Hi everyone.

I'm new, I'm the happy owner of a Volvo V50 petrol from 2004 (early S/N), and I try and take care of her as well as I can.

However, I am not a mechanic by trade, and I still have much to learn.

A little background for my question: In the Haynes manual for the car, I can see that the ground strap goes straight to the engine block, via an outlet on its side. However, when I got the car (used), the ground strap was routed through a screw on the top of the engine block, that is in plastic. The screw was making contact with the block, but it also added resistance. I suspect the mechanic who sold me the car did this on purpose, to throw the ECM/ECU off, because the car had engine problems and having a MIL go on during a sale is problematic. But I am not sure how sensitive ECM/ECU circuits are to additional resistance, and also I am unsure how much resistance this added (I didn't really measure).

So my question is the following: where does the ground strap goes exactly? I cannot seem to find a precise answer in the Haynes manual, and I would personally say "straight to the engine block, not via a screw, but with direct contact", however, cars aren't exactly my specialty.

So, thanks for taking the time to read, and I look forward to your answers!
cheers!

 

IIRC the ground strap is bolted to the top of the block with a hex bolt. I am not sure what plastic you are referring to, do you have a picture? Adding resistance to a ground aka a weak ground won't fix or hide any problems. Rather I think it would exacerbate them.
The ground straps I have seen on my volvos have all been a loop terminal fixed via a bolt.

 

Either the bolt on the engine side goes to metal on the block (or other metal assembly bolted to the block), or it doesn't. If the bolt goes through plastic on the way to that metal, it won't change the resistance in a meaningful way to anything other than the starter's ability to draw enough current to start the car. Which is to say, if the car starts, the block IS grounded, and no diagnostics are impeded.

 

Thank you guys for your answers. It's not the answers I was hoping for, but it's the answers I needed

I mean the cylinder head cover or rockers cover in resin. Here is a photo:

I am sorry for being imprecise, I will do better next time.

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OK. I was thinking that since the ECU/ECM is expecting parts to be within a given range, plus or minus a tolerance, adding a resistance might throw the sensors off completely (because the current flowing through them would be vastly different). But all things considered, even though we are talking about a (rather old) car, it's probably not like the sensor's impedances would be so low that a fluctuation of a few KΩ, or even MΩ would drastically change the readings enough to "lose" the ECU. Especially since those sensors are probably optimised for low electrical consumption, thus have a rather high impedance.

Now I'm wondering if having a weak ground would be enough to "nudge" some faulty readings back in check... But that's pushing it a bit far, and even if it could, there's no guarantee the resistance would match what is needed.

Right, that makes sense. Thanks for your answer.

All right. So the faulty ground couldn't be a trick to hide a defect. However, I still would like to know, where the ground strap is connected on stock V50. Is it at the top of the engine block or at the back (facing the cabin) of it?

Thanks!

 

The resistance (impedance if you prefer) of the ground strap on an engine that can turn over is going to be a small fraction of one ohm (as in a small fraction of 0.001 Kohms). That's orders of magnitude less resistance than can possibly make a difference on the finickiest (sic?) module or sensor. Forget that line of reasoning, as it will only cause you future confusion.

I long since sold off my V50, so really don't recall where the ground strap is. But hey - it's a ground strap, so just poke around the periphery of the engine block and you're sure to see it running toward the body somewhere. It'll be the only thing that looks like a ground strap. ;-)

 

Ok - trying to help here - Your picture is of a 4 cyl plastic cam cover. There are no 4 cyl gas engines listed for any part of the world that Volvo sells cars that are used in a 2004 V50. All engines that Volvo offer have a aluminum cam cover that doubles as the camshaft bearings.
If you can give more details ( your location is France) - choices listed (for your specified car) in the Volvo parts catalog are below - 3 - 5cyl gas (1 turbo) , 2- 4 cyl diesel turbo - all have aluminum cam covers. What exactly do you have? Does your car look like the one in the picture? Whats the engine code on the sticker on the front of the engine? Is your car really a 2004 V50 and not a 2004 V40? Does your car look the V40 in the bottom picture? - I don't see any plastic cam covers for Volvo engines for that year also - but I may have missed something. With correct info I might be able to answer your question.

 

I googled that photo- that valve cover fits a mid 2000's Ford focus!