure the replacement throttle body is compatible with your car, depending if your car has ASR or not.
 

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2016 E350 wagon; **1994 E320 wagon SOLD**
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green label == no ASR. white label == ASR.

the date code sbaert is talking about is printed in black 'dot matrix' on the lower line, between the VDO number and the (03). its of the format yyMww, as long as the year is 98 or newer, its a good one. Some people claim to rebuild (rewire) them but I'm suspicious of the quality of said rebuilds.

the cloth tag on the main harness should have two dates on it, one is the design date, the other later date is the build date. its the build date that has to be 1998+ ... there's a couple different harnesses for M104 engines, depending on the engine serial number (changes are minor, one or two sensor connectors changed on late production cars).
 

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1994 E320 Sedan
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41 Posts
Discussion Starter · #17 ·
Hey guys, sorry random question unrelated. I just noticed a leak of what appears to be water from the undercarriage from the hoses in the center of the picture. It's a hot day and I've been running the ac, though not high. Thank you all very much for the help so far. This is my first "old" car so all this is a learning experience for me.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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19,778 Posts
IF that water only appears when the A/C is on, then it is normal evaporation. Even modern cars still have that, though less noticeable because they only use a fraction of the refrigerant amount
 

Premium Member
2016 E350 wagon; **1994 E320 wagon SOLD**
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8,138 Posts
if its hot and humid out, the A/C evaporator condenses water out of the air, that drains out of some small drain tubes near the transmission. *ALL* cars do this.
 

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'95 E320, 221k miles, fair cond
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608 Posts
It looks like your upper engine harness has been replaced from the eco-junk harness. Your non-ASR throttle actuator looks like it still has the eco-junk wires.

But, I'll say it again, you really need to build or buy a DTC LED code reader to find out what sort of problems your engine is having before you replace that throttle actuator.

I have an original throttle actuator on my M104 engine and it's still working fine. I've had idling issues that were resolved by replacing other components like:

1. Cruise Control/Idle Speed Control Module
2. Coil packs
3. Plugs and plug wires
4. Valve cover gasket and oil dipstick O ring
5. Purge valve
6. Various vacuum hoses

Learn to read codes as you'll need that device for diagnosing it later on anyways.


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