406oc.co.uk

A couple of weeks ago the car started backfiring while i was playing racey (on a private track of coarse) its been doing it ever since... 99% of the time while engine braking but sometimes just after i've put the throttle down it'll make a pop and the engine will hesitate for a fraction of a second then be on its way again. As well as this the already not amazing fuel economy appears to have gotten worse? not sure if its related. If anyone could shed some light on any possibilities I would very much appreciate it. Power doesn't seem to have been affected.

Thanks
Andy

Don't know why it's doing it, but I can tell you for sure, that it is it backfiring that's causing your poor economy.

Well i figure that modern (or at least semi modern) fuel injected cars shouldn't be putting fuel in when i let off the accelerator. Though it doesn't always backfire when i let off. So i'm at a bit of a loss.

sounds like you need to check the engine out
could be a plug thats on its way out or more than
one, too much air in the system, pump not
working correctly, i'd get plugs changed first
and see what happens

I'm (obviously) no expert at these things, but could a failing throttle position sensor cause it?

I shall change the plugs at the weekend cause its worth a shot and they're cheap. Throttle pot had crossed my mind with the thought that it would be making the ecu think the throttle was open when its not? Hopefully it will be that and not something expensive! lol

generally backfiring is caused by a lean situation (contarary to popular belief) this would explain the fact that your flooring the accel getting no fuel, backfires, fuel starts arriving and off you go.So a lean condition either means we have too little fuel (fueling problem) or too much air (air leak).

few things we can rule out.

1. not lambda, the condition is occuring on wide open throttle the lambda on mp3.2 does nothing over about 70% throttle and 3000rpm

2. not ignition the ignition timing cannot be out on these engines its non adjustable and the map is not going to be changed unless you got henry and his laptop to play with the ecu.


it could be as i said hardware in the term of the fuel supply, or sensor in the way of the tps being when your jumping on the throttle the ecu detects a quick change (tpsDOT acceleration enrichment) and fuels accordingly.

my plan of action would be
1. grab a tps from a scrappy,All XU (1.8>2l) pugs/citreons from 1993>2000 use the same 3 pin tps

2. Check manifold for leaks, by spraying an aerosol (easy start or something similar) around the manifold joins while the engine is idling, if the idle changes significantly you have found a leak.


These 2 are easy and cheap. after that id start checking fuel pump and fuel pressure reg and give the injectors a sonic tank clean.

Regards
Andy

just found abit of info on what a backfire is for anyone interested explains it better than what i can

http://en.wikipedia.org/wiki/Back-fire

Thanks matey. Hopefully this will help me. My mum has a 1.8 16v XU 406 on a T plate. Would the TPS fit from that? not permanently obviously but just while i test it?

acqu135c3 wrote:Thanks matey. Hopefully this will help me. My mum has a 1.8 16v XU 406 on a T plate. Would the TPS fit from that? not permanently obviously but just while i test it?

might do but a t plate might be a ew ??? not xu

T plate is 98/99