Cranks but won’t start

[DarkStar]

1992 500E M119

Hey guys!

I have not been on the site in a while. I have not had time to play with my E and it’s had a parasitic drain that I wanted to correct before it becomes a big problem.

That said, I try to drive it once a month or so.
I drove it a month ago, ran fine after it started a bit rough. Drove for 30 minutes and parked it in the driveway. Flew to DC for a week. Returned home and tried to start it the next morning. Cranked, sputtered a bit but did not start.

Fuel pump relay was turning on pumps, pumps made a groaning noise so I pulled them.

Had a bad pump, a second groaning pump. Installed new pumps, new filter.
Gas smelled bad so I drained it and refilled.

It has pressure at the rail, but I didn’t measure the pressure.

I’ve got spark at plugs. Pulled caps and rotors and cleaned up a mild bit of corrosion. No moisture.

Runs for a second if I spray it with maf spray.

Pulled the cap on the CAN box and found some corrosion on a couple pins, deteriorating foam on the pins but nothing exciting.

Crank sensor should be good if I have spark. So I think I’m down to LH module or clogged injectors..?

Thanks for any advice!

Bryan
(DarkStar)

 

[gerryvz]

It's likely you have the classic M119 distributor cap situation.

Lots of threads about this.

Good starting points to read:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

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• 
• 

Thread 'M119 engine coughs, stutters, backfires, won't rev'

Feb 10, 2015

We have acquired my in law 1995 E420 with only 54k on the clock. Several months ago, I changed oil, brake fluid, installed new pads & rotors, replaced 12 year old Michelins, fuel filter and caps/rotors ...car ran great, 23mpg highway. After sitting for about 3 weeks, it made it about 2 miles and started missing then...kerblam! backfire while traveling at about 40mph and did not want to start. Almost seems like carbon tracking that these are known for in distributors. I have not pulled them yet. Any other ideas from the experts on this site?
Thanks, any input greatly appreciated!!
Brian

• maplevalleyhammer
• Replies: 122
• Forum: M119 Engine

Thread 'HOW-TO: Solving M119 Stumbling at Ignition Distributor Caps'

Sep 5, 2025

It is a common malady to nearly all M119 engines with dual-distributor systems, sooner or later, that the engine will suffer stumbling and cutting out. This condition is because there is inadequate air circulation inside the closed environment of the distributor caps, which causes condensation to form inside of the caps, effectively electrically "shorting" the flow of electricity to the spark plugs inside of the cap.

There is MUCH more background about this condition here on the forum, in this thread: FYI - Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot] | M119...

• gerryvz
• Replies: 28
• Forum: "HOW-TO" Tutorial Articles

• 
• 
• 

 

[gsxr]

It has pressure at the rail, but I didn’t measure the pressure.
Runs for a second if I spray it with maf spray.

If it runs with starting fluid sprayed down the MAF, you have a fuel supply issue. Connect the pressure gauge to the rail and measure it. Should be ~55psi after the pumps prime, and while cranking.

Pulled the cap on the CAN box and found some corrosion on a couple pins, deteriorating foam on the pins but nothing exciting.

This could be the cause of your parasitic drain... read this thread for details.

Crank sensor should be good if I have spark. So I think I’m down to LH module or clogged injectors..?

Unlikely to be the LH module, or injectors, but if you have normal fuel pressure at the rail... next step would be checking for a pulse at the injectors while cranking. Injectors should not be clogged if it was running only 1 month ago.

 

[DarkStar]

It's likely you have the classic M119 distributor cap situation.

Lots of threads about this.

Good starting points to read:

FYI Thread 'Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot]'

Jul 18, 2021

Moderator edit: In addition to cutting extra vent slots to reduce/eliminate condensation inside the caps causing misfiring, oil leaks must also be completely eliminated from the cam solenoid and exhaust cam seals. If there's the slightest trace of oil at the lower edge of the cap, this misfire issue can still pop up occasionally, even with the slotted caps. Read this entire thread. A related "How-To" thread is located here that is also required reading....

