Mk2.5 running rough & Exhaust fumes through Air vents - FIXED

Technical Area Engine, Transmission, Exhaust etc
2

Hello Guys,

My 1.8, Mk2.5 is running quite roughly. The engine visibly shakes on tickover, and there is a smell of exhaust fumes through the air vents.

I have replaced:

Sparkplugs, HT leads, Air Filter and Coil packs.

Any idea what it might be?

Car has done 85,000 miles (2003)

 

Thanks

Rob

3

Possibly a blown exhaust manifold gasket.

4

Would that make it run roughly?

5

This car has onboard diagnostics - OBD port is near the drivers right knee.

You need to run a diagnostic check using an OBD reader - cheap from ebay or borrow one.

  

6

Inlet, outlet if not sealed correctly it will upset the engine balance.

I had a Vauxhall with a cracked exhaust manifold, that was rough running until warmed up due to the crack.

Not saying it’s that could be other stuff but worth investigating.

7

Rob (Golders) where abouts are you?

8

I’ve known failed mass air flow sensors to give similar symptoms.

9

Hello, I am in Maidstone, Kent.

I have a obd Bluetooth scan gadget which works with the Torque app. It has found no codes and the CEL has not come on.

I cleaned the MAF with proper MAF cleaner.

10

 

 

As MickAP said, yes.

There will be less back pressure on the cylinder/s it’s blown on. It would explain the exhaust fumes coming into the car. Also check the exhaust manifold for cracks.    

11

You don’t say whether it was running rough before or after you replaced these parts.

Easy mistake, check your firing order.

12

Check your HT leads are not breaking down or furry /tarnished end plugs, and for any furring/tarnishing in the coil pack pots, also the coil pack itself,sounds like she is not running on all 4, but also as above form safetymatch, check that the HT lead are in the correct firing order to, although you coil packs are on top of the rocker cover down the centre with her being a VVT, the pic above is for a MK 1/MK 2.

M-m

13

Hello, I had the guys at MX5 restorer (Eastbourne) take a look at the car today.

Only thing that could be found was a hole in the centre pipe, so will get that replaced and see if that helps it.

THanks,

Rob

 

 

PS: I changed the HT leads, same on both sets. Also popped in a different MAF and still the same issue. Seems the fumes come through the air vents when sitting still at the lights etc.

 

 

 

.

14

“Only thing that could be found was a hole in the centre pipe, so will get that replaced and see if that helps it”.

I suspect it will! That is almost certainly where your fumes are coming from.

Also, an exhaust leak can upset the fuel / air mixture. The lambda sensor will sense “extra” oxygen in the exhaust gases which the ECU will interpret as weak mixture and put in extra fuel to compensate for it.

15

Just an update to this problem:

 

I had a Mobile Mechanic check the OBD2 port with his Snap-On Ipad type scanner. (Much better than my bluetooth OBD2 / Torque App).

It flagged up that the car thought the engine coolant/temperature was running at -40c (minus).

He disconnected the grey electrical clip at the top / rear of the engine and the idle fixed itself straight away. (very easy to get to on the Mk2.5, even I could disconnect it). The thought is the car thinking the temp was -40c was putting more fuel into the engine resulting in fumes through the air vents and a slight misfire (skip in the idle speed).

The part to fix it is only £35 and took him 10minutes to change it. The car is much smoother to drive in traffic now too.

This is the part:

http://www.mx5parts.co.uk/engine-coolant-temperature-sensor-mk2-25-p-1864.html

Hopefully your problem might be the same issue. It worth disconnecting the port to see if it helps you.

Hope that helps,

Rob

16

Final Update

The mx5 was still running roughly and still had fumes coming into the cabin through the air vents.

I got Mark at Freelance Mazda in Chatham,Kent do a compression test on the Mk2.5 this morning.

Compression is fine, but he found the cause of my rough running. One of the NGK Spark plugs tip had broken off! No wonder it was running roughly and had exhaust fumes coming into the car through the air vents.

These spark plugs were only put in in JUne and I have covered only 3000miles on them. So even if your spark plugs are quite new they could be the problem.

So thanks to the guys at Freelance Mazda the MX5 is running great again. The exhaust fumes have vanished.