OVP relay

[turnipsock]

Just a thought on the OVP relay...

Basically this is just a relay that drops the power to the modules. (It also serves to cut the power if the voltage becomes to high...presumably if the engine is running and the battery becomes disconnected).

The relay kicks in when the key is turned, therefore the easiest way to test this would be to bypass the relay contacts when they are closed, ideally with a switch so that when a suspected fault occurs, you can close the switch to see if the fault vanishes. You could also rig up a light or led to the 12V for the modules and see if this flickers.

 

[Keith]

good idea

like the idea will install myself a temporary switch in cabin in case it happens again!

good posting turnipstock

Keith

 

[Keith]

bridging out OVP for a few days ?

As I am not main user of the car I am wondering about bridging out the OVP for a few days and asking my wife if she notices better results.
Do you think this is a big risk?

Keith

 

[turnipsock]

You have to 'unbridge' it when you switch off the car, otherwise your battery will run down.

I meant it as a quick check for problems relating to things relating to some of the module problems. If your car is running crap and you short out the relay then you will know if it's the relay or something else that is causing the problem.

It would actually be easier to just to get a relay out of the scrappies and wire a switch into this. I'm not sure of you can pull this thing apart, if you could there is a tool, from Maplins, to clean up the contacts (also handy for rotor arms) that would help.

 

[Keith]

glad i asked!

will stick to the switch idea then

ta
K

 

[Keith]

non the wiser - but still trying

first I took a wire from the 87 with the OVP still in its socket. I measured the voltage. On glow I got 11.5v then on ignition it went haywire between 0 and 12v.

I then took out the OVP and bridged 87, 30 and 31 so to have 12v everywhere. I restarted the engine but it still seemed a bit rough.

basically not much the wiser . Unfortunately the weather has warmed up so the rough running wears off quite quickly compared to before but its still not right.

one idea (next time I have the chance) is to monitor voltage on both the switched and unswitched output simultaneously during start up . If the unswitched is constant and the other jitters around would that condemn the OVP?

K

 

[Keith]

OVP outputs look fine - still rough idling when cold

I have now started up with live monitoring of both the protected and unprotected output from the OVP . Both look AOK hovering between 12.5 and 13v. The engine still idled roughly after starting until warm. Do you think it could still be the OVP or what else?

your help appreciated

Keith

 

[turnipsock]

If the voltage is staying constant, it would suggest the OVP is ok.

This would tie in with when you bypassed the OVP and the idle problem still remained.

 

[pascal]

The next no cost item on my list would be to give the idle valve a good clean.

Also plugs and distributer.

After that would be an almost gone fuel pump relay; beside over voltage one. But that often ends in the car not starting at all.

Pascal

 

[Keith]

its a diesel - any other ideas

Pascal

thanks for the suggestions but the car is a diesel which I guess rules out distributor and plugs. do I have an idle valve?

The exact sypmtoms are (from cold start)
- car starts first turn of key as usual
- it then idles very roughly until warmed up, it then idles fine.
- restarting from warm is no problem at all.

In very cold weather the idling problem requires careful coaxing using the throttle to avoid stalling.

I have rules out OVP and air in fuel lines.

any items I can check?

Keith

 

[Chazchuzzlewitt]

Hi Keith- I had similar problems as yours but not a severe. I'm not sure if the warmer weather has helped but I recently had the air intake and EGR valve off the car to clean which had tons of carbon in them, so much that some of the moveable flaps inside the intake were stuck in one position. The car now starts and runs better.
Have to tried disabling the EGR vacuum line and seeing how it starts? I believe the EGR opens when the car is cold but less so/not at all when warm.

 

[Keith]

How does EGR affect cold start?

Chaz
thanks for this , it sounds promising and certainly my E300 has slightly more miles on that yours so I could well have same issue.

Can you just run me through what disconnecting the vacuum from the valve might show?

Keith

 

[Keith]

picture of EGR - please explain

Chaz
i have just taken this picture of my EGR and flap, but there's a third component I dont understand the purpose of which I have numbered '3'. any idea what this does.

http://photos.wanadoo.co.uk/album/1403350

Is it ok to dismantle the whole lot for cleaning , are there any little gaskets or seals I will need on reassembly that I need to buy in advance?

 

[Chazchuzzlewitt]

no.1 is the one to disconnect, 2 & 3 are for one of the flaps in the intake. I took this and the EGR assembly off (4 bolts on side of engine) and cleaned that, as well as the large bit of intake that runs over the top of the engine- this part has another vacuum-controlled flap in the middle of it that was stuck on mine due to crud. There's only one gasket- between the EGR valve itself and the intake part it's bolted on to. I re-used the same gasket on re-assembly as it looked fine.
There's rubber seals between the different intake parts, these need a bit of forceful coaxing to come apart.

On disconnecting the EGR, I think I read that it's operational on start-up so I was thinking if there was something wrong there it might be obvious if disconnected. Of course it could be, in the words of John Cleese, something completely different!

I'm by no-means an expert but I figured cleaning that lot couldn't hurt.

 

[Keith]

will clean mine too

Chaz
thanks, its always good to know someone who has been there before. I generally dont get involved with the engine or drivetrain, leaving it to a couple of trusted techs. But I think a bit of cleaning is within my capability so I'll give it a go and let you know if it improves anything.

best
Keith