W124 E320 starting problem

[westcliff]

My 1994 E320 estate has a problem starting the engine. So far it has always started, but it can take a dozen attempts before it fires up and I worry about draining the battery.

I took it to a specialist, who changed the crank sensor, cam sensor and fuel pump relay. After that, it was starting perfectly for a week, then the problem came back.

I guess the sensors and the relay aren't the problem but the specialist did say it may be the ECU or the throttle body. (To be fair to the specialist, he didn't charge me for any of the work he did).

Could it be a case of components within the throttle body needing a good clean? I have to admit that I don't know what a throttle body is, my DIY days were long ago, working on BMC A- and B-series engines with SU carbs.

I have a feeling I can't afford a new throttle body or ECU and would welcome any DIY hints. I have a long journey coming up and I don't want to be stuck on a service area somewhere on the M6, or worse.

Thanks in advance for any info.

 

[westcliff]

Something I didn't mention is that the engine occasionally cuts out before it has properly warmed up. This occurs when steering, with my foot off the accelerator, for example parking in a tight space.

A search of this forum mentioned the OVP relay. Could the OVP relay cause these problems?

 

[Ellsy Tanners]

A possible air leak on the inlet manifold , or vacume system. The ovp relay can indeed cause these syptoms but might be a expensive gamble.

 

[westcliff]

Thanks for your help (again) Ellsy. I'm hoping that the specialist tested for these things you mention and eliminated them as the cause of the problem. One thing that made me think it's the OVP is that the OVP can cause bad diagnostic readings for the crank sensor and my car certainly had a bad crank sensor diagnostic reading, I saw it myself. Changing the crank sensor did no good though.

I'll order an OVP relay and fit it, mainly because it's something I can do myself. And I'll rent a car for my weekend trip.

 

[jibcl500]

if the car wont start pull the OVP relay and plug it back in if the cars starts its the OVP relay.

jib

 

[westcliff]

Cheers jib. Is it a straight pull, or undo a screw/bolt first, then pull? Just so I know to have the correct tools with me when it happens.

 

[jibcl500]

behind the battery is a plastic cover, its a fiddle but it does come out with the battery in place, you will see the ECU and to the right of it is a silver box with a clear plastic flap and a red fuse inside, if you push the relay to the right one side comes free and the move it left to release it. Then unplug it.

jib

 

[westcliff]

Many thanks. I have now found my OVP just where you said it was and I'll probably be following your advice tomorrow morning.

 

[westcliff]

Well I got round to buying and fitting an OVP relay and the car now starts every time. Each start is identical, two coughs from the starter motor, then vroom, the engine's running.

I was driving to work today, all smug because I'd sorted my Mercedes cheaply, when the engine cut out going round a corner on a trailing throttle. Did it again tonight. From asking questions here and searching the forums, two possible causes present themselves.

The first is that there may be a vacuum leak. Where and how should I look for a leak? I've no experience with these engines and I don't want to cause any more damage while I'm tracking the problem down.

The other thing I read about is that there is an electrical plug somewhere, which when plugged into its socket, raises the idle speed and prevents the engine from cutting out. Any idea where this plug and socket can be found? Currently the engine idles at 500 rpm in drive and around 550 rpm in neutral. I think that's around 150 - 200 rpm too low.

 

[demagod]

I dont think it will help, due to the fact its a totally different car, but I used to have a similar problem on a 2.8i Capri, It had something to do with the fueling system, I changed the fuel accumulator, and a sensor, which were common faults for the problem i had, which was similar, except for it had a hot starting problem, but it would stall when steering sometimes due to fuel shortage at that point? Possibly by the power steering. Turned out to be the stupid K Jet system it ran for fueling, but the problems sound vaguely similar????