not a guru

[smart142 605]

I've got a ''smart'' problem I would like to share with you.

 

I was asked to have a look at a members smart that had an intermittent starting problem.

I ran the Mercedes codes and the only thing that came up was C1121 - L rear rpm sensor.

I replaced that and she started up and ran just fine for me.

The owners pick it up, drive to a grocery store, and then it won't restart. After about 15 minutes it starts and its right back to the shop.

 

No codes and in my experience the intermittent start is caused by a failing relay for the fuel pump. So I bypass the relay and she starts up ok. I drive it about 5 minutes to a restaurant. After lunch she turns over but won't fire. I call for a tow. After 15 minutes I try again and she starts up. Cancel the tow and back to the shop.

 

OK, so now I'm thinking that maybe the actual fuel pump is failing so I replace that with a working used one.

Drove it the 13kms home with no issues and then hours later turns over but won't fire.

Later it starts so back to the shop. No codes.

 

At the shop it always starts. So I try again - a 5km drive to the restaurant. Lunch and then the no start again. This time I had a 14mm wrench and loosened the line to the common rail. When the ignition was turned on the fuel poured out so the fuel pump is not the issue.

After the 15 minutes she fires up and its back to the shop.

Hooked up the computer - ZERO CODES.

 

Now I'm thinking maybe injectors so I do the compression test

1. -0.560

2. +0.340

3. +0.140

Good numbers when the parameters are + or - 2.5

Next I examine the injectors and they are dry - no signs of any leakage or blow by.

 

Now I'm stumped!

 

Last year I did work on a smart that stalled out when it warmed up and was driving. That turned out to be a failing crankshaft position sensor. This seems to be different?

Maybe a failing ECU ?

 

Any suggestions?

[Willys 747]

I would say it's a cold solder joint in one of the three computers somewhere .....as it operates fine when cold but opens when hot resulting in an open circuit etc. I'd be opening up the ECU and having a peek. Have you checked for green pins, there are 2 or 3 that get green. 2 are at one end of the plug and the third is somewhere near the middle.   Beware of discharging capacitors...!!!!  Ask me how I know...lol.

just my bent nickel's worth...hope it helps.

 

[Sydney 218]

you are the smart wizard.  and this has you stumped.   lol.

 

[BWM 87]

When mine quit starting it was always after it had been run.

In my case it wouldn't start for 3 days.

Since I ran a jump ground battery to the block and then to the clump of six wires bottled to the floor pan in the engine bay between the inter cooler and motor there's been no more problems.

I had previously cleaned those grounds twice, then replaced the eyes with soldiered on ones, even drilled a new hole cleaned off the paint on both sides of steel and used a stainless bolt to give a perfect ground and had the no start.

Try the simple things 1st.

 

 

[stickman007 309]

In my experiences, when the engine doesn't start, but no codes...it means that one of the internal conditions to start for the ECU is not met. For example, if the ECU is not seeing a clear crank rpm, then it will not time the injections properly, but may not necessary log a code because its normal to take a few revolutions of the crank to establish that. I would dig into any info you can find on the OM660 sensors and start conditions for the ECU.

 

If the ECU is dying, I would expect more codes - may not be able to see the EDC module with STAR. You've already confirmed that you have low pressure fuel, maybe try keeping an eye on the rail pressure while cranking? Though if rail pressure is low, it should log a code. Keep an eye on cranking rpm?

 

Good Luck

[LooseLugNuts 557]

i would go after the crank position sensor

 

my experiences on many cars that quit or wont start when warm but work fine cold with no codes has almost always ended up being a crank sensor or a faulty coil ....and the 450 obviously has no coil 

[smart142 605]

On 08/07/2019 at 0:21 PM, smart142 said:

 

Last year I did work on a smart that stalled out when it warmed up and was driving. That turned out to be a failing crankshaft position sensor. This seems to be different?

 

 

 

Drove it today and it stalled out after the coolant reached 80 degrees.

Started after a short wait and right back to the shop. And finally this time it had a code - crankshaft position sensor.

 

So after a struggle I got it out. First it was the T30 bolt and then the sensor itself - that proved reluctant.

The new sensor would not go into the shaft smoothly and I had to use some 400 emery cloth to clean it out.

Quit at 6pm and tomorrow morning will put the I/C, fan and hoses back on and keep my fingers crossed

[smart142 605]

Success!!!  This morning after the crank sensor was installed I got the I/C and fan installed, raised the engine and had a few tense moments - wouldn't start. No codes. After about 6 trys she fired and everything is good. Took it for a test drive bringing her up to temp - no issues! Finally!

Kudos to stickman and loose lug nuts for good advice!