Jerky after driving home in rain

[ex-Chinese Dave]

I drove home last night and from the start the car was perfect. I went through one large puddle, but not quickly and also there was a little standing water on the motorway. Once I came off the slip road I could feel that the car was very jerky below 2000 RPM. It starts fine and runs fine above 2000 revs. This morning I took off the inlet manifold and made sure there was no water down the plug holes. I didn’t see any moisture at all and I gave everything a good spray of WD-40. I’ve re-fitted everything and I’m now on a test drive, but I’m not convinced everything is perfect. The car is a 172 Cup and has just recently been fully serviced, it’s been running perfectly. Could it be something to do with the O2 sensor that may have gotten wet and will clear itself? I’m a little baffled as it wasn’t like I went driving through a river.

 

[JamesBryan]

Worth checking the engine bay fuse box.

 

[ex-Chinese Dave]

I've checked the fuse box. Nothing looked damp but I took out the fuses and relays and gave them a squirt of WD. Hoping this will work later when I go out.

Under the car, on the passenger side, I could see some wires going into a connector. Do I take it that that is for the O2 sensor? I've given that a WD, too.

 

[JamesBryan]

O2 sensor wires/plug joins around the rear of the subframe iirc

 

[ex-Chinese Dave]

O2 sensor wires/plug joins around the rear of the subframe iirc

Could that be the problem? I'm sure it gets soaked when ever it rains, not just after going through a few big puddles.

 

[JamesBryan]

Could that be the problem? I'm sure it gets soaked when ever it rains, not just after going through a few big puddles.

Plug is weather sealed and it's up on top of the subframe (or should be), so shouldn't really be a problem unless there's a dodgy wire.

 

[Matt Cup]

Does yours have the shield in front of the alternator? If it’s missing could water ingress there cause issues?

 

[ex-Chinese Dave]

Does yours have the shield in front of the alternator? If it’s missing could water ingress there cause issues?

I’m not sure without having a look. What would it expose if it’s not fitted?

 

[ex-Chinese Dave]

Well it seems to be back to normal now. I put it into 4th gear at 1200rpm and it sluggishly pulled away as opposed to what it was doing before which was jerking forward. I can still feel sometimes it seems to cut whilst pulling away in low gears from below 1500rpm as per this thread ( https://cliosport.net/threads/o2-sensor-fault.851384/ ) but at least the problem caused by the water seems to have gone.

 

[Matt Cup]

I’m not sure without having a look. What would it expose if it’s not fitted?

It just covers the alternator. It was a bit of a long shot as to it causing the issue you had though.

 

[ex-Chinese Dave]

This again!

Due to a massive amount of bird s**t on my car yesterday I decided to wash it on the driveway. The driveway is quite steep and my car was facing downhill. I only used a hose pipe which doesn’t have too much pressure. I did put the hose pipe under the wheel arches to remove any remnant of the salt we’ve had put down recently. I didn’t lift the bonnet or get any water directly onto the engine. When I started the car I found it was running very rough under 2000 revs. I’ve taken the engine bay fuses out, and given them all a clean and a spray of WD-40 this morning. I’m just in the car now taking it for a test drive, but I can feel it’s not as it should be. What is this horror? Is there anything else I should be looking at Where there may be some moisture causing an electrical issue?

 

[Flob]

I did this once and it was water down the plug holes.

 

[ex-Chinese Dave]

I did this once and it was water down the plug holes.

It won’t be that. I can piss harder than the pressure from the hose pipe. The bonnet was not lifted. After going through a massive puddle a few weeks ago I took the inlet manifold off and checked the plugs. The were totally dry.
I’m beginning to think that any problem on an old 172 needs the plugs checking for water!

 

[ex-Chinese Dave]

Been for a test drive and there’s no difference. The car idles a little lumpy and up to 2000rpm I can feel it struggling. After that it feels fine but seems to be a little down on power and throttle response.

 

[ex-Chinese Dave]

I’m thinking that maybe one or more of the relays has got moisture in it. Has anyone opened these up or just replaced them?

 

[ex-Chinese Dave]

I've just pulled the large white plug off, blown it out, sprayed WD40 in and around it and refitted it. It was hard to tell if there was any water in it as there was also WD on from this morning. I'll drive to work and see how it is......

 

[ex-Chinese Dave]

The car does now feel back to normal after driving for 40 minutes. I’ve no doubt now that water got onto the large white connector and sat in the bottom of it. I will know for sure later on when I drive the car at 1 AM if it is perfect.

I will have to have a look at someway of protecting the fuse box as it seems all too easy to get water onto the wires and the fuses. It does have the lid, although the catch for it is broken and it sits loosely.

 

[JamesBryan]

Is the cover on properly?

Only thing i can think of is it's not and water is running down the wing into the box.

 

[ex-Chinese Dave]

Is the cover on properly?

Only thing i can think of is it's not and water is running down the wing into the box.

The cover is on, but it fits loosely. I’ve noticed that the clip that is on the car side is missing.

 

[JamesBryan]

The cover is on, but it fits loosely. I’ve noticed that the clip that is on the car side is missing.

Mine was like that, never a problem tbh.

 

[Mr Underhill]

Was there any sign of water around the fuse box area? Just thinking if it’s on a hill and the engine area is facing downwards, water could easily run down along the inner wing and into the bay.

Long shot - It might still be fuel related as in the fuel pump relay - B in this image. Ultimately a relay is just like an on/off switch but can still function if faulty. If that relay is malfunctioning then you could be getting inadequate fuel supply - symptoms being engine hesitation, stalling, or failure to start.

For what they cost, try replacing it.

 

[ex-Chinese Dave]

There was some moisture in the fuse box, yes.

Here's a thing, that other problem that i've posted about, the car 'cutting' under 2000rpm sometimes, wasn't evident this morning or last night. The car seems to be driving just as it was when I got it tuned at EFI. I'll see how it goes but if it doesn't return I'm going to say that water in the white connector has been the cause of all of these issues. If it does return i'll buy a new fuel pump relay and see how that goes.