Starting problems with 420SEC HELP!!!!!!!!!

[stuartj53]

For a while had very intermittent staring problems. Car starts then after a few moments cuts out. Then turns over fine and starts up then dies. Does this for a while then starts. It?s slowly got worse to the point where twice I have flattened the battery. When jumped, I have managed to get the car restarted.

My mechanic has looked at then usual things. He now thinks the problem is the slide valve. He notes that when he cleans this it starts up OK then problem returns. Also when it refuses to start if he taps this it starts. Any advice I don?t want to spend the money to replace this expensive part for it not to fix the problem. HELP

 

[ant500sl]

When you refer to "slide valve" to which component are you referring as I have not seen this term used before.

I just happen to be breaking a complete running 420SEL so I may well have one?

 

[stuartj53]

Thanks for post. Its the idle valve merc part no 0001411625

 

[guydewdney]

thats a std bosch part.

that is just an idle REGULATOR - the engine should start and run fine assuming a low electrical load (so heaters etc off) and low pump load (so no turning of steering / no air con on)

what it does is allow EXTRA air in to give slightly more power to compensate for the extra load from the air con etc.

the idle adjustment should be done first - there should be a small screw somewhere to adjust the idle itself (i.e. the closed posistion of the main throttle plate)

The valve should also default 'open' or half open whn the plug is disconnected - try unplugging it?

 

[stuartj53]

For me the question is "Is this part likely to be causing my problem with starting?" Unhappy to waste money replacing if not.

 

[stuartj53]

For me the question is "Is this part likely to be causing my problem with starting?" Unhappy to waste money replacing if not.

 

[Mikesmerc]

Stuart, my 560sec idle valve packed in a year ago and replace it with ine I got from a breakers yard, approx 35Stg. Worth a try for little money spent.
Saying that I still have a hard start problem but now idles at the correct speed. Got new fuel pumps , just have to find time to fit em
Regards
Mike

 

[stuartj53]

Mike

Was your problem as bad as mine? i.e. could it take quite a bit of time to start.

 

[Mikesmerc]

Still have the problem Stuart. With mine originally it refused to start one morning after a year of perfect starts. I could keep the key turned until the battery died. Then I found if I released the key after a couple of seconds or so it would fire (backfire usually). About 15 attempts at this it would start. I believe that it was the backfiring that had an adverse effect on my idle air valve, and so now I had a hard start prob plus a high idle prob. Replace the valve and noew idles fine. Replace the spart plugs with Bosch and started first time. Short lived Im afraid, back to a hard start. Have new fuel pumps and filter at the ready, just waiting fuel pressure test kit from the States to confirm a fuel pump problem.
Let me know if yours backfires
Regards
Mike

 

[stuartj53]

Mike no backfire just a problem starting. Not every time. I am still not sure that its just the slide valve. Anyone else any thoughts on this? Its an expensive bit to replace if its not the cause of the problem!!!!!!!!!

 

[jberks]

Stuart,
A little while ago, my throttle actuator was suspected as the cause of poor idle. Again a pretty expensive part. I considered doing it myself but in the end I took it to a local specialist, who fitted one off another car, tested it and then put the old one back as there was no improvement. All I paid for was the labour - a lot cheaper than the 100's for the part. At the same time, they succesfully diagnosed and cured the actual fault. If you're not sure you need one - and with these problems it's almost impossible to be certain, (they originally thought it was the actuator too) it may be a better way to go. Then again, they may be able to diagnose it, saving you a lot of heartache. Specialists are generally very helpful and knowledgable and whilst they may be more expensive than your normal mechanic, in tricky cases like this, a second expert opinion can be invaluable.

 

[stuartj53]

Thanks sounds a good idea. My mechanic quite good on mercedes but he has checked with the local merc forman (who is a mate of his) and he also thinks this is the root cause of the problem. But they will not confirm 100%. :cry:

 

[bandant]

Simple way of testing the part. There is a limp home mode built into the ECU whereby if the idle valve fails the engine will bypass it and run at 1100 rpm.

Disconnect the cable to the valve, engine should start ok and idle at the 1100 rpm mark. If it does the fault is with the valve or controller, if not then its something else.

Good luck

 

[stuartj53]

Thanks for that. We are still not there. Changed the slide air valve not solved the problem. Mechanic now thinks it may be fuel related.

Bill gets bigger by the day.

 

[guydewdney]

these things are difficult to diagnose without being there - sorry to hear u replaced the IAC valve with no gain - I would dispute the labout with the mechanic if i were u on this bit...

fuel pressure regulators have been known to give up - v cheap (20 quid) and easy (30 seconds) to fit - u just need a circlip plier.. (assuming its the same basic thing as on mine (1996 SEC 420 effectivly)

 

[stuartj53]

Thanks for that mechanic now thinks that there may be two problems with the second being fuel related.

Anyone any ideas??????????????????????

I would change mechanic but this guy has a very good record with local taxi drivers.

 

[Mikesmerc]

There is a way for checking fuel pressure reg without eqiupment. I think you leave the car run until it reaches working temp, then shut it off for 20 min and depress the metering plate with your hand and you should feel some resistance this indicating that it is holding pressure.
All from memory of another post., worth doing a search for all Talbirs posts its in there somewhere.
Regards
Mike

 

[paulcallender]

Have you had the fuel injection system diagnostic codes read off? I looked into this, you cannot simply walk into Halfords and buy a "diagnostic reader" - unlike other makes/models of cars. So, you would need to find a garage with the appropriate equipment.

The second suggestion, does it start and run better with "cold start" spray? Definitely a useful thing to have, although not obviously long term.

Unless you can disgnose, and then replace, the component that is faulty, then you face an uphill struggle with the lack of information on the problem. Even if you do replace a component, what tends to happen is that all the components are old/worn so the engine never really runs as sweetly as a new engine.

It may be worth buying a donor car in the £500-1000 range, eg off ebay, swap all the components one by one until you find the fault, then buy this part and re-sell the donor.