• JC220
• Replies: 58
• Forum: M119 Engine

• 
• 
• 

Thread 'M119 engine coughs, stutters, backfires, won't rev'

Feb 10, 2015

We have acquired my in law 1995 E420 with only 54k on the clock. Several months ago, I changed oil, brake fluid, installed new pads & rotors, replaced 12 year old Michelins, fuel filter and caps/rotors ...car ran great, 23mpg highway. After sitting for about 3 weeks, it made it about 2 miles and started missing then...kerblam! backfire while traveling at about 40mph and did not want to start. Almost seems like carbon tracking that these are known for in distributors. I have not pulled them yet. Any other ideas from the experts on this site?
Thanks, any input greatly appreciated!!
Brian

• maplevalleyhammer
• Replies: 122
• Forum: M119 Engine

Thread 'HOW-TO: Solving M119 Stumbling at Ignition Distributor Caps'

Sep 5, 2025

It is a common malady to nearly all M119 engines with dual-distributor systems, sooner or later, that the engine will suffer stumbling and cutting out. This condition is because there is inadequate air circulation inside the closed environment of the distributor caps, which causes condensation to form inside of the caps, effectively electrically "shorting" the flow of electricity to the spark plugs inside of the cap.

There is MUCH more background about this condition here on the forum, in this thread: FYI - Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot] | M119...

• gerryvz
• Replies: 28
• Forum: "HOW-TO" Tutorial Articles

• 
• 
• 

Thanks GVZ! Having owned this car for 30 years, the cap and rotor was my first suspect, spark was good and the caps and rotors looked dry but slightly worn.

 

[DarkStar]

after

Thanks GSXR ! I hope to dig into the CAN wiring soon.

The pressure could be below the 55psi, possibly the fuel pressure regulator. I’ll try to source a pressure gauge tonight. Fingers crossed it is just a lack of pressure. I wouldn’t expect anything to gum up in a couple weeks. Not 8 injectors all at once. That was why I suspected something more central like the LH unit.

Any suggestions on reading the trigger pulse to the injectors?

Thank you!

 

[gsxr]

The pressure could be below the 55psi, possibly the fuel pressure regulator. I’ll try to source a pressure gauge tonight. Fingers crossed it is just a lack of pressure. I wouldn’t expect anything to gum up in a couple weeks. Not 8 injectors all at once. That was why I suspected something more central like the LH unit.

As long as pressure is 45+ that should be fine. Normal with no vacuum to the FPR will be 50-55 ballpark.

Any suggestions on reading the trigger pulse to the injectors?

I've never actually done this. I'm guessing a meter tapped into the injector wires and look for a 12v blip periodically. I'm hoping it's something simple. Do you have a spare LH module to try? Any M119 LH will work for testing (can be 4.2L, etc). Don't forget to check all fuses for grins, including the ones in the BM/GM module.

 

[dreaming.haze]

Any suggestions on reading the trigger pulse to the injectors?

You can pick up a noid tester to check the trigger pulse timing. Amazon.com: Lisle 27800 Universal Noid Light : Automotive - cheaper options out there as well.

 

[DarkStar]

In the picture, are the check valves the brass pieces screwed into the pumps? My pumps came with new check valves but not sure how they should be connected?

 

[nocfn]

If you have not changed the fuel rail pressure regulator during your ownership, it may be a good time to replace it out of an abundance of caution. I had my injectors cleaned and tested by a bosch place. Many were missing pintle caps, O rings disintegrated etc. Only one was bad IIRC but many were in vary stages of gunk as OE and about 128k on them.

 

[gsxr]

In the picture, are the check valves the brass pieces screwed into the pumps? My pumps came with new check valves but not sure how they should be connected?

Yup. The check valves are usually pre-installed on the pumps. Look at your photo back in post #1 to see how they go together. Use a smear of green wheel bearing grease on all the copper washers when installing. This seems to eliminate leaks vs installing them dry (no idea why).

 

[nocfn]

me thinks the grease properties react with the copper initially, and the response is malleable initially, thus enhancing the sealing properties mo' better.

 

[DarkStar]

Ok,
I checked the fuel pressure. Was not looking right, 10 lbs. I ordered a FPR and got it quickly, I replaced the FPR and it now pumps to 45lbs, holds for an hour or more and slowly bleeds off.
Still no start.
I sprayed some starting fluid into the throttle body, and it fired for a second.

I also tried an LH module, I had one I pulled from a 4.2L car at the wrecking yard. Didn’t seem to make a difference.

So next I guess I try a noid light.

 

[gsxr]

I checked the fuel pressure. Was not looking right, 10 lbs. I ordered a FPR and got it quickly, I replaced the FPR and it now pumps to 45lbs, holds for an hour or more and slowly bleeds off.

That is perfect. Fuel pressure can be checked off the list.

Still no start. I sprayed some starting fluid into the throttle body, and it fired for a second.

Hrmmm. Still no fuel being injected...

I also tried an LH module, I had one I pulled from a 4.2L car at the wrecking yard. Didn’t seem to make a difference.

Well shoot. That is pointing towards the injectors. No fault codes on the LH module, correct?

So next I guess I try a noid light.

Correct.

 

[DarkStar]

Not sure how to check for error codes…
I need to learn. Bought a code reader of some sort from someone online a while back. Honestly haven’t looked at it. I need to.

 

[gsxr]

Not sure how to check for error codes…
I need to learn. Bought a code reader of some sort from someone online a while back. Honestly haven’t looked at it. I need to.

Everything you need to know is in the thread linked below:

FYI Thread 'HOW-TO: Checking DTC's (Diagnostic Trouble Codes) on the 500E/E500'

Jul 30, 2012

UPDATE: To buy a pre-built code reader, click here (NLA by 2023) or click here (still available in 2023) for an affordable one from eBay. If you do not have a "breakout box", make sure you select the type of reader with the small 1mm pins, i.e. for 400E, not the type with the large 4mm pins. A breakout box is highly recommended... this has numbered 4mm sockets, makes it much easier to use the code reader. The breakout box is $300+ from Mercedes as of early 2014, but clones are available from Chinese...

• gsxr
• Replies: 18
• Forum: De-Coding

• 

 

[nocfn]

You can also remove a plug, lay the plug on a blanket with wire (not touching anything) turn off the lights and have a helper turn the engine over. See if you get spark. If you do, then on a whim, remove the cables from the EZL and replace (pull on plug not wire). Test is a four-letter word but you want to be sure you have spark as the remedies are bending over the low car for hours, farting with coils and headlights and on and on and on. Fuel CHECK! Spark, need to be checked... Air, well you got air.....

 

[DarkStar]

Noid light works…
Pressure is good (45lbs).

I realized the mechanic at MB Austin kept my 500E specific LH module years ago and I e been running a 4.2L module for 20+ years. I recall my harness failed and the LH was swapped out to one that he had on hand. He did me a solid by swapping it for free. Just wish I could have kept the original.

I can’t recall if I had one of Run.EXE’s chips in my LH but it seems to be working.

Injectors next?

 

[DarkStar]

You can also remove a plug, lay the plug on a blanket with wire (not touching anything) turn off the lights and have a helper turn the engine over. See if you get spark. If you do, then on a whim, remove the cables from the EZL and replace (pull on plug not wire). Test is a four-letter word but you want to be sure you have spark as the remedies are bending over the low car for hours, farting with coils and headlights and on and on and on. Fuel CHECK! Spark, need to be checked... Air, well you got air.....

I have spark at the plugs. Checked caps and rotors first, then spark.
If I spray starting fluid into the throttle body it fires.

 

[DarkStar]

Injectors are getting a signal but not injecting.
Rags are dry…
So are my 30 year old seals…

I have a hard time believing all 8 are plugged up.
Noid light flashes so the signal is being sent.

At this point I guess I need to replace the seals and have injectors tested/cleaned?

 

[gsxr]

That is REALLY strange. But yes... with 45psi+ at the rail and nothing coming out the injector, and the noid light indicating the injectors are getting a pulse... it does look like you need the injectors serviced or replaced. Click here for more info.

As a last resort you could try connecting a brief +12v pulse directly to an injector, with pressure in the rail. It should click and squirt. But the pulse from the LH module should suffice, so this probably won't do anything.

 

[DarkStar]

That is REALLY strange. But yes... with 45psi+ at the rail and nothing coming out the injector, and the noid light indicating the injectors are getting a pulse... it does look like you need the injectors serviced or replaced. Click here for more info.

As a last resort you could try connecting a brief +12v pulse directly to an injector, with pressure in the rail. It should click and squirt. But the pulse from the LH module should suffice, so this probably won't do anything.

Does polarity matter on the injector?

 

[DarkStar]

My noid light kit has GM and Bosch labeled lights in it. Initially I used a GM but later noticed the Bosch. Both blinked but the GM seemed to be brighter. I’m guessing they are rated to similar impedance levels as the injectors.

 

[gsxr]

Does polarity matter on the injector?

I think so - but I'm not 100% certain.