New exhaust now engine cuts out.

[rossrox]

Hey guys, so past few days I have fitted a set of stainless downpipes and an evo 4-6 stainless mongoose system.

Once completed I let the car warm up and once it was warm it would idle at about 800 rpm and then after 30 seconds or so just die.

I'm going to hazard a guess and say something to do with the lambda sensor?

Unsure what to do really... Worrying thing is I'm supposed to be going to France in it on Friday!

Cheers, Ross.

[c0xxy]

These cars run fine with out any of the exhaust system so wont be lambda sensor.
Does it do that repetitively? Or you tried once n asked the question?

sent from ash

[Davezj]

Have you removed anything else on the engine when fitting the exhaust?
Like the MAF sensor wire.
Or did you disconnect the battery
Idle control will take a little time to get back to normal.



Sent from my space-aged gizmo

[Louis]

If only exhaust replaced I would guess the lambda could have been damaged, check no wires have been pulled from it!. Also I reckon the engine would run with no exhaust but the ecu Does rely on info from lambda so if no sensor it would not run for long.
Have you got an engine warning light?, any damaged sensor should light up the engine management light.

[Confused]

The car will run just fine without an O2 sensor - I've been running my Anglia on a standard pre-facelift ECU with no mods for 500+ miles this last weekend.

The most it might give is a check engine light.

[Louis]

13 years and Still learning lol!
I would have thought input to ecu from lambda would have Been required!
(Ecu , afr info and fueling without lambda info?)

[rossrox]

I did disconnect the battery as was welding the exhaust whilst it was on the car and didn't want to screw any wiring up.

It gets to temp fine and then once warm the revs drop to maybe 200 and it tries to catch itself and sometimes manages and sometimes just dies. Car is absolutely fine when driving though, but then cuts out when coming to traffic lights or junctions.

[c0xxy]

Possibly a leak, I changed to vta blow off valve and it did that at lights.
A faulty maf can cause weird stalling issues. Unplug it n it should run rough but still run

sent from ash

[fassi1]

I would check for any exhaust leaks especially pre O2 sensor. 800rpm is incorrect rpm idle for this car when warm, 640rpm or max 700rpm.
Incorrect idle already indicates problem. It could be air leak, exhaust leak or damaged O2 sensor.
No fuel injected and ECU controlled engine runs fine without O2 sensor. It may not stall but it won't be running fine.
All engines age differently and in most cases they all have different mods and for that reason some may stall without O2 sensor and some may not.
O2 sensor allows ECU to run AFR 14.7 for idle and mid load and anything different than 14.7 more likely will cause problem.
Further away from 14.7 the more likely there will be an issue with an engine.
I noticed that all these engines, as they age, they tend to run much leaner than 14.7 at idle and thanks to ECU which by looking at O2 sensor, pulls AFR back to desired 14.7 by adding more fuel, but in most cases it is near the border of its adjustment range. For that reason, when you disconnect O2 sensor, ECU can't do its magic any more and engine runs very lean at idle something arount AFR 17 or worse. The warmer the engine becomes the leaner the idle.
Similar thing happens when we have air leak or exhaust leak. There is too much air passing O2 sensor and with O2 plugged in, ECU either runs out of the adjustment or simply can't quickly enough react to incorrect AFR, notice that O2 sensor on these cars is qiute far away from the engine.
In your case I would look for any air and exhaust leaks. I would recommend to use any kind of exhaust paste with the gaskets when bolting downpipes to the turbos.

[adaxo]

I was running loooong time with wrongly connect o2 sensor, ecu not get any information from it, find this out only as I play with evoscan, it was running great on idle afrs was spot on, just a lot richer on wot than after plug in o2 sensor correctly.

[fassi1]

What do you mean by wrongly connected O2 sensor.
Well sorted, maintained and looked after VR4 shouldn't be far away from correct AFRs and I bet your engine is almost tip top. Other thing is that VR4's ECU is very basic
and hardly ever complaints, but that doesn't mean that everything is fine. I think you know this stuff, at least should know. You can't be trying to resolve the problem with ECU running limp mode and open loop.
Try to disconnect O2 sensor on Audi same age as VR4 ☺

[c0xxy]

Honestly mate, if you unplug the o2 sensor on a vr4, you'd barely notice a difference day to day

sent from ash

[adaxo]

That is what i was trying to say, vr4 ecu is so basic it will run fine with no lambda input, not like vag ecu.
So its very unlikely it would cause op car to stall, I would bet on some air leak or maf dying.

[fassi1]

Honestly mate, if you unplug the o2 sensor on a vr4, you'd barely notice a difference day to day

sent from ash
You can notice a difference with engine warm at idle as soon as AFR gets to 16 and I don't need to unplug O2 sensor.

[Confused]

Ross - where abouts in the UK are you?

The simplest way to see what is happening is to get a laptop with EvoScan hooked up to your car, and log what's going on at these points in time.

It could be an O2 sensor failure (maybe it's giving out an incorrect reading, rather than none at all)? It could be an air leak. It could be a MAF failure. It could be idle speed control valve not working quickly enough to maintain the idle. It could be a number of things - but logging with EvoScan will be by far the best way.

If you're near to me in Mansfield, then I'll be more than happy to take a look for you - as I'm sure other members will be, if anyone knows where you are!


A simple exhaust change won't cause the issues you're experiencing.

[Grid]

Do you have a cold air intake? If so it may be messing with your MAF, and then the exhaust change does matter as it affects the maximum airflow through the engine, since exhaust restrictions are relaxed